Path: utzoo!attcan!uunet!tektronix!tekcrl!tekfdi!videovax!bill
From: bill@videovax.Tek.COM (William K. McFadden)
Newsgroups: sci.electronics
Subject: Re: Variable bandwidth 6 pole Butterworth LPF
Keywords: variable bandwidth,10KHz-1MHz
Message-ID: <5310@videovax.Tek.COM>
Date: 11 Nov 88 17:39:51 GMT
References: <787@mplvax.nosc.MIL>
Reply-To: bill@videovax.Tek.COM (William K. McFadden)
Organization: Tektronix Television Systems, Beaverton, Oregon
Lines: 27

In article <787@mplvax.nosc.MIL> david@mplvax.nosc.MIL (David Almagor) writes:
>I need to design a variable bandwidth low pass filter, whose
>programmed pass band will span 10kHz to 1MHz.
>The input's dynamic range is about 40dB, and the filter should 
>have the properties of a 6 pole Butterworth. Budget should 
>be kept at a min. Any ideas out there?

Sounds like a switched-capacitor filter would work.  The filter's cutoff
frequency is proportional to the input clock frequency.  Monolithic devices
are available from National Semiconductor, Linear Technology, Maxim, and
others.  Unfortunately, none of them will work up to 1 MHz.  The closest I know
of is the new MAX260 series from Maxim.  Some devices in this family offer
cutoff frequencies up to 140 KHz.  Switched capacitor technology makes it
possible to implement highpass, lowpass, bandpass, and notch functions
simultaneously.  However, achieving a 1 MHz response will probably require a
discrete design (I don't know if this is feasible).  In any case, check out the
data sheets and app. notes from the manufacturers listed above.  It should be
educational and useful information.

The only other alternative I know of is a voltage controlled filter (VCF).
Again, I don't know how feasible a 1 MHz passband would be.

Good luck!
-- 
Bill McFadden    Tektronix, Inc.  P.O. Box 500  MS 58-639  Beaverton, OR  97077
UUCP: bill@videovax.Tek.COM,  {hplabs,uw-beaver,decvax}!tektronix!videovax!bill
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