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Design >> Mixed-Signal Design >> frequency analysis of ADC
https://designers-guide.org/forum/YaBB.pl?num=1319187061

Message started by singh on Oct 21^st, 2011, 1:51am

Title: frequency analysis of ADC
Post by singh on Oct 21^st, 2011, 1:51am

ineed to plot gain curve for the transfer function,

to see frequency response, we need to keep input fix suppose vin =1 and vary the frequency. and then get the corresponding output
now i get say output vector and input vector,

Suppose i have out vector B and input vector A with (j-1) rows
i calculate TF as :

TF = fft(B,j-1)./ fft(A,j-1);

now in order to plot magnitide plot ... is it ok to do mag = abs(TF) ??

please suggest regarding this

Title: Re: frequency analysis of ADC
Post by loose-electron on Oct 21^st, 2011, 6:02am

you are taking the FFT of a nonlinear circuit?
does not make sense

Title: Re: frequency analysis of ADC
Post by singh on Oct 21^st, 2011, 6:59am

hmm ya its a mistake..

i plot phase vs digital out code for specific input value .

and now i want to take rms of the digital out obtained for the phase o to 2pi

how can i do that

Title: Re: frequency analysis of ADC
Post by loose-electron on Oct 23^rd, 2011, 7:37pm

Phase of what to what?

Please clarify what the question is.

Title: Re: frequency analysis of ADC
Post by singh on Oct 24^th, 2011, 3:12am

i want to see plot of rms value of digital output code Vs frequency
my digital out code is a function of input ,frquency and phase
I keep input value same as vin =1,
for different frequencies, I am getting output digital codes by varying phase from 0 to 2pi

suppose for freq = 1 to 10
for phase 0 to 2pi
get output = f(phase,frequncy,input)
out"(i) = output
rms = (out(i)) ???????
now i want to take rms values of different output codes obtained by varying phase from 0 to 2 pi in each frequnecy.how to caluclate rms value to know the output power spectrum.(whichi s i guess rms value Vs frequency)

Title: Re: frequency analysis of ADC
Post by sheldon on Oct 24^th, 2011, 5:40am

Singh,

You probably need to start at the beginning, that is, by telling
people what you want to do. Basically, you can not analyze an ADC
using small signal techniques. The approach I have seen most often
is to make many measurements or run many simulations, each at a
different frequency and then plot the result vs. input frequency. You
can repeat the process for different input levels if you would like but
usually you just run that tests near the maximum input level. Next
question, why do you think that phase is effecting the response of
the ADC?

Best Regards,

Sheldon

Title: Re: frequency analysis of ADC
Post by singh on Oct 24^th, 2011, 6:45am

vref is 3V so i m trying at amplitude as 2.5V. my input is sinusoidal (frequncy ,phase) so i wanted to see the effect of changing phase value on the output code.
so therefore,
for different frequencies, I am getting output digital codes by varying phase from 0 to 2pi

suppose for freq = 1 to 10
for phase 0 to 2pi
get output = f(input=f(fre,phase))
out"(i) = output
rms = (out(i)) ???????
now i want to take rms values of different output codes obtained by varying phase from 0 to 2 pi in each frequnecy.how to caluclate rms value to know the output power spectrum.(whichi s i guess rms value Vs frequency)

Title: Re: frequency analysis of ADC
Post by loose-electron on Oct 24^th, 2011, 3:19pm

Below is a good suggestion. In addition:

1. Give us a picture or block diagram of what you are trying to do.

You mention changing the phase.
Changing to phase of what?
The input signal to the clock?
Describe a specific problem, and we can try to help.

sheldon wrote on Oct 24^th, 2011, 5:40am: