Patent ID: 8139789

Claim:
A signal amplifier circuit comprising: n main amplifiers (n is an integer greater than or equal to 2) which receive n input signals and amplify each of the input signals with respective adjustable gains; a first selector which receives the n input signals and selects any of the n input signals; an auxiliary amplifier which receives an output of the first selector and amplifies the output with an adjustable gain; a second selector which receives n outputs from the n main amplifiers, and selects any of the n outputs; a soft switching circuit which receives an output of the second selector at a first input terminal, receives an output of the auxiliary amplifier at a second input terminal, and makes an output of the soft switching circuit transition gradually from one of the input terminals to another of the input terminals; n output switches which are provided for the respective n main amplifiers, each output switch receiving an output of a corresponding main amplifier at a first input terminal of the output switch and receiving the output of the soft switching circuit at a second input terminal of the output switch, to select and to output one of the outputs; and a controller which controls gain of the n main amplifiers and the auxiliary amplifier, and selection states of the first selector, the second selector, the soft switching circuit, and the output switches.