Patent ID: 7719357

Claim:
A differential amplifier with a plurality of input pairs, comprising: a first load unit, comprising a first terminal and a second terminal, wherein the first terminal of the first load unit is coupled to a first voltage; a second load unit, comprising a first terminal and a second terminal, wherein the first terminal of the second load unit is coupled to a second voltage; a first transistor, comprising a gate, a first source/drain and a second source/drain, wherein the gate of the first transistor is coupled to a first voltage bias of a first input pair and the first source/drain of the first transistor is coupled to the second terminal of the first load unit; a second transistor, comprising a gate, a first source/drain and a second source/drain, wherein the gate of the second transistor is coupled to a second voltage bias of the first input pair and the first source/drain of the second transistor is coupled to the second terminal of the second load unit; a first current source, comprising a first terminal and a second terminal, wherein the first terminal of the first current source is coupled to the second source/drain of the first transistor and the second terminal of the first current source is coupled to a third voltage; a third transistor, comprising a gate, a first source/drain and a second source/drain, wherein the gate of the third transistor is coupled to a first voltage bias of a second input pair and the first source/drain of the third transistor is coupled to the second tenninal of the first load unit; a fourth transistor, comprising a gate, a first source/drain and a second source/drain, wherein the gate of the fourth transistor is coupled to a second voltage bias of the second input pair and the first source/drain of the fourth transistor is coupled to the second terminal of the second load unit; and a second current source, comprising a first terminal and a second terminal, wherein the first terminal of the second current source is coupled to the second source/drain of the third transistor and the second source/drain of the fourth transistor, and the second terminal of the second current source is coupled to a fourth voltage; wherein the differential amplifier determines on/off state of the first current source according to a first control signal and determines on/off state of the second current source according to a second control signal, so as to switch the input pairs by turning on one of the first current source and the second current source.