Cancellation of common-mode output signal in Class-BD audio amplifiers

In the paper new topologies of the Class-BD amplifiers with Common-Mode (CM) free outputs have been presented. They are composed of the typical H-bridge output stage with four MOSFETs controlled by the optimal NBDD PWM signals and two additional switches separating the H-bridge from the power supply during the time intervals in which either high-side or low-side MOSFETs of the H-bridge are closed at the same time. The proposed amplifiers have been compared to the Class-BD configuration using the optimal NBDD modulation with respect to audio performance of the differential and CM outputs. Experimental models of the presented in the paper Class-BD audio amplifiers have been realized using digital audio MOSFETs IRF6775MTRPbF, single-output gate drivers with self-boost charge pump bias supply and with capacitor-based signal isolation for floating single-output gate drivers. Intensive SPICE simulations of the real output stage circuits of the proposed Class-BD amplifiers have pointed out that proposed new configurations have similar audio performance as the prototype using optimal NBDD modulation, besides keep the CM outputs constant, thereby removing a major contributor to radiated emissions.