Patent ID: 7358805

Claim:
An input common-mode feedback circuit, applicable to a differential amplifier, the differential amplifier includes a positive input node and a negative input node for respectively receiving a first input signal and a second input signal, the input common-mode feedback circuit comprising: a common-mode error amplifier, having a first input node, a second input node, a third input node, and an output node, wherein the first input node and the second input node are used to respectively receive the first input signal and the second input signal from positive and negative input nodes of the differential amplifier, and after comparing the common-mode voltage of the first input signal and the second input signal with a set common-mode voltage received by the third input node, the output node gives an amplified difference voltage; and a plurality of adaptive conductance elements comprising: a first adaptive conductance element, having an anode coupled to the output node of the common-mode error amplifier, and a cathode coupled to the positive input node of the differential amplifier; a second adaptive conductance element, having an anode coupled to the negative input node of the differential amplifier, and a cathode coupled to the output node of the common-mode error amplifier; a third adaptive conductive element, having an anode coupled to the positive input node of the differential amplifier, and a cathode coupled to the output node of the common-mode error amplifier; and a fourth adaptive conductance element, having an anode coupled to the output node of the common-mode error amplifier, and a cathode coupled to the negative input node of the differential amplifier, every adaptive conductance element behaves with a low impedance characteristic when its anode voltage is greater than its cathode voltage by a positive threshold voltage (Vtp) or when its anode voltage is lower than its cathode voltage by a negative threshold voltage (Vtn), otherwise, the aforementioned adaptive conductance element behaves with a high impedance characteristic, wherein the adaptive conductance elements and the common-mode error amplifier form a negative feedback loop to inhibit shift of the common-mode voltage of the first input signal and the second input signal received by the differential amplifier.