From: Brett Nordgren 
To: psnlist 
Sent: Mon, 30 Sep 2013 15:41
Subject: Re: nice online Opamp Input Noise Voltage Tutorial

Geoff,
I agree with you, Dave S has found a very nice tutorial.  It's
probably worth watching more than once.
****There are several OTHER worthwhile technical electronics
lectures on this web site and ALSO several on seismology !

>What is the noise at DC ?

Actually, DC by definition, does not vary, and so has zero noise.
****Umm ? DC =3D Direct Current. The Voltage is NOT defined !
'DC' voltage sources all have some drift and noise on them. The
outputs of bipolar opamps show this + 1/f noise.

There's also the possibility of using an auto-zero (chopper) device.
They work well with both high and low impedance sensors, but
they are at their best at low frequencies, below a few Hz.
****These are VERY NOISY compared to TRUE chopper amplifiers.

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

>There has to be one best opamp for 100Hz to 100seconds,
>What Op Amp is it ??

Unfortunately, the choice will depend entirely on the circuit it is
being used in.  In the FBV designs, after much testing, the AD706 has
proven to be a truly excellent all-around device.
****Also look at the OPA227 and the LT1007CN?

    Regards,

     Chris Chapman


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