Digital Power Amplification based on Pulse-Width Modulation and Sigma- Delta Loops. A comparison of current solutions

A digital power amplifier provides a direct conversion of a digital signal into the analogue domain where the signal has the capability to drive a high-power load such as a loudspeaker. Figure 1 shows the basic outline of such a system. The first stage performs interpolation of a Nyquist rate PCM (pulse coded modulation) signal to produce an oversampled PCM digital signal. This signal is then fed into a modulation circuit. The modulation is typically sigma delta (Σ-∆) or pulse width modulation (PWM) and thus produces a final signal that has only two voltage levels. The key aim of the modulation is to produce a signal where the information of the PCM signal value is represented by the mean-value of the bitstream. This allows the original signal information to be extracted by a simple analogue lowpass filter. This filter is typically constructed from passive components like inductors and capacitors. Figure 2 shows how the mean value can be represented by digital pulses.