PSN-L Email List Message

Subject: Re: (No subject)
From: "Larry Cochrane" lcochrane@..............
Date: Wed, 30 Jun 2004 21:30:41 -0700

> 5. Put a one microfarad capacitor across the input terminals of your
amplifier. I have amplifiers
>of differing designs, and they all oscillate internally if there is no
shunt capacitance across
>the input terminals when the source is inductive (i.e., a sensor coil). You
cannot see this
>oscillation at the output terminals; it manifests itself as excess output
noise, and in the
>case of my DC amplifiers, a large and fluctuating bias.

I question this one... I have never seen a need to place a cap on the input
of an op-amp to stop internal oscillations. If you are getting some RF into
the input you can place a .01 ceramic cap across the input to shunt out the
RF before it gets into the op-amp. I have seen oscillation problems with
op-amps driving large capacitance or inductive loads.

-Larry Cochrane
Redwood City, PSN


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