Patent ID: 6429733
Filing Date: 2002-08-06
Classification: H03H

Abstract:
In a filter for filtering selected frequencies from a differential input signal wherein the differential input signal has a positive input signal and a negative input signal, the filter effectively removing a first frequency from the differential input signal while effectively passing a second frequency, the filter having a positive input terminal for receiving the positive input signal of the differential input signal and a negative input terminal for receiving the negative input signal of the differential input signal, wherein the improvement comprises:comparing means for comparing the positive input signal and the negative input signal, and providing a control signal that is related to the difference between the positive input signal and the negative input signal; filter means for filtering the control signal, said filtering means substantially preventing the control signal from tracking the difference between the positive input signal and the negative input signal at the second frequency, while substantially allowing the control signal to track the difference between the positive input signal and the negative input signal at the first frequency, said filter means including matched capacitors; and offset means for receiving the control signal and for providing one or more offset signals to the positive input terminal and the negative input terminal of the filter, the one or more offset signals effectively removing the difference between the positive input signal and the negative input signal of the differential input signal at the first frequency, and not substantially affecting the difference between the positive input signal and the negative input signal of the differential input signal at the second frequency, the first frequency being higher than the second frequency.