Topics on switching audio amplifiers.

摘要

Switching audio amplifiers are becoming the choice for portable and energy-conscious electronic products. This research focused on developing solutions to reduce the total harmonic distortion (THD) in switching audio amplifiers.; A multi-loop filterless topology with hi-fi characteristics was designed and characterized. The amplifier had a flat frequency response up to 20 kHz, free of any phase distortion. The measured THD was less than 0.05%. A dead time compensation algorithm was also developed to reduce the distortion in this amplifier. Simulation results yielded a reduction of the THD from 18.6% to 0.27%, for an open-loop filterless amplifier.; A new topology of a current-source switching audio amplifier was developed for low power applications. In this topology, the DC bus voltage follows the audio signal. This is significantly different from other amplifier topologies. Open-loop simulation results showed that this amplifier could achieve the required hi-fi performance. The simulated THD was lower than 0.06%. This topology did not require an output filter. Its frequency response starts at DC. However, the DC offset across the voice coil was minimized using a differential output configuration. The variations on the power supply did not modulate the output current, because the current was shaped by the current loop.; The distortion problem due to the power supply quality was also addressed. A new method to calculate the sensitivities of the duty cycle in the current-mode control was derived. The method, based on simple matrix calculations, can be useful for controllers using a state-space model. The controller needs to recalculate the system matrices and sensitivities for different operating points. Computation time can be saved by using the system matrices to re-calculate the sensitivities, instead of performing the calculations required in the geometric method.; Lastly, a DSP-based digital control technique for switched-mode power supplies is proposed. Both digital current-mode and voltage-mode controllers were successfully implemented for the synchronous buck converter to demonstrate the feasibility of the proposed ideas.