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From: rickk@hpvcla.UUCP (rickk)
Newsgroups: net.analog
Subject: Re: filter circuit Q
Message-ID: <1200001@hpvcla.UUCP>
Date: Thu, 19-Dec-85 16:00:00 EST
Article-I.D.: hpvcla.1200001
Posted: Thu Dec 19 16:00:00 1985
Date-Received: Sat, 21-Dec-85 06:37:27 EST
References: <35500001@ICO.UUCP>
Lines: 17
Nf-ID: #R:ICO:35500001:hpvcla:1200001:000:871
Nf-From: hpvcla!rickk    Dec 19 14:00:00 1985


  The "Q" (quality) of a filter is defined as:

     omega * L         1                                          1
Q =  ---------  =  ---------   ;      omega= resonant freq =  ---------
         R         omega*R*C                                  sqrt(L*C)

It is a measure of the bandwidth of the filter in that the higher the "Q",
the smaller the bandwidth.  To vary the "Q" of a circuit, you just need to
manipulate the terms in the above expression.  The most obvious way to increase
"Q" is to reduce the circuit resistance.  However it can also be varied by
increasing L and decreasing C to give the proper omega and at the same time 
increasing "Q".  Note however, that larger inductors usually have larger
resistances, so "Q" in a real circuit will not necessarily increase in the 
second instance.

Rick "I really are a digidul n-gineer" Klaus @ hpvcla!rickk