Q about testing ADC in simulation level

[yushen_yang]

Hi All,

For testing 10bits ADC in simulation level, I extract data from Hspice and import the data into Matlab to do FFT. Suppose my input is 2.11MHz and sampling rate is 10MHz, I use matlab codes to DAC in order to get the ideal analog output and then test SNR, ENOB, THD.

The problem is should I add a low pass filter before doing FFT?
Thx in advances.

YuShen

 

[flushrat]

Don't use lpf.

 

[dspman]

hi,

you sould not add a low pass filter, since it changes the received signal and then you can not evaluate the features of your ADC.

yours.

 

[sankudey]

Hi yang,
That much theory I know is that, if use a ideal DAC...u don't need to use LPF....for ur case , as u are doing it in MATLAB, the DAC is definitely IDEAL.....

sankudey

 

[ezt]

Hi.
I agree with others. If you do the D/A conversion in MATLAB so you should not use LPF. But I just want to mention a few things:
If fs is samplinf freq and fin is input frequency:
fin = (N/M) * fs
and GSD(M,N) = 1
in this case you don't have to use windowing and then get FFT. You just get FFT, halve it, find the main bin and the rest is noise plus distortion (but ofcourse in your case it's just distortion. because HSpice can't calculate noise power unless you have modeled it somehow.)

Regards,
EZT

 

[sankudey]

Hi EZT,
What u mentioned is correct. ALthough I am not aquinted with HSPICE, I think the noise model u are talking about is correct for all simulator. But I have a confusion here.
-->WHAT THE NOISE ARE U TALKING ABOUT?
If it is the noise from device, then perhaps u r right. But probably the concerned noise is the QUANTISATION NOISE, which straightway comes from the (Vin-Vout), as is the case for ADC.

Please rectify me if I am wrong.

One more question I have here. Once the spectrum is got, how to calculate the SNR,SINAD,ENOB etc. I got some theoritical explanations of the same but not very confirmed of the same and yet not have done in hand. Thus it would be of great help if u gve some light on the matter and also give some good reference on the same.

Regards
sankudey