Patent ID: 6861898

Claim:
A loop filter for receiving a control current and generating a control voltage, the loop filter comprising: a first resistor having a first terminal and a second terminal, the first terminal receiving the control current; a capacitor connected to the second terminal of the first resistor; a second resistor having a first terminal and a second terminal, the first terminal being connected to the first terminal of the first resistor; a compensating unit for generating a compensating voltage and having a first terminal and a second terminal, the first terminal being connected to the second terminal of the second resistor; an OP amplifier having an output terminal connected to the second terminal of the second resistor, a first input terminal connected to the second terminal of the first resistor, and a second input terminal connected to the second terminal of the compensating unit; and a current source connected to the second terminal of the compensating unit to provide a compensating current to the compensating unit; wherein the voltage of the output terminal of the OP amplifier substantially equal to that of the first input terminal of the OP amplifier.