A low-power class-AB negative-feedback output amplifier for a 1 V LW receiver

The design and the measurement results are presented of a low-voltage (1 V) class-AB negative-feedback output amplifier. The amplifier is designed for use in a single-chip LW receiver, which can be put completely in the ear, supplied by a 1 V power supply and is capable of driving a load with an imp edance of 30 Omega. The maximum output current of the amplifier is approxim ately 2.5 mA and its quiescent current is approximately 100 mA. This high e fficiency is obtained by means of biasing two of the three amplifying stage s in class-AB operation. With the aid of negative feedback, the total harmo nic distortion for a single 1 kHz tone at 1 mA level is kept below 1%. The output amplifier is integrated in a bipolar process which has vertical NPN transistors with a maximum f(T) of 5 GHz and lateral PNP transistors with a maximum f(T) of 20 MHz.