Patent ID: 8102208

Claim:
A signal amplifier comprising: an amplitude-control-word generator that generates a 2N-bit amplitude control word, N being an integer equal to or more than 1; and a signal amplifying unit that comprises 2N number of first switch circuits and 2N number of second switch circuits that are turned on and off based on the amplitude control word, and 2N number of first amplifier circuits and 2N number of second amplifier circuits that correspond to the 2N number of the first switch circuits and the 2N number of the second switch circuits, respectively and amplify input complementary radio-frequency signal, and outputs complementary first and second output signals, wherein the signal amplifying unit causes each N number of the first and the second switch circuits to be always on and causes each n (n=0 to N) number of the first and the second switch circuits out of remaining each N number of the first and the second switch circuits to be on, based on the amplitude control word, wherein each of the 2N number of the first and the second switch circuits comprises a first MOS transistor and a second MOS transistor that are connected in parallel, the first MOS transistor is turned on and off by the value (N+n) based on the amplitude control word, the second MOS transistor is turned on and off by the value (N−n) based on the amplitude control word, and the signal amplifying unit comprises a matching circuit that converts to the value (N+n) and the value (N−n) that are complementary based on the amplitude control word output from the amplitude-control-word generator.