A FPGA-Based Approach to the Digital Control of a Class-D Amplifier for Sound Applications

The continuing trend in audio amplifier technology is towards more compact systems, lower distortion levels, and greater power efficiency. Thus, the relatively new consensus in the audio industry is the class-D amplifier, which generally uses compact H-bridge power inverters and a highly power-efficient, high frequency PWM switching scheme which yields little distortion after filtering. This paper presents an on-going research effort with the class-D amplifier that focuses on keeping the audio signal chain in the digital domain until just before the output filter stage that drives the speaker, which prevents transmission noise from distorting the audio signal and also provides the opportunity for a digital closed-loop control system for generating switching commands. Different solutions for the control system are theoretically and experimentally compared. The hardware structure is composed of a host computer, a board featuring a DSP chip coupled with a FPGA, a silicon H-bridge power inverter, a signal conditioning stage, and an ultra fast ADC