Patent ID: 7816978

Claim:
An operating circuit, comprising: an amplifier, having a first input terminal coupled to a reference voltage; a first transconducting element, coupled to an output terminal of the amplifier for selectively generating a first current according to an output of the amplifier; a second transconducting element, coupled to the output terminal of the amplifier for selectively generating a second current according to the output of the amplifier; a resistive element, having a first terminal coupled to the first transconducting element; a capacitive element, having a first terminal selectively coupled to the second transconducting element, wherein at least one of the resistive element and the capacitive element is an adjustable element; and a switching device, coupled to the amplifier, the first transconducting element, the second transconducting element, the resistive element, and the capacitive element, wherein the switching device is arranged to have a first configuration under a first mode of the operating circuit to connect the first terminal of the capacitive element to the second transconducting element and connect the first terminal of the resistive element to a second input terminal of the amplifier, and is arranged to have a second configuration under a second mode of the operating circuit to disconnect the first terminal of the capacitive element from the second transconducting element and connect the second input terminal of the amplifier to the first terminal of the capacitive element instead of the first terminal of the resistive element.