Patent ID: 7031682

Claim:
A gain control circuit, comprising: a transmission power amplifier which amplifies a transmission signal to a predetermined level; an adjacent channel leak power ratio monitor which finds a ratio of a distortion element corresponding to adjacent channel leak power to a main element from an output signal of the transmission power amplifier, and outputs the found ratio as an ACPR monitor value; a power supply control section which variably controls power supply to the transmission power amplifier with use of the ACPR monitor value supplied from the adjacent channel leak power ratio monitor; a transmission signal level variable section which varies a level of the transmission signal by controlling a gain of a transmission signal path on the basis of a transmission level monitor value supplied from the adjacent channel leak power ratio monitor; and wherein the adjacent channel leak power ratio monitor comprises: a squaring circuit which squares an output signal of the transmission power amplifier; a first band path filter which extracts a distortion element corresponding to the adjacent channel leak power from an output signal of the squaring circuit; a second band path filter which extracts an element corresponding to a main part of the output signal of the squaring circuit; and a subtracter which performs a subtraction process between an output of the first band path filter and an output of the second band path filter.