A spread spectrum modulation method based on dual-clock for filterless digital class-D audio amplifiers

A spread spectrum modulation method based on dual-clock to solve the problem of high Electro Magnetic Interference (EMI) in filterless digital class-D audio amplifiers is proposed in this paper. This method can be used in Uniform Pulse Width Modulation (UPWM) type filterless digital class-D audio amplifiers. For this method, two different Pulse Repetition Frequencies (PRFs) of UPWM signals are changed randomly by the parity of the random numbers generated by pseudo-random sequences to spread the spectrum of the carrier harmonic component. A test system based on the field programmable gate array (FPGA) is established to check the effect of spread spectrum. The proposed method is compared with the traditional UPWM. The experimental results show that the output carrier harmonic component amplitude of the digital PWM generator can be significantly reduced (i.e. up to 17.4 dB) when the proposed method is used.