Ultra low cut-off frequency filter

摘要

An ultra low cut-off frequency filter. A filter circuit includes a control circuit responsive to an input signal and a feedback signal to generate a control signal. The filter circuit includes a controllable resistor coupled to the control circuit. The controllable resistor is responsive to a reference signal and the control signal to generate the feedback signal. The filter circuit includes a feedback path coupled to the control circuit and the controllable resistor to couple the feedback signal from the controllable resistor to the control circuit, thereby removing noise from at least one of the input signal and the reference signal, and preventing voltage error in the filter circuit.

主权项

1. A filter circuit having a selectively set cut-off frequency comprising:
a capacitor device; a control circuit responsive to an input signal and a feedback signal to generate a control signal; a controllable resistor coupled to the control circuit, and the capacitor device, the controllable resistor being responsive to a reference signal and the control signal to generate the feedback signal, a resistance of the controllable resistor being proportional to a voltage difference of the reference signal and the input signal wherein the resistance of the controllable resistor is inversely proportional to a current at output of the controllable resistor; and a feedback path coupled to the control circuit and the controllable resistor to couple the feedback signal from the controllable resistor to the control circuit, the control circuit controlling the controllable resistor to adaptively minimize leakage voltage drop thereacross by modulating resistance thereof, thereby preventing noise from at least one of the input signal and the reference signal from appearing at an output of the filter circuit, and preventing voltage error at the output of the filter circuit.