will frequency division cause change in phase difference?

[saurabh17g]

I have two frequencies of 10MHz each just that one of them is lagging behind other by some interval.
for the purpose of measurement, i have constructed a circuit that divides the frequencies by say 32.
so will the phase difference between the older frequencies and the newer frequencies be different?

 

[keith1200rs]

The problem is when the counters are started or reset. However, even if you start the dividers at the same time the 'phase' will not be the same. The time shift will be the same. For example, if one frequency lags the other by 20ns then they will have the same time delay after dividing. But 20ns at the lower frequency is not the same phase shift as 20ns at the high frequency.

If the dividers are not simultaneously reset, even the time shift will be wrong.

Keith

 

[nsingh95]

Re: will frequency division cause change in phase difference

The problem is when the counters are started or reset. However, even if you start the dividers at the same time the 'phase' will not be the same. The time shift will be the same. For example, if one frequency lags the other by 20ns then they will have the same time delay after dividing. But 20ns at the lower frequency is not the same phase shift as 20ns at the high frequency.

If the dividers are not simultaneously reset, even the time shift will be wrong.

Keith

Hi ,
No there will be no difference. Just analyze yourself thinking practically.

 

[keith1200rs]

Re: will frequency division cause change in phase difference

The problem is when the counters are started or reset. However, even if you start the dividers at the same time the 'phase' will not be the same. The time shift will be the same. For example, if one frequency lags the other by 20ns then they will have the same time delay after dividing. But 20ns at the lower frequency is not the same phase shift as 20ns at the high frequency.

If the dividers are not simultaneously reset, even the time shift will be wrong.

Keith

Hi ,
No there will be no difference. Just analyze yourself thinking practically.

I did analyse it myself thinking practically and have given my answer and reasons. Perhaps you would like to explain the rationalle behind asserting that I am wrong? Just saying 'think about it' is a pointless answer.

Keith

 

[keith1200rs]

Re: will frequency division cause change in phase difference

Here is an example. I have used two 10kHz clocks divided by 8. The difference between the two clocks is 10us = 36 degrees. The phase difference in the output waveforms is also 10us = 4.5 degrees (because the output frequency is 1250Hz). So phase is not preserved. This also assumes that your counters are simultaneously reset to ensure initial synchronisation.

I hope that answers the question.

Keith.

 

[FvM]

Re: will frequency division cause change in phase difference

You're of course right about phase difference scaling by the division factor. But the input referred phase difference could be
still easily calculated. The fact, that the divided output signals can't be expected correctly synchronized is the real problem,
however.

 

[keith1200rs]

I said that in my first answer.

Keith.