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Bandpass filter for DC removal and >20kHz noise rejection

I have a signal that has a 1V DC bias on it that I want to remove and also perform some smoothing to reduce high frequencies. The reason for removing the DC is that I want to rectify the AC component of the signal.

On the face of it a bandpass filter from ~5Hz to 20kHz would seem to do the required filtering. The shape of the transition is not really that important - anything "reasonable" would do. Does such a thing exist? I've been looking around for a vendor or possible thinking of getting out the soldering iron and throwing something crude together myself.

Is there a better way to achieve what I want to do? (Yes, obviously - but please tell me!).

Reply to
spasmous2
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Look in the text for "coupling capacitor".

Good Luck! Rich

Reply to
Rich Grise

a capacitor ?

if that isn't to your liking, then inject the signal into a split rail driven op-amp and apply a -1 offset to the + input and your reference signal to the - input via some resistors of course. That method will allow you 0..20khz pass with no DC component.

and generating the DC from the AC component, you can use a precision rectifier for that. etc..

--
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Reply to
Jamie

You have a reasonable idea. Use the java app below to design the circuit.

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Reply to
Mook Johnson

What are the source and load impedances? It could be as simple as 2 r's and 2 c's, or even simpler.

John

Reply to
John Larkin

How do you intend to rectify the signal. Chances are, you can combine the whole process.

Reply to
MooseFET

Yes, you COULD do a bandpass filter, but when the low frequency cutoff is a small fraction of the high frequency cutoff, you're almost always better off to use a high pass filter and a low pass filter. The high pass function you want is commonly done simply with a capacitor. The low pass filter you want depends a LOT on just what you need to accomplish. You might do OK with a very simple filter, or you might decide you need something fancier there.

If you look for a "precision rectifier" op amp circuit, you should find one that will do a good job, and might even already include a capacitor. However, beware of rectifiers that present different loads on the positive and negative half-cycles. That can cause a simple coupling capacitor to not have only AC at the output...that is, the differing loads will cause a dc component to appear at the input terminal. (Why is it that things that seem so simple end up being complicated?? ;-)

Cheers, Tom

Reply to
Tom Bruhns

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