To prevent an element for amplification of a final stage from being broken even if a load suddenly becomes light at high-output time and a collector voltage rises in a high-frequency power amplifier circuit which uses an InGaP-HBT as the element for amplification of the final stage.
The InGaP-HBT is used as the transistor (Q3) for amplification of the final stage of the high-frequency power amplifier circuit and its bias voltage is controlled according to the voltage from a circuit (260) generating the control voltage (Vapc) based upon the error voltage between an output power detection signal and an output level specification signal. The high-frequency power amplifier circuit (RF power module) is provided with a control voltage suppressing circuit (100) which detects a source voltage applied to the transistor for amplification and prevents the bias voltage of the transistor for amplification of the final stage from being too high when the source voltage is higher than a certain voltage.
SOGA TAKASHI
SUGIYAMA HIROKI
IMAI TAKASHI
HITACHI ULSI SYS CO LTD
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