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William Murray

RF Susceptibility & Operational Amplifiers

William Murray
Brad Albing
Brad Albing
3/14/2013 11:05:43 AM
User Rank
Blogger
Re: RF Susceptibiilty and Operational Amplifiers
Certainly care must be exercised when adding caps at or near the inputs of the op-amps. Sometimes, making the leads/foil traces on the PC board as short as possible; and then adding caps (or inductors/ferrite beads) before the input resistors is better. That way, you can avoid introducing an extra pole into the feedback loop. Of course, on an existing piece of bench equipment, it's not practical to redesign the PCB.

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WKetel
WKetel
3/13/2013 4:40:47 PM
User Rank
Artist
Re: RF Susceptibiilty and Operational Amplifiers
Understanding the reason that all of those "extra" capacitors and choke coils are needed is indeed a valuable education. You are fortunate that the ouput dropped instead of going up to the maximum. Those extra parts are what to look for when purchasing a power supply for radio equipment. 

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DEREK.KOONCE
DEREK.KOONCE
3/12/2013 1:48:19 PM
User Rank
Master
Re: RF Susceptibiilty and Operational Amplifiers
Good lesson to learn. Need the rib-punch sometimes to look at the real-world details to work with.

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John Dunn
John Dunn
3/11/2013 7:07:54 PM
User Rank
Blogger
RF Susceptibiilty and Operational Amplifiers
I had a brief moment about this with the late Bob Pease at one of his lectures. Please see this URL:

http://licn.typepad.com/my_weblog/2011/09/beware-of-loop-gain-john-dunn-consultant-ambertec-pe-pc.html 

 

 

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