Patent ID: 6680645
Filing Date: 2004-01-20
Classification: H03H

Abstract:
An active filter circuit having a signal input (L1), said active filter circuit comprising:an operational amplifier (Op) that includes a transconductance amplifier having a transconductance (gm) controlled by a bias circuit to be inversely proportional to a value of a transconductance determining resistor Rb within said bias circuit, wherein said operational amplifier (OP) has a frequency response that has a low-pass characteristic controlled by said transconductance (gm); an RC network that includes a first resistor (R1) connected between the signal input (L1) of said filter circuit and an inverting input of said operational amplifier (Op), and a first capacitor (C1) connected between said inverting input and a fixed reference potential; a second resistor (R2) and a second capacitor (C2) connected between said inverting input and an output of said operational amplifier (Op), which output also forms the signal output of said filter circuit; and a noninverting input of the operational amplifier (Op) is connected to the fixed reference potential.