conglinghu
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Posts: 4
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Hi Andrew,
Thank you so much for your comments.
I did try voltage source to do pnoise, but when I asked for "input-referred noise", the output window still complains there is no port.
As for the sweep frequency range, my understanding is: the ADC will convert a continuous time signal to a discrete time signal. So in frequency domain, the signal's spectrum is duplicated in peroid of "fsample". All duplicated signal's strength are the same. So if the signal or noise's bandwidth is wider than fsample/2, we will see aliasing.
In cadence, the tdnoise analysis can simulate this aliasing effect and only 0-fsample/2 sweep is needed. For example, the KT/C noise power is folded, then if I integrate the power from 0 to fsample/2, I can get KT/C power.
But in "source" simulation, the analysis does simulation on the ADC's _analog_ output, which is usually a step response in time domain, which means the ADC samples the continuous time signal input and outputs a flat step voltage(still analog), to represent the input signal at the sampling time. So, in frequency domain, the signal spectrum is duplicated first, then modulated by a Sinc function. Therefore, in "source" simulation, the spectrum output's strength is modulated by "Sinc" function. Although all sideband's power are folded into (0 ~ fsample/2), but it is modulated by sinc function, it is not flat any more. So if I integrate this bandwidth, the power is less than the theory value. But if I integrate all the sidebands, the more sidebands I integrate, the more accurate the power is.
I did not go deep in the math here, I just guess and try. Maybe it is true that the integral of Sinc function equals to one. I am not sure.
If I am wrong, please correct me. Thank you very much again.
Best Regards,
cong
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