An All-Digital Spread Spectrum Method with Distortion Correction for Filterless Digital Class-D Amplifiers

Filterless digital class-D amplifiers (CDAs) are very attractive for audio-visual devices thanks to their high efficiency, small size and low cost. However, their high-frequency switchingmode operation will cause electromagnetic interference (EMI) problems. Spread spectrum techniques are often used to solve the EMI problems but will cause baseband distortions in amplifiers. In this article, an all-digital spread spectrum method with distortion correction is proposed to make filterless digital CDAs achieve low EMI emissions and high signal to noise and distortion ratio (SNDR). This method mainly utilizes the random numbers generated by a pseudo-random number generator to randomize the pulse position and pulse repetition frequency (PRF) of the uniform-sampling pulse width modulation (UPWM) generator output signal to achieve the effect of spread spectrum. Moreover, the high open-loop gain characteristic of the digital sigma-delta modulator in the baseband and the state-space reconstruction technique are utilized to correct the baseband distortions caused by UPWM and spread spectrum. The feasibility and effectiveness of the proposed method are verified by simulation and experimental results.