Designing LC filters for amplifiers?

billcalley · 2007-07-29T06:41:43+00:00

Hi All, Something has me stumped, and it's pretty fundamental: If I'mdesigning an LC bandpass filter for the output of my narrow-bandamplifier, how could I possibly do this with any accuracy whatsoever,considering that when I design each separate stage I must initially"assume" that each will see an infinitely wideband and perfect 50 ohmmatch at both their input and output ports. But this is certainly*not* what the amp and the filter will see when they are cascadedtogether, since the stopbands of the filter (and the amplifier) willbe anything *but* 50 ohms. This would dramatically (I would think!)change the response of the filter near and in the stopbands, as wellas affect the amplifier's stability and gain. How could anyone even remotely be able to take this into accountin the initial design stage? Perhaps I'm completely wrong about thisbeing an issue at all? I realize we can cascade and then tweak thestages after designing them, but I would like to know how to take thisinto account before that -- or if I even have to?Thanks!-Bill

Jul 29, 2007 40 Replies

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Phil Hobbs 19 years ago

Yeah, but when you take the magnet away, they basically recover.

Cheers,

Phil Hobbs

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Designing LC filters for amplifiers?

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