Patent ID: 7304539

Claim:
A high frequency power amplifier circuit, comprising: an amplifying transistor for amplifying a high frequency signal; and a current-voltage converting element for converting a current into a voltage by applying a predetermined current, wherein a voltage corresponding to the voltage generated by said current-voltage converting element is applied to a control pin of said amplifying transistor thereby to make flow the current that is proportional to the current flowing to said current-voltage converting element, said high frequency power amplifier circuit including: a bias generation circuit which includes a current simulating transistor having the same channel length or base width and formed in the same process as said amplifying transistor, and a diode-connected transistor connected in series to said current simulating transistor, said a bias generation circuit comparing the voltage formed based on the current flowing to said diode-connected transistor with a reference voltage generated by the current-voltage converting element that converts the current from a constant current circuit into the voltage, and supplying such a bias that inhibits an idle current of said amplifying transistor from varying due to a short channel effect or an Early effect to said amplifying transistor and current simulating transistor.