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

Hi Dave,

****SEE:- http://cds.linear.com/docs/en/application-note/an45f.pdf

****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
http://www.analog.com/static/imported-files/data_sheets/ADA4528-1_4528-2.pd=
f

****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
frequencies.

> 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
http://www.analog.com/static/imported-files/application_notes/AN-1114.pdf

My testing has not found any better opamp for telesesimic frequencies
and
source resistances from 100 ohms to 10k ohms (geophones to
coil/magnets).

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.
    Regards,
    Chris Chapman


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