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Design >> Mixed-Signal Design >> track and hold THD issue
https://designers-guide.org/forum/YaBB.pl?num=1299267900

Message started by ontheverge on Mar 4^th, 2011, 11:45am

Title: track and hold THD issue
Post by ontheverge on Mar 4^th, 2011, 11:45am

Hi,

I'm simulating a flip around track and hold circuit as 1st block for a 10bit pipeline ADC. circuit diagram and output waveform are as below: when I measure the THD at A (differential) it's ~-80dB, however only ~-30dB at B. all switches are bootstrapped ones and op-amp works fine (enough gain, no stb issue).

my questions are :
1. ideally, should A and B give the same THD ( A tracks and hold the input sinusoidal wave, B is either 0 or the hold value of A); how much degradation should we expect in practice.
2. how do i improve THD at B, which is actually the input of the 1st pipeline stage (other than impoving feedback switch)

Thanks a lot,
Steve[edit][edit][/edit][/edit]

Title: Re: track and hold THD issue
Post by boe on Mar 29^th, 2011, 8:14am

ontheverge,

How do you calculate the THD?
Note that at point B you have a sampled system. Did you take this into account?

B O E