PLL Analysis Tool Quick Reference Guide
Contents
1. Frequency W Wn For Help press F1 X 6 243 Y 13 127dB Figure 4 2 order PLL Bode plot Visi AdvancedPLL1 vtd BB Tool Edit Action Display View Utilities Help l x ajea H elea o Hae Ial eeN View Advanced PLL Poles amp Zero Acquire Options Arming Voltages Initial Conditions View Options 1 1 0 5 0 1 Unit normalized to Wn For Help press F1 x 0 003 Y 0 998 Fig 5 2 order PLL poles and zero PAGE 6 OF IO 200033 00 REV A Viewing the Data Summary To view the 2 order PLL data summary select Bis i sn nss u ume ne Summary under the View menu Information included favanceaPu summary in this view include Sigma 13 6ps 1 524ps 17 377ps 15 858ps e Statistics of the 1 Sigma measurements such aS bampingrsctor os4s866 mean minimum maximum and peak to peak PSD oae Sheth e The value of the carrier frequency ae eee e PLL characteristic parameters PuloulRange 247 71628ekt e Goodness of fit Chi Squared ee Po The PLL characteristics provided in the summary window are the following iv e Damping factor as defined in Eq 1 e Natural frequency as defined in Eq 1 Fate pu e PSD of noise level of white input noise Figure 6 Data summary and PLL characteristics e Lock range frequency range in which a PLL can lock within one beat note between the rer and Woy e Lock in time time scale for PLL to lock into from the lock range e Pull in time time sc2. 11 PLL ANALYSIS TOOL FOR THE SIA 3000 PAGE IO OF IO WAVECREST CORPORATION 2002 200033 00 REV A
3. Factor Either sets or displays the initial guess for fitting of the damping factor depending on the setting of the Init Damping Factor Init Nat Freq kHz Either sets or displays the initial guess for fitting of the natural frequency depending on the setting of the Init Damping Factor Init PSD dBc Hz Either sets or displays the initial guess for fitting of the input noise level depending on the setting of the Init Damping Factor Optimize If Calc Initial Conditions is set to On this will estimate initial conditions based on prominent features of the data and perform least squares fitting of data to 2 order PLL transfer function If Calc Initial Conditions is set to Off this will perform least squares fitting of data to 2 order PLL transfer function using user entered initial conditions PLL ANALYSIS TOOL FOR THE SIA 3000 PAGE 4 OF IO WAVECREST CORPORATION 2002 200033 00 REV A View Options Menu view X axis 1 Sigma Selects the parameter plotted on the x axis when View is set to 1 Sigma e Span Time plots the time span of the measurement on the x axis e Span Periods plots the number of periods spanned on the x axis Init Off Freq kHz Offset Frequency Sets the lowest frequency displayed when View is set to PLL Transfer Init OFF Freg kHz 1 000000 Sample Measurement with the Advanced PLL Tool Experimental Setup As an example we perform Advanced PLL measurements on a PLL clock output The experime
4. PLL ANALYSIS TOOL QUICK REFERENCE GUIDE FOR THE SIA 3000 Applications of PLL Analysis Tool e Find the transfer function of a 2 order PLL e View the Bode plot of a PLL e Identify poles and zero of a 2 order PLL e Determine PLL characteristics such as lock in damping factor natural frequency lock range lock in time pull in time pull out range etc Introduction The focus of this guide is to familiarize the user with the Advanced PLL tool allowing quick and easy measurements and interpretation of results Refer to the SIA 3000 User s Manual and the VISI help files for more information Theory of Operation The PLL measurement tool is based on a white paper authored by WAVECREST Corporation i The fundamental measurement of this tool is the 1 sigma o vs UI plot similar to the High Frequency Modulation tool ii The relationship between the jitter variance o and the jitter power spectral density PSD is well established iii The jitter PSD of the PLL output clock is related to the PLL reference clock noise via the transfer function Therefore with reasonable assumptions about the input noise of the PLL reference clock we can infer the transfer function of the PLL At the current time we assume that the input noise spectrum is white and the PLL is of 2 order The 2 order PLL transfer function in Laplace space is given by 2 Eq 1 aoje e y s 220 s o where s i is the complex frequency is the
5. ale for the PLL to lock from the pull in range which is the range within which the PLL will always lock e Pull out range the dynamic limit for stable operation of a PLL e Noise bandwidth PLL output phase noise integrated over the bandwidth of the PLL PLL ANALYSIS TOOL FOR THE SIA 30O00O PAGE 7 OF IO Visi Advance dPLL1 vtd Aem Hn Hea ep Hl aE 2 pone Mean Minimum Maximum Pk Pk WAVECREST CORPORATION 2002 200033 00 REV A Understanding Results and Troubleshooting It is important to also know when results are bad and cannot be fitted There are conditions under which the PLL curve fitting algorithm will not be able to fit the 1 sigma values The following examples highlight some of these results along with good results that may have problems fitting for other reasons Also note that if problems show up on the output of the PLL it is often because the Reference Clock is bad If you are able to analyze the output of the Reference clock verify that it is good before assuming the PLL is bad Figures 7a and 7b show typical PLL curves with some amount of Periodic jitter present Periodic Jitter PJ is apparent by the ripple on the 1 sigma results PJ will cause the algorithm to either not be able to fit or if it does fit the results may be questionable PJ can be analyzed and identified using the High Frequency Modulation tool If you get these results you may have some sort of interference present Usi
6. er Measure a00 Edge to Measure Fising z Record Length Units Time Interval g Rec Len pz 10 000000 Meas Incr Pernods 1 5igma Arm Delay 19 21ns 13 750000 Arming Mode Arm On Stop Arm Number Arming Edge Channel Opens the channel selection menu Use the keypad or mouse to select a measurement channel Hits Per Measure Determines the number of time measurements that will be made for each edge or point on the plot Edge to Measure Select Rising or Falling edge to measure Record Length Units Sets the unit of measurement for the data record length Options are Time Interval Periods and Bandwidth Record Length Options depend on the selection of Record Length Units e Rec Len us for Time Interval Number of cycles to measure determined by the time entered e Rec Len Periods for Periods Number of cycles to measure determined by the number of periods e HPF 3dB Freq kHz for Bandwidth Number of cycles to measure determined by the half power point of the 20dB decade low frequency roll off Meas Incr Periods Choose the increment step size of the number of cycles to measure Arm Delay 19 21ns Sets the minimum delay time from an arm event to the first measurement edge Arming Mode Arming is required to make every measurement e Arm on Stop uses a falling edge from the measurement channel to arm the instrument e Arm on Start uses a rising edge from the meas
7. er match the data This is performed under the Initial Conditions menu PLL ANALYSIS TOOL FOR THE SIA 3000 PAGE 5 OF IO WAVECREST CORPORATION 2002 200033 00 REV A Viewing the 2 order PLL Transfer Function To view the 2 order PLL transfer function select PLL Transfer under the View menu The domain of the transfer function is frequency normalized to the natural frequency The y axis is magnitude in dB Viewing the Bode Plot To view the 2 order PLL Bode Plot select Bode Plot under the View menu The domain of the Bode plot is frequency normalized to the natural frequency n The upper plot is amplitude in dB and the lower plot is phase in degrees Viewing the Poles and Zero Plot To view the 2 order PLL poles and zero select Poles amp Zero under the View menu The axes of the plot are complex frequencies normalized to the natural frequency p PLL ANALYSIS TOOL FOR THE SIA 3000 WAVECREST CORPORATION 2002 Visi Advance dPLL1 vtd BB Tool Edit Action Display View Utilities Help Advanced PLL Transfer Function 10dB Acquire Options Arming Voltages 30dB Initial Conditions View Options 70dB 0 1 10 1 000 Frequency W Wn For Help press F1 M7A17 147dB 185 0123 Fig 3 2 order PLL transfer function Visi Advance dPLL1 vtd BB Io Edit Action Display View Utilities Help m Asme n Hea ep Ha aE 2 a lee i ms 02 Plot kA Advanced PLL Bode Plot 0 1 10 1 000
8. igma values just that the Variance Fit green line matches The Variance Fit line should model the 1 sigma values plot line is Siqma vs Span silarmna War Fit Ini ond Us ADUS SOLIS Figure 11 Shows a typical best case PLL The Good results are good because the Variance Fit line closely follows the trend of the 1 sigma values Summary of the Advanced PLL Tool The Advanced PLL tool allows users to study characteristics and parameters of a 2 order PLL With a simple set of variance measurements the tool can extract information such as damping factor natural frequency input noise level lock range lock in time pull in time pull out range and noise bandwidth The tool also presents a transfer function and Bode plots up to the natural frequency as well as a plot of the poles and zero for a 2 order PLL References i Li M A New Method for Simultaneously Measuring and Analyzing PLL Transfer Function and Noise Processes DesignCon Proceedings 2002 ii For more information refer to High Frequency Modulation VISI 7 Quick Reference Guide WAVECREST Corporation ili Wilstrup J A Method of Serial Data Jitter Analysis Using One shot Time Interval Measurements ITC Proceedings p 819 1998 iv Best R Phase Locked Loops 4 ed McGraw Hill New York 1999 FOR MORE INFORMATION CONTACT WAVECREST CORPORATION 7626 GOLDEN TRIANGLE DR EDEN PRAIRIE MN 55344 WWW WAVECREST COM 1 952 646 01
9. natural frequency and is the damping factor The parameters and the input noise level is found from a least squares fit of the variance Once H s is determined PLL characteristics such as natural frequency damping factor damping frequency pull in range pull in time pull out range pull out time lock range lock time lock frequency Bode plots root locus poles zeros and stability are readily obtained PLL ANALYSIS TOOL FOR THE SIA 3000 PAGE OF IO WAVECREST CORPORATION 2002 200033 00 REV A Advanced PLL Tool Main Menu The main menu of the Advanced PLL tool is found in the VISI menu path shown below Oscilloscope Views 1 Sigma T Clock Acquire Options Adjacent Cycle Chan To Chan ieli Dl l FEEL Arming DACG Advanced Clack fod aoe n Baca Voltages Advanced PLL dataCOM Tools Initial Conditions Utilities View Options Composite Flot Getting Started Wizard View Provides the user with several different ways 1 Sigma PLL Transfer Bode Plot Poles amp Zero Summary to visualize the acquired data Acquire Options Opens the Acquire Options menu Arming Opens the Arming menu Voltages Opens the Voltages menu Initial Conditions Opens the Initial Conditions menu View Options Opens the View Options menu PLL ANALYSIS TOOL FOR THE SIA 3000 PAGE 2 OF IO WAVECREST CORPORATION 2002 200033 00 REV A Acquire Options Menu View 1 Sigma Z Channel i Hits F
10. ng the High Frequency Modulation tool you can identify the magnitude and frequencies of these periodic components PLL ANALYSIS TOOL FOR THE SIA 3000 WAVECREST CORPORATION 2002 Periods fU0Fernods 400 Periods A Figure 7a Periodic Jitter PJ present PLL Analysis 1 Sigqma ws Soan 250p5 12505 Ls OPeriads U0Perods 400 Feroads A Figure 7b PJ present sigma Vor FIT Ini ond l Silarmcad War Fit Ini ond PAGE 8 OF IO Z00033 00 REV A Figure 8 shows the 1 sigma_ values constantly rising This can be indicative of two things Either the Span needs to be increased because we are only seeing a small portion of the rise and level off or the plot does not level off If the span is increased and the plot does not level off this could mean that the PLL reference clock has long term accumulation of jitter or the PLL itself passes this accumulation of jitter Note that certain signal generators exhibit this performance and if B l used as a reference clock may be the A Figure 8 Constantly rising 1 sigma values source of the problem Check the output of the Ref Clock before changing any PLL designs Typically the Ref Clock should have a flat response on this plot slarna War Fit Ini ond Us ADHS SOLIS Figure 9 shows the typical response of an under damped PLL The highest damped line red is the Initial conditions line I sigma Initial conditions is the function that the Wor Fit cur
11. ntal set up is shown in Fig 1 For this example the PLL is has a reference clock of 10 MHz and an output clock of 1 2525 GHz Berrie eee om maas nataba na P Acquiring Data The following steps describe the data acquisition process in VISI 1 Open the Advanced PLL tool 2 Connect the signal to a measurement channel Fig 1 Set the measurement channel in VISI by going to the Acquire Option menu and choosing Channel 3 Confirm that a vald signal exists at the measurement channel by using Pulsefind s 4 For this example the Rec Length us is 50 and the emei 0 sems oki sia saia wie OOOO Meas Incr Periods is 10 All other parameters are ee left as default 5 Begin acquisition by pressing Single Stop button on the front panel Lal 6 When acquisition is complete the Single Stop button will cease to illuminate Viewing Data in Time Domain 1 Sigma The initial default view is the time series shown in Fig 2 The time domain data can be viewed by selecting 1 Sigma under the View menu The x axis shows the span of the jitter accumulation l The y axis shows the rms standard deviation of the Fig 2 1 Sigma vs UI span plot accumulated jitter as a function of span The magenta line is the acquired data The red line is the behavior based on initial conditions The blue line is the converged fit If the converged fit does not agree with the data the initial conditions may be manually modified to bett
12. urement channel to arm the instrument e External Arm uses a signal from a channel different than the measurement channel to arm the instrument Arm Number Opens the channel selection menu for choosing a channel to be used for arming when External Arm is selected Arming Edge Selects Rising or Falling edge to arm the measurement when External Arm is selected PLL ANALYSIS TOOL FOR THE SIA 3000 PAGE 3 OF IO WAVECREST CORPORATION 2002 200033 00 REV A Voltages Menu View 1 Sigma Threshold Voltage Auto bul Channel Voltage Threshold Voltage e Auto sets measurement start and stop reference voltage based on the minimum and maximum levels of the measurement channel found from Pulsefind The threshold is automatically set to the 50 point The voltages are shown in the Channel Voltage display after a successful Pulsefind is completed e User Volts allows the user to set the reference voltage Channel Voltage Either sets or displays the reference voltage for the measurement channel depending on the setting of the Threshold Voltage Arm Voltage Either sets or displays the arming voltage for the measurement channel depending on the setting of the Threshold Voltage Initial Conditions Menu View 1 Sigma Calc Initial Conditions On Init Damping Factor Optimize Calc Initial Conditions Chooses whether to automatically calculate the initial conditions or allow user entry Init Damping
13. ve fitting algorithm uses as the starting Inj Cone values The 1 sigma values noisy flat line in purple are the actual acquired values The smooth line over layed green on the 1 sigma values is the Us ZOL8 SULS resulting variance curve fit This is the Good result of the algorithm acy Figure 9 Shows the typical response from an under damped PLL The results are good because the Variance Fit line closely follows the These results are good The fit matches trend of the 1 sigma values the 1 sigma values and there is no PJ present The ringing at the left of the 1 sigma values is due to the characteristics of the PLL and is not considered PJ because the values level off or dampens to a level value Figure 10 shows an example of another PLL Note that the Initial Conditions red line may be very different from the final result Variance Fit line l signmna Wor Fit Ini and Us 2 OLS SOLS Figure 10 Shows the typical response of another PLL The results are good because the Variance Fit line closely follows the trend of the 1 sigma values PLL ANALYSIS TOOL FOR THE SIA 3000 PAGE 9 OF IO WAVECREST CORPORATION 2002 200033 00 REV A Figure 11 shows a typical best case PLL PLL Anal There is a slight rise then level off In this case the Initial conditions just happened to be very close to the final result Remember that it is not necessary for the Initial Conditions red to match the 1 s
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