A novel amplifier system combining Class D D /A conversion and low -power Class AB operation

This dissertation describes a novel approach to reducing amplifier power consumption. With a traditional DC powered amplifier, the voltage difference between the power supply and the output signal is a time varying drain to source voltage (VDS). The DC voltage must accommodate the largest output signal at all times. With a small output swing the driving device V DS is large and wastes power. Extending battery life and reducing cost of portable devices motivates novel circuitry and algorithms to increase efficiency. For non-portable power systems, improved efficiency reduces or eliminates the need for heat sinks and fans.;In the amplifier system of this dissertation, the power supplies mimic the output. Their offset from the output is the constant VDS of the driving devices. The power supplies become tracking rails, reducing the power consumption of the driving devices and improving amplifier efficiency. The tracking rails are developed by a pulse width modulation (PWM) D/A converter and deliver power to a Class AB amplifier. Performance and efficiency is analyzed and compared to the same Class AB amplifier using DC power supplies. An efficiency increase of 45% is predicted from analysis. With a PWM system producing half-tracking rails (only tracking the output during the conducting interval of a driving device), the simulated efficiency nearly coincides with the predicted efficiency, with only a modest sacrifice in total harmonic distortion (THD).;After reviewing amplifier classification, several approaches overcoming the drawbacks of Class D amplifiers are presented, including two methods of combining Classes AB and D. The selected approach uses a very simple PWM D/A converter comprising a digital counter, logic and switches to form PWM pulses, and passive filtering to reconstruct the waveform. The method is shown to work with three Class AB amplifier structures.;A top-down design approach is used. A mathematical model is first developed and tested. Building blocks of the system are designed and simulated from interconnected transistors, capacitors, resistors and inductors. The completed system is analyzed with a mixed simulator, and its performance examined graphically and mathematically.;This is the first published system using half-tracking rails for power amplifiers.