The design of high efficiency power amplifiers for in-car audio use.

Switched mode, Class-D power amplification allows for high efficiency power
amplification of an audio signal. This thesis investigates its application to high power
car audio systems where there is a demand for efficient high power amplification.
Examination of the present car audio power amplifiers, which comprise a switched
mode power supply combined with a linear output stage, has shown that there is
significant scope for improvement in efficiency and power density.
A novel power stage in which the attributes of a switched-mode power supply and full
bridge output stage is presented. It is demonstrated that elimination of the intermedjate
DC supply results in an amplifier which has a significantly lower part count, size and
cost compared to conventional designs.
Two different modulation schemes are explored (PWM and PDM) with a view to
finding the most suitable for the new power stage. The theoretical performances of the
modulators are verified by practical measurements. The design of high order DeltaSigma
modulators is difficult as they show unstable behaviour and an alternative design
methodology has been presented to ease this task.
The mechanisms which introduce distortion in a practical amplifier are discussed, and
for the case of a PWM driven output stage, a new model is presented to predict the
effect of dead time on harmonic distortion. This form of distortion is shown to be the
dominant cause of open loop non-linearity. The use of feedback is also investigated and
yields a factor of 20 improvement in amplifier total harmonic distortion .
The design throughout has been supported with practical results and these have
illustrated the importance for careful circuit layout in high frequency switching systems.