HdrChopper wrote on Aug 18th, 2009, 4:45am:Hi subgold,
Running a pnoise analysis with "sources" in the Noise type option is correct, as you suggested.
The effect of 1/f removal can be observed in two different ways:
1) From pnoise you should see the 1/f noise components modulated at odd harmonics of your chopping frequency...
2) Simply look at the pnoise results at base band and compare them to a plain noise analysis on your amplifier (without chopping clock activated). The difference betwen both cases should be clear.
In the lab: with an oscilloscope just set your time base at - say - 2s/div and stop the chopper clock. You should see the typical noise floor (like a noise band) slowing drifting upwards and downwards, always around its mean value.
If you turn on the chopper clocks, you should see the same noise floor (or band) wihtout any drift, i.e. just a straight noise band.
The pkpk noise from that band is the white noise.
Hope this helps
Tosei
Hi Tosei,
although i have already known what you said, thanks for your reply anyway.
maybe i should state my question more specifically: how to observe the 1/f noise removal effect in frequency domain?
i have seen many papers presenting a nice picture of noise PSD with a flat white noise down to near 1Hz or even dc (e.g. C. Enz et al "A CMOS chopper amplifier" JSSC 1987). is this really possible unless we do some data processing afterwards? according to my design experience, the chopping does reduce 1/f noise significantly, but there is always some residual noise up to at least 100Hz, which is as expected and understood. i never see a complete 1/f noise removal.
do you have any comments?