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1. transmission circuits AN95050 DPN FLN R17 CE BC558 BSP3044 on 470k R2 619 RI m Piee eo H gt VCC TR3 Li BATS9 0 339 R11 i 719 8 2 TRI Zo o Ci i BZXTSC gt SREF Bzx79c J R21 i gt SUP 47104 Rea RS C14 BATS R22 10M 470k 130k mE ee Ager p gt VDD i M ae c7 02 R23 470k C15 i i LED 36G 3 T 100uF 100uF BF 420 TR2 Sy 2 0nF eN hor yal m DA H ir LN veces NS T x E 100nF IC4 ce 2 2nF s BR211_220 r 2 ISL PE GARE En 13 i RG R3 3 14 200k Cie 2 3 92k 100k TILED OR 2 2nF D18 Bee ange Y I8pF gt RIN iA P REG IL veek 2 anF i CE D1 D2 RT asi MEME WS m irali T cite EN CUM 39 47 5k C2 ae e Bel xd BASE gaa Re E G3 S MMUTE MICH CUNT MICP T E pm i T 8 E 1 ig C18 To 2nF 2 1V 8u DTMF AGC 2 2n 2 1V l m LKL e 5 Pun Ka S MUTE IRS IR E 2 2nF C31 D7 pg Res 825 D 1 SuF 2 2 I 2 20nF T I SLPE BASIIF aw an lt MUTE S 47k SLPE
2. Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 c ER pe cac Br ET EE 1 J3 TIN e d 9 visi E D GP e diciES MS gs imas ciglo 3 Y S JTR 1 S e C8 NA olo C9 E85 N ni K Wr NP Ms alt ry dja c19 c12 C 13 MIC wie VEE ELAB 822 411 46801 Fig 58 Components side of the OM4776 evaluation board 822 411 46802 242 Fig 59 Layout of the wiring of the OM4776 61 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits Application Note AN95050 60 0 detected level dBV A 70 0 A B B A terminals
3. Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 DPN FLN 3 VDD I 2 e e e 5 rue tt LL 1N4148 V T T D17 C35 Jt 713 4 ROW2 TX FT ee ROW eeQuF BZX79C B lt row2 Rowe gt 25V 5 6V R35 Ico 470k ROWS A Cc A lt ROW3 HF RTE L ROMA T lt t row4 DMO KTE S ROWS lt 4 R0W5 vole DIODE p lt DI0DE VOD R36 S MUTE TONE 00k es H EARTH Qd VSS Qv 8 22 21 r ses Q2 voz R37 n px a FEJ 2 2M Co R38 D14 TIOTAL DPN FLNES 3 58MHz a 470k MUTE D gt INGE RESET cote gt E C37 pag gh COL2 a IcE FOI coL2 4 gt 4inF kaoh pis COLG e col CSI e oML P tNa148 lt COLS coL3 E gt Jir n i 3 T COL4 eos COL4 e gt ihe TUR R42 10k C38 100nF DTMF lt Q Il R43 LFE C 00k HE RTE lt aie COL6 COL4 COLI COL2 COL3 VEE lt I beg 4 poh 4 beg 4 pod p FTSA pstore H 1 H 2 H 3 D20 c ROW lt a o tod nmm Lo Lo Lob 4148 rJ 0 rJ rJ P FTSB MRC H TONE 4 5 6 D21 ROW lt E L 1 l a re bed bod chads 4148 1 1 1 IBTA 1 g g D22 ROW3 3 E I i d ced tod bob soe 1N4148 i
4. transmission circuits AN95050 DPN FLN lt cE X VDD gt o e e C70 C71 gOW2 ROW 7r TRO bee ee ou rr Ron 7 eou c 1500F A 40V IC 225 O ROWS BZXT9C AN R71 I lROW3 HF RTE EZ 5 6V R70 1M BC558 BAS11 ROMA 470k C ROW4 DMO KTEJ S nc RWS de COL4 lt ROWS VOL1 DIODE 5 lt DOIDE VDD MUTE lt SIMUTE TONES x OD CRADLE SWITCH nc lEARTH vss ON HOOK position cx RIS 8 PA 21 CSI gt O SICSI Qa VOL 470k R73 T cA ITALI KO LFE nc 2 2M zt D2T za 16 19 Y XTAL2 DPN FLN 1N4148 3 58MHz ia COLI TRESET coL t gt CI2 R74 cole FOI gt tote CE FDI COLa gt 4 4j 470k L prep cos COLS CTS im amp lt coL 6 coL 3HE gt Aon BASM pers y CO4 L lt cos coL 4e R77 Tene R78 10k C741 100nF DTMF lt p l TONE lt HF RTE VOL2 VOLI lt VEE lt h COL4 COLS COLG COL COL2 COL3 tot pot tot tot LB tot 4 a a o LJ a FTSA eSTORE H M1 H M2 L1 i2 H3 D30 ROW lt i l l l i i S um Lop Lop Lot teg mm 4148 4 L a o a a FTSB H TONE 3 H m4 4 5 6 D31 ROW J 1 E i AP tot bap sot eat
5. transmission circuits AN95050 DPN FLN RI TR3 BC558 BSP304A LN ETA D16 E 619 R a FEARS n n 5 e V R20 C30 el 0 me BAT85 5 TIME 25 IEEE IE C NM BZXT9C 2 C14 PK C15 TB bua pe ne 77 4 1 l 2 2 8 dn ue en i R22 470k T OK ge H1 l 4p Ly eds x R23 470k gt IR als LN vcc T a ow TR2 ele er d 048 331 5 R13 BF 420 a1 al is ud R6 ILED oe L2 4p CRADLE SWITCH m pel e R4 C2 eJ 3 J f Sta Stigo e REC I VEE Ore di ce fp m ee a A B tO ood aks Tt 5s Lj WIE 2420 S 392 1099F z R15 10k C3 IMMUTE MeH C12 RS Ra a Te Ru 30 20L T ue 22 2 2nF DIS E 50V prwr aoche e ls L T BR211 220 Dli De r E MUTE R n cts m C18 2 2nF Aa D3 D4 HRe L gt MUTE B A x x 825 TS C11 oat ee 220nf l R25 IR gt _ 22k i 180nF 5u gt csI R28 FDI 5 6 Z11 BZXT9C 18V D12 K Pl Sica C6 100nF R27 Il DTMF 22k LFE 5v HF RTE C33 100k 22u TONE 50V C3 d il C VEE R31 x C19 2 2nF RIT dk x ja MICROPHONE e X C201 2 2nF RIE ik 7 Ww Im EARPIECE BS 4 x C21 2 2nF R14 22 1 x EMC components Fig 45 Application example 1 line interface TEA1112 discrete ringer 40 Philips Semiconductors
6. MN 80 0 t it i Wi i m ahd HAN li TRES i i 90 0 i 23s fh a li l T hi lj i WI M ll li 1 fL EH MI I f iN ved Mh MI Hl IL i CHT a En th pel LENT MM il OUI ul P E Ag HW d n EH AN AA I WU NAR MAL M CREE CRUDUM 100 0 i Ll i all i i oui LR LPS P MAN hd f TATE E i Ir k i al 1 TIBI if HI Wie i iM il im mee il A i earpiece n Yi dut TD LT HM Ah uL rna MAT tee ie l Tots WEY DUNT j We We d ARIAT Mr 1100 t ws per ae RU UEM 100 0k 10 0M 200 0M 1 0M gt f Hz 1000M Fig 60 EMC behaviour of the OM4776 conducting test 60 0 detected level J V dBV LAN 70 0 E A A f H AI M A B B A terminals MN aan Psa NND An i 80 0 est Pits f fy o ER l d i 1 f j ij Ti n n H E LOWE INL gal 90 0 JLA E I i p V 1 PSU CV UT NP Wf EU ME ker P M lh e MI 100 0 TOL UNE a A Vis p 110 0 f Hz 1 0G Fig 61 EMC behaviour of the OM4776 radiation test 62 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 The second test 12 of the OM4776 is carried out in an electro magnetic field The field strength is 3 V m over the frequency range 80 MHz to 1 GHz while the signal is modulated with an AM signal of 1 kHz a
7. Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 BRL dB PN nk ipic ia nF a 45 0 In 40 0 500 0 35 0 400 0 30 0 300 0 Sama 20 0 200 0 15 0 100 0 10 0 100 0 1 0k 90 0k 100 0k 100 0 Ok 5 0k f Hz f Hz Fig 14 Set impedance and Balance Return Loss at 600 ohms reference impedance Adjustment When decreasing the reference voltage VREF a resistor is connected between LN and REG in parallel of Rp See Fig 13 so slightly modifying the set impedance If complex set impedance is required the Rcc resistor must be replaced by an equivalent complex network Keep in mind that the DC resistance of this network influences the VCC voltage and current supply capability See section 3 1 2 Supply for peripheral circuits 3 3 Supply for a LED pin ILED Principle of operation The TEA1112 A give an on hook off hook status indication This is done by a current available to drive a LED connected between pins ILED and LN In the low voltage area which corresponds to low line current condition no current is available for this LED For line currents higher than a threshold lled starts at 18mA typically the lled current increases proportionally to the line current with a ratio of approximately one third The Iled current is internally limited to 19 5 mA typical value
8. Akts dB Microphone channel MEL Receiving channel 0 0 0 0 E 10 04 20 0 20 0 30 0 30 0 40 0 40 0 50 0 50 0 60 0 60 0 70 0 70 0 80 0 80 0 posa 100 0 90 0 110 0 100 0 2 0 0 1 0 2 0 3 0 4 0 5 0 FR 1 0 2 0 3 0 4 0 5 0 f kHz f kHz Fig 42 Microphone gain and earpiece gain reduction in MUTE condition 34 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 The MUTE function works down to a voltage on VCC equal to 1 6V Iline 2 5 mA in the basic application Below this threshold the microphone amplifier stays always enabled independently of the MUTE input level The maximum voltage allowed at the MUTE input is VCC 0 4V 3 12 Anti sidetone circuitry Principle of operation To avoid the reproduction of microphone signals in the earpiece the anti sidetone circuit uses the microphone signal from pin SLPE to cancel the microphone signal at the input IR of the receiving amplifier The anti sidetone bridge already used for the TEA106x family or a conventional Wheatstone bridge as shown in Fig 43 may be used as the basis for the design of the anti sidetone circuit R Restl Rec Zbel Zline 2 A Zline ey O1 26k s Rast2 Rslpe Rslpe Restl Rast3 R amp SLP
9. AN95050 1 L Br VCC 16 2 SLPE GAR 15 3 ILED QR 4 4 REG VEE iis TER11128 5 GAS IC 12 6 MMUTE IC 11 7 DTMF AGC 10 8 MUTE IR 9 Fig 3 TEA1112A pinning 11 Pin ON OOA ON Name LN SLPE ILED REG GAS MMUTE DTMF MUTE IR AGC MIC MIC VEE QR GAR VCC Description Positive line terminal Slope adjustment Current available to drive a LED Line voltage regulator decoupling Sending gain adjustment Microphone mute input Dual Tone Multi Frequency input Mute input Receiving amplifier input Automatic gain control Non inverting microphone input Inverting microphone input Negative line terminal Receiving amplifier output Receive gain adjustment Supply voltage for speech and peripherals Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 3 DESCRIPTION OF THE IC All the curves shown in this section result from the measurement of a typical sample All the component names refer to the basic application of the IC shown in Fig 4 Telephone TER1112 TER1112R MES Signal fron line dial end control Supply for gen J BENT E circuits CVoc ion uc peripheral circuits Fig 4 Basic application used for measurement 3 1 Supply pins LN SLPE VCC REG 3 1 1 TEA1112 A Supply Principle o
10. Noise dBmp Nominal ain TEA1112 influence of the microphone gain on the noise on the line 68 9 A resistor is connected between MIC and MIC Noise dBmp 68 0 bs 718 kohns 70 70 0 body 200 ohms ae WA 72 0 72 Pw TNI TSI 70 eua 16 0 74 LA L75 78 0 SNO 80 0 15 0 25 0 35 0 45 0 55 0 65 0 75 0 39 0 41 0 43 0 45 0 47 0 49 0 51 0 Iline mA Gutx dB Fig 22 Noise on the line versus the line current and the microphone gain The amplifier gain is temperature compensated The gain adjustment by an external Rgas resistor connected between pins GAS and REG may slightly change the temperature coefficient see reference 2 Fig 23 shows the common mode rejection ratio at 15 mA and at nominal microphone gain Two curves are present on this figure The first one is the spectrum of the signal on pin LN when a sending signal is applied on pin MIC pin MIC being shorted to VEE by a decoupling capacitor The second curve is the spectrum of the sig nal on pin LN when an sending signal is applied on the microphone inputs MIC and MIC being shorted Both signals are at a frequency of 1 kHz The difference between the two curves at this frequency gives the CMRR 23 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits Application Note AN95050 Htt dB llinez15mH 100 Fig 23 Common mod
11. o7 0 100 0 140 0 180 0 220 0 260 0 Or nm Q c HD NI O 0 qc var mVrms Fig 33 Distortion of the receiving signal for two loads Dx UG Rl 450 ohms 0 o o o l 0 o l o l 0 0 100 0 140 0 180 0 220 0 260 0 300 0 340 0 380 0 var mVrms Fig 34 shows the noise on QR loaded with 150 Q psophometrically weighted P53 curve as a function of the line current This curve has been done with an open input IR With the anti sidetone connected to the input the noise generated on the line will add via the anti sidetone circuitry to the equivalent noise at the input IR The total noise generated at the earpiece output depends on the microphone amplifier gain that has been set the sidetone suppression and the receiving amplifier gain The influence of the AGC on the noise appears clearly in Fig 34 29 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Noise uV 60 0 Nominal gain 50 0 30 0 w Bi we cw 20 0 0 15 0 25 0 35 0 u5 0 55 65 0 75 0 Iline mA Fig 34 Noise on the earpiece The amplifier gain is temperature compensated The gain adjustment by an external Rgar resistor connected between pins GAR and QR may slightly change the temperature coefficient 3 8 Automati
12. APPLICATION NOTE Application of the TEA1112 and TEA1112A transmission circuits AN95050 Philips PHILIP S Semiconductors DH LI p Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Abstract The TEA1112 and TEA1112A are bipolar transmission circuits for use in electronic telephone sets They are added to the range of well known transmission circuits of the TEA1060 family This report contains a detailed description of the circuit blocks of the TEA1112 and TEA1112A Two application examples of the TEA1112 are given The report handles the consecutive steps to design or to adjust the basic application with these ICs The EMC behaviour of an evaluation board with the TEA1112 or TEA1112A is included The general notation in this report for both ICs TEA1112 and TEA1112A is TEA1112 A Philips Electronics N V 1995 All rights are reserved Reproduction in whole or in part is prohibited without the prior written consent of the copy right owner The information presented in this document does not form part of any quotation or contract is believed to be accurate and reliable and may be changed without notice No liability will be accepted by the publisher for any consequence of its use Publication thereof does not convey nor imply any license under patent or other indus trial or intellectual property rights Philips Semiconductors Appli
13. Do TBTB ROW4 3 E 1 I O 34 tap top bet bab 4148 MICMUTE H HFLASH t PAUSE t LNR 4148 RFS ROWS 1T 5 m y 5 R44 p INA148 gy INA148 4 1NA148 4 INA148 1N4148 680k T D25 D26 D27 D28 D29 oosa PTs S AS ws S EN 000 S o o o 9 DIODE lt a i i i Fig 46 Application example 1 dialler ringer PCD3332 3 41 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Complex set impedance can be realised by means of the network R1 R2 and C1 The application is intended for use with a dynamic microphone and dynamic earpiece Use of an electret micro phone requires a modification of the application A supply has to be made from VCC while the gain has to be adapted by resistor R4 which has no value in Fig 45 see application example 2 chapter 5 Buffer capacitor C7 is discharged heavily during the break periods at pulse dialing with the result that the VDD buffer capacitor C35 will not be charged during the whole dialling digit The supply voltage VCC has to be increased for pulse dialling applications see chapter 4 2 The microphone amplifier can be disabled by a high level at the MMUTE input pin In this example is the MMUTE input coupled with output LFE of the PCD3332 3 LFE can be toggled by the MICMUTE key to disable or enable the handset microphone PCD3332 3 dialler ringer The dial parameters of the PCD3332 3 can b
14. gt MUTE D9 D10 gt CsI cio gt Fpp uF 211 BZXTSC 18V D12 BAS11 ERI ie lbs R27 R29 od x R14 D TRAY Bobet 1006 oo 56 ur 1 DTMF 22 SV t6V Ce 100nF 49dBpa V C33 o L VR 22u C34 33nF 50V um Il TONE TRS BC556 diramal HS i R29 100k Cell e o o BC548 R30 E 4 lt VOL2 n VEE R32 R31 5 62 i lt VOL gt VEE ne 8 25 3 32 iE gt interconnect ions with Controller PCD3332 3 a gt J1 interconnect ions with Handsfree TEAIOS3 local EMC components Fig 51 Application example 2 line interface TEA1112 electronic hook switch and discrete ringer 50 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits Application Note AN95050 C49 MUTER 3 R47 3 92k ND DLC M ed TSEN iu 470nF or er ba ewa 40nF IM SSOP wg C81 A TUF R48 10k IRIN2 TNOI Il T C42 33nF SREF ES al
15. 32 Fig 39 Microphone gain attenuation and MUTE input current vs Vmute llle 33 Fig 40 Microphone gain and earpiece gain reduction in MUTE condition lll 33 Fig 41 Microphone gain attenuation and MUTE input current vs Vmute aa 34 Fig 42 Microphone gain and earpiece gain reduction in MUTE condition 34 Fig 43 TEA106X family anti sidetone bridge left and Wheatstone bridge right 35 Fig 44 Equivalent average line impedance 2 rs 36 Fig 45 Application example 1 line interface TEA1112 discrete ringer lcs 40 6 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Fig 46 Application example 1 dialler ringer PCD3332 3 0 lll 41 Fig 47 Line voltage across the set as a function of line current 2200000005 44 Fig 48 Start up after off hook 2 lll sss 44 Fig 49 BRL of application example 1 at real and complex termination 45 Fig 50 Behaviour of application example 1 during pulse dialingat20mA 47 Fig 51 Application example 2 line interface TEA1112 electronic hook switch and discrete ringer 50 Fig 52 Application example 2 handsfree application TEA1093 llle 51 Fig 53 Application example 2 dialler ringer POD3332 3 2 000002 eee eee 53 Fig 54 Currents Isup lled Itr and Ivcc asafunction
16. Fig 20 Distortion on the line as a function of the input signal for two microphone gains m Oc a osoo o o o o o o o o ooo L CO or nn rn CQ CQ fF fF Ul e uo Fig 21 shows the distortion of the line signal versus the rms voltage on the line at line currents equal to 4 mA and 15 mA at the nominal gain of 52 dB 22 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 THD Z b line 15 mA THD OD a Iline U mA 14 0 oF FFF O O O O O o or nm Qc Uu og o xq 8 350 0n u50 0m 550 0m 650 0m 750 0m E 0 75 1 0 1 25 1 5 1 75 2 0 vln Vrms vin Vrms Fig 21 Distortion of the line signal versus the rms voltage on the line To obtain optimum noise performance on the line the microphone inputs must be loaded Fig 22 shows the noise on the line psophometrically weighted P53 curve as a function of the line current and the microphone gain with a 200Q connected between the microphone inputs typical application These curves show the sensitivity of the noise to the microphone gain The noise measures 79 5 dBmp at minimum send gain
17. to keep the send stage fully functional Start up After connecting the application with the line supply the very first time the handset has to be lifted to charge the VCC and VDD supply capacitors The set is operational within 200 ms at 20 mA line current During on hook the VDD capacitor C35 is kept charged by R28 The DC current in this stand by mode has to be more than 6 LA Start up after off hook t 0 VDD capacitor has been charged is given in Fig 48 by means of the voltage VA B across the set and the supply voltages VCC and VDD versus time The set is supplied from an exchange voltage of 48 V while the line current is 20 mA during off hook R3 40 kQ 43 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits 10 0 VA B V 9 0 8 0 6 0 5 0 4 0 3 0 2 0 1 0 0 0 50 0 VA B V 40 0 30 0 20 0 10 0 0 0 Application Note AN95050 R3 40 ka ud ae R3 not placed 0 0 40 0 80 0 20 0 60 0 lline mA 100 0 Fig 47 Line voltage across the set as a function of line current 5 0 VDD VAB VCC 4 0 V VDD oo 4 TE zs EE PEDE ait Sera sete Me PD ICM ER MEME 30 p VCC 2 0 E a 1 0 i 0 0 0 0 100 0 200 0 50 0 150 0 gt t ms Fig 48 Start up after off hook 44 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmis
18. tap tot 4148 TBTA e VOL MS s M6 H S 9 D32 ROW lt i l l l l i rr tap tat tap tat tap 4148 TBTB Hvo 4H M7 H mg O lio Da 033 ROW4 3 i l 4 l 4 i ams 4 tot bap sot bot tap bot 4148 V HOOK M9 MO o FLASH PAUSE LNR 4148 RFS ROWS lt p e s m O 4 VR 3 R79 1N4148 L 1N41484 1N4148 J 1N41484 1N41484 1N4148 y BASII Liegok 7 D40 D39 D38 D37 D36 D35 D41 T p Q E los MLA i AP S ts ws EN 000 S vec D42 prope 3 i gt Fig 53 Application example 2 dialler ringer PCD3332 3 53 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 5 2 Settings and performance of the application DC settings The stabilized voltage of the TEA1112 VREF between LN and SLPE is increased by means of R3 100 kQ to adjust the voltage difference between SUP and VBB of the TEA1093 to 600mV The voltage at the A B B A line terminals measures 6 6 V at 20 mA The DC slope of the Vline lline characteristic is about 45 Q due to R20 R9 and the channel resistance of TR1 The stabilized voltage VBB TEA1093 can be adjusted 3 Take into account that VSUP VBB has to be at least 600 mV to maintain maximum efficiency of the current switch of the TEA1093 at mean speech levels The line current can be split up in isup flowing into SUP of the TEA1093 to supply the internal circuitry including loudspeaker amplifier and
19. Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Adjustment As the impedance connected between LN and VCC also determines the set impedance the easiest way to increase the current capability of the supply point VCC is to increase the reference voltage VREF by connecting an Rva resistor between REG and SLPE see Fig 11 The maximum preferable value of VREF 7 V see Adjustment in section 3 1 1 3 2 Set Impedance Principle of operation The ICs behave like an equivalent inductance that present a low impedance to DC Rslpe and a high impedance Rp to speech signals Rp is an integrated resistance in the order of 15 5 KQ 15 It is in parallel with the external RC filter realized by Rcc and Cvcc Thus in the audio frequency range the set impedance is mainly determined by the Rcc resistor Fig 13 shows an equivalent schematic for the set impedance while Fig 14 shows measurement results of the set impedance and the Balance Return Loss BRL BRL measures the matching of the set impedance to a reference impedance of 600Q in this case according to the formula Zset 6000 BRL 20 log SS2t 6000 Zset 600Q LN j i e Vref K REG VCC Leq Creo x ReH pe x Rp Rp internal resistor Rp 15 5k SUPE tre Cvcc Bslpe ay Pup 100 uF VEE o Fig 13 Equivalent set impedance 18 Philips Semiconductors
20. If no AGC function is required the AGC pin must be open circuit So no gain control is applied the gain control factor stays at 1 and both controlled gains have their maximum value 30 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 CurveRagc 1 0 2 2 10k 3 15k za u 22k lt 5 27k 4 5 RS 6 1 A 5 7 eB 15 0 25 0 35 0 us g 55 0 65 0 75 0 85 0 Iline mA Fig 35 Automatic gain control on the microphone amplifier 3 9 DTMF amplifier pin DTMF Principle of operation In Fig 36 the block diagram of the DTMF channel of the TEA1112 A is depicted Internal From MUTE From earpiece Rgerint val g aR From MUTE DTMF From MMUTE Rgasint From Micro Rcc Rexch REG 5Cucc Cexch SLPE Creg Rslpe Fig 36 DTMF channel The DTMF amplifier has an a symmetrical high input impedance The impedance between DTMF and VEE is typically 20 kQ with maximum tolerances of 15 The DTMF amplifier is built up out of three parts an atten uator by a factor 10 a pre amplifier which realizes the voltage to current conversion and the same end amplifier as the microphone amplifier No AGC is applied on the DTMF channel Fig 37 shows the frequency response of the DTMF amplifier at 15 mA at differ
21. It only provides protection against current surges The electronic hook switch interrupter TR1 is controlled by inverter TR2 via the DPN FLN open drain output of the PCD3332 3 During off hook when the handset is lifted or when the HOOK key is activated DPN FLN is high resulting in a conducting TR1 Conducting of TR2 is initiated by the high ohmic resistor R22 and is taken over by R24 Interruption of the line current is achieved by DPN FLN is low When the application is connected with the line supply the very first time the electronic hook switch is switched on for a short time resulting in a quick charge up of the supply capacitors of VCC and VDD During stand by the VDD capacitor is kept charged by means of R28 Handset Handsfree application The handsfree circuit TEA1093 is connected between the positive line wire which is connected to LN of the TEA1112 via R11 and R12 and SLPE of the TEA1112 The current into LN of the TEA1112 is as low as 3mA to have most of the line current available for the loudspeaker function of the TEA1093 Resistor R12 keeps the TEA1093 operational at saturation the line signal at large negative amplitudes The base microphone HF mic or the handset microphone HS mic are switched to the MIC input of the TEA1093 by means of TR7 respectively TR8 depending on the HF RTE level of the PCD3332 3 Handsfree is switched on when HF RTE high resulting in transfer of the HF mic signal to the transmit input of the
22. See curves shown in Fig 15 ILED mA D mA 20x0 90 0 teipe 18 0 80 0 nio 78 0 Ish 14 0 60 0 12 0 50 0 dl 10 0 40 0 8 0 eS 6 0 30 0 u o 20 0 Iled lee 2 8 18 0 8 0 LE 9 8 p 10 0 20 0 30 0 40 0 50 0 68 0 70 0 80 0 90 0 10 0 20 0 38 0 40 0 50 0 60 0 70 0 80 0 90 0 ILINE mA ILINE mA Fig 15 LED supply current versus the available line current 19 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 As the LED driver is connected to SLPE all the lled supply current will flow through the Rslpe resistor Conse quently the AGC characteristics are not disturbed Adjustment The ICs have been designed for use with all kind of LED s as long as the voltage across this device at 20 mA current flowing through it is lower than VREF 0 8 V The start and stop line currents as well as the maximum lled current are internally fixed If no LED is required the ILED output can be shorted to SLPE to avoid a floating pin 3 4 Microphone amplifier pins MIC MIC GAS Principle of operation In Fig 16 the block diagram of the microphone amplifier of the TEA1112 A is depicted The microphone amplifier has symmetrical very high input impedances The input impedance between pins MIC and MIC is typically 64 KQ
23. microphone signal in the earpiece is reduced by the anti sidetone circuit consist ing of the components R5 R6 R7 and Zbal with R8 R10 and C4 The principle of the applied TEA1060 family bridge is given in chapter 3 12 and fully described in 8 In case AGC is not applied pin AGC open the anti sidetone circuit has to be re calculated for a mean cable length of 5 km Readjustment of the balance circuit is necessary for other cable types different line length etc 4 2 3 Dialling DTMF dialling The DTMF signal from the TONE output of the PCD3332 3 is attenuated by the network R41 and R42 and applied to the DTMF input of the TEA1112 Resistor R41 is in parallel to the input impedance of the DTMF ampli fier 20 kQ typ During dialling MUTE is high the signal is amplified by the DTMF stage and transferred to the line resulting in a total level of 6 dBm at 600 set impedance and 600 O line load The gain of the DTMF stage is 25 5 dB typical A reduction of the microphone gain by means of external resistor R4 reduces also the DTMF gain and transmit ted signal levels The attenuation network R41 R42 has to be redefined to correct the reduced signal transfer Take in account that VDD decreases during DTMF dialling because of the enlarged current consumption of the PCD3332 3 in this mode Pulse dialling Flash The line current will be interrupted by the electronic interrupter TR1 under control of the DPN FLN signal Dur ing prog
24. small current can be drawn to supply peripheral circuits having VEE as a ground reference The VCC supply volt age depends on the current consumed by the IC and the peripheral circuits as shown by formula 3 See also curves at Fig 11 and equivalent schematic of this supply point at Fig 12 Recint is the output impedance of the voltage supply point As can be seen from Fig 6 the internal supply current Icc depends on the voltage on the pin VCC it means that the impedance of the internal circuitry connected between VCC and VEE is not infinite While supplying a peripheral circuit on VCC the Ip supply current flows through the Rcc resistor decreases the value of the voltage on the pin VCC This voltage reduction affects the Icc consumption and than the voltage drop across the Rcc resistor So to calculate the voltage drop across this resistor both effects must be taken into account The impedance to use in combination with Ip is not Rec but Rec in parallel with the impedance of the internal circuitry connected between VCC and VEE That is what is called Recint For a line current equal to 15 mA and Rcc equal to 6209 this Rccint impedance is equal to 5500 The worst case for Rccint is Rcc VCC VCCo Rceint Irec Ip 3 VCCo VLN Rec Icc Irec internal current necessary to supply the earpiece amplifier to realize an AC peak voltage Vq across the earpiece impedance HI _ Mq eee mxRI Rccint is due to the fact that Icc slightly
25. 67
26. Rcc resistor the Icc current consumption of the circuit the Ip current consumption of the peripheral circuits and the load impedance on QR The receiving input IR can handle signals up to 18 mVrms with less than 296 THD Fig 32 shows the distortion on QR as a func tion of the input voltage for a line current equal to 75 mA The two curves correspond to a measurement with and without the AGC function which results in a difference of 6 dB in the receiving gain With AGC the gain is only 25 28 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits Application Note AN95050 dB and the distortion is due to the input while without AGC the gain is 31 dB and the distortion comes from the output THD Iline 75 mA 10 0 9 0 8 0 ND RGC 7 0 6 0 5 0 u 0 3 0 2 0 AoC O ee 1 0 m 0 0 2 0 6 0 10 0 14 0 18 0 22 0 vin mVrms Fig 32 Distortion on QR versus the input signal on IR The maximum level on QR for 2 THD increases with line current due to the increase of VCC and then is limited to a maximum value due to the input limitation Fig 33 shows the distortion of the signal on QR as a function of the rms voltage on QR at lline 15 mA for two different loads 150 Q and 450 Q Lo Or C N Rl 150 ohms C NM Ct E amp E Ul C N CO O og oO O O O O O O o
27. TEA1093 MIC Handset mode is achieved at HF RTE is low the HS mic is operational while the TEA1093 is forced into the transmit mode by a low level of MUTER generated by TRY Transmit or receive state is under control of the duplex controller of the TEA1093 The discrete switching circuitry for the microphones could be replaced by the 74HC4053 multiplexer demulti plexer IC as applied in 7 48 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 The transmit output signal between MOUT and MICGND in HS or HF mode is transferred to the MIC inputs of the TEA1112 via attenuator R42 R43 and R15 The signal between the MIC inputs is amplified to the line The receive signal is transferred to the QR output of the TEA1112 and offered to the HS earpiece and RIN1 of the TEA1093 RIN2 is connected to VEE which is the ground reference of the receive signal of the TEA1112 The signal between RIN1 and RIN2 is amplified by means of the loudspeaker amplifier and supplied to the loud speaker Volume control is performed by a simple potentiometer R41 Transmit and receive gains of the transmit and receive channels of the TEA1093 and TEA1112 are in conformity with the sensitivities of the applied microphones earpiece and loudspeaker see Settings and performances of the application chapter 5 2 The TEA1112 is described in chapter 3 of this report while the settings of the duplex contr
28. it reduces the maximum power in the loudspeaker at lower line currents as shown in Fig 56 45 0 40 0 7 Pout Z mW 35 0 25 0 r 50Q T f p 200 f zs Wo wf d 15 0 NT CEN J F 7 P ni GUT ITE xw Ern cere ee ee erre werd a So 10 0 A PU GENE 1000 2p 7 Aa without LED ex 7 2 P VBB 3 55 V Wo age supplied LED E pe 10 0 20 0 30 0 40 0 15 0 25 0 35 0 45 0 lline mA Fig 56 Maximum power into 1009 50Q respectively 25Q loudspeaker versus lline Dialling DTMF The signal from the TONE output is attenuated by R77 and R78 12 5 dB and amplified by the TEA1112 17 5 dB to get a DTMF level of 6 5 dBm at 600 Q line load Pulse dialling The line voltage of this application has been increased to create a voltage space of 600 mV between SUP and VBB of the TEA1093 This results in a VDD back up level of more than 2 5 V during pulse dial ling and flash times up to 600 ms maximum selectable flash time 56 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 6 DESIGN ADJUSTMENT STEPS TEA1112 A APPLICATION This chapter gives a number of adjustment steps which should be made to design or to adjust the basic applica tion of the TEA1112 A For every Adjustment the Components are given The influence on the characteristics of the application and the consid
29. microphones Med through D6 which is a function of the line current Refer to chapter 3 3 tr flowing into LN of the TEA1112 realised by VSUP VSREF R11 0 32 100 3 2 mA typical d vcc which includes the current consumption of the TEA1112 see chapter 3 1 and the current con sumption of the PCD3332 3 in conversation mode 1 Fig 54 shows these currents as a function of lline in the conversation mode while Fig 55 gives the line voltage VA B supply voltages VCC and VDD both with respect to VEE and the stabilized voltage VBB with respect to SLPE versus lline 80 0 a 4 35 ltr 4 mee Itr Te te ed oe Vamenta Slee enolate l 60 0 j l li mA 7 2 50 0 p amp a a 40 0 LL vcc Sees RP Ed EIS 2 Zr m p m ail t 20 0 E 4 lsup lled 10 0 an 500 0m di n E 0 0 0 0 20 0 40 0 60 0 80 0 Too 10 0 30 0 50 0 70 0 di lline mA Fig 54 Currents Isup lled Itr and Ivcc as a function of lline 54 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 11 0 vee 10 0 ae VDD v0 ES VBB 8 0 ae eee V VAB 7 0 i 6 0 n zs VCC Xe VDD N sabe SoS 4 0 me D Lp oL sej 2T ED 3 0 DELL VBB a 2 0 7 1 0 0 0 0 0 20 0 40 0 60 0 80 0 100 0 10 0 30 0 50 0 70 0
30. the same time enables the DTMF channel if needed for some specific applications If a high level is applied to the MMUTE input the microphone amplifier can be activated depending on the MUTE level See TABLE 1 while the DTMF chan nel is disabled The DTMF channel is enabled by either applying a low level lt 0 3 V typically at the MMUTE input or leaving it open Fig 26 shows the microphone amplifier gain reduction and the input current as a function of the input voltage on MMUTE The threshold voltage level is 0 68 V typically base emitter junction with a tem perature coefficient of 2 mV 9C Gutx dB Immute uf 60 0 50 8 ug 6 30 20 10 Je 0 IB 0 8 20 0 6 30 40 IN f 0 4 so JM I INI ooh 0 2 y l SUN 60 0 0 0 0 0 1 0 2 0 3 0 Uu 0 5 0 6 0 7 0 8 0 9 1 0 8 8 509 0m 1 0 155 2 0 2 5 3 0 Vmmute V Vmmute V Fig 26 Microphone gain and MMUTE input current vs Vmmute 25 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 The MMUTE function has no effect on the receiving channel which is fully determined by the MUTE level Performance Fig 27 shows the microphone amplifier gain reduction at lline 15 mA for an input signal at 1 kHz Two curves are drawn in this figure The first one shows
31. 1112A transmission circuits 3 12 2 Wheatstone bridge The conditions for optimum suppression are given by Rastl Rccx Zline DB Rslpe Rcc Zline Application Note AN95050 Also for this bridge type a value for Zbal has to be chosen that corresponds with an average line length The attenuation of the received line signal between LN and IR is given by Vir _ Rast1 Zir Ra Vin Zbal Rast Zir Ra Ra is used to adjust the bridge attenuation its value has no influence on the balance of the bridge 37 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 38 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 4 APPLICATION EXAMPLE 1 LOW VOLTAGE BASIC SET Two application examples are described in this report a low voltage basic set in this chapter and a handsfree application with on hook dialling in chapter 5 Both examples are general purpose applications for exchanges with voltage regulation Fine tuning is required to fulfil specific country requirements Both applications have been build and tested on their functionality 4 1 Description of the application An application example for a low voltage basic telephone set is shown in Fig 45 and Fig 46 It is build up with the TEA1112 transmission IC and a discrete ringer circuit as shown in Fig 45 and the PCD3332 3 pulse tone rep
32. 2 x 32 kQ with maximum tolerances of 15 Thanks to this high input impedance the ICs are suitable for several kinds of microphones dynamic piezoelectric or electret microphones with symmetrical or a symmet rical drives See Fig 17 for some examples From DTMF Internal From MUTE LN From AGC Rec Rexch 5Cucc 5 Cexch REG SLPE Creg Bslpe Fig 16 Microphone channel VCC MIC MIC c MIC MIC MIC MIC VEE Dynamic Electret capacitor Piezoelectric Microphone Microphone Microphone Fig 17 Microphone arrangements examples As can be seen in Fig 16 the microphone amplifier itself is built up out of two parts a pre amplifier which real izes a voltage to current conversion and an end amplifier which realizes the current to voltage conversion The 20 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 overall gain Gvtx of the microphone amplifier from inputs MIC MIC to output LN is given by the following equation Gvtx 20 x log Avtx Rgasint Ri Zline X XK BUB Es Rrefint Rslpe with Ri the dynamic set impedance Rcc Rp typically 619 Q 15 5kQ Rgasint internal resistor realizing the current to voltage conversion typically 69 kQ with a spread of 15 Rrefint internal resistor determining the current of an internal current stabilize
33. 3 with Rgarint Take into account the attenuation from QR output to earpiece due to R14 Overall receive gain from line to earpiece depends on attenuation from line to IR input C10 in combination with earpiece impedance C11 in combination with source impedance and Zir 20 kO typ Value of C8 in combination with R13 Rgarint C9 has to be 20 x C8 MUTE is active high MUTE from dialler has to be high during dialling Apply a series resistance in the MUTE wire from dialler to TEA1112 ca 50 kO to prevent discharge of the VDD capacitor during break periods at pulse dialling or flash at MUTE high MUTE is active low MUTE from the dialler has to be low during dialing Current consumed by the LED is not available for an added HF applica tion The ILED pin can be connected with SLPE when the LED function is not used 58 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 LN R1 H A 619 R HH VCC w R12 12 1 m VEE E il VEE ie vis ae x 4 i C7 100uF vec 47 a E Dy Jp J1 if y m aok T I C144 7nF brs 2 2nF x x A B BAS
34. 4 dB The receive gain of the TEA1112 application is reduced from 1 dB default to 4 5 dB by means of R13 200 kQ Volume control is achieved by potentiometer R41 A proposal for volume control by the PCD3332 3 can be found in 3 while a cir cuit realisation is offered in 6 55 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 The BRL is more than 18 dB at 300 Hz to 3400 Hz complex set impedance R2 220 Q R12 825 Q C12 115 nF and same reference impedance while measured without handset C3 has to be at least 6 8 uF for complex set impedances but can be 4 7 uF for 600 O set impedance to meet BRL requirements Fig 56 shows the maximum power generated into a loudspeaker of 100 Q 50 Q and respectively 25 Q as a func tion of the available line current with and without connected LED The nominal VBB supply voltage measures 3 55 V At the rising edges of the curves the power is limited by the available supply current The power in the flat area of the curves is limited by the supply voltage VBB The power in this area can be increased by an enlarged VBB voltage VBB 3 55 V by means of a resistor between pin VA and pin GND of the TEA1093 3 Adjust in this case also the voltage at SUP by means of R3 to get a minimum DC level of 600 mV between SUP and VBB The current consumed by the LED see Fig 54 is not available for the handsfree loudspeaker function
35. 776 9 has been made for the TEA1112 A with the basic application according Fig 57 The components side is shown in Fig 58 and the board layout in Fig 59 The dimensions of the board are 6 5 x 8 cm It is provided with connection terminals at the PCB edge and jumpers J3 J4 to define the state of the logic inputs of the TEA1112 as well as the TEA1112A Jumpers J1 and J2 are for the LED and AGC function respectively Some of the components are mounted on soldering pins to simplify modification of the application Components R3 R4 R13 and C1 are not placed while R11 and C5 are intended for use of the board with the TEA1113 The TEA1113 is not described in this report refer to 10 See Fig 57 for components values The OM4776 has a single sided wiring with filled ground plane between the interconnections The EMC meas ures on the PCB are A Filtering from A B B A terminals to line input LN of the TEA1112 A by means of C12 and C13 at the line terminals R12 and C14 from pin LN to VEE Filtering from the PCB terminals MIC MIC to the MIC inputs of the IC by C20 and C21 at the PCB terminals series resistors R16 and R17 and decoupling at the MIC pins by means of C16 and C17 The bandwidth of microphone amplifier is limited by C2 Filtering of the receiver channel at input IR by C18 and from output QR to the earpiece terminals by means of R14 and C19 Furthermore is the bandwidth of the receiver amplifier limited by C8 and stability guarantee
36. 90 0 pe line mA Fig 55 Voltages VA B VCC VDD and VBB with respect to SLPE versus lline At 20 mA line current the current into SUP measures 13 8 mA from which 5 5 mA typ is consumed by the inter nal circuitry of the TEA1093 and 250A by the external circuitry connected to VBB The remaining supply current to generate the loudspeaker signal at 20 mA line current is thus about 8 mA which gives a maximum output power of 15 8 mW theoretically into a 50 Q loudspeaker Measured is 12 5 mW at 20 mA see also Fig 56 Transmission Transmit and receive gains are in conformity with the sensitivities of the proposed microphones earpiece and loudspeaker and the performance of the application used as handset or handsfree set The applied handset Ericsson RLGN40201 8B6 contains an electret microphone with a sensitivity of 44 5 dBV Pa 1 kHz 2 KQ load and a dynamic earpiece of 150 Q and 49 dBPa V The base contains the HF microphone with a sensitivity of 46 dBV Pa 1 kHz 2 KQ load and a 50 Q loudspeaker Philips type AD2071 Z50 The overall transmit gain at 600 O line load from R56 or R57 to the line measures 48 dB as a result of 24 dB gain from R56 or R57 to MOUT 20 dB attenuation from MOUT to the MIC inputs of the TEA1112 and 44 dB gain from MIC inputs to the line The default microphone gain of the TEA1112 is reduced to 44 dB by means of R4 47 5 kQ The receive gain from line to earpiece is 6 5 dB from line to loudspeaker about 2
37. BAS11 Sua 54 E x a ax t S ves L C9 cis BASI BAS11 LED 36 C duae ee SL PE Ie CAR e r qme R14 22 1 2 2nF es 3n gp oR T j y TEL 4 lt 1000F C10 tour C13 2 92k LE 4tepg D vee 8 1 b VEE m e T 5 VEE 2 2nF R7 ra T Jt x Sng 4165 MIC H 5 MIC g Ls 392 4 ur 1000F Yt R15 10k BIS 1k B A pnt Foz SIMMUTEI MICH E z T f MIC 9 ee Ono WSS One HTF acc R9 R11 NE 1 C 1 3 0 20 100 MUTE IRA RIS 1 J2 caL cs L T os 220nF TOnF i ef MUTE T pig C6 68nF E ME p 825 T f MMUTE a VEL Los Om J4 V CI 1000F TT onf a EMC components Not placed R3 R4 R13 and C1 R11 and C5 are mounted on the PCB to demonstrate the TEA1113 Fig 57 Circuit diagram of the OM4776 evaluation board with the basic application of the TEA1112 A 59 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 7 RF IMMUNITY OF THE TEA1112 A The TEA1112 and TEA1112A have been designed with on chip measures to keep RF disturbances away from sensitive circuit parts at higher RF frequencies gt 80 MHz For the lower frequency range from 150kHz upwards the coupling into the IC occurs mainly via the A B lines and the handset cord Improvement of the immunity at those frequencies can be realised by filtering at the PCB connectors and IC pins and a PCB layout which is designed with respect to EMC An evaluation board OM4
38. CONTENTS 1 INTRODUCTION 2 BLOCK DIAGRAM AND PINNING 3 DESCRIPTION OF THE IC 3 1 Supply pins LN SLPE VCC REG 3 1 1 TEA1112 A Supply 3 1 2 Supply for peripheral circuits 3 2 Set Impedance come 3 3 Supply foraLED pinILED 3 4 Microphone amplifier pins MIC MIC GAS 3 5 MMUTE function TEA1112 only pin MMUTE 3 6 MMUTE function TEA1112A only pin MMUTE 3 7 Receiving amplifier pins IR GAR QR 3 8 Automatic Gain Control pn AGC 3 9 DTMF amplifier pin DTMF 3 10 MUTE function TEA1112 only pin MUTE 3 11 MUTE function TEA1112A only pin MUTE 3 42 Anti sidetone circuitry 3 12 1 TEA106x family bridge 3 12 2 Wheatstone bridge 4 APPLICATION EXAMPLE 1 LOW VOLTAGE BASIC SET 4 1 Description of the application 4 2 Settings and performance of the application 4 2 1 DC behaviour 4 2 2 Transmission 4 2 3 Dialling 2 eR tS es 5 APPLICATION EXAMPLE2 HANDSFREESET 5 1 Description of the application 5 2 Settings and performance of the application 6 DESIGN ADJUSTMENT STEPS TEA1112 A APPLICATION 7 RFIMMUNITY OF THE TEA1112 A 8 REFERENCES APPENDIX 1 List of abbreviations and definitions Application Note AN95050 Philips Semiconductors Application
39. E i SLPE Fig 43 TEA106X family anti sidetone bridge left and Wheatstone bridge right The TEA106x family anti sidetone bridge has the advantage of a relatively flat transfer function in the audio fre quency range between pins LN and IR both with real and complex set impedances Furthermore the attenuation of the bridge for the received signal between pins LN and IR is independent of the value chosen for Zbal after the set impedance has been fixed and the condition shown in equation 6 is fulfilled Therefore readjustment of the overall receive gain is not necessary in many cases The Wheatstone bridge has the advantages of needing one resistor fewer than the TEA106x family bridge and a smaller capacitor for Zbal But the disadvantages include the dependence of the attenuation of the bridge on the value chosen for Zbal and the frequency dependence of that attenuation This necessitates some readjustment of the overall receive gain 3 12 1 TEA106x family bridge The anti sidetone circuit is composed of Rcc Zline Rast1 Rast2 Rast3 Rslpe and Zbal Maximum compensa tion is obtained when the following conditions are fulfilled Rslpe x Rast Rec x Rast2 Rast3 6 k Rast2 x Rast3 Rslpe Rast x Rslpe Zbal k x Zline 35 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 The scale factor k is chosen to meet the compatibilit
40. Mark Space ratio selection PCD3332 3 65 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits M0 M9 MIC MLA MOUT MRC MUTE MUTER MUTET OM4776 PCB PCD3332 3 PTS PXE Power Down PD Ra Rast RESET RF RFS RINn ROW Rexch Rgarint Rgar Rgasint Rgas Rp SREF STORE SUP TEA1093 TEA1112 TEA1112A TEA1112 A TEA1113 THD TONE VA B VBB VCC VDD VEE Application Note AN95050 Memory location keys PCD3332 3 Microphone input TEA1093 Memory Location Access selection PCD3332 3 Microphone amplifier output TEA1093 Memory Recall key PCD3332 3 MUTE output PCD3332 3 MUTE input TEA1112 Receive channel MUTE input TEA1093 Transmit channel MUTE input TEA1093 Evaluation board for the TEA1112 A Printed Circuit Board Multi standard pulse tone repertory dialler ringer IC Pulse Tone Selection PCD3332 3 Piezo Ceramic Buzzer Element Reduced current consumption mode during pulse dialling or flash Resistor to adjust the sidetone bridge attenuation Anti sidetone resistor Reset input PCD3332 3 Radio Frequency Ringer Frequency Selection PCD3332 3 Receiver amplifier inputs TEA1093 Row keyboard input PCD3332 3 Bridge resistance of exchange Internal resistance 100 kO to define receive gain TEA1112 A External resistance to reduce receive gain TEA1112 A Internal resistance 69 kQ to define microphone gain TEA1112 A External resistance to reduce microphone gain TEA1112 A Internal r
41. agnetic or piezo electric earpieces See Fig 29 for some arrangements examples Dynamic Earpiece Piezoelectric Earpiece Fig 29 Earpieces arrangements examples As can be seen in Fig 28 the receiving amplifier itself is built up out of two parts a pre amplifier which realizes a voltage to current conversion and an end amplifier which realizes the current to voltage conversion The overall gain Gvrx of the receiving amplifier from input IR to output QR is given by the equation Gvrx 20 x logAvrx E Rgarint Avrx ax 1 21 x Rrefint with Rgarint internal resistor realizing the current to voltage conversion typically 100 kQ with a spread of 15 Rrefint internal resistor determining the current of an internal current stabilizer typically 3 4 kQ witha spread of 15 correlated to the spread of Rgarint gain control factor varying from 1 at lline 15 mA to 0 5 at lline 75 mA when AGC function is applied Using these typical values in the equation we find a gain equal to Gvrx 20 x log Avrx 31 dB at lline 15 mA The gain controls AGC and MUTE act on the receiving pre amplifier stage modifying its transconductance Adjustment and performance The receiving gain can be decreased by connecting a resistor Rgar between pins GAR and QR It can be adjusted from 31 dB down to 19 dB to suit application specific requirements The gain dependency to this exter nal resistor is calculate
42. ain DC voltages as a function of the line current while Fig 8 shows the behaviour in the low voltage area v ov 7 0 VLN 6 0 L d m vcc u 8 ES t VREG oem Lt v REF 3 0 L ft LER 2 8 eq 1 0 0 0 19 20 30 40 50 60 70 80 90 100110120130140 Iline mA Fig 7 Main voltages versus line current 14 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits Application Note AN95050 VLN VREF VCC Adjustment Uu 5 cb 7 8 9 10 11 12 ILINE mB Fig 8 Low voltage behaviour The reference voltage VREF can be adjusted by means of an external resistor Rva It can be increased by con necting the Rva resistor between pins REG and SLPE or decreased by connecting the Rva resistor between pins REG and LN However this voltage reduction is possible it is not recommended to use it because it reduces the peripheral supply capability Fig 9 shows the reference voltage VREF as a function of an Rva resistor To ensure correct operation the reference voltage is preferably not adjusted to a value lower than 3 V or higher than 7 V These adjustments will slightly affect a few parameters there will be a small change in the temperature coef ficient of VREF and a slight increase in the spread of this voltage reference F
43. both 1 KQ in series with the MIC inputs and the termination resistor R15 10 kQ across the MIC inputs The send gain of the TEA1112 may be decreased to a minimum of 39dB according 2 The overall send gain results in 37 dB with R4 20 kQ The maximum swing of the line signal measures 5 5 dBm over the frequency range 300 Hz 3400 Hz at 600 Q set impedance 600 Q line load and 20 mA line current Capacitor C30 between the gate source of TR1 keeps TR1 conducting at negative swings of the line signal it improves the maximum swing of the line signal at lower frequencies 45 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 The overall receive gain from line to earpiece is about 2 5 dB at an earpiece impedance of 150 This is due to the attenuation of 32 dB from line to IR input the internally determined gain of the receive stage of 31 dB typically and the 1 5 dB attenuation due to EMC component R14 22 Q The gain values are given without activated AGC function The receive gain can be reduced from 31 dB to 19 dB minimum by means of resistor R13 At R13 100 kQ the receive gain is reduced by 6 dB which result in an overall receive gain of 8 5 dB typically Send and receive gains are internally defined by on chip resistors Reduction of these gains by external resistors R4 R13 result in matching inaccuracies Side tone AGC Reproduction of the electrical
44. c Gain Control pin AGC Principle of operation The TEA1112 A perform automatic line loss compensation The automatic gain control varies the gain of the microphone and receiving amplifiers in accordance with the DC line current To enable the AGC function the pin AGC must be connected to the pin VEE For line currents below a current threshold Istart typical 26 mA the gain control factor o is equal to 1 giving the maximum value for the gains Gvtx and Gvrx If this threshold current is exceeded the gain control factor and the gain of both controlled amplifiers are decreased When the line current reaches a second threshold current Istop typical 61 mA the gain control factor is limited to its mini mum value equal to 0 5 giving the minimum value for the gains Gvtx and Gvrx The gain control range of both amplifiers is typically 5 85 dB This corresponds to a line length of 5 km for a 0 5 mm diameter twisted pair copper cable with a DC resistance of 176Q km and an average attenuation of 1 2 dB km Adjustment and performance The ICs have been optimized for use with an exchange supply voltage of 48V a feeding bridge resistance of 2 times 300 Q and the previously described line To fit with other configurations a resistor Ragc can be con nected between pins AGC and VEE This allows to increase the threshold currents Istart and Istop Fig 35 shows the control of the microphone gain versus the line current for different values of Ragc
45. cation of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 APPLICATION NOTE Application of the TEA1112 and TEA1112A transmission circuits AN95050 Author s Fernand Courtois Communication IC s development group Caen FRANCE Fred van Dongen Product Concept amp Application Laboratory Eindhoven The Netherlands Keywords Telecom Analog telephone set Speech transmission IC TEA1112 A Supply for a LED Date 11 November 1995 3 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Summary This report is intended to provide application support for designing electronic telephone sets with the bipolar transmission ICs TEA1112 and TEA1112A It contains a detailed description of the several circuit blocks of both ICs as well as the possible settings to adjust the DC and transmission characteristics Two application examples of the TEA1112 are given by means of descriptions settings measurement results and performances The report handles the consecutive steps to design or to adjust the basic application with the TEA1112 A An evaluation board for the TEA1112 or TEA1112A has been made The results of the EMC measurements are shown in this report The general notation in this report for both ICs TEA1112 and TEA1112A is TEA1112 A Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits
46. d by means of the combination of C8 and C9 Decoupling at VCC pin by means of C15 General recommendations of EMC measures to design the PCB are Use a filled ground between the wires in case of a single sided PCB or a ground plane when a double sided PCB is applied Place line and handset connectors close to each other on the same side of the PCB and decou ple the connections by means of EMC capacitors Place EMC capacitors as close as possible to the corresponding IC pins Use small size ceramic capacitors Make interconnection wires as short as possible Use wire bridges instead of a clever design with long wires Design a symmetrical microphone entry from connector to MIC inputs of the IC Test method and results The RF immunity test is split up in two test methods The conducting test 11 in the frequency range of 150 kHz to 150 MHz is carried out with a RF disturbance signal coupled into the A B B A cable via coupling decoupling networks The RF signal with an amplitude of 3 V for f 30 MHz and 0 5 V for f gt 30 MHZ is modulated with an AM signal of 1 kHz sinewave and 8096 modulation depth The results of the measurements are given in Fig 60 by means of detected levels at the A B lines and receiver output with respect to 1 Vrms 0 dBV reference level 60 Philips Semiconductors
47. d in equation 5 and shown in Fig 30 The gain adjustment by an external Rgar resistor connected between pins GAS and REG may slightly change the gain spread 27 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 35 0 33 0 31 0 29 0 27 0 25 0 23 0 21 0 5 0k10 0k 100 0k 1 0M 0 0M Rger ohms Fig 30 Receiving gain function of the Rgar resistor connected between GAR and QR Rgarint a Gvrx 20 x log 1 21 x Rrefint 5 Two external capacitors Cgar connected between GAR and QR and Cgars connected between GAR and VEE ensure stability The relationship Cgars gt 20 x Cgar should be fulfilled to ensure stability The Cgar capacitor provides a first order filter which cut off frequency is determined by the relation Cgar x Rgarint Rgar Fig 31 shows the frequency response of the receiving amplifier at different temperature Cgar 100pF Cgars 2 2 nF e 3 x a v 32 Sis 31 31 31 31 30 30 30 30 N 180 0 Ok Cr Fig 31 Receiving gain versus frequency influence of temperature On c gg o o nm c goo o 30 The maximum output swing on QR depends on the DC line voltage the
48. depends on the MMUTE level See TABLE 1 The DTMF input is enabled by either applying a low level 0 3 V typically at the MUTE input or leaving it open In this mode a confidence tone is provided in the earpiece and the microphone and receiving amplifiers are disabled Fig 41 shows the microphone amplifier gain reduction and the input current as a function of the voltage on MUTE The threshold voltage is 0 68 V typically base emitter junction with a temperature coefficient of 2 mV uen Gutx dB Imute uR 60 2 0 50 8 ug 6 30 20 10 2 0 0 10 0 8 20 0 6 30 0 4 40 50 N AVI li N Nn 0 2 60 VEEN M o o 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 0 9 0 9 5 1 0 hes 2 0 euo 3 0 Vmute V Vmute V Fig 41 Microphone gain attenuation and MUTE input current vs Vmute Adjustment and performance Fig 42 shows the microphone and receiving gains reduction at lline 15 mA for an input signal at 1 kHz Two curves are drawn on each graphic The first one shows the spectrum of the signal on the line QR in speech con dition when a signal is applied on the microphone inputs IR input The second curve shows the same signal in DTMF condition Both signals are at a frequency of 1 kHz The difference between the two curves at this fre quency gives the gain reduction
49. determined by the MUTE level Performance Fig 25 shows the microphone amplifier gain reduction at lline 15 mA for an input signal at 1 kHz Two curves are drawn in this figure The first one shows the spectrum of the signal on the line in speech condition when a sig 24 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 nal is applied on the microphone inputs The second curve shows the same signal in DTMF condition Both sig nals are at a frequency of 1 kHz The difference between the two curves at this frequency gives the gain reduction Att dB Microphone channel p 20 30 4 ug 5 A 60 70 80 i2 X9 QU X eS B 1 90 tanc 100 0 0 0 0 f kHz Fig 25 Microphone gain reduction in MMUTE condition The MMUTE function works down to a voltage on VCC equal to 1 6V Iline 2 5 mA in the basic application Below this threshold the microphone amplifier stays always enabled independently of the MMUTE input level The maximum voltage allowed at the MMUTE input is VCC 0 4 V 3 6 MMUTE function TEA1112A only pin MMUTE Principle of operation The MMUTE function realizes an electronic switching between the microphone amplifier and the sending DTMF amplifier This function disables the microphone channel to provide such kind of privacy and in
50. e Me dran scu R49 4 T5k SUP D gt TM H i C52 150nF ca CRI Soar RENV 4 uF C53 470nF E18 sp RNOI sll C55 180pF 221k ed AE ZA AD2071 Z50 v u 2 2nF F C 4 SREF P MIC MICO p R51 C56 L 1 ND 5 GNI s gopr 1K R50 SS SLPE 2 A C57 AEREA SUP MOUT Ee nF C45 95 3k 120nF VBB 3 10 gylis is vpg MUTET K RIN k R52 47k D20 BAS11 C41 a C46 470u lyol MICG ps i R42 4 75k nt R41 R44 365k gt IT C58 MICN FF ok ISUR PD nc 120nF R45 3 65 IC2 MICP ASlorag iors 4 G 55 C48 220nt i WT VA nc R46 2 21M SLPE Bi 4 SLPE MUTE HF R53 1k RTE MUTER VBBI C ie E 4TuF 10V C60 150nF j BC558 p iss II m R60 150k 10 ik i R59 R53 TRS 6ny Pa ET 16k MICO T m bs BC548 BAS11 R62 5mv Pa Y D21 C HF MIC lO 0 C62 47K TRT DE C20 R55 4 68nF X 68nF R64 IR BC558 TRE 470k 4 TnF 4 7nF i Lr VEE i ces 4 4 BC558 R56 Peon ra egei 100 R57 LI T 18nF 2 21k e e LI LI BSS SLPE Fig 52 Application example 2 handsfree application TEA1093 51 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 lt this page is left blank intentionally gt 52 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note
51. e rejection ratio 3 5 MMUTE function TEA1112 only pin MMUTE Principle of operation The microphone mute function realizes an electronic switching between the microphone amplifier and the send ing DTMF amplifier This function disables the microphone channel to provide such kind of privacy and in the same time enables the DTMF channel if needed for some specific applications If a high level is applied to the MMUTE input the sending DTMF channel is activated while the microphone amplifier is disabled The micro phone amplifier can be enabled depending on the MUTE level see TABLE 1 by either applying a low level 0 3 V typically at the MMUTE input or leaving it open Fig 24 shows the microphone amplifier gain reduction and the input current as a function of the input voltage on MMUTE The threshold voltage level is 0 68 V typically base emitter junction with a temperature coefficient of 2 mV C Gutx dB Immute uf 50 2 0 50 1 75 ug 30 1 5 20 1 25 10 ea 9 1 0 l bs 8 75 20 30 98 5 es 0 25 50 bla Mul 68 T 0 0 8 8 208 0m Uu00 0m 608 0m 800 0m 8 9 0 9 5 1 0 1 5 2 0 2 5 3 0 Vmmute V Vmmute V Fig 24 Microphone gain and MMUTE input current vs Vmmute The microphone mute function has no effect on the receiving channel which is fully
52. e set by diode options to specific country requirements A single contact keypad matrix is connected with the corresponding COL and ROW l O s This simple keypad offers no direct access of the stored numbers as proposed for application example 2 The STORE key and MRC key has to be used to store and recall telephone numbers Diode switch MLA has to be open As explained before is the MICMUTE key applied to toggle the microphone amplifier during conversation by means of the LFE output However use of the MICMUTE key during ringing toggles also the ringing melody Reset is performed by the internal reset of the PCD3332 3 mainly Reset components C36 R35 compensates the spread of the internal reset voltage Output DPN FLN drives the interrupter to perform pulse dialling PTS switch closed and flash function F E switch open The position of cradle switch S1 determines the CSI level during stand by CSI low and conversation mode CSI high Input CE FDI is connected to the positive line wire and the diode bridge to detect the operation mode of the PCD3332 3 in combination with CSI Resistor R36 in the MUTE wire is required to prevent discharging of the VDD capacitor during the break periods at pulse dialling or flash when VCC is reduced below the VDD voltage level at MUTE is high Output TONE delivers the melody for the ringer circuit at HF RTE high and the DTMF dialling signal to the DTMF input of the TEA1112 via attenuat
53. ected or changes over to the handset mode when CSI goes high or comes in the on hook dialling or handsfree mode when the HOOK key is activated Ringer mode CE high CSI low resulting in HF RTE high The ringer mode is left when CE goes low for time out stand by mode when the handset is lifted handset mode or when the HOOK key is pressed handsfree mode Handset mode CE high CSI high resulting in HF RTE low The handset mode is left when the hand set is put back on the cradle stand by mode or when the HOOK key is pressed while the handset is put back handsfree mode Handsfree mode HF RTE high CSI low This mode can be entered by pressing the HOOK key The handsfree mode can be left by pressing the HOOK key stand by mode or by lifting the handset handset mode Dialling operations are possible in the handset and handsfree mode Pulse or DTMF dialling can be selected by diode switch PTS 1 Ringer circuit The discrete ringer stage from example 1 is extended in this application with volume control by keypad via the PCD3332 3 outputs VOL1 and VOL2 The sound pressure from the PXE Murata PKM34EW 1224 can be changed by 4 steps Maximum volume is obtained when both VOL1 and VOL2 are low 49 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note
54. ectronic switching between the speech mode and the dialling mode If a high level is applied to the MUTE input the DTMF input is enabled and both microphone and receiving amplifiers are disabled In this mode a confidence tone is provided in the earpiece The microphone and receiving amplifiers are enabled by either applying a low level 0 3 V typically at the MUTE input or leaving it open keep in mind that the microphone channel depends on the MMUTE level See TABLE 1 In this case the DTMF input is disa bled 32 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Fig 39 shows the microphone amplifier gain reduction and the input current as a function of the voltage on MUTE The threshold voltage is 0 68 V typically base emitter junction with a temperature coefficient of 2 mV eC Gutx dB Imute uf 60 2 0 50 1 75 ug 30 15 20 10 14 25 o 1 0 a 10 0 75 20 30 8 50 ug i i 50 pai R 0 25 60 0 0 0 0 0 1 0 2 0 3 O 4 O 5 0 6 0 7 0 8 O 9 1 0 0 0 0 50 1 0 1 5 2 0 e 5 3 0 Vmute V Vmute V Fig 39 Microphone gain attenuation and MUTE input current vs Vmute Adjustment and performance Fig 40 shows the microphone and receiving gains reduction at lline 15 mA for an input signal at 1 KHz Two curves are d
55. ent temperatures Cgas 100 pF 31 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Adjustment and performance When a resistor Rgas is connected between GAS and REG to decrease the microphone gain the DTMF gain varies in the same way the DTMF gain is 26 5 dB lower than the microphone gain without control of AGC Gudtmf dB s 26 25 26 0 25 75 25 25 5 LTT 25 25 10 25 0 24 75 35 2u 5 E 24 25 2u 0 100 0 1 0k 10 0k f Hz Fig 37 DMTF gain versus frequency influence of temperature The input of the DTMF amplifier can handle signals up to180 mVrms with less than 2 THD Fig 38 shows the distortion of the line signal versus the rms input voltage for two different gains aii VA Gudtmf 25 5 dB Pair UJ Gudtmf 12 5 dB 9 0 9 8 8 0 8 0 7 0 7 0 6 0 6 0 5 0 5 0 4 0 ia 4 0 3 0 3 0 E 2 0 2 0 1 0 1 8 La 6 9173 30 0 50 0 70 0 90 0 110 0 9 fo 5 150 0 200 0 250 0 308 0 350 0 vin mVrms vin mVrms Fig 38 Distortion on the line function of the DTMF input signal for two different gains 3 10 MUTE function TEA1112 only pin MUTE Principle of operation The mute function realizes an el
56. erations which have to be taken into account are added as Remarks The com ponents refer to circuit diagram Fig 57 which is the application of evaluation board OM4776 as described in chap ter 7 Adjustment Component s Remark s Set impedance R1 or Z1 Zset depends mainly on R1 or network Z1 R2 R1 C1 for frequen cies from 300 Hz up to 3400 Hz R12 is in series with R1 or Z1 VCC supply depends on DC resistance of R1 or Z1 BRL R1 Z1 C3 BRL depends on Set impedance with respect to reference impedance PTT requirement Value of Leq depends on the values of C3 R9 and resistor between LN and REG if applied is important at the lower fre quencies 300 Hz Adapt C3 to improve BRL at 300 Hz if necessary Value of C3 has also influence on the start up time Side tone Zbal R8 R10 C4 R5 R6 R7 Depends on cable type mean cable length AGC function and Zset DC slope R12 R9 R12 is the best choice Modification of R9 means also an adaption of Leq VLN low voltage threshold current microphone gain AGC function and side tone ba lancing VLN increase R3 REG SLPE Refer to local PTT requirements Increases VCC supply possibilities VLN decrease R LN REG Reduces Leq reduces the BRL at lower frequencies see BRL Reduces VCC supply voltage level take in account the minimum oper ating level of VCC 2 V at 20 mA and the minimum permitted voltage space between VCC and SLPE 1 6 V VCC supply R1 Z1 C1 VCC supply level de
57. ertory dialler ringer IC PCD3332 3 according Fig 46 The interconnections between both figures are indi cated The application offers the following features Transmission functions with adjustable parameters as described for the TEA1112 in chapter 3 Microphone mute function Pulse DTMF and mixed mode dialling redial 13 number repertory dialling as specified in 1 Ringer signal detection and melody generation The application is build up around the TEA1112 The individual settings of the TEA1112 are for 600 O set imped ance and 2 5 V minimum supply voltage for the PCD3332 3 at dialling The several blocks of the application are briefly described in this chapter details concerning the performances are given in chapter 4 2 The TEA1112 in this application cannot be replaced by the TEA1112A version because of the inverted MUTE and MMUTE MUTE and MMUTE of the TEA1112A Polarity guard and protection One diode bridge is applied for the transmission circuit part as well as for the ringer stage to ensure proper func tioning independent of the polarity of the line voltage respectively to rectify the ringer signal Protection is achieved by a break over diode D18 between the A B B A terminals the current limiting components R20 and TR3 the 11 V zenerdiode Z5 between LN and VEE of the transmission IC and by a 5 6 V zener diode Z13 between VDD and VSS of the PCD3332 3 The current limiter R20 and TR3 provides protection against curre
58. esistance of TEA1112 A between LN and REG Supply reference input TEA1093 Store key programming mode PCD3332 3 Supply input TEA1093 Handsfree IC Transmission IC MUTE and MMUTE active high Transmission IC MUTE and MMUTE active low General notation of the TEA1112 as well as the TEA1112A Transmission IC of the TEA111X family with dynamic limiter Total Harmonic Distortion 96 Tone generator output PCD3332 3 Voltage across the A B B A line terminals Supply output TEA1093 Supply pin supply voltage of TEA1112 A Positive supply PCD3332 3 Ground reference TEA1112 A 66 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 VLN DC level at LN of the TEA1112 A with respect to VEE VOL Receiver volume adjustment TEA1093 VOLn Volume control outputs PCD3332 3 VREF Stabilized reference voltage between LN and SLPE of the TEA1112 A VSLPE DC level at SLPE TEA1112 A DC level at GND TEA1093 of HF application VSS Negative Supply PCD3332 3 Vexch Exchange voltage XTALn Oscillator inputs PCD3332 3 Zir Input impedance of receive amplifier TEA1112 A Zmic Symmetrical Input impedance of microphone amplifier TEA1112 A Z1 Complex network between LN and VCC TEA1112 A Zbal Balance network to reduce side tone Zset Set impedance between A B B A terminals a Gain control factor of AGC function 0 5 lt lt 1 x Reference to REFERENCE chapter x Reference to equation x
59. f operation The supply for the TEA1112 A is obtained from the telephone line The ICs generate a stabilized voltage called VREF between pins LN and SLPE This reference voltage typically 3 35 V is temperature compensated The voltage at pin REG is used by the internal regulator to generate the stabilized VREF voltage and is decoupled by a capacitor Creg connected to VEE For effective operation of the telephone set the TEA1112 A must have a low resistance to DC and a high impedance to speech signals The Creg capacitor converted into an equivalent inductance as mentioned in the set impedance section realizes this set impedance conversion from its DC value Rslpe to its AC value Rcc in the audio frequency range The DC voltage at pin SLPE is proportional to the line current The general supply configuration is shown in Fig 5 12 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Zline TER1112 jl TER1112R CVcc 100u Ish peripheral LED E M aet circuits sip Ire n cl Fig 5 Supply configuration The ICs regulate the line voltage at the pin LN The voltage on pin LN can be calculated as VLN VREF Rslpe x Islpe 1 Islpe lline Icc Ip I Iled Ish 2 line Line current Icc Current consumption of the IC Ip Supp
60. f the board wiring Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 2 BLOCK DIAGRAM AND PINNING The block diagram of TEA1112 A is shown by means of Fig 1 The pinning is shown in Fig 2 and Fig 3 current reference Low voltage circuit TEA1112 TEA1112A Fig 1 TEA1112 A Block Diagram 10 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits Pin o NOOA WD vcc 16 PE GAR 15 ED QR 14 EG VEE 13 TER1112 aS MIC 12 UTE MIC 11 DTMF AGC 10 UTE IR 9 Name LN SLPE ILED REG GAS MMUTE DTMF MUTE IR AGC MIC MIC VEE QR GAR VCC Fig 2 TEA1112 pinning Description Positive line terminal Slope adjustment Current available to drive a LED Line voltage regulator decoupling Sending gain adjustment Microphone mute input Dual Tone Multi Frequency input Mute input Receiving amplifier input Automatic gain control Non inverting microphone input Inverting microphone input Negative line terminal Receiving amplifier output Receive gain adjustment Supply voltage for speech and peripherals Application Note
61. h depends of the line current Important for the minimum line voltage A B B A is the minimum supply voltage VDD required by the PCD3332 3 VDD is supplied by VCC which depends on the resistance value of R1 or network between LN and VCC in case of complex impedance and the total current consumption from VCC To guarantee a minimum VDD supply voltage of 2 5 V during DTMF as well as pulse dialling VCC has to be increased by an enlarged reference voltage of the TEA1112 by means of R3 between REG and SLPE In case of 600 set impedance the A B B A voltage measures 6 0 V at 20 mA line current to get a minimum VDD of 2 5 V at DTMF as well as pulse dialling R3 40 kQ The minimum VDD level is reached at pulse dialling long digits when VCC decreases below the VDD level Fig 47 shows the line voltage VA B across the A B B A terminals as a function of line current lline at nominal and increased line voltage by means of R3 40 kQ Supply possibilities VCC can be applied to supply peripherals such as the PCD3332 3 and an electret microphone The possibilities are rather limited and depend in general of the LN SLPE setting the DC resistance of the network between LN and VCC and the total current consumption from VCC Take in account that the minimum VCC level to keep the TEA1112 functioning is about 2 0 V at 20 mA line cur rent Furthermore the voltage difference between VCC and SLPE has to be more than 1 6 V over the whole line current range
62. line ggasint Bgas arene 4 Gvtx 20 x log 1 31 x Rrefint x Rsipe A capacitor Cgas is generally connected between pins GAS and REG to provide a first order low pass filter which cut off frequency is determined by the product Cgas x Rgasint Rgas Fig 19 shows the frequency response of the microphone amplifier at different temperatures Cgas 100 pF Rgasint 69 kQ no external Rgas Gutx dB 53 0 52 8 52 6 52 4 52 2 75 Mee OT 52 0 EM 25 Bug 51 8 AA erT 10 LN N OPTS S ii 225 oo 51 6 LL LL BN 25 len N 51 4 N 51 2 y 51 0 A 100 0 Ok 10 Ok Hz Fig 19 Microphone gain versus frequency influence of temperature Fig 20 shows the distortion of the signal on the line as a function of the microphone input signal for two different gains at nominal DC settings The inputs of the microphone amplifier can handle signals up to 18 mVrms with less than 2 Total Harmonic Distortion THD For overall gains Gvtx larger than 40 dB the distortion will be determined by the output stage clipping of the line signal So Fig 20 a shows a saturation due to the output stage while Fig 20 b shows a saturation due to the input stage T C UL a Gutx 52 dB THD X b Gutx 39 dB i 0 1 5 2 0 25 3 0 3 5 4 0 4 5 5 0 sls 6 0 0 7 0 9 0 LO L3 0 15520 Or 7193 0 vin mVrms vin mVrms
63. lle 22 Fig 20 Distortion on the line as a function of the input signal for two microphone gains 22 Fig 21 Distortion of the line signal versus the rms voltage ontheline llle 23 Fig 22 Noise on the line versus the line current and the microphone gain lll 23 Fig 23 Common mode rejection ratio 2 2s 24 Fig 24 Microphone gain and MMUTE input current vs Vmmute lens 24 Fig 25 Microphone gain reduction in MMUTE condition lr 25 Fig 26 Microphone gain and MMUTE input current vs Vmmute lens 25 Fig 27 Microphone gain reduction in MMUTE condition a 26 Fig 28 Receiving channel i east Se eA v WR VR EUREN qe 26 Fig 29 Earpieces arrangements examples s 27 Fig 30 Receiving gain function of the Rgar resistor connected between GAR andQR 28 Fig 31 Receiving gain versus frequency influence of temperature llle 28 Fig 32 Distortion on QR versus the input signalon IR aa 29 Fig 33 Distortion of the receiving signal for two loads lens 29 Fig 34 Noise onthe earpiece leo oss 30 Fig 35 Automatic gain control on the microphone amplifier llle 31 Fig 36 B EMF channel z nh RR on Rx em Ea A Tee Lm PCR IER e Rex Ge eR IRR qus 31 Fig 37 DMTF gain versus frequency influence of temperature llle 32 Fig 38 Distortion on the line function of the DTMF input signal for two different gains
64. ly current for peripherals I Current consumed between LN and VEE lled Supply current for a LED component Ish Excess line current shunted to SLPE and VEE from LN The DC line current Iline flowing into the set is determined by the exchange supply voltage Vexch the feeding bridge resistance Rexch the DC resistance of the telephone line Rline and the voltage across the set including diode bridge Below a threshold line current Ith is typically equal to 7 5 mA the internal reference voltage generating VREF is automatically adjusted to a lower value This means that more sets can operate in parallel with DC voltage down to an absolute minimum voltage of 1 6 V excluding the diode bridge For line currents below this threshold current the circuit has reduced sending and receiving performances This is called the low voltage area 13 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 The internal circuitry of the TEA1112 A is supplied from pin VCC This supply voltage is derived from the line volt age by means of a resistor Rcc and must be decoupled by a capacitor Cvcc Fig 6 shows the IC current con sumption Icc as a function of the VCC supply voltage ICC mA 7 6 5 4 8 2 xi 0 900 Om 800 Om EE 3 0 8 5 u g 4 5 s g 5 5 6 0 6 5 7 0 vec V Fig 6 ICC versus VCC Fig 7 shows the m
65. nd 80 modu lation depth The results of the measurements are shown in Fig 61 by means of detected levels at the A B lines and receiver output with respect to 1 Vrms 0 dBV reference level The OM4776 evaluation board meets the requirements according 11 and 12 The detected signal levels as a result of the measurements are in both cases less than the 60 dBV demands Note The logic inputs MUTE MMUTE TEA1112 and MUTE MMUTE TEA1112A are sensitive because of the rather low internal pull down currents When they are not used connect them to VEE in case of the TEA1112 or to VCC in case of the TEA1112A 63 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 8 REFERENCES 1 Philips Semiconductors DATA DHEET PCD3332 3 Multi standard pulse tone repertory dialler ringer 2 Philips Semiconductors Tentative Device Specification TEA1112 TEA1112A Low voltage versatile tele phone transmission circuits with dialler interface 3 Philips Semiconductors Application Note ETT AN93015 Application of the TEA1093 handsfree circuit by C H Voorwinden amp K Wortel 4 Philips Semiconductors Application Note ETT AN94001 User Manual for OM4750 Demonstration board TEA1093 and TEA1094 by R v Leeuwen amp C Voorwinden 5 DATA HANDBOOK IC03 Semiconductors For Telecom Systems 6 Philips Semiconductors Application Note ETT AN94002 Design consideration
66. needed for some specific appli cations The difference between the TEA1112 and the TEA1112A concerns the MUTE and MMUTE inputs For TEA1112 the MUTE and MMUTE functions are active for a high level at the inputs while for TEA1112A the MUTE and MMUTE functions are active for a low level on these inputs TABLE 1 shows the enabled channels depending on the levels on these two inputs It can be seen that the MUTE function acts on both sending and receiving channels while the MMUTE function only acts on the sending channel TABLE 1 Channel selection TEA1112 MUTE MMUTE Microphone DTMF Earpiece Confidence Tone TEA1112A MUTE MMUTE Microphone DTMF Earpiece Confidence Tone The report is divided into two parts The first part up to chapter 3 gives a detailed description of the different cir cuit blocks of the TEA1112 A consisting of operating principles settings of DC and transmission characteristics and performances of the different functions The second part describes two application examples of the TEA1112 by means of descriptions settings meas urement results and performances The consecutive steps to design or to adjust the basic application of the TEA1112 A are handled An evaluation board with the basic application of the TEA1112 A is available 9 The results of the RF immunity tests of this board are shown in this report extended with a brief description of the board and the layout o
67. nt surges exceeding 150 mA It is not designed for continuous limitation of the line current The voltage across the ringer output stage is limited at 24 V by means of the zener diodes Z11 and Z13 and diode D12 Interrupter The interrupter consists of TR1 P channel enhancement D MOS BSP304A and inverter TR2 controlled by the DPN FLN open drain output of the PCD3332 3 When the handset is lifted cradle switch S1 changes from ringer state on hook to transmission state off hook DPN FLN is high resulting in a conducting TR1 Interruption of the line current is achieved by a low DPN FLN level Speech transmission The TEA1112 stabilizes the DC voltage between LN and SLPE It delivers the supply voltage VCC for internal use and for the PCD3332 3 via diode D16 VCC is buffered by C7 while VDD is buffered by C35 The set impe dance will be mainly determined by the impedance of the network between LN and VCC This application has a set impedance of about 600 realised by R1 619 Q and R2 0 Q 39 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note
68. of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Tables and figures TABLE 1 Channel selection lll sss sos 9 Fig 1 TEA1112 A Block Diagram lo ss 10 tig 2 TEATIA2Z pinning ez eie ps Ea Seat ERA wur ex EC Be Rue 11 Fig 3 JTEATTT2A PINNING x oe RR DO a ee a a Su Ae hod ri 11 Fig 4 Basic application used for measurement 2n 12 Fig 5 Supply configuration 2 aaa sss hs son 13 Fig 6 CG versus VCG sou denso ere eee etc guru eem Ax 14 Fig 7 Main voltages versus line current lll s 14 Fig 8 Low voltage behaviour lh os 15 Fig 9 Influence of an Rva resistor between REG and SLPE on VREF 15 Fig 10 Influence of Rslpe on the DC slopeofthelinevoltage llle 16 Fig 11 VCC supply voltage versus Ip consumed current forlrec O lll 17 Fig 12 VCC supply point equivalent schematic 1 a ee 17 Fig 13 Equivalent setimpedance 2 0 e e ae e e n e ea a e E a a 18 Fig 14 Set impedance and Balance Return Loss at 600 ohms reference impedance 19 Fig 15 LED supply current versus the available line current 2 aaa a a 19 Fig 16 Microphone channel sec are aa e a e a a oss 20 Fig 17 Microphone arrangements examples a a 20 Fig 18 Microphone gain function of the Rgas resistor connected between GAS andREG 21 Fig 19 Microphone gain versus frequency influence of temperature l
69. of the handsfree application is split up in three figures It consists of an electronic hook switch TEA1112 transmission IC and discrete ringer circuit as shown in Fig 51 the TEA1093 handsfree applica tion Fig 52 and the PCD3332 3 pulse tone repertory dialler ringer IC according Fig 53 Interconnections between Fig 51 and Fig 52 are indicated by means of net in net out symbols while interconnections between Fig 51 and Fig 53 are given by offpage symbols The application offers Pulse DTMF and mixed mode dialling redial 13 number repertory dialling with the PCD3332 3 1 Transmission functions with adjustable settings as described for the TEA1112 chapter 3 Handset operation Handsfree operation Ringer signal detection melody generation and volume control Line connection electronic hook switch interrupter The transmission circuitry and the ringer stage are connected with the line by two separate diode bridges to ensure proper functioning of the application independent of the polarity of line voltage and to rectify the ringer sig nal The two zener diodes Z14 and Z15 in series with the ringer bridge reduce the line load from the ringer stage during transmission The application is protected against over voltages at the line input by break over diode D18 Components R20 and TR3 limit the current through TR1 when the line current exceeds about 150mA This current limiter is not designed for continuous limitation of the line current
70. oflline a 54 Fig 55 Voltages VA B VCC VDD and VBB with respect to SLPE versus lline 55 Fig 56 Maximum power into 100W 50W respectively 25W loudspeaker versus line 56 Fig 57 Circuit diagram of the OM4776 evaluation board with the basic application of the TEA1112 A 59 Fig 58 Components side of the OM4776 evaluation board 0022 ee eee 61 Fig 59 Layout of the wiring of the OM4776 ls sss 61 Fig 60 EMC behaviour of the OM4776 conducting test 2n 62 Fig 61 EMC behaviour of the OM4776 radiationtest 2l 62 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 1 INTRODUCTION The TEA1112 A offer all the speech and line interface functions required in electronic telephone sets They per form the interface between the telephone line and transducers such as microphone capsule s earpiece loud speaker in case of LI or HF functions as well as dialler circuit for DTMF and pulse dialling Moreover they offer a hook status indicator by means of LED output Both ICs have a MUTE function to switch between conversation and dialling as well as a MMUTE function to disable the microphone channel to give some privacy furthermore this MMUTE function enables the sending DTMF channel if
71. oller of the TEA1093 are according the Application Note of the TEA1093 3 and the demonstration model of the TEA1093 4 PCD3332 3 dialler ringer A single contact 6 x 5 matrix keypad is connected with the corresponding COL and ROW I O s The keypad includes 10 memory keys MO to M9 for direct access of the stored numbers in case the MLA diode switch is closed PCD3332 3 output DPN FLN drives the electronic hook switch to perform pulse dialling and flash func tion F E diode option not applied Reset is performed by the internal reset of the PCD3332 3 mainly Reset components C71 R71 compensates the spread of the internal reset voltage Input CE FDI is connected to the positive line wire and the ringer bridge to detect the operation mode of the PCD3332 3 in combination with CSI Series diode D17 in the positive line wire is applied to get a fast trailing edge of the CE pulse after on hook or at line breaks Output MUTE is wired to the TEA1112 via R16 and to the TEA1093 via R52 and D20 This diode prevents levels at MUTET below the GND reference of the TEA1093 Output TONE delivers the melody for the ringer circuit at HF RTE is high and DTMF dialling signal to the DTMF input of the TEA1112 via the attenuator R41 R42 The different modes of the PCD3332 3 are Stand by mode CE CSI and HF RTE are low during a specific time The stand by mode is left when CE goes high It changes over to the ringer mode when an incoming ringer signal is det
72. or R41 R42 ROW 5 of the PCD3332 3 is an open drain output which is pulled up by R44 Ringer circuit The VDD capacitor is kept charged during stand by to speed up initialization of the PCD3332 3 at incoming calls see Start up in this chapter Supply of the ringer is delivered by the ringer signal from the exchange via the bridge and the series network C31 R25 When CE becomes high and CSI is kept low the PCD3332 3 enters the ringer mode at frequencies of the ringer signal between 20 Hz and 57 Hz RFS switch is open or between 14 Hz and 75 Hz RFS switch is closed Output HF RTE will be high during ringing to select the ringer circuit Volume control is performed by potentiometer R30 In application example 2 the volume of the ringer sound is controlled by means of the VOL1 and VOL2 outputs and the VOL1 VOL2 keys This principle can be applied for this example also The ringer melody can be changed by means of the key board buttons 1 2 and 3 42 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 4 2 Settings and performance of the application 4 2 1 DC behaviour DC settings The DC voltage at the A B B A terminals is a result of the voltage drop across the TEA1112 line interrupter and diode bridge The voltage drop across the TEA1112 depends on the setting of the reference voltage VREF between LN and SLPE and the voltage drop across R9 whic
73. pends on VLN resistance of R1 or network Z1 between LN and VCC and current consumption from VCC Take in account the minimum operating level of VCC and the minimum voltage space between VCC and SLPE AGC R18 Internally defined when AGC pin is connected to VEE Adjustable by R18 to increase start and stop currents in relation with Vexch and Rexch See chapter 3 8 AGC function can be disabled by leaving pin AGC open 57 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits Microphone gain R4 High pass Lowpass C2 Supply DTMF gain Receive gain R13 High pass Lowpass C8 Stability C9 MUTE TEA1112 MUTE TEA1112A LED Application Note AN95050 Internally defined at 52 dB by internal resistance Rgasint Can be reduced by R4 No matching of R4 with Rgasint Take into account the attenuation from capsule to MIC inputs due to R16 and R17 with respect to R15 in parallel with Zmic 2 64 kO typ Value of couple capacitors of microphone with respect to input imped ance of external microphone network Value of C2 in combination with R4 Rgasint Electret microphone supplied from VCC via extra RC filter DTMF gain is microphone gain 26 5 dB Total DTMF gain has to be set by means of the attenuation network between DTMF generator and TEA1112 A DTMF input Internally defined at 31 dB from IR to QR by internal resistance Rgar int Can be reduced by R13 No matching of R1
74. r typically 3 4 kQ witha spread of 15 correlated to the spread of Rgasint Zline load impedance of the line during the measurement amp gain control factor varying from 1 at lline 15 mA to 0 5 at lline 75 mA when AGC function is applied see chapter 3 8 Using these typical values in the equation we find a gain equal to Gvtx 20 x log Avtx 52 dB at lline 15 mA The different gain controls AGC MUTE MMUTE act on the microphone pre amplifier stage modifying its transconductance Adjustment and performance The microphone gain can be decreased by connecting a resistor Rgas between pins GAS and REG It can be adjusted from 52 dB down to 39 dB to suit application specific requirements The gain dependency to this exter nal resistor is calculated in equation 4 and shown in Fig 18 at 1 kHz and for a typical sample The gain adjust ment by an external Rgas resistor connected between pins GAS and REG may slightly change the gain spread Gutx dB 55 0 53 0 51 0 1 49 0 47 0 45 0 43 0 41 0 39 x d 5 0k 10 0k 1898 0k 1 0M 0 8M Rges ohms Fig 18 Microphone gain function of the Rgas resistor connected between GAS and REG 21 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 Rgasint Rgas Ri Z
75. rawn on each graphic The first one shows the spectrum of the signal on the line QR in speech con dition when a signal is applied on the microphone inputs IR input The second curve shows the same signal in DTMF condition Both signals are at a frequency of 1 kHz The difference between the two curves at this fre quency gives the gain reduction a dB Microphone chennel Fb dB Receiving channel 10 0 20 0 30 0 40 0 50 0 60 0 70 0 80 0 90 0 100 0 1 0 3 0 0 5 0 4 0 f kHz f kHz Fig 40 Microphone gain and earpiece gain reduction in MUTE condition The MUTE function works down to a voltage on VCC equal to 1 6V lline 2 2 5 mA in the basic application Below this threshold the microphone amplifier stays always enabled independently of the MUTE input level The maximum voltage allowed at the MUTE input is VCC 0 4V 33 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 3 11 MUTE function TEA1112A only pin MUTE Principle of operation The MUTE function realizes an electronic switching between the speech mode and the dialling mode If a high level is applied to the MUTE input the microphone and receiving amplifiers are enabled and the DTMF input is disabled keep in mind that the microphone channel
76. ress of the dialled digit or flash the PCD3332 3 has to be supplied by the stored energy of C35 because the level of VCC is too low to charge up this capacitor The value of buffer capacitor C35 has a value of 220 uF to keep the VDD supply level at gt 2 5 V Fig 50 shows the voltage at the A B B A terminals supply voltages VCC and VDD and the line current during dialling of a zero at R3 40 kQ Vexchange 48 V and 20 mA line current The VDD voltage is reduced to about 2 5 V at the end of dialling phase as a test result for this application example Take into account that VDD could be lt 2 5 V at worst case conditions The selectable maximum FLASH time of the PCD3332 3 is 600 ms At flash times of 600 ms the VDD voltage remains gt 2 5V 46 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 50 0 T VA B R3 40 kQ V 25 0 4 0 0 vec 9 V 3 0 bo VRAIN 1 0 VDD 4 0 V gp eee LL LL ed nuu eiui A 2 0 1 0 lline 30 0m A 200m A 10 0m 0 0 0 0 500 0m 1 0 1 5 t s 2 0 Fig 50 Behaviour of application example 1 during pulse dialling at 20 mA 47 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 5 APPLICATION EXAMPLE 2 HANDSFREE SET 5 1 Description of the application The circuit diagram
77. s for a high_end telephone set with PCA1070 TEA1093 and PCD335X by K Wortel 7 Philips Semiconductors Application Note ETT95007 OM4757 Demonstration Board PCD3332 3 TEA1064B 1062 TEA1093 1094 by F v Dongen 8 Philips Components Laboratory Report ETT89009 Application of the versatile speech transmission cir cuit TEA1064 in full electronic telephone sets by F v Dongen amp P J M Sijbers 9 Philips Semiconductors User Manual ETT UM9501 1 Evaluation board for the TEA1112 A and TEA1113 by E Bosma 10 Philips Semiconductors Tentative Device Specification TEA1113 Low voltage versatile telephone trans mission circuit with dialler interface 11 IEC Publication DIS 1000 4 6 formerly 801 6 Electromagnetic compatibility for electrical and electronic equipment Part6 Immunity to conducted disturbances induced by radio frequency fields above 9 kHz 12 IEC 1000 4 3 Draft International Standard Annex B Immunity to radiated radio frequency electromag netic fields formerly IEC 801 3 64 Philips Semiconductors Application of the TEA1112 and TEA1112A transmission circuits APPENDIX 1 A B B A AGC APT BRL CE FDI COL CSI DIODE DOO DPN FLN DTMF EMC Electret F E GND GNDMIC Gvrx Gvtx HC4053 HF HF mic HF RTE HOOK HP HS mic ICC Icc lled lline Ip Irec Ish Istart Istop Ith Itr k LED LFE LI Leq M S Application Note AN95050 List of abbreviations and defini
78. sion circuits AN95050 4 2 2 Transmission Set impedance and BRL A set impedance of 600 can be realised with R1 619 O while for complex set impedance the network between LN and VCC has to be defined Fig 49 shows the BRL dB of a 600 Q set measured with 600 Q reference In the same graph is given the BRL dB of a complex set consisting of R1 825 Q C1 115 nF and R2 220 measured with a reference impe dance of 825 Q 115 nF 220 Q In case of complex set impedance the value of capacitor C3 has to be increased to meet BRL requirements In this example at R1 825 Q C1 115 nF and R2 220 Q the value of C3 6 8 uF To eliminate the influence of the transducers in the handset they have been replaced by 200 resistors during the measurement The line current is 20 mA 40 0 E BRL gg 4 30 0 Zset 600 Q C3 4 7 uF d 25 0 20 0 T Zset 220048250 115nF C3 6 8 uF 15 0 10 0 ae 5 0 100 0 5 0k 1 0k f Hz Fig 49 BRL of application example 1 at real and complex termination Send and receive This application is intended for use with a dynamic microphone The total gain from microphone terminals to the line measures 50dB at 600 set impedance and 600 Q line load without AGC function The internal setting of the TEA1112 is 52 dB typical while about 2 dB is lost due the EMC components R16 and R17
79. the spectrum of the signal on the line in speech condition when a sig nal is applied on the microphone inputs The second curve shows the same signal in DTMF condition Both sig nals are at a frequency of 1 kHz The difference between the two curves at this frequency gives the gain reduction Att dB Oi ekophone Sabtnal 0 0 18 8 20 0 30 8 40 0 50 0 60 0 70 0 80 0 90 04 SEE T 1 8 2 0 3 9 Uu 5 0 kHz Fig 27 Microphone gain reduction in MMUTE condition The MMUTE function works down to a voltage on VCC equal to 1 6V Iline 2 5 mA in the basic application Below this threshold the microphone amplifier stays always enabled independently to the MMUTE input level The maximum voltage allowed at the MMUTE input is VCC 0 4 V 3 7 Receiving amplifier pins IR GAR QR Principle of operation In Fig 28 the block diagram of the receiving amplifier of the TEA1112 A is depicted From DTMF Rgarint QR From MUTE i From AGC VCC 2 Fig 28 Receiving channel 26 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 The receiving amplifier has an a symmetrical high input impedance between pins IR and VEE It is equal to 20 kQ with maximum tolerances of 15 The ICs are suitable for several kind of earpieces and can drive either dynamic m
80. tions Line terminals of application examples Automatic Gain Control line loss compensation facility Access Pause Time selection PCD3332 3 Balance Return Loss Chip Enable Frequency Discriminator Input PCD3332 3 Column keyboard input PCD3332 3 Cradle switch input PCD3332 3 Diode option input PCD3332 3 DTMF output selection PCD3332 3 Inverted Dial Pulse FLash output PCD3332 3 Dual Tone Multi Frequency Electro Magnetic Compatibility Electret microphone with amplifier Flash Earth selection PCD3332 3 Ground reference TEA1093 Ground reference microphone amplifier TEA1093 Gain factor of receive stage TEA1112 A Gain factor of transmit stage TEA1112 A Philips IC with 3 2 channel analogue switches Handsfree Handsfree microphone Handsfree Ringer Tone Enable output PCD3332 3 HOOK key PCD3332 3 High Pass Handset microphone Current consumption of the TEA1112 A from VCC Current through the LED connected between LN and ILED Line current Current consumption of the peripheral devices connected to VCC Internal current consumption from VCC of the receiver amplifier of the TEA1112 A Excess of line current from LN to SLPE Start and stop currents of the AGC function Threshold current of low voltage function Current in transmission circuit of HF application Scale factor of balance network Light Emitting Diode Enable output PCD3332 3 Listening in Artificial inductor of voltage stabilizer TEA1112 A Leq R9 C3 Rp
81. urthermore the Rva resistor con nected between REG and LN will slightly affect the set impedance See section Set impedance 3 2 Vref V 7 0 3i Q 5 Ok 9 Ok 100 0k OM Rue REG SLPE 0 0M ohms Fig 9 Influence of an Rva resistor between REG and SLPE on VREF The DC slope of the voltage on pin LN is influenced by the Rslpe resistor as shown in Fig 10 The preferred value for Rslpe is 20 Q Changing this value will affect more than the DC characteristics It also influences the 15 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 microphone and DTMF gains the LED supply current characteristic the gain control characteristics the sidetone level the maximum output swing on the line and the low voltage current threshold Ith VLN V 9 0 Rslpe 33 ohms 8 0 Pd 27 ohms 7 0 L zer 20 ohms 6 0 pue 15 ohms 5 0 10 ohms ee eee eee 4 0 qe 3 0 y M 1 0 0 0 20 0 40 0 60 0 80 0 100 0 120 0 140 0 Iline mA Fig 10 Influence of Rslpe on the DC slope of the line voltage 3 1 2 Supply for peripheral circuits Principle of operation The supply voltage at pin VCC is normally used to supply the internal circuitry of the TEA1112 A However a
82. varies with the voltage on VCC A worst case value for Recint is Rec Rccint Rec internal impedance between VCC and VEE 16 Philips Semiconductors Application of the TEA1112 and TEA1112A Application Note transmission circuits AN95050 vcc V 4 0 3515 Rec 619 Q 315 3 25 3 0 2577 No Rva 2 75 E 2 5 2 25 2 0 1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 8 Ip mA Fig 11 VCC supply voltage versus Ip consumed current for Irec 0 Recint VCC Peripheral ies Irec Ip circuit VEE Fig 12 VCC supply point equivalent schematic As VCC is limited to a minimum value to ensure correct functioning Ip will be limited to a maximum value The limit is imposed by the requirement to maintain a minimum permitted voltage between VCC and SLPE which is called Vmin So the maximum current available depends on the DC settings of the IC VREF Rcc Rslpe and the required AC signal level at the line and receiver outputs To simplify the calculation we will use the worst case for Rccint which is Rcc It gives VCC VLN Rcc lIcc Irec VCC VREF Rslpe lline Icc irec Rec Icc Irec VCCmin Vmin Rslpe lline Icc Irec Ip VCC VCCmin Ipmax Ace Ipmax aS ae VN CS fice e ire Rcc Rslpe Rcc Rslpe Sr Rslpe Vmin LIV vin anel Ro 17 Philips Semiconductors
83. y with a standard capacitor from the E6 or E12 range for Zbal In practice Zline varies strongly with the line length and line type Consequently the value for Zbal has to be cho sen to fit with an average line length giving satisfactory sidetone suppression with short and long lines The sup pression further depends on the accuracy with which Zbal equals this average line impedance Example Let s optimize for a line length of 5 km 0 5 mm diameter copper twisted pair with an average attenuation of 1 2 dB km a DC resistance of 176 km and a capacitance of 38 nF km The approximate equivalent line imped ance is shown in Fig 44 1265 ohns 210 ohms 140 nF Fig 44 Equivalent average line impedance For compatibility of the capacitor value in Zbal with a standard capacitor from the E6 series 220nF _ 140nF np 496 For Rast3 a value of 3 92 kQ has been chosen So using the previous equations we can calculate Zbal Rast1 Rast2 We find Rast1 130 kQ Rast2 390 and for Zbal 130Q in series with 220nF 820 Q The attenuation of the received line signal between LN and IR can be derived from equation 7 Vir _ Zir Rast2 7 Vin Rastl Zir Rast2 if Rast2 gt gt Rast3 Zbal With the values used in the example it gives 32 dB at 1 kHz Zir is the receiving amplifier input impedance typically 20 KQ 36 Philips Semiconductors Application of the TEA1112 and TEA

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