PSN-L Email List Message

Subject: Re: OpAmp noise
From: chrisatupw@.......
Date: Mon, 7 Oct 2013 11:35:24 -0400 (EDT)

From: David Saum 
To: psnlist 
Sent: Sun, 6 Oct 2013 16:23
Subject: Re: OpAmp noise

Hi Dave,


****This has less than 40 Nano V p/p noise over 0.1 to 10 Hz bandwidth

for a very low noise chopper opamp with NO 1/F noise, see the ADA4528

****This has 97 Nano V p/p noise over 0.1 to 10 Hz bandwidth

> Here the noise is expressed as a constant noise density at higher
> frequencies and a corner frequency, below which the noise becomes 1/F
> in nature.
> Voltage noise density, nV/root Hz     Corner frequency, Hz
> AD706         14.6          8.45Hz
> OPA227       2.47         19.9Hz
> LT1007CN   3.14         36.9Hz
   ADA4528       ~6          0Hz (no 1/F noise)

Since we are often interested in teleseismic signals <0.1Hz
the chopper ADA4528 with no 1/f is much superior at these low

> Current noise densiity - fA/root Hz,    Corner frequency - Hz
> AD706           44.6        4Hz
> OPA227         379        26.7Hz
> LT1007CN     434        36.9Hz
   ADA4528        500        0Hz (no 1/F noise)
The ADA4528 looks highest noise here at first glance
but the steep increase of 1/f noise below their 1/f corner frequencies
for the others negates this again.

See this app note on the ADA4528 for noise calcs vs source resistance

My testing has not found any better opamp for telesesimic frequencies
source resistances from 100 ohms to 10k ohms (geophones to

Hi Dave,
     Jim Williams' 22 year old circuit STILL seems to have the lowest=20
noise !
    But the ADA4528 does look attractive - so long as you can use the
small chip.
    Chris Chapman


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