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How to measure noise of an amplifier?

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Advanced Member level 4
Dec 7, 2004
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I'd like to measure noise of a chopper amp, but I have not tested noise befoe. Anyone can give me some suggestions? Thanks!

If you are using spectre:

Setup a noise analysis. Choose the output node, input source and frequency range. Then Run the noise analysis.

You can plot output noise voltage or input noise voltage versus frequency...

Concerning a chopper amplifier, I think you will need to use a PSS analysis followed by pnoise analysis...

Hope this helps

One quick way with to visually see typical noise is to do Transient Noise. This will give you a visual of what the output noise would look like.

Otherwise, like said before, you could do PSS or PXD analyses, though for that you need a repeating input signal to produce a steady state output.


measure or simulate?

I mean in testing not simulation, thanks.

Now that depends on what you want. If you are looking for 1-sigma noise voltage, then put a scope on it, turn on trace overlay and see how thick the bar gets for a specific DC input.

If you are looking for noise performance over frequency, hook up a spectrum analyzer and for a given DC input (i.e. set up the chopper as a follower and have it's output mid-rail) look at the spectral power.

If you want an agregate noise to relate to a rms noise voltage or a noise power, you need a power meter. Set the op-amp as a follower, put a power meter on the output but make sure it has a DC blocker on it. The power you read will be your noise power which can be related to a noise voltage.

If you are using the chopper for mid to high frequency signal processing and you want the noise figure of it, then use a Noise Figure module available for most spectrum analyzers. Put the caliberated noise source at the input and measure the noise power at the output.


How to simulate the noise performance of chopping amplifier using Hspice ? Is it possible for Hspice to do noise simulation with switch and clock ?

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