In this article, the authors introduce the design of a power amplifier with only three necessary active devices; a normal high-quality opamp and two lateral power MOSFETs. The design is based on an inverting grounded-source output stage that is directly driven by the opamp, with the power output terminal being the bipolar power supply centre tap. Thus each channel must have a separate supply. Design concepts are presented and measurements on complete prototypes show excellent distortion and signal behaviour. Theory and measurements of performance (including distortion) show good agreement.
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