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Simulators >> Circuit Simulators >> calculating SNR from dft on Spectre
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Message started by iris on Aug 29^th, 2017, 12:51am

Title: calculating SNR from dft on Spectre
Post by iris on Aug 29^th, 2017, 12:51am

Hi

I simulate 8-bit current-steering DAC. Fsine=prime_number*Fsample/(number_of_dft_bins). I'm doing a transient simulation on Spectre, stop_time=(number_of_dft_bins/Fsample), and then using dft function on the output, to produce the SNR from SpectrumMeas.
I don't understand what exactly affects the noise floor, how does the dft calculate the noise floor? because changing the number of transistors in the DAC, fro example, changes the SNR.
Appreciate any help,
Iris

Title: Re: calculating SNR from dft on Spectre
Post by sheldon on Aug 29^th, 2017, 3:29pm

Iris,

Fin = (prime number / number of FFT points) * sample,
where number of FFT points > 2 * prime numbers

Adding more FFT points decreases the noise floor. It would be better
to use the spectrum function in the ViVA.

Remember that an ADC has quantization noise, so the noise floor is limited by the 6.021* number of bits + 1.76 divided by the 10 dB (bin width/bandwidth).

Sheldon