ywguo
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Hi Guys,
As well known, we usually measure output spectrum of DAC with spectrum analyzer. It is easy to calculate SFDR or HDs automatically. However, is it a reliable tool to calculate SNR? For example, the following is a picture that is measured with Agilent E4404B spectrum analyzer. The clock frequency is 50 MHz, and the signal frequency is 813 kHz. The SFDR is 69.94 dB. To calculate SNR, I use the formula below.
signal_dB = -5dB noise_floor_dB = -88dB signal = 10^(signal_dB/10) = 0.316 mW RBW = 1000 Hz Assume Nyquist_band = 25 MHz and noise floor is flat in Nyquist band, although the stop frequency is 2.5MHz only in that spectrum plot. noise = 10^(noise_floor_dB/10)*(Nyquist_band/RBW) = 39.6 μW SNR = 10*log10(signal/noise) = 39.02 dB
It seems that SNR is too low for a 10-bit DAC. But I don't know what's wrong with the above derivation. Any comments are appreciated.
Yawei
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