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Measurements >> RF Measurements >> Input Referred Noise of Pipeline ADC
https://designers-guide.org/forum/YaBB.pl?num=1232729064

Message started by Scott on Jan 23^rd, 2009, 8:44am

Title: Input Referred Noise of Pipeline ADC
Post by Scott on Jan 23^rd, 2009, 8:44am

I am trying to match lab measurement of short circuit noise for my pipeline ADC. In order to accomplish this, I set up a PSS/PNOISE/PAC analysis for the first 3 MDAC stages and the S/H stage of the pipeline. I set PSS to have a beat F=fs/4. This appears to work fairly well, but I have a couple questions.

First, the PAC predicts a 6dB voltage attenuation across the S/H. Is this expected? The S/H does have a return to VCM forced during the sample stage by shorting the S/H positive and negative outputs.

In the simulation I have 3 MDAC stages with a 2X gain per stage, resulting in a 8X gain from the output of the 3rd MDAC to the output of the S/H. Referring the noise at the MDAC output to the S/H input is easy (divide by 8), but when referring to the S/H input (to match the lab data) should I include the 6dB attenuation of the S/H?

Thanks,
Scott

Title: Re: Input Referred Noise of Pipeline ADC
Post by Ken Kundert on Jan 23^rd, 2009, 10:58am

Does the output of you S/H have a 50% duty cycle?

-Ken

Title: Re: Input Referred Noise of Pipeline ADC
Post by Scott on Jan 23^rd, 2009, 1:00pm

Yes, The output is very nearly 50% duty cycle.

Title: Re: Input Referred Noise of Pipeline ADC
Post by Ken Kundert on Jan 23^rd, 2009, 1:52pm

There you go. That is your 6db. The size of the Fourier coefficient for a sine wave with 50% duty cycle is half the size of one with the same amplitude that has 100% duty cycle.

Title: Re: Input Referred Noise of Pipeline ADC
Post by Scott on Jan 26^th, 2009, 12:51pm

Thanks, that's what I thought. It also corresponds with the pnoise analysis showing 6dB higher when I use the time domain analysis as opposed to the sources analysis.

Scott