Conducted EMI of integrated switching audio amplifier for mobile phone applications

In this paper, conducted EMI measurements of two integrated Class D audio amplifiers are realized using the EN55022 standard, in order to compare the EMI behavior of two modulation techniques. The first circuit uses a carrier-based pulse-width modulation (PWM) and the second one uses a self-oscillating modulation based on sliding-mode (SM) control. Measurement results show that SM circuit has better EMI behavior compared to PWM circuit, thanks to spread spectrum effect of the SM circuit. Spice simulations using full transistor circuit model are realized to evaluate the range of validity of the used model in large frequencies. Simulation results are very closed to the measurement ones, especially for low and medium frequencies (up to 10MHz).