Jitter: Seconds to dB?

[watchnerd]

What's the formula for translating jitter from seconds (picoseconds, femtoseconds, etc.) to dB?

Here is an example of jitter data for an Allo USB bridge, but it's in seconds and I'm not sure how to rate it vs, say, a J test in dB:

https://www.amazon.com/clouddrive/s...ncoding=UTF8&mgh=1&ref_=cd_ph_share_link_copy

 

[amirm]

20*log(jitter_second*jitter_freq*2*pi/4).

I can't read anything in that link. If you give me the jitter number I can convert it to db.

 

[DonH56]

For SNR the equation is: SNR (dB) ~= -20 * log10(2 * pi * fin * tj) where pi = 3.14159..., fin = input frequency (Hz), and tj = jitter in time (s pp)
This is for uncorrelated random Gaussian jitter, assumes a pure single-tone sinusoidal input, and no other error sources. Note that the sampling rate drops out of the SNR equation.

Real jitter is much more complicated, natch, but this simple formula correlates very well to the data presented in the plots in the Jitter 102 thread. It is a little off but close enough for general use (ADI uses it in some of their white papers).

Quantization noise and other things may limit the performance of a DAC (or ADC, or DSO).

HTH - Don

 

[watchnerd]

20*log(jitter_second*jitter_freq*2*pi/4).

I can't read anything in that link. If you give me the jitter number I can convert it to db.

660 fs

 

[amirm]

660 fs

At 20 Khz source frequency that translates to -153 db!

 

[watchnerd]

At 20 Khz source frequency that translates to -153 db!

Sounds like I need to order one of these Allo USB bridges for testing, in that case.

Or maybe they'd donate one to the site?

https://www.allo.com/sparky-eu/usbridge.html

 

[amirm]

I have one of their streamers on loan already to test. When I get a chance I will get it going and post the review.

 

[j_j]

You ask a question that only has half of the information. The other half is "what is the input signal". The higher the derivative of the input signal, the more error results from a given jitter.

You also need to know the frequency content of the jitter.