| 摘要 |
A high-frequency power amplifier (13) in which the negative feedback control system linearity is maintained and non- linear distortion is stably compensated has: a variable gain circuit (12), disposed as a prestage of the power amplifier (13), in which the control voltage vs. gain characteristic is an antilogarithm characteristic, which performs variable control on the level of the input signal supplied to the power amplifier; a gain detecting circuit (25), which detects the gain of the high frequency power amplifier; and a loop filter (28), which supplies the output signal of this gain detecting circuit to the variable gain circuit as a control voltage. This gain detecting circuit (25) is made up of: a first logarithmic convertor circuit (22), which performs logarithmic conversion on an envelope detection signal of the signal inputted into the variable gain circuit; a second logarithmic convertor circuit (23), which performs logarithmic conversion on an envelope detection signal of the output signal of the high-frequency power amplifier; and a subtraction circuit (24), which outputs the differential signal of the output signals of the first and second logarithm converting circuits. <IMAGE> |
