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Analog Verification >> Analog Performance Verification >> How to calculate and simulate the noise of MOS-R as feedback resistor?
https://designers-guide.org/forum/YaBB.pl?num=1384244877

Message started by Davidy on Nov 12^th, 2013, 12:27am

Title: How to calculate and simulate the noise of MOS-R as feedback resistor?
Post by Davidy on Nov 12^th, 2013, 12:27am

We want to design a front-end circuit with the MOSFET as feedback component (Resistance is about 10e12ohm) of a amplifier as the jpg in attachment. But we wonder if the simulation results given by spectre is true? Because the simulation result is worse than the measurement results given by papers. And we also wonder how to calculate the noise of the MOSFET used as the feedback componet which works in cutoff region or very weak reversion normally as the structure in attached jpg?
Thank you!
(The structure is from: A Low-Power Low-Noise CMOS Amplifier for Neural Recording Applications,Reid R. Harrison and Cameron Charles,IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 38, NO. 6, JUNE 2003)

Title: Re: How to calculate and simulate the noise of MOS-R as feedback resistor?
Post by sheldon on Nov 13^th, 2013, 5:14am

David,

First more information on what simulated parameter or phenomena
doesn't match simulation measurement would be useful: noise,
distortion, ...

While I haven't tested this or looked at this in detail yet, but my
first reaction is that wouldn't this have the same issues as a passive
mixer? That is, if you are using a non-surface potential model then
there will be issues with models characteristics around 0 Volts.
Next if the resistance is 10e12, then you might need to set gmin
to a different value so it does not effect dc operating point calculations
and potentially small signal simulation results.

Finally, maybe I need to read the paper :-) but how does a device
in cutoff act as a feedback component and contribute noise?

Sheldon