Clock Frequency Synthesis

I failed to put two and two together earlier.

By the time you get up to 16-bit ADCs being sampled at 200ksps, your quantization noise is being swamped by random noise in the ADC. This action whitens the ADC quantization noise, so you can treat it as more random noise, to be filtered out with your FFT process.

As far as the DAC noise goes, it'll still be there, and it'll still be correlated to the same degree. It shouldn't cause in-channel problems, but it may cause some slight harmonic "bleeding".

You can, of course, dither the DAC to whiten the quantization noise:

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I don't justify it - I merely report it. One of the - many - reasons that I'd like to get myself a job is that it provides a structure where I'm encouraged to get things done and rewarded when I've got things done. I don't have much of a problem keeping up with the domestic chores, though I'm no longer prone to keeping ahead of them, but stuff where there's no immediate encouragement does tend to get neglected.

-- Bill Sloman, Nijmegen

Dithering theory for conventional DACs lays some emphasis on the probability distribution of the dithering signal - which should ideally be triangular.

Comment on =93Noise averaging and measurement resolution=94[Rev. Sci. Instrum.[bold 70], 2038=962040 (1999)] AW Sloman - Review of Scientific Instruments, 1999.

lists a few references, including an impressive paper by R M Gray and T G Stockman, IEEE Trans. Inf. Theory IT-39, 805 (1993)on what goes wrong if you use a dithering signal with the wrong probability distribution.

-- Bill Sloman, Nijmegen

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Added dithering will not be necessary for what I am doing. The number of A to D bits was chosen so the voltage value of an LSB is well under the system noise I am expecting. This is thermal noise from resistors, equivalent input voltage and current noise from op amps, etc. That noise will dither for me.

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IIRR white noise hasn't got an ideal probability distribution, but it's not far off.

-- Bill Sloman, Nijmegen