Atmel AVR2092: REB232ED
Contents
1. il Jo 12249 L O SUOISIADY LLOZ Z0 6L awd YOAMZON 19 essenspueliexoeniss ueoxj dPHd 0 L 7 A 291024 25 V 66010 Sal 4 3H SOWO 7 n 1 0774 an Ene pm zdz 19862 5 VOLOSZLV NG 09 19906 IN 9 lt T NS See 19461 MUL TAS YIN 680 9 09852 POAMZON NOS amg 2 ata 5o Oy E oer 2 voer ajpped oq o1 E PA 90 jou pue do uo auejd T OSIIN 0 suid 86 oimoy T TAS HH TAS Pu Bor J VOIOSCLV 19862 1 NISA 97991 AND 2991 ANO AND sn ZEdMLON WN me 855 159 955 IS KR IS Em uo ouop 94 1861 2552 AND punog AND O pens A ala 5 2 Ss E E n O a O Kk a TIVIX 2 ssaa 19 61 9004 el veo 559 SSAV ZHINOOL o 40052 a jalan a zed ORI DIAD Umm SSAG 4 981 a SSAV UL 415 idis SSAV cola Zia Ze SSAV 73 6 5 lt TA A 3 gerez 25 n n n 2624H981LY o Ga CS SN ES l2. Atmel AVR2092 REB232ED Hardware User Manual 8 bit Atmel Aa Microcontrollers High performance 2 4GHz RF CMOS Atmel AT86RF232 radio transceiver targeted for IEEE 802 15 4 ZigBee and ISM applications Industry leading 104dB link budget Ultra low current consumption Application Note Ultra low supply voltage 1 8V to 3 6V Hardware supported antenna diversity RF reference design and high performance evaluation platform Interfaces to several of the Atmel microcontroller development platforms Board information EEPROM MAC address Board identification features and serial number Crystal calibration values 1 Introduction This manual describes the REB232ED radio extender board supporting antenna diversity in combination with the Atmel AT86RF232 radio transceiver Detailed information is given in the individual sections about the board functionality the board interfaces and the board design REB232ED connects directly to the REB controller base board REB CBB or can be used as an RF interface in combination with one of the Atmel microcontroller development platforms The REB232ED together with a microcontroller forms a fully functional wireless node Figure 1 1 Top with removed RF shield and bottom views of the REB232ED J pus 09 51 01 Jem MAC Aman Rev 8427A AVR 10 11 AIMEL Ss 2 Disclaimer Typical values contained in this application note are based o
3. Coupling between left and right antennas 1 Active ChiTrace 2 Response 3 Stimulus 4MkrfAnalvsis 5 Instr State Trigger 4 000 amp 000 Hald All Channels 10 00 Continuous Disp Channels 12 00 Trigger Source Internal 14 00 Trigger Ewent On Sweep 16 00 Restart Trigger 20 00 1 Start 2 3 GHz IFBIN 70 kHz Stop 2 6 GHz 239 1 Stop ExtRef Ready Svc 2007 05 30 18 41 If practical situations are further analyzed see Figure 5 10 page 19 one can derive a practical antenna gain for the diversity setups To ensure robust and reliable communication a single antenna system has to consider at least a 30dB link margin as fade margin Considering the multipath setup used for the experiment a signal level of 70dBm is the worst case receiver signal strength when operating on antenna diversity A single antenna system could get into a spot where the receive power is as low as 85dBm It might be too optimistic in an indoor environment to take the 15dB and state that an antenna diversity system has four times the range compared to a non antenna diversity system But antenna diversity cuts deep fades and strongly increases the Stability of a radio link This is essential for radio nodes that get installed in a fixed position as with wall mounted equipment The location of deep fades can move over time due to small changes inside the room or building as
4. During tuning the best compromise in between RX and TX performance has to be found Tuning should be done for the receiver first First step should be to verify 500 matching at U1 pin 5 After that the capacitor position and value can be slightly varied The reception performance should be measured using a packet error test Typical tuning capacitor values are 1pF 0 5pF To simplify the tuning the receiver input power should be adjusted to a value where a PER of 1 can be measured For the measurement 5000 to 10 000 Frames should be used to get a clear PER value After a board tuning change the PER should be measured with the same environment as before Now the new sensitivity can be evaluated based on a simple rule of thumb A PER change by one decimal power from 1 up to 10 or down to 0 1 corresponds in average with a 1dB change in sensitivity The tuning measurements have to take the whole frequency band into account The matching point for best sensitivity can but may not be identical with the best S11 matching point The matching point for the lowest noise figure will be different from the best S11 matching point that can be measured When satisfying reception sensitivity was achieved the transmitter performance should be tested Main parameters are transmitting power EVM spurious emissions and performance flatness over the whole frequency band 5 7 Ceramic antenna 5 7 1 Antenna design study Part of the diversity b
5. MCU 16MHz int RC 32 2 7 3 5 Suppl t 30 Atmel AVR2092 8427A AVR 10 11 8 Abbreviations AD AES BB CBB REB CBB ETSI EVM FCC ISM LNA MAC NWA PA PDI PER R amp TTE REB RF RX SMA SPI TX USART XTAL 8427A AVR 10 11 Atmel AVR2092 Antenna diversity Advanced encryption standard Baseband Controller base board European Telecommunications Standards Institute Error Vector Magnitude Federal Communications Commission Industrial scientific and medical frequency band Low noise amplifier Medium access control Network analyzer Power amplifier Program debug interface Packet error rate Radio and Telecommunications Terminal Equipment Directive of the European Union Radio extender board Radio frequency Receiver Sub miniature A connection Serial peripheral interface Transmitter Universal synchronous asynchronous receiver transmitter Crystal ATMEL MEL Appendix PCB design data A 1 Schematic Figure 8 1 REB232ED schematic 8 L 9 5 v T 20049507721 ZEZH3H JU 09852
6. resolution 1 10dBi For example 15 will indicate a gain of 1 5dBi The values 00h and FFh are per definition invalid Zero or 0 1dBi has to be indicated as 01h or FEh char 30 Textual board description Ox3E CRC uint16 16 bit CRC checksum standard ITU T generator polynomial G4e X x e x x 1 Figure 4 3 Example EEPROM dump EEPROM dump 0000 49 41 17 FF FF 25 04 00 D6 11 00 00 2 00 00 00 GAB kayat GP 0010 02 04 01 01 06 02 A8 A9 01 FF FF FF FF FF FF FE 0020 52 61 64 69 6F 45 78 74 65 6E 64 65 72 32 33 32 RadioExtender232 0030 45 44 00 00 00 00 00 00 00 00 00 00 00 00 8D 9B Ij AA Ar 0040 FF FF FF FF FF FF FF FF a axe 0050 FF FF FF FF FF FF FF 0060 FF FF FF FF FF FF FF PE ece cede nace aed 0070 EE EH 7 8427A AVR 10 11 e AIMEL es 4 3 Supply current sensing NOTE The power supply pins of the radio transceiver are protected against overvoltage stress and reverse polarity at the EXPAND1 pins net CVTG net using Zener diode D1 and a thermal fuse F1 see Exhibit Appendix A This is required because the Atmel STK500 will provide 5V as default voltage and the board can also be mounte
7. 11 e AIMEL es 4 Functional description The block diagram of the REB232ED radio extender board is shown in Figure 4 1 The power supply pins and all digital I Os of the radio transceiver are routed to the 2 x 20 pin expansion connector to interface to a power supply and a microcontroller The Atmel AT86RF232 antenna diversity AD feature supports the control of two antennas 1 A digital control pin DIG1 is used to control an external RF switch selecting one of the two antennas During the RX listening period the radio transceiver switches between the two antennas autonomously without the need for microcontroller interaction if the AD algorithm is enabled Once an IEEE 802 15 4 synchronization header is detected an antenna providing sufficient signal quality is selected to receive the remaining frame This ensures reliability and robustness especially in harsh environments with strong multipath fading effects Board specific information such as board identifier the node MAC address and production calibration values are stored in an ID EEPROM The SPI bus of the EEPROM is shared with the radio transceiver s interface Figure 4 1 REB232ED block diagram TP6 TP7 O ANTO 500hm RF Switch Balun EXPANDI ANT1 XTAL eee 4 1 Interface connector specification The REB is equipped with a 2 x 20 pin 100mil expansion connector The pin assignment enables a direct interface to the
8. CE YY Atmel Corporation 2325 Orchard Parkway San Jose CA 95131 USA Tel 1 408 441 0311 Fax 1 408 487 2600 www atmel com Atmel Asia Limited Unit 01 5 amp 16 19F BEA Tower Milennium City 5 418 Kwun Tong Road Kwun Tong Kowloon HONG KONG Tel 852 2245 6100 Fax 852 2722 1369 2011 Atmel Corporation All rights reserved Atmel Munich GmbH Business Campus Parkring 4 D 85748 Garching b Munich GERMANY Tel 49 89 31970 0 Fax 49 89 3194621 Atmel Japan 16F Shin Osaki Kangyo Bldg 1 6 4 Osaki Shinagawa ku Tokyo 104 0032 JAPAN Tel 81 3 6417 0300 Fax 81 3 6417 0370 Atmel Atmel logo and combinations thereof AVR STK and others are registered trademarks or trademarks of Atmel Corporation or its subsidiaries Other terms and product names may be trademarks of others Disclaimer The information in this document is provided in connection with Atmel products No license express or implied by estoppel or otherwise to any intellectual property right is granted by this document or in connection with the sale of Atmel products EXCEPT AS SET FORTH IN THE ATMEL TERMS AND CONDITIONS OF SALES LOCATED ON THE ATMEL WEBSITE ATMEL ASSUMES NO LIABILITY WHATSOEVER AND DISCLAIMS ANY EXPRESS IMPLIED OR STATUTORY WARRANTY RELATING TO ITS PRODUCTS INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTY OF MERCHANTABILITY FITNESS FOR A PARTICULAR PURPOSE OR NON INFRINGEMENT IN NO EVENT SHAL
9. REB CBB 2 Further the interface connects to the Atmel STK 500 501 microcontroller development platform to enable support for various Atmel 8 bit AVR microcontrollers The REB is preconfigured to interface to an STK501 with an Atmel ATmega1281 If an Atmel ATmega644 is used as the microcontroller the resistors R10 through R18 must be removed and re installed on the board manually as resistors R20 through R28 see exhibit Appendix A Other microcontroller development platforms need to be interfaced using a special adapter board 4 Atmel AVR2092 8427A AVR 10 11 Atmel AVR2092 4 1 1 Atmel ATmega1281 configuration Table 4 1 Default expansion connector mapping ATmega1281 configuration Pint Function _ _____ n ew 0 2 oo son lg nm 4 1 2 Atmel ATmega644 configuration 8427A AVR 10 11 Table 4 2 Expansion connector mapping when assembled for ATmega644 Pint Function Pime Function AIMEL 5 e 4 2 ID EEPROM 6 Atmel AVR2092 ATMEL Pin Pm Function To identify the board type by software an optional identification ID EEPROM is populated Information about the board the node MAC address and production calibration values are stored here An Atmel AT25010A 9 with 128 x 8 bit organization and SPI bus is used because of its small package and low voltage low power operation The SPI bus is shared between the EEPROM and the tran
10. behavior the board must be placed in a position similar that of the final application If the final application has a housing installed then all these measurements must be done with the housing attached Any piece of metal or plastic can tune the antenna to a different frequency In the case of small boards with an edge length of less than 10cm the connected RF cable is often a source of measurement errors The outer conductor of the coaxial cable could interact with the field radiated by the antenna and therefore create an additional counterpart ground for the antenna To avoid this effect the coaxial cable can be fed through several ferrite beads The ferrite beads need to be placed close to the test board The initial measurement shows that the antenna is already working nicely in the desired frequency band The feed resistance is a bit low and the antenna has an inductive behavior AIMEL 21 ATMEL Figure 5 13 Antenna without tuning elements 50 00 xt 1 Start 2 3 GHz IFB 70 kHz Stop 2 6 GHz 37 The first tuning step will use the series capacitor to tune the band center down to a pure resistive behavior The band center is crossing the 30 degree 1 3 x Zo line Therefore the tuning capacitor can be determined by 1 C 27fXc with 5 f 2 450GHz We get a capacitance of 3 89pF and can simply use a 3 9pF value The result of this tuning step can be seen i
11. l 60 80 42 90 eo KO o e ko gt 8 L E 50 uonipuoo 2591 Og SION SSE oN oso dn ayem INHOOS 1499 INHOOS 149 eureNsse 5 29 La O OWT zHOSr 2 a ZHOSPZ I y ek YIM 51011891 558 85862 85862 IND 1 UND Jo osn oL IK LOGALS 8 L 9 5 v I Atmel AVR2092 32 8427A AVR 10 11 Atmel AVR2092 A 2 Assembly drawing Figure 8 2 REB232ED assembly drawing Al NAT 4 SAN a REB232ED U 1 0 DE 5 449 30 00 260 00 TP4 AMEL a 8427A AVR 10 11 AIMEL as A 3 Bill of materials Table 8 1 Bill of materials Qty Designator Description Footprint Manuf Part Manufacturer Comment RF Connector Build in antenna 1 X2 MS 147 MS147 CL358 150 5 06 Hirose switch 500 1 X1 NAPALA es HEADER 20X2 90 degree Top Invers 1 U5 EEPROM MiniMap 8 2X3 2227 Atmel AT25010A 10YH 1 8 1 U4 Logic gate MO 187 NV7WP32K8X Fairchild NC7WP32K8X 1 U3 si lod Ca MLF 32 AT86RF232 Atmel AT86RF232 radio transceiver 2 U2 U6 Dual INV ULP SC 70 6 NC7WV04P6X Fairchild NC7WV04 U1 RF switch SC 70 6 AS222 92 SkyWorks AS222 92 1 S1 SMT RF Shield Shield BMIS LTO8AD4303 Laird Frame amp Lid R5 R7 R10 R12 R14 R17 R19 R21 Re
12. microcontroller pin with sufficiently Suppressed harmonics CLKM frequencies above 1MHz require a redesign of R8 and C36 In case of RC cut off frequency adjustments depending on the specific load and signal routing conditions one may observe performance degradation of channel 26 Channel 26 2480 2 is affected by the following harmonics 155 x 16MHz or 310 x 8MHz By default CLKM is routed to a microcontroller timer input check the individual configuration resistors in the schematic drawing To connect CLKM to the microcontroller main clock input assemble R3 with a 00 resistor The Atmel AT86RF232 radio transceiver incorporates all RF and BB critical components necessary to transmit and receive signals according to IEEE 802 15 4 or proprietary ISM data rates A balun B1 performs the differential to single ended conversion of the RF signal to connect the AT86RF232 to the RF switch U1 The RF switch is controlled by the radio transceiver output DIG1 and selects one of the two antennas The signal is routed to the ceramic antenna passing a tuning line Solder pads located along the tuning line allow for the optimization of antenna matching without the need for redesigning the REB Detailed information about the antenna diversity feature is given in 1 and 3 Optionally one or two SMA connectors can be assembled if conducted measurements are to be performed Refer to the schematic and populate coupling capacitors C11 C12 and C1
13. seen from the PCB bottom side There is one radiation direction where no diversity effect exists The direction is A 0 F 180 and P 0 For that case both antennas have a polarization that is turned by 180deg against each other However it is still horizontal and the antenna gain is similar for both antennas Table 5 1 Measured radiation power for different radiation directions Antenna Azimuth Phi F Polarization P dBm EIRP According to the manufacturer datasheet the antenna has a typical average gain of 1dBi with a peak gain of 3dBi Considering the fact that the RF232 provides 3dBm of transmitting power after the balun these measurements prove the maximum TX performance AIMEL 27 8427A AVR 10 11 AIMEL Ss 6 Mechanical description The REB232ED is manufactured using a low cost two layer printed circuit board All components and connectors are mounted on the top side of the board The format was defined to fit the EXPAND1 connector on the Atmel AVR STK500 STK501 microcontroller evaluation board The upright position was chosen for best antenna performance Table 6 1 REB232ED mechanical dimensions with many Atmel AVR2092 8427A AVR 10 11 Atmel AVR2092 7 Electrical characteristics 7 1 Absolute maximum ratings Stresses beyond the values listed in Table 7 1 may cause permanent damage to the board This is a stress rating only and functional operat
14. the FR4 material Any wave propagation in between the copper layers across the RF4 will become impossible This way for an external electromagnetic field the board will behave like a coherent piece of metal When a trace is cutting the plane on one side the design should contain vias along this trace to bridge the interrupted ground on the other side Place vias especially close to corners and necks to connect lose polygon ends The pads where the shield is mounted also need some attention The shield has to be integrated in the ground planes Vias in a short distance to the pads will ensure low impedance integration and also close the FR4 substrate as mentioned above 5 6 PCB detail 6 transceiver RF tuning The REB232ED implements a tuning structure to optimize the transceiver matching A transmission line in combination with a capacitor is used to vary the load impedance The capacitance value and the position of the capacitor can be changed to tune the system To vary the position along that line the tuning capacitor can be assembled on to the footprint of C23 C26 or C27 To measure the tuning result U1 has to be removed and a piece of rigid 50Q cable can be soldered to its pin 5 The measurement using X2 is not impossible but much harder to calibrate and a way to control U1 has also to be found AIMEL 15 e 8427A AVR 10 11 ATMEL Figure 5 7 Board layout transceiver RF tuning 2
15. there are doors windows furniture and people that may move Atmel AVR2092 8427A AVR 10 11 Atmel AVR2092 Figure 5 10 Local fading effects in an indoor multipath environment 40 1 i 1 i i i 1 1 i 1 1 1 1 1 D i 1 1 a FE H H H 1 H H H 45 Tere cree ee TT eee Pe eee Teer Ty eee eT eee eT aaa ee ee eee ey 1 1 D r i 1 i receive signal strength dBm Dual Antenna Single Antenna worst case Minimum Diversity gain 0 5 10 15 20 25 30 35 40 45 50 55 60 55 70 75 80 8 90 95 100 105 110 115 120 125 130 135 140 position cm 5 7 2 Antenna design in This section describes the antenna design in and the implementation of the antenna tuning structure An overview of the layout can be found in Figure 5 11 Figure 5 11 Antenna PCB environment and tuning structure The antenna is available from two sources 1 Johanson 2450AT45A100 2 Wurth 7488910245 AIMEL 19 8427A AVR 10 11 5 7 3 Antenna tuning 22 Atmel AVR2092 AIMEL es The antenna test board as specified by the manufacturers has a ground plane size of 20mm x 40mm an antenna placed in a 12mm x 20mm FR4 area and an FR
16. 4 substrate height of 0 8mm This is the expected environment where the antenna performance should be equivalent to the datasheet values On the REB232ED the environment differs considerably because the FR4 height is 1 5mm the antenna is placed in a triangular corner and the ground plane geometry is different too To compensate for the larger substrate height a 2mm not plated drill hole is placed underneath the antenna ceramic core see Figure 5 11 detail 1 The PCB ground is designed with a 45 degree angle along the red line Figure 5 11 detail 2 forming an optimum antenna ground reference The antenna tuning requires two more elements a series capacitor at the antenna feed point Figure 5 11 detail 3 and a capacitor that can be moved in position along the feed line Figure 5 11 detail 4 The series capacitor must be placed at the antenna feed point Under normal conditions only one capacitor is required within the detail 4 section of the PCB By choosing the correct footprint the capacitor can be moved along the line The impedance transformation across the transmission line depends on the distance between the antenna feed point and the capacitor in detail 4 resulting in the tuning effect The tuning procedure is explained in Section 5 7 3 The first step for the measurements is a board rework to access the RF line with 500 coaxial cable In the case of the REB232ED the balun B1 was removed and a small rigid 50Q cable wi
17. 8 C19 accordingly AMEL AIMEL Ss 5 PCB layout description This section describes critical layout details to be carefully considered during a PCB design The PCB design requires an optimal solution for the following topics Create a solid ground plane for the antenna The PCB has to be considered as a part of the antenna it interacts with the radiated electromagnetic wave Isolate digital noise from the antenna and the radio transceiver to achieve optimum range and RF performance Isolate digital noise from the 16MHz reference crystal to achieve optimum transmitter and receiver performance Reduce any kind of spurious emissions below the limits set by the individual regulatory organizations The REB232ED PCB design further demonstrates a low cost two layer PCB solution without the need of an inner ground plane The drawing in Figure 5 1 shows critical sections using numbered captions Each caption number has its own subsection below with detailed information Figure 5 1 Board layout RF section 1 Atmel AVR2092 Al A2 goo 558 8 C1 amp 5888 9 51 REB232ED 7 1 0 5 JP1 a d Fl DI fatal an ny Hp ur bi 8427A AVR 10 11 Atmel AVR2092 5 1 PCB detail 1 balanced RF pin fan out Figure 5 2 Board layout RF pin fan out a The Atmel AT86RF232 antenna port should be connected to a 100Q load with a small series inductance of 1nH to 2nH Th
18. L ATMEL BE LIABLE FOR ANY DIRECT INDIRECT CONSEQUENTIAL PUNITIVE SPECIAL OR INCIDENTAL DAMAGES INCLUDING WITHOUT LIMITATION DAMAGES FOR LOSS AND PROFITS BUSINESS INTERRUPTION OR LOSS OF INFORMATION ARISING OUT OF THE USE OR INABILITY TO USE THIS DOCUMENT EVEN IF ATMEL HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES Atmel makes no representations or warranties with respect to the accuracy or completeness of the contents of this document and reserves the right to make changes to specifications and product descriptions at any time without notice Atmel does not make any commitment to update the information contained herein Unless specifically provided otherwise Atmel products are not suitable for and shall not be used in automotive applications Atmel products are not intended authorized or warranted for use as components in applications intended to support or sustain life 8427A AVR 10 11
19. The tuning determined in this example is only valid for the antenna example board The REB232ED with its different ground plane design and many more differences may have other parts assembled 5 7 4 Final board antenna radiation pattern The actual radiation pattern for the final board is rather complicated and very difficult to describe Traditional radiation diagrams where the device under test is turned in all three axes and the received power for a vertical and a horizontal antenna are shown in a polar diagram do not provide a correct picture Due to the antenna placement in a 45deg angle the polarization changes dramatically for such a turn To see the full RF power the RX Antenna would require maintaining the correct polarization angel for such a measurement No matter what problems this setup creates when measuring the radiated power such a radiation pattern is exactly what is required to reduce fading effects in indoor 2 Atmel AVR2092 8427A AVR 10 11 8427A AVR 10 11 Atmel AVR2092 multipath environments The dual antenna setup has access to many more propagation modes than a single antenna By switching from one antenna to the other the physical antenna location is changing because of the antenna distance and on top of that the wave polarization is changing as well The achieved propagation path effect of this switch was already illustrated in Figure 5 10 page 19 Figure 5 17 Radiated measurement for Azimut 50d
20. atterns and minimal coupling Because the polarization of a received wave is not deterministic in a multipath environment this setup is also capable of selecting the optimum polarization match for an incoming wave The other design aspect is the antenna distance The antenna distance has to be large enough to ensure only one of the two antennas is present in a local fading minimum Figure 5 10 page 19 shows the field strength plot for both antennas dependent on the board position For this test the antenna board was moved along a workbench using a stepper motor The transmitter was positioned several meters away on another workbench No direct line of sight connection is ensured using a AIMEL 17 e 8427A AVR 10 11 AIMEL large metal plate The graph shows receive signal strength variations caused by the interference of reflected waves reaching the receiver via different propagation paths From Figure 5 10 page 19 one can conclude key parameters for such an indoor scenario 1 For one antenna multipath fades can exceed 30dB 2 For the 2 4GHz ISM band a local fading minimum is typically below 5cm 2in This number is expected considering the wavelength Conclusion an antenna diversity design should place antennas at a distance larger than that 3 For almost all positions only one antenna is in a deep fade The setup prepared for this test demonstrates the advantage of using antenna diversity Figure 5 9
21. ctrostatic discharge and any other technical or legal concerns EXCEPT TO THE EXTENT OF THE INDEMNITY SET FORTH ABOVE NEITHER USER NOR ATMEL SHALL BE LIABLE TO EACH OTHER FOR ANY INDIRECT SPECIAL INCIDENTAL OR CONSEQUENTIAL DAMAGES No license is granted under any patent right or other intellectual property right of Atmel covering or relating to any machine process or combination in which such Atmel products or services might be or are used Mailing Address Atmel Corporation 2325 Orchard Parkway San Jose CA 95131 Copyright 2009 Atmel Corporation AMEL s 9 Table of contents 33 Atmel AVR2092 1 1 2 AA AA 2 OVET VIO W masa NATA 3 4 Functional 4 4 1 Interface connector aa 4 4 1 1 Atmel ATmega1281 configuration 5 4 1 2 Atmel ATmega644 configuration 5 4 2 ID EEPROM 6 4 3 Supply current sensing 8 4 4 Radio transceiver reference 8 AO Fer SS AA 9 5 PCB layout description 10 5 1 PCB detail 1 balanced RF pin fan 11 5 2 PCB detail 12 5 3 PCB detail crysta
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23. d with reverse polarity Depending on the actual supply voltage the diode D1 can consume several milliamperes This has to be considered when the current consumption of the whole system is measured In such a case D1 should be removed from the board To achieve the best RF performance the analog EVDD and digital DEVDD supply are separated from each other by a CLC PIl filter Digital and analog ground planes are connected together on the bottom layer underneath the radio transceiver IC Further details are described in Section 5 page 10 A jumper JP1 is placed in the supply voltage trace to offer an easy way for current sensing to occur All components connected to nets DEVDD EVDD contribute to the total current consumption While in radio transceiver SLEEP state most of the supply current is drawn by the 1MQ pull up resistor R9 connected to the ID EEPROM and the EEPROM standby current Figure 4 4 Power supply routing L1 F1 JP1 CVTG 2229 miniSMDC020 DEVDD EVDD 2200hm 100MHz C30 C31 DGND AGND 4 4 Radio transceiver reference clock 8 Atmel AVR2092 The integrated radio transceiver is clocked by a 16MHz reference crystal The 2 4GHz modulated signal is derived from this clock Operating the node according to IEEE 802 15 4 4 the reference frequency must not exceed a deviation of 40ppm The absolute frequency is mainly determined by the external load capacitance of the crystal which depends on th
24. e crystal type and is given in its datasheet The radio transceiver reference crystal Q1 shall be isolated from fast switching digital signals and surrounded by a grounded guard trace to minimize disturbances of the oscillation Detailed layout considerations can be found in Section 5 3 page 12 The REB uses a Siward CX4025 crystal with load capacitors of 10pF and 12pF The imbalance between the load capacitors was chosen to be as close as possible to the desired resonance frequency with standard components To compensate for fabrication and environment variations the frequency can be further tuned using the radio transceiver register XOSC_CTRL 0x12 refer to 1 Section References page 36 The REB production test guarantees a tolerance of within 20ppm and 5ppm The correction value to be applied to TRX register XOSC_CTRL 0x12 is stored in the onboard EEPROM see Section 4 2 page 6 8427A AVR 10 11 NOTE 4 5 RF section 8427A AVR 10 11 Atmel AVR2092 The reference frequency is also available at pin CLKM of the radio transceiver and depending on the related register setting it is divided by an internal prescaler CLKM clock frequencies of 16MHz 8MHz 4MHz 2MHz 1MHz 250kHz 62 5kHz are programmable refer to 1 The CLKM signal is filtered by a low pass filter to reduce harmonic emissions within the 2 4GHz ISM band The filter is designed to provide a stable 1MHz clock signal with correct logic level to a
25. ed in the final product a submission must be made to a notified body for compliance testing to all required standards The CE marking must be affixed to a visible location on the OEM product The CE mark shall consist of the initials CE taking the following form e f the CE marking is reduced or enlarged the proportions given in the above graduated drawing must be respected e The CE marking must have a height of at least 5mm except where this is not possible on account of the nature of the apparatus e The CE marking must be affixed visibly legibly and indelibly More detailed information about CE marking requirements you can find at DIRECTIVE 1999 5 EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on 9 March 1999 at section 12 1 AT86RF232 Low Power 2 4GHz Transceiver for ZigBee IEEE 802 15 4 6LoWPAN RF4CE and ISM Applications Datasheet Rev 8321A MCU Wireless 10 11 Atmel Corporation 2 AVR2042 REB Controller Base Board Hardware User Guide Application Note Rev 8334A AVR 08 10 Atmel Corporation 3 AVR2021 AT86RF232 Antenna Diversity Application Note Rev 8158B AVR 07 08 Atmel Corporation 4 IEEE Std 802 15 4 2006 Wireless Medium Access Control and Physical Layer PHY Specifications for Low Rate Wireless Personal Area Networks LR WPANSs 5 FCC Code of Federal Register CFR Part 47 Section 15 35 Section 15 205 Section 15 209 Section 15 232 Section 15 247 and Section 15 249 Uni
26. eg Phi 35deg Polarization 65deg The measurement setup inside of an anechoic chamber is shown in Figure 5 17 A measurement position is characterized by three angels There is the azimuth angle where the whole test device carrier is turning around a vertical axis The turning angle of the test board around a horizontal axis is called Phi In Addition the receive antenna can be turned to adjust the polarization angle The following 3D models show the board and the radiation properties for some of the main radiation directions The cylinders point into the measured radiation direction the arrows at the end of each pointer indicate the wave polarization direction The yellow pointers belong to antenna A1 while the green pointers indicate radiations from A2 Please refer to Figure 5 1 for the antenna reference markers A1 and A2 or have a look at the physical board AIMEL 25 e Figure 5 18 Some main radiation directions with polarization angle seen from Antenna A1 All three figures show the same 3D model from different directions The board has a rather smooth radiation characteristic but these spots have been selected to show the varying polarization Figure 5 19 Some main radiation directions with polarization angle seen from Antenna A2 26 Atmel AVR2092 8427A AVR 10 11 Atmel AVR2092 Figure 5 20 Some main radiation directions with polarization angle
27. in an increased noise level transferred to the analog domain There is a number of pro s and con s when it comes to the shielding topic The major con s are Cost of the shield e Manufacturing effort naccessibility for test and repair The number of pro s might be longer but the cost argument is often very strong However the reasons to add the shield for this reference design are e Shield is required for a certification in Japan e Shield is recommended for FCC certification in North America e Increased performance 4 Atmel AVR2092 8427A AVR 10 11 Atmel AVR2092 Figure 5 6 Board layout GND and shield REB232ED UZ 1 0 TN OQ T rp m Atmegal 281 gt C C p a pa Besides the function to provide supply ground to the individual parts the ground plane has to be considered as a counterpart for the antenna Such an antenna base plate is required to achieve full antenna performance It has to be a continuous sustained metal plate for that purpose The shield covering the electronic section will help to form this antenna base plate For that reason any unused surface should be filled with a copper plane and connected to the other ground side using sufficient through hole contacts Larger copper areas should also be connected to the other side layer with a grid of vias This will form kind of a RF sealing for
28. interference to radio communications However there is no guarantee that interference will not occur in a particular installation If this equipment does cause harmful interference to radio or television reception which can be determined by turning the equipment off and on the user is encouraged to try to correct the interference by one or more of the following measures Reorient or relocate the receiving antenna e Increase the separation between the equipment and receiver e Connect the equipment into an outlet on a circuit different from that to which the receiver is connected e Consult the dealer or an experienced radio TV technician for help Warning Part 15 21 Changes or modifications not expressly approved by this company could void the user s authority to operate the equipment AIMEL 35 e B 2 Europe ETSI References Atmel AVR2092 AIMEL Ss If the device is incorporated into a product the manufacturer must ensure compliance of the final product to the European harmonized low voltage safety standards A Declaration of Conformity must be issued for each of these standards kept on file as described in Annex Il of the R amp TTE Directive The manufacturer must maintain a copy of the device documentation and ensure the final product does not exceed the specified power ratings and or installation requirements as specified in the user manual If any of these specifications are exceed
29. ion of the device at these or any other conditions beyond those indicated in the operational sections of this manual are not implied Exposure to absolute maximum rating conditions for extended periods may affect device reliability For more details about these parameters refer to individual datasheets of the components used Table 7 1 Absolute maximum ratings supaywonago 95 V 2 V 715 Supply current bateries Sum veralpowerpns 05 7416 To m Note 1 Keep power switch off or remove battery from REB CBB when external power is supplied 7 2 Recommended operating range Table 7 2 Recommended operating range Parameter Condition Mmm Maximum Unit 721 Operaing 20 0 6 7 3 Current consumption Test conditions unless otherwise stated 3 0V Top 25 C Table 7 3 lists current consumption values for typical scenarios of a complete system composed of REB CBB and REB232 The Zener diode has been removed as described above Table 7 3 Current consumption of REB CBB with 232 MCU power down Supply current transceiver in state SLEEP serial flash in Deep Sleep MCU 2MHz MCU 16MHz int RC 32MHz AIMEL 8427A AVR 10 11 AMEL parame vinima Mamon Uni 16MHz int RC 32MHz 7 3 4 Suppl t
30. is is achieved with the connection fan out in between the IC pins and the filter balun combination B1 The trace width is kept small at 0 2mm for a length of approximately 1 5mm The REB232ED is a two layer FR4 board with a thickness of 1 5mm Therefore the distributed capacitance between top and bottom is low and transmission lines are rather inductive B1 has the DC blocking built in Only pin 2 requires DC blocking within its GND connection since this is considered as bias access pin The distance of 1 5mm also allows GND vias for pin and pin 6 of the AT86RF232 Such a low inductance GND connection is really desirable for the RF port AMEL 8427A AVR 10 11 ATMEL 5 2 PCB detail 2 RF switch Figure 5 3 Board layout RF switch The RF switch requires a solid grounding to achieve the full isolation and RF filter capacitors for the control pins A parasitic inductance within the ground connection may reduce the RF isolation of the switch in the off state To achieve a hard low impedance ground connection vias are placed on each side of the ground pad Additionally the ground pad is connected to the top layer ground plane Blocking capacitors C24 and C25 are placed as close as possible to the RF switch to short any control line noise Noise interfering on the control pins may cause undesired modulation of the RF signal C11 and C12 will block any DC voltage on the RF line On the input side C28 next to the balu
31. l routing 12 5 4 PCB detail 4 transceiver analog GND 13 5 5 PCB detail 5 digital GND routing and 14 5 6 PCB detail 6 transceiver RF 15 la jai TT 16 5 7 1 Antenna design study GAAN NG AKA Aah 16 5 7 2 Antenna design in mr 19 Di AMEN UNG rm 20 5 7 4 Final board antenna radiation 24 6 Mechanical description 28 l Electrical characteris lOS venus 29 1 1 Absolute MAXIMUM ratings one io tonat GAAN 29 7 2 Recommended operating 29 7 3 Current 29 PFC VALOIS PA Gak 31 Appendix A PCB design 32 na REOR 32 2 Assembly drawing 33 AS AA 34 Appendix Radio certification 35 United Comas paga ba ana 35 8427A AVR 10 11 8427A AVR 10 11 Atmel AVR2092 BCU 36 5 PA 36 EVALUATION BOARD KIT IMPORTANT NOTICE 37 9 Table e 38 AIMEL 29
32. n Figure 5 14 page 23 2 Atmel AVR2092 8427A AVR 10 11 Figure 5 14 Antenna tuning with series capacitor bul 511 Smith Log Fhase Scale 1 0000 F2 D amp M Tra 511 Log Mag 10 00dB Ref 0 000dB F2 D amp M 50 00 AU 8 068 dB l127 12 5 11 012 dE 151 28 40 1 Start 2 3 GHz IF BM 70 kHz Atmel AVR2092 Stop 2 6 GHz 121 The final tuning step will use a shunt capacitor to correct the antenna load impedance A 0 5 capacitor has been used to tune the antenna resonance frequency to the band center If the antenna resonance frequency is too low the capacitor needs to be moved towards the antenna and vice versa Figure 5 15 Final tuning 8427A AVR 10 11 23 page 23 and show the final result as a diagram and on the board Figure 5 16 Antenna tuning with series and shunt capacitor HILE 511 Log Mag 10 0098 Ref O 000dB F2 D amp M 1 2 4050000 GHz 12 527 dB 2 2 4850000 GHz 24 705 dB 40 00 20 00 10 00 10 00 20 00 40 00 1 Start 2 3 GHz IFBIA 70 kHz Stop 26 GHz In most cases it is beneficial to tune the antenna a little towards higher frequencies The reason is that environmental changes in most cases tune the antenna down to lower frequencies Such environmental changes can be any kind of object that is situated near the antenna such as a housing or table surface
33. n provides the required DC blocking 5 3 PCB detail 3 crystal routing The reference crystal PCB area requires optimization to minimize external interference and to keep any radiation of 16MHz harmonics low Since the board design incorporates a shield the crystal housing has been tied hard to ground This method will minimize the influence of external impairments such as burst and surge Against board internal crosstalk the crystal signal lines are embedded within ground areas Special care has to be taken in the area between the IRQ line and the crystal Depending on the configuration the interrupt may be activated during a frame receive Crosstalk into the crystal lines will increase the phase noise and therefore reduce the signal to noise ratio 12 Atmel AVR2092 8427A AVR 10 11 Atmel AVR2092 Figure 5 4 Board layout XTAL section The reference crystal and load capacitors C36 37 form the resonator circuit These capacitors are to be placed close to the crystal The ground connection in between the capacitors should be a solid copper area right underneath the crystal including the housing contacts 5 4 PCB detail 4 transceiver analog GND routing With the Atmel AT86RF232 consider pins 3 6 27 30 31 and 32 as analog ground pins Analog ground pins are to be routed to the paddle underneath the IC The trace width has to be similar to the pad width when connecting the pads and increase if possible i
34. n simulations and testing of individual examples Any information about third party materials or parts was included in this document for convenience The vendor may have changed the information that has been published Check the individual vendor information for the latest changes 2 Atmel AVR2092 8427A AVR 10 11 Atmel AVR2092 3 Overview The radio extender board is assembled with an Atmel AT86RF232 radio transceiver 1 and two ceramic antennas and demonstrates the unrivaled hardware based antenna diversity feature which significantly improves radio link robustness in harsh environments The radio extender board was designed to interface to the Atmel microcontroller development or evolution platforms The microcontroller platform in combination with the REB provides an ideal way to e Evaluate the outstanding radio transceiver performance such as the excellent receiver sensitivity achieved at ultra low current consumption Test the radio transceivers comprehensive hardware support of the IEEE 802 15 4 standard e Test the radio transceivers enhanced feature set which includes antenna diversity AES high data rate modes and other functions The photograph in Figure 3 1 shows a development and evaluation setup using the REB controller base board REB CBB 2 in combination with the REB232ED radio extender board Figure 3 1 The REB232ED with removed RF shield connected to a REB CBB el 3 8427A AVR 10
35. n some distance from the pad Each ground pin should be connected to the bottom plane with at least one via Move the vias as close to the IC as possible It is always desired to integrate the single pin ground connections into polygon structures after a short distance Top bottom and on multilayer boards the inner ground planes should be tied together with a grid of vias When ground loops are smaller than one tenth of the wavelength it is safe to consider this as a solid piece of metal AMEL ATMEL Figure 5 5 Board layout transceiver GND JC3O TUT uso 715 EZ The soldering technology used allows the placement of small vias 0 15mm drill within the ground paddle underneath the chip During reflow soldering the vias get filled with solder having a positive effect on the connection cross section The small drill size keeps solder losses within an acceptable limit During the soldering process vias should be open on the bottom side to allow enclosed air to expand 5 5 PCB detail 5 digital GND routing and shielding With the Atmel AT86RF232 consider pins 7 12 16 18 and 21 as digital ground pins Digital ground pins are not directly connected to the paddle Digital ground pins may carry digital noise from pad cells or other digital processing units within the chip In case of a direct paddle connection impedances of the paddle ground vias could cause a small voltage drop for this noise and may result
36. nal Equipment Manufacturer OEM must comply with the following regulations e The modular transmitter must be labeled with its own FCC ID number and if the FCC ID is not visible when the module is installed inside another device the outside of the device into which the module is installed must also display a label referring to the enclosed module e This exterior label can use wording such as the following Any similar wording that expresses the same meaning may be used Contains FCC ID VNR E32ED X5B 00 This device complies with Part 15 of the FCC Rules Operation is subject to the following two conditions 1 this device may not cause harmful interference and 2 this device must accept any interference received including interference that may cause undesired operation Use in portable exposure conditions FCC 2 1093 requires separate equipment authorization Modifications not expressly approved by this company could void the user s authority to operate this equipment FCC Section 15 21 Compliance Statement Part 15 105 b This equipment has been tested and found to comply with the limits for a Class B digital device pursuant to Part 15 of the FCC Rules These limits are designed to provide reasonable protection against harmful interference in a residential installation This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with the instructions may cause harmful
37. oard development was the evaluation of the antenna setup A dedicated board was designed to determine the key design parameters for a diversity antenna configuration Atmel AVR2092 8427A AVR 10 11 Atmel AVR2092 Because the antenna has to operate in an environment different from that of the manufacturer s evaluation board the correct frequency tuning has to be verified The antenna distance required for optimum diversity operation provides enough board space to use a low cost tuning method based on a transmission line and capacitors The actual tuning procedure is explained in Section 5 7 3 page 20 Figure 5 8 Initial antenna tuning and test board D Besides the antenna tuning the test board was used to measure the diversity effect and the coupling between the two antennas The better the two antennas are isolated from each other the higher is the diversity advantage for the receiver It has to be considered that the unused antenna is operating against an open line end because the RF switch U1 has high impedance in the off position A low coupling in between the antennas is therefore required Direct coupling measurement results between both antennas are shown in Figure 5 9 page 18 Over the operating frequency range the antenna separation is gt 15dB That is achieved mainly with the 45 degree installation The 90 degree turn between left and right antennas causes orthogonal radiation p
38. sceiver The select signal for each SPI slave EEPROM radio transceiver is decoded with the reset line of the transceiver RSTN Therefore the EEPROM is addressed when the radio transceiver is held in reset RSTN 0 see Figure 4 2 Figure 4 2 EEPROM access decoding logic Atmel ATmega1281 configuration PB5 RSTN IRST Transceiver PBO SEL PB1 3 SPI On Board EEPROM CS The EEPROM data are written during board production testing A unique serial number the MAC address and calibration values are stored These can be used to optimize system performance Final products do not require this external ID EEPROM All data can be stored directly within the microcontroller s internal EEPROM Note MAC addresses used for this package are Atmel property The use of these MAC addresses for development purposes is permitted 8427A AVR 10 11 Atmel AVR2092 Table 4 3 shows a detailed description of the EEPROM data structure Table 4 3 ID EEPROM mapping address Name 0x14 Feature uint8 Board features coded into seven bits 6 Reseved 02 0 SMA connector 0x15 Cal OSC uint8 RF232 XTAL calibration value register XTAL_TRIM 16MHz 0 16 Cal RC 3 6V juint8 8 Atmel ATmega1281 internal RC oscillator calibration value 3 6V register OSCCAL 0x17 Cal RC 2 0V uint8 ATmega1281 internal RC oscillator calibration value 2 0 register OSCCAL 0x18 Antenna gain 8 Antenna gain
39. sistor 0603H0 4 Generic 00 R23 1 R25 Resistor 0402A Generic 4700 2 R8 R15 Resistor 0402A Generic 2 2kO 1 R27 Resistor 0402A Generic 10kO 2 R24 R26 Resistor 0402A Generic 1MO XTAL 4X2 5 XTL551150NLE 1 Q1 Crystal 16MHz sal 16MHz 9 0R Siward CX 4025 16MHz 1 L1 SMT ferrite bead 0603H0 8 74279263 W rth 2200 100MHz 1 JP1 Jumper 2 pol JP 2x1 1001 121 002 CAB JP 2 1 F1 PTC fuse 1812 miniSMDC020 Raychem miniSMDC020 1 D1 Z Diode DO 214AC BZG05C3V9 Vishay BZG05C3V9 1 C35 Capacitor 0402A Generic COG 12pF 5 2 C37 C38 Capacitor 0402A Generic COG 10pF 5 2 C35 C36 Capacitor 0603H0 8 Generic X5R 1uF C30 C31 C32 C33 6 C34 C39 Capacitor 0402A Generic X7R 100n 2 C15 C20 Capacitor 0402A Generic COG 0 56pF C11 C12 C24 C25 6 C28 C29 Capacitor 0402A Generic COG 22pF 2 C1 C10 Capacitor 0402A Generic COG 3 3pF 1 C40 Capacitor 0402A Generic COG 2 2pF 1 C23 Capacitor 0402A Generic COG 1 2pF 1 B1 Balun 0805 6 2450FB15L0001 JTI Filtered Balun 2 A1 A2 Ceramic antenna oo 2450AT45A100 JTI 2 45GHz 34 Atmel AVR2092 8427A AVR 10 11 Atmel AVR2092 Appendix Radio certification B 1 United States FCC 8427A AVR 10 11 The REB232ED mounted on a REB controller base board REB CBB has received regulatory approvals for modular devices in the United States and European countries Compliance Statement Part 15 19 The device complies with Part 15 of the FCC rules To fulfill FCC Certification requirements an Origi
40. ted States 6 ETSI EN 300 328 Electromagnetic Compatibility and Radio Spectrum Matters ERM Wideband Transmission Systems Data transmission equipment operating in the 2 4GHz ISM band and using spread spectrum modulation techniques Part 1 3 7 STD T66 Second Generation Low Power Data Communication System Wireless LAN System 1999 12 14 H11 12 14 Version 1 0 8 AT25010A SPI Serial EEPROM Datasheet Rev 3348J SEEPR 8 06 Atmel Corporation 8427A AVR 10 11 Atmel AVR2092 EVALUATION BOARD KIT IMPORTANT NOTICE 8427A AVR 10 11 This evaluation board kit is intended for use for FURTHER ENGINEERING DEVELOPMENT DEMONSTRATION OR EVALUATION PURPOSES ONLY It is not a finished product and may not yet comply with some or any technical or legal requirements that are applicable to finished products including without limitation directives regarding electromagnetic compatibility recycling WEEE FCC CE or UL except as may be otherwise noted on board kit Atmel supplied this board kit AS IS without any warranties with all faults at the buyer s and further users sole risk The user assumes all responsibility and liability for proper and safe handling of the goods Further the user indemnifies Atmel from all claims arising from the handling or use of the goods Due to the open construction of the product it is the users responsibility to take any and all appropriate precautions with regard to ele
41. th an SMA connector was connected to the balun pin 1 pad The ground planes next to this feed point where used to create a solid ground connection for this cable This feed point will allow the measurement of both antennas because of the on board RF switch The RF switch was controlled by applying the correct voltage levels from a lab power supply Figure 5 12 Antenna feed line short for extended length calibration 8427A AVR 10 11 8427A AVR 10 11 Atmel AVR2092 The second step is to calibrate the network analyzer NWA to the 500 connector as usual After normal calibration the reference point for the NWA is at the cable SMA connection To determine the tuning elements the reference point has to be moved to the antenna feed point using the extended length parameter inside the NWA To determine this parameter a hard short is required at the antenna feed line end Remove the solder resist on the left and right sides of the feed line end and short the line end to ground with two solder bumps see Figure 5 12 Do not use any wires to create a ground connection The calibration procedure will only work when the short is exactly at the line end and has a minimum of parasitic inductance Now the NWA extended length parameter can be adjusted until the NWA s Smith chart displays a nice short for the desired frequency range In the third step the antenna behavior can be measured without any tuning elements To see the real antenna
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