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External clock for Analog to Digital Converter

Hi Everyone, I am working on Jitter in Analog to Digital Converters(ADCs). I am trying to setup an experiment to see the effects of jitter in real time ADCs. I have an ADC evaluation board with external clock input for sampling (i.e Sampling clock). Now I want to produce a self created jittery signal to see the effects of jitter in ADC. Can anyone out there have any idea(s) how I can produce a real time clock signal with "variable jitter" for the input of external clock? Producing a simple clock signal (i.e. without jitter) is straight forward with the help of any signal generator but a clock signal with "variable jitter" is a problem.

Thanks for your help.

Cheers

Bilal

Reply to
East Hunk
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Get a fast analog comparator or a differential-LVDS-to-CMOS converter chip.

Apply your low-jitter logic-level signal generator to the + input of the comparator. Bias the - input to about logic mid-swing and AC couple a noise source into that. The output clocks your adc, and the jitter will depend on the slew rate of the edge at the + input and the ac noise level at the - input; the math here is direct. The noise source can be any waveform you like and will determine the probability distribution of the jitter; random, gaussian noise would be the typical choice, or use a triangle wave for a flat probability distribution.

To get lots of jitter, you may have to reduce the slew rate of the clock generator. Some pulse generators have adjustable slew rate, but if yours doesn't, a simple r-l-c lowpass filter can control edge rate pretty accurately.

Some of the adc's around these days need femtosecond RMS clock jitter to meet their accuracy specs.

John

Reply to
John Larkin

What sort of clock frequency does your ADC need, how much jitter do you want, & how precisely to you need to control it?

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Reply to
Lionel

Hi John,

Thank you for your reply. This is indeed an excellent idea. Let me try this and then I will get back to you.

Cheers

Bilal

Reply to
East Hunk

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