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Simulators >> Circuit Simulators >> How to simulate noise figure of SC-amplifier?
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Message started by Jacki on Apr 27^th, 2012, 9:18am

Title: How to simulate noise figure of SC-amplifier?
Post by Jacki on Apr 27^th, 2012, 9:18am

Hello,

I want to design a switched-capacitor amplifier (SC-amplifier), but the noise spec is not integrated noise. It is noise figure (3dB). The input source resistor is 1kohms.

I am familiar with LNA and mixer NF simulation. But for the SC-amplifier, I don't know how to simulate the NF. For my own opinion, NF is a kind frequency spectrum sweep. But for SC-amplifier, it is integrated noise. How to equalize these two concepts?

Also, I try PNoise simulation in Spectre, a very strange thing happens, when I reduce the source resistor value from 1kohms to 50ohms, the NF increases.

Anybody can give me some hints?

Thank you very much!

Jacki

Title: Re: How to simulate noise figure of SC-amplifier?
Post by RFICDUDE on May 3^rd, 2012, 5:09am

I am not that experienced with SC amps, but I would think that the integrated noise method is used because the switching would alias higher frequency noise back into the bandwidth of the amplifier (?). If this is the case then if you simulate NF using PSS/PNOISE you will receive a result that includes noise folding effects do to switching, so perhaps integration isn't needed (not sure).

To understand the relationship between integrated noise and NF you need to look at why integrated noise is used in the first place.

As for NF increasing with decreased source resistance, it is difficult to say why this is happening without seeing what exactly you are measuring. What is connected to the source resistor when you changed the value from 1k to 50 ohm?