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Coherent Sampling of Sampling Circuits and DFT

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Puppet123

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I want to measure the SNDR and SFDR of a sample and hold.

The clocks are at 2GHz. Input Frequency is 50MHz.

For coherent sampling to calculate this in Cadence Spectre for the DFT

fin=K*FS/N.

So I pick k=1023, N=2048, FS=2GHz. Then FIN = 999.0234375MHz.

Then run the simulation for 2048/FS or 1.024uS.

Calculate the DFT on this waveform.

What strobe period do I put in the transient options ? 2G/2048 ?

Is this the correct approach ?
 
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I think pretty much it is the correct approach. Since it is a sample and hold circuit and not really a continuous signal, you should be ok if just collecting samples at the end of the hold phase, which means you just need to have a strobe period of 1/2GHz. Also, leave some time in the beginning to let initial transients die out before you start collecting samples.
 

Oops, I think I made a mistake.

I think that K should be 27 to get FIN=51.7578125M which is the input frequency I want which is close to 50MHz.

And yes, the strobe period should be 1/2GHz.
 

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