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Measurements >> Other Measurements >> Measure noise of Switched-capacitor amplifier.
https://designers-guide.org/forum/YaBB.pl?num=1385230940

Message started by Jacki on Nov 23^rd, 2013, 10:22am

Title: Measure noise of Switched-capacitor amplifier.
Post by Jacki on Nov 23^rd, 2013, 10:22am

Hello,

Now I plan to measure the noise of a switched-capacitor amplifier with Agilent PSA series spectrum analyzer E4445A. Is it straightforward to measure the noise? I am thinking some examples here.
Example 1: step 1. Turn on the signal generator, measure the gain
step 2. Turn off the signal generator, measure the noise at the output.
step 3. Calculate the input referred noise based on the output noise and gain.
Is it correct?
Example 2: step 1. Turn off the signal generator, measure the noise at the output.
step 2. Add a noise source, measure the noise at the output (set the gain of SC-amp to 0dB).
step 3. Calculate the noise.

In spectre simulation, usually I use PNoise to simulate the noise of SC-circuits. Can I get the same results when I use spectrum analyzer to measure the chip compared with the PNoise simulation?

Any comments for the noise measure of SC-circuits are appreciated.
Jacki

Title: Re: Measure noise of Switched-capacitor amplifier.
Post by Jacki on Nov 25^th, 2013, 9:06am

I wonder if the PNoise in the simulation can display the similar results as spectrum analyzer in the measurement.

Jacki.

Title: Re: Measure noise of Switched-capacitor amplifier.
Post by Ken Kundert on Nov 25^th, 2013, 4:20pm

Yes, of course. A spectrum analyzer measures the time-averaged noise. In SpectreRF PNoise analysis direct plot form, this is referred to as "Sources" (I don't know why it is called Sources, but it is). SpectreRF's effective noise bandwidth is 1Hz.

-Ken

Title: Re: Measure noise of Switched-capacitor amplifier.
Post by Jacki on Nov 26^th, 2013, 2:02am

Thank you very much, Ken. I think I need to use the bandwidth of 10Hz in the spectrum analyzer, but it is really slow, then use the equation to calculate the noise at 1Hz bandwidth.

Jacki.

Title: Re: Measure noise of Switched-capacitor amplifier.
Post by Andrew Beckett on Dec 27^th, 2013, 1:51pm

Ken Kundert wrote on Nov 25^th, 2013, 4:20pm:

I don't know why it is called Sources, but it is)

Ken,

I assume this is because it was originally either outputting the noise source information, or the cross-power densities (from "spectre -h pnoise"). I assume the parameter got hijacked to be the mode of operation (hence it now supports timedomain and pmjitter), and so the original meaning is a bit mixed up (I think this happened in something like IC445, which is when timedomain noise was introduced). Probably seemed like a good idea at the time ;)

Andrew.