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manisms

Junior Member

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Posts: 17

how to measure the THD of sample and hold circuit
Mar 15^th, 2007, 12:14am

how i calculate the THD of sample and hold circuits in cadence tool
actually the normal procedure as the select the net and take special function of THD and then plot .
but this is ok with the continuous wave and any amp.
but here the input signal is getting sampled at every clock cycle.
so i need to calculate the THD ...in this regards.
and please tell me how to measure the gain error and nonlinearity and pedestal error of s/h circuit in cadence ..
and docs for test benchs available plese please send to me..
i will be really obliged ..
regards

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vivkr

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Posts: 780

Re: how to measure the THD of sample and hold circ
Reply #1 - Mar 15^th, 2007, 6:22am

Hi,

I would recommend using the strobe feature of transient analysis to begin with. This guarantees that the simulator
places a timestep at the point where you want to observe the sampled output. Without this, you are likely to get
very bad results. After this, you can use the inbuilt "dft" function of the calculator.

However, this feature which used to work well earlier seems to give me some trouble nowadays. So, I print out
the output values into a text file at the strobed points, and perform an FFT with any convenient tool - MATLAB,
Excel etc. Normally though, the calculator should do a good job if you have properly strobed the output at the right
point.

Regards
Vivek

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Andrew Beckett Senior Fellow Offline Life, don't talk to me about Life... Posts: 1742 Bracknell, UK	Re: how to measure the THD of sample and hold circ Reply #2 - Mar 15^th, 2007, 6:24am PSS or QPSS (depending on the frequency relationship) is how I'd do this. See http://www.designers-guide.org/Analysis/sc-filters.pdf Regards, Andrew.
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manisms

Junior Member

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Posts: 17

Re: how to measure the THD of sample and hold circ
Reply #3 - Mar 17^th, 2007, 8:18am

hi VVkr
thanz for reply ..
as i am not very use to this cadence tool.
my question is that when i havea strobed the output of my s/h in transient analysis and run my simulation.
then after running the simulation if i plot the output it will show me the result of output where i strobed the signa.
then after that what i will do means how i proceed to calculate the thd .
i want to know the procedure of which net i click and choose the dft funtion in calculator.
please tell me how i proceed as i am very new for this tool.
hope u will help .
regards
manish

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