A micropower low-distortion digital pulsewidth modulator for a digital class D amplifier

We describe the design of a micropower digital pulsewidth modulator (PWM) for a hearing instrument class D amplifier. The PWM embodies a novel delta-compensation (δC) sampling process and a novel pulse generator. The δC process is sampled at the same low rate as reported algorithmic sampling processes and it features a similar low total harmonic distortion (THD). Its arithmetic computation is however, substantially simplified. We analytically derive the double Fourier series expression for the δC process and show that the THD is low. The pulse generator is based on a hybrid 9-b counter 3-b tapped-delay-line. We investigate the compromise between the different design parameters that affect its power dissipation and THD. The complete proposed PWM features a simple circuit implementation (small IC area), micropower low voltage operation (~22.1 μW at 1.1 V), low sampling rate (48 kHz) and low harmonic distortion (~0.2%), thereby rendering it suitable for a practical digital hearing instrument. We verify our design by means of computer simulations and on the basis of experimental measurements