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Nov 18th, 2019, 9:18am
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Eldo noisetran Problem on Fully Diff. Amp (Read 2018 times)
gcorrig
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Eldo noisetran Problem on Fully Diff. Amp
Apr 06th, 2007, 8:54pm
 
I am getting odd results for Eldo transient noise analysis on a fully differential OTA I designed.  I get 7 nV/rt.Hz input referred using AC noise analysis on both neg and pos signal paths.  When I run noisetran on the amplifier open loop with a uVolt differential sinusoidal input I get several millivolts of common mode noise with hundreds of uVolts riding on top  (the transient output looks great, no clipping or slewing).  I am not sure if this is statistically valid, but I diff the two rms_noise output signals and get about 600uV of zero mean noise, which itself has a 385uV rms value.  My amp has 90dB of gain and a dominant single pole roll off at 1.2kHz.  I would expect 2*((7nV/rt.Hz)^2*GBW*Pi/2)^1/2 = 108uV total integrated noise, but I am not even close with 600uV (or 385uV!)

I have run the same cross check on a single ended amp I built and everything ties out between AC Noise and noisetran using the GBW for that amp.  Am I doing something stupid with my test bench or committing some major statistical blunder?

Thanks in advance
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mg777
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Re: Eldo noisetran Problem on Fully Diff. Amp
Reply #1 - Apr 6th, 2007, 9:23pm
 

Try an FFT on the single ended output and see what the PSD looks like (note: FFT is not a good PSD estimator, but it's a start).

It's good to see an Eldo post on this forum.

M.G.Rajan
www.eecalc.com

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monglebest
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Re: Eldo noisetran Problem on Fully Diff. Amp
Reply #2 - Sep 23rd, 2017, 2:54pm
 
May I know is the equation right?
2*((7nV/rt.Hz)^2*GBW*Pi/2)^1/2 = 108uV

I thought it should be *f(3dB BW) instead of *GBW.
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