A High-Performance 3-Watt Monolithic Class-B Power Amplifier

A monolithic class-B power amplifier has been built that is capable of delivering 3 watts sinewave power to a direct-coupled load with less than 0.4 percent total harmonic distortion over the range from 20 Hz to 20 kHz. It occupies a single 45 by 60 mil die and is fabricated using conventionrd all-diffused processing technology. The circuit employs an all n-p-n, direct-coupled, transformerless output stage which is well suited for fabrication in integrated form. Excellent biasing characteristics are achieved by introducing a deadband at the output of the amplifier and using overall feedback to linearize the response. Analyses are made of the amplifier linearity, dc drift, stability, and large signal behavior. Simple design equations are derived which accurately relate the important circuit variables to amplifier performance.