CMOS POWER AMPLIFIER

A CMOS power amplifier is disclosed having a differential input amplifying stage for amplifying differential input signals, a high-gain amplifying stage, and an output stage. The high-gain amplifying stage includes a first amplifying section and a second amplifying section. The first amplifying section drives a first output section of the output stage when the voltage difference between the two inputs of the differential input amplifying stage exceeds a certain voltage value. The second amplifying section drives a second output section of the output stage when the voltage difference between the two inputs is below a certain voltage value. The output stage includes a first output section and a second output section, and the first output section consists of plural pairs of transistors for receiving the output signals of the first amplifying section of the high-gain amplifying stage, and serves as a class B push-pull amplifier. The second output section has pairs of transistors for receiving output signals of the second amplifying section of the high-gain amplifying stage to their gates, and serves as a class AB push-pull amplifier. According to the present invention, DC operating point current is decreased, and an output power equal to the supply voltage swing is produced to a low-impedance load at low current.