Patent ID: 7928804

Claim:
A power amplifier comprising: a semiconductor substrate; preceding-stage amplifying device on the semiconductor substrate, amplifying an input signal; a following-stage amplifying device on the semiconductor substrate, amplifying an output signal of the preceding-stage amplifying device; a preceding-stage bias circuit supplying bias currents to an input terminal of the preceding-stage amplifying device; a following-stage bias circuit supplying bias currents to an input terminal of the following-stage amplifying device; and an inter-stage matching circuit connected between an output terminal of the preceding-stage amplifying device and the input terminal of the following-stage amplifying device, wherein the preceding-stage amplifying device includes a first field effect transistor, which is an enhancement mode field effect transistor including a source, a gate, and a drain, the following-stage amplifying device includes a heterojunction bipolar transistor, the inter-stage matching circuit includes a capacitance which galvanically separates the output terminal of the preceding-stage amplifying device from the input terminal of the following-stage amplifying device, and the preceding-stage bias circuit includes: a second field effect transistor that is an enhancement mode field effect transistor, having a gate through which a reference voltage is input, a drain connected to a power supply, and a source, a resistor, and a third field effect transistor, which is an enhancement mode field effect transistor, having a source that is grounded, and a gate and a drain which are connected to the source of the second field effect transistor via the resistor, and to the gate of the first field effect transistor.