bunny
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huh...analog design..
Posts: 8
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Hello all, I have a doubt in using the SNR function in the spectre wavescan calculator. I am trying to find the SNR of a 10bit ADC. I interfaced it with an ideal 10bit DAC (spectreHDL model). I performed the FFT of reconstructed signal(a sine wave) from ideal DAC output. I followed all the rules of coherent sampling. Now I used the SNR function and performed the following operation
snr(fft(V(vo),2.6u,259u,128),27.3k,249.6k,27.3k,249.6k)
where my input freq: 27.3K Fs= 499.2K (Fs/2= 249.6k) I am performing 128-point fft i.e., signal_from:27.3K signal_to: 249.6K (Fs/2) Noise_from: 27.3K Noise_to: 249.6K
but it resulted in InfinitydB
Now I reduced the signal_to range from 249.6K to 245K i.e., snr(fft(V(vo),2.6u,259u,128),27.3k,245k,27.3k,249.6k)
it results in SNR= 80.768dB (I am not sure of this value as I was expecting SNR around 60dB for 10-bit ADC)
can anybody explain me if I am doing it right. I am not sure abt the frequency ranges I am using for SNR. Even a small change in the frequency range is affecting my SNR values as they are jumping wildly from one value to another.
One more doubt...the magnitude of the fundamental(27.3K in my case) in the fft plot is exactly half of the maximum value of the reconstructed sinewave. I was expecting it to be Vm/root(2)(rms value). Why is it showing Vm/2?
thanq
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