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Cyclostationary device noise (Read 3986 times)
nrk1
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Cyclostationary device noise
Jul 28th, 2014, 8:38pm
 
How is cyclostationary device noise modeled in circuit simulators(Spectre in particular)? i.e. The shot noise of a BJT is 2qIc. Ic is periodically varying in a circuit. Is the output noise spectrum calculated as [average of 2qIc(t) over one cycle] times the relevant (LPTV) transfer function to the output?

Similarly, the MOS transistor's drain current noise is constant*|Qi| where Qi is the channel charge. Again, is it the average of |Qi| over one cycle that is used for noise calculations? What happens to the gate current noise in this calculation?

Thanks


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Ken Kundert
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Re: Cyclostationary device noise
Reply #1 - Jul 31st, 2014, 12:51pm
 
No. Shot noise is modeled as 2qIc, meaning that noise is modulated by the instantaneous junction current, as you would expect.

-Ken
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nrk1
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Re: Cyclostationary device noise
Reply #2 - Aug 7th, 2014, 7:08pm
 
I understand that the noise is modulated by the instantaneous current. But how is the spectrum modeled? In a time-invariant case, the spectrum of the collector current noise is 2qIc and at some other point it would be 2qIc*|H(f)|^2 and everything is independent of time. In the cyclostationary case, how is the time dependence eventually removed? (The final noise spectrum is independent of time, right). I was guessing that it is the average(over one period) of 2qIc(tau) or 2qIc(tau*|H(f,tau)|^2) where Ic and H are periodic in tau.

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Ken Kundert
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Re: Cyclostationary device noise
Reply #3 - Aug 11th, 2014, 12:05pm
 
It is more like the latter. The true cyclostationary noise on the output is computed internally by PNoise, and then the noise is averaged over one cycle and output.

-Ken
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