Active electrical filter

Claim 2

An active electrical filter having an input, output and circuit common, and providing Q variation without affecting onresonance gain, comprising: amplifier means including an inverting input and an output and having a complex gain function G(S) which equals K (ST/((ST)2+1)) where: S complex frequence sigma + jw T 1/2 pi fo fo resonance or ''''set'''' frequency K a constant associated with the magnitude of the gain at any given frequency; said output of said amplifier means connected to said active electrical filter output; and combining means for combining said filter input and output and for applying the resultant thereof to said inverting input of said amplifier means, said combining means including a single variable element the adjustment of which provides said Q variation without affecting on-resonance gain of said filter.

Claim 3

An active electrical filter having an input, output and circuit common, and providing Q variation without affecting on-resonance gain, comprising: amplifier means including an inverting input and an output and having a complex gain function G(S) which equals K (ST/((ST)2+1)) where: S complex frequence sigma + jw T 1/2 pi fo fo resonance or ''''set'''' frequency K a constant associated with the magnitude of the gain at any given frequency; said output of said amplifier means connected to said active electrical filter output; and combining means for combining said filter input and output and for applying the resultant thereof to said inverting input of said amplifier means, said combining means including a single variable element the adjustment of which provides said Q variation without affecting on-resonance gain of said filter.

Claim 4

An active electrical filter having an input, output and circuit common, and providing Q variation without affecting on-resonance gain, comprising: amplifier means including an inverting input and an output and having a complex gain function G(S) which equals K (ST/((ST)2+1)) where: S complex frequence sigma + jw T 1/2 pi fo fo resonance or ''''set'''' frequency K a constant associated with the magnitude of the gain at any given frequency; said output of said amplifier means connected to said active electrical filter output; and combining means for combining said filter input and output and for applying the resultant thereof to said inverting input of said amplifier means, said combining means including a single variable element the adjustment of which provides said Q variation without affecting on-resonance gain of said filter.

Claim 5

A filter according to claim 1 wherein said combining means comprises a network of impedancEs and said variable element comprises a variable impedance in said network.

Claim 6

A filter according to claim 1 wherein said combining means comprises: a first fixed resistive element connected between the input of said filter and said inverting input of said amplifier means, a second fixed resistive element connected between the output of said amplifier means and said inverting input of said amplifying means, and a variable resistive element, comprising said variable element, connected between said inverting input of said amplifier means and said circuit common.

Claim 7

A filter according to claim 1 wherein said amplifier means comprises at least one operational amplifier and associated resistive and active circuit elements for providing said complex gain function.

Claim 8

A filter according to claim 1 wherein said amplifier means comprises a plurality of cascaded operational amplifiers with each operational amplifier having an inverting and a non-inverting input and an output, and wherein the output of the next to last operational amplifier in said cascade is coupled to said output of said electrical filter, wherein the non-inverting input of the first operational amplifier in said cascade is coupled to said circuit common of said filter by said single variable element, and wherein the output of the last operational amplifier in said cascade is coupled to the inverting input of said first operational amplifier in said cascade.