[TC23x] Accuracy of frequency measurement GTM (jitter and PLL)

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User20354
Level 1
Level 1
First question asked First reply posted
Hello Everybody,

I try to find the worst case for accuracy for frequency measurement. The frequency of the input signal is between 100Hz to 15kHz at the input of the µC.


We used GTM timers at configured at 4MHz.
Tolerance and temperature drift for the Quartz at 20Mhz is 0.03%

I would like to know, the influence of the jitter on the PLL of the microcontroler with modulated clock at 1%.

Withtout taking account the jitter, in worst case we could have +/- one period of the GTM_timers according to the synchronisation of the edge, is it right?
To measure 100Hz, the number of the edge of GTM_timer will be : 40000
To measure 15kHz, the number of the edge of GTM_timer will be : 266.7

How can I compute of the effect of the jitter for the PLL at 4MHz?
-According to the datasheet, JtotCC = 12.2ns and DPCC is +/-200ps

Do I only need to add the time of the Peak_Period_Jitter to the period of the GTM_timers?

4688.attach

Thank you for your help,
ES
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2 Replies
NeMa_4793301
Level 6
Level 6
10 likes received 10 solutions authored 5 solutions authored
Nice work - yes, you add one period of GTM and JtotCC together.

See AP32244 AURIX SYSPLL Frequency Modulation for a very long discussion of PLL modulation effects on short and long term jitter.
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User20354
Level 1
Level 1
First question asked First reply posted
UC_wrangler wrote:
Nice work - yes, you add one period of GTM and JtotCC together.

See AP32244 AURIX SYSPLL Frequency Modulation for a very long discussion of PLL modulation effects on short and long term jitter.


Thank you for your answer.
I add the JtotCC one the tranfert function.

Input informations
Etime is the worst case time with the noise calculated from simulation for the electronic part. 41ns in our case.
4689.attach

Results :
4690.attach

ES
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