PSN-L Email List Message
Subject: Re: Op amp front end noise
From: Brett Nordgren Brett3kg@.............
Date: Thu, 10 Mar 2005 07:51:41 -0500
Another factor that you may want to consider is thermal variation. At very
low frequencies, below 1Hz, the effects of micro-variations in the device
temperature can add additional "noise". I would imagine that in
characterizing low-frequency noise, the op-amp manufacturers take pains to
hold the temperature very steady, which is not what you're going to see in
the real world. In real world conditions, it is possible that a device
with very good temperature properties will perform better (less low
frequency "noise") than one with much better noise specs, but having larger
Just an aside, but related, in building very long time-constant RC filters,
say 1000sec or so, if you use the lowest leakage capacitors, the largest
noise source seems to be due to the variation of capacitor value with
temperature and is proportional to the DC voltage on the capacitor. The
capacitor charge Q=CV, and in the steady-state can be assumed to be
constant. If C goes down due to a temperature change, V goes up--and the
effect is fairly large.
At very low frequencies, temperature effects look a lot like noise.
At 08:57 PM 3/9/2005 -0500, you wrote:
>I am getting pretty deeply into the design process for a velocity coil
>seismometer amplifier and filter and have decided to try ot quantify
>the relative noise performance of various candidate opamps versus coil
>resistance. Here is the list of low noise and general purpose types
>(which I have on hand) that I am comparing:
If my e-mail address above is not working
you can always reach my mail form at: http://bnordgren.org/contactB.html
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