| 摘要 |
PROBLEM TO BE SOLVED: To improve the power efficiency of an A class operation power amplification part in the radio transmitter of aπ/4QPSK modulation system and the like. SOLUTION: An I signal voltage level detection part 11 and a Q signal voltage level detection part 12 detect the voltage levels of an I signal S1 and a Q signal S2 based on the I signal S1 and the Q signal S2 of base bands from root Nyquist roll-off filters 4 and 5 for I signal and Q signal. A power calculation part 13 calculates a power level from the detected I signal voltage level and the Q signal voltage level. Bias voltage Vg is outputted from a bias voltage output part 14 in accordance with the calculated power level and the bias of a power amplification part 10 is set with bias voltage. Thus, bias is set to be shallow when the input level to the power amplification part 10 is small and it is set to be deep when the level is large, so that the power efficiency of DC power (B) is improved.
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