Efficient and distortion-free audio power amplifier with active negative feedback circuit

摘要

Task: Modern audio power amplifiers are characterized by high linearity and high efficiency. Efficiency-enhancing circuit concepts such as current dumping and AD class amplifiers (known as switch-assisted linear amplifiers) belong to the state of the art in the audio field. The two topologies contain an A-Class power amplifier that reduces efficiency because it has to be designed for a full output voltage swing with an output that is as distortion-free as possible. With a new amplifier topology, the aim is to replace the A-class power amplifier with a conventional operational amplifier. The operational amplifier offers a large gain surplus, which is necessary to suppress the nonlinear distortions and at the same time increases efficiency due to its low current consumption. Solution: Two essential functional units of the new amplifier circuit are an active negative feedback circuit and an efficient power amplifier in the B or D class a differential input referred to as a main amplifier. The main task of the active negative feedback is a linearization of the non-inverting main amplifier, which has relatively small no-load gain. Compared to the operation of the main amplifier with the same amplification with classic negative feedback, however, with the active negative feedback, lower distortions, an expansion of the frequency band and unconditional stability can be achieved with the active negative feedback.