Patent ID: 7511576

Claim:
A high frequency power amplifying circuit for outputting an orthogonal frequency-division multiplexed signal as a radio wave, comprising: a first bipolar transistor arranged for amplifying a high frequency signal, and having an emitter terminal connected to ground; and a bias circuit connected to a base terminal of the first transistor, wherein impedance (R) of the bias circuit as seen from the base terminal of the first transistor satisfies the following impedance relation at baseband frequency: 1.5 Â· [ Vt lbq - ( Î² Â· Re + Rb ) ] â‰¥ R â‰¥ 0.5 Â· [ Vt lbq - ( Î² Â· Re + Rb ) ] , where Î² is the gain of the first transistor, Re is the parasitic resistance (Î©) of the emitter terminal, Rb is the parasitic resistance (Î©) of the base terminal, Ibq is the static current flowing into the base terminal of the first transistor when the amplitude of an input signal is zero, k is the Bolzman constant (J/K), q is the absolute value (C) of electronic charge, T is the absolute temperature (K), and Vt is the voltage defined by the following formula: V t = k â¢ â¢ T q .