Closed-Loop Class-D Amplifier With Nonlinear Loop Integrators

In many integrated class-D audio amplifiers large linear capacitors are used to create the triangular reference signals for generation of PWM signals. In this paper, an integrated class-D amplifier is presented that uses a control loop with area efficient nonlinear gate oxide capacitors. A model is used to show that the nonlinearity does not degrade the THD performance. To limit the maximum voltage on the gate oxide capacitor, a method was used to prevent voltage drift of the integrator output in case the amplifier is clipping. This method also improves the clipping recovery behavior. Measurements and simulations on two amplifiers with linear and nonlinear capacitors confirm that nonlinear capacitors do not introduce additional distortion. Measurements on the amplifier with and without the clipping recovery method confirm the improvement in clipping recovery.