High frequency power amplifier and operating method thereof

A radio-frequency power amplifier comprising:

• a bias field effect transistor;
• a power amplification field effect transistor;
• a bias control circuit;
• and
• a gate length monitor circuit comprising an amplifier replicating transistor,
• wherein the bias field effect transistor and the power amplification field effect transistor are coupled so as to configure a current mirror,
• wherein the bias field effect transistor, the power amplification field effect transistor, the bias control circuit, and the gate length monitor circuit are provided on a semiconductor chip,
• wherein the power amplification field effect transistor comprises a source terminal coupled to a ground potential, a gate terminal supplied with a radio-frequency input signal, and a drain terminal generating a radio-frequency amplified output signal,
• wherein the bias field effect transistor is supplied with a bias current generated by the bias control circuit, and a gate-to-source voltage of the bias field effect transistor is supplied to between the gate terminal and the source terminal of the power amplification field-effect transistor,
• wherein the amplifier replicating transistor, the bias field effect transistor, and the power amplification field effect transistor are designed to exhibit almost same variation in gate length, by fabricating the amplifier replicating transistor, the bias field effect transistor, and the power amplification field-effect transistor on the semiconductor chip by the same semiconductor manufacturing process,
• wherein the gate length monitor circuit generates a detection voltage indicative of the gate length dependence detected by the amplifier replicating transistor,
• wherein the bias control circuit is controlled by the detection voltage generated by the gate length monitor circuit, and
• wherein, when the gate length exhibits variation, the dependence of transconductance of the power amplification field effect transistor on the gate length is compensated, by the bias control circuit controlling a value of the bias current according to the detection voltage.