Design of a class D audio power amplifier with negative feedback

Abstract

This report describes the analysis and design of a Class D amplifier with emphasis on low Total Harmonic Distortion (THD).

Class D amplifiers are power amplifiers which are often used in the reinforcement of sound systems where high output power is required. In comparison to the active resistance used in a linear mode Class AB amplifier, a Class D amplifier uses a switching mode of transistor to regulate the delivery of power, thereby providing power efficiency of a very high level.

In this project, the performance of a Class D power amplifier Integrated Circuit (IC) (TDA7490L) from STMicroeletronics was evaluated. The Class D amplifier IC was designed and built on a Printer Circuit Board (PCB) board and measurements were carried out to evaluate the THD of the integrated amplifier. Thereafter, the measurement results obtained were compared against specifications in the datasheet.

Further work was done by applying a negative feedback to the inverting input of the second-order integrator of the Class D amplifier. This was done to study the effects of negative feedback on the Total Harmonic Distortion (THD) of the amplifier. This application of a negative feedback also served to offer a different approach to the amplifier’s input. Using this configuration, we should still obtain a THD on par, or even better that which was specified in its datasheet.

Lastly, changing the component values of the negative feedback circuit was also done to observe the hysteresis and effects of the change. The critical parameters of frequency and power were analyzed with respect to THD.