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Question on PSS+PNoise simulation for a Track and Hold circuit

YutaoLiu

Hi everyone,

I am studying how to run PSS+PNoise sim to get total output noise of a Track and Hold circuit. 

I am using Virtuoso version ICADVM20.1-64b.500.15 for simulation.

Below is my test bench, in which the switch is driven by a 8GHz 25% duty cycle clock. The closed switch resistance is 0.1Ohm, while the open resistance is 1T Ohm. And the RC time-constant is 15GHz, which is higher than the Nyquist frequency (4GHz).

In document "Simulating Switched-Capacitor Filters with SpectreRF" , it is written that the total noise of T/H circuit is kT/C, which is 41.4nV^2 in this case. 

I expect that the noise higher than 4GHz would be folded back into 0~4GHz, so I set the output frequency is from 1~4GHz. And to get a more result, maximum sideband was set as 50 (Because 4GHz *50= 200GHz >> 15GHz).

However, the total noise integrating from 1Hz to 4GHz is only 27nV^2. Moreover, the total noise increases as the duty cycle decreases. 

Did I misunderstand anything about the total noise of T/H or do anything wrong in the simulation setup?

Thanks and regards,

Yutao

       

Parents

  • Hi Frank, Andrew and Shawn,

    Thanks for your explanation and suggestion.

    I kind of understand why Frank suggest to use "sampled (jitter)" noise type if setting stop frequency only up to half the "Beat Frequency".

    Following is my understanding,

    a) My circuit is a track and hold circuit. In the hold phase, circuit samples the noise at the end of track phase, and then hold it for the rest of the period. It can be separated into two parts.

        First, it samples the noise in time domain, so noise is folded back into 0~ half of beat frequency in frequency domain.

        Second, the sampled noise goes through a zero-order hold convolving in time domain (multiplying a sinc function in frequency domain). The resulting noise spectrum spread to +/- infinity due to the effect of sinc function. I thinks this is what we should see in the sprectrum analyzer as mentioned by Andrew. So that is the reason why stop frequency need to set 10x of  "beat frequency" to get a closer result as possible.

    b) As explained by Andrew, with "sampled (jitter)" noise type, an ideal sampler (working at beat frequency) folds back all the noise into 0~half of beat frequency range again. So with this setup I can see the integrated noise power from 0~half of "beat frequency" matches to kT/C.

    Is my understanding correct?

    Thanks and regards,

    Yutao

Reply

  • Hi Frank, Andrew and Shawn,

    Thanks for your explanation and suggestion.

    I kind of understand why Frank suggest to use "sampled (jitter)" noise type if setting stop frequency only up to half the "Beat Frequency".

    Following is my understanding,

    a) My circuit is a track and hold circuit. In the hold phase, circuit samples the noise at the end of track phase, and then hold it for the rest of the period. It can be separated into two parts.

        First, it samples the noise in time domain, so noise is folded back into 0~ half of beat frequency in frequency domain.

        Second, the sampled noise goes through a zero-order hold convolving in time domain (multiplying a sinc function in frequency domain). The resulting noise spectrum spread to +/- infinity due to the effect of sinc function. I thinks this is what we should see in the sprectrum analyzer as mentioned by Andrew. So that is the reason why stop frequency need to set 10x of  "beat frequency" to get a closer result as possible.

    b) As explained by Andrew, with "sampled (jitter)" noise type, an ideal sampler (working at beat frequency) folds back all the noise into 0~half of beat frequency range again. So with this setup I can see the integrated noise power from 0~half of "beat frequency" matches to kT/C.

    Is my understanding correct?

    Thanks and regards,

    Yutao

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