Patent ID: 6121908
Filing Date: 2000-09-19
Classification: H03H

Abstract:
A substantially monolithically integrated filter circuit for filtering an input signal v.sub.in, said filter circuit having a passband gain and comprising:an input for receiving said input signal;an output for producing a filtered output signal v.sub.out, said output signal including a component of electrical noise produced by said filter circuit; anda frequency-shaping circuit coupled between said input and said output that governs the passband gain of said filter circuit including:a variable impedance element coupled to said input such that the passband gain of said filter circuit is substantially inversely proportional to the impedance value of said variable impedance element;an active circuit having a virtual ground node coupled to said variable impedance element, and an output node coupled to said output; anda feedback network coupled to said virtual ground node and to said output node and including resistors and operational amplifiers, such that the electrical noise in v.sub.out is dominated by electrical noise from said resistors of said feedback network.