Patent ID: 7675356

Claim:
A filter system, comprising: a subtractor which is adapted to receive an analog input signal and a reference voltage at a first input, and an analog feedback signal, supplied through a feedback loop, at a second input, and to output a difference between the analog input signal and the analog feedback signal; and a low pass filter which is adapted to output a digital signal by comparing the output signal of the subtractor and the reference voltage, to integrate a duty of the digital signal and to calculate a following error amount, and to convert a low pass filtered signal based on the calculated following error amount into the analog feedback signal to be output to the second input of the subtractor, the low pass filter including a comparison unit adapted to receive the output signal of the subtractor at a first input and the reference voltage at a second input, and to output a digital value, a duty counter adapted to count duties of the output of the comparison unit, a control unit adapted to control the duty counter, a following error amount generation unit adapted to generate the following error amount by comparing the duty error amount with a target value, a ripple removal and DC gain control unit adapted to remove a ripple component in the following error and controls the DC gain using an integral, and a digital analog conversion unit which converts the calculated error integral to the analog feedback signal.