The simplest PDM amplifier - pulse duration modulation

The term PDM merely stands for pulse duration modulation. A PDM amplifier consists of a pulse duration modulator, which converts an analogue audio signal into a digital PDM signal, and an +5 V amplifier connected to an integrator which together convert the amplified PDM signal back into an analogue signal. This particular circuit is prob- ably the most straightforward PDM amplifier in the world. In the wake of digital audio technology "break- throughs", PDM devices (or digital amplifiers) are rapidly gaining popu- larity. Some Japanese manufacturers are even including PDM technology 1-00 82507 in their current ranges of stereo amplifiers equipment. The circuit described here is based on the fact that the transmittance curve of a buffered (B version) 4066 CMOS switch is extremely steep. As a result, the device can be used to reliably obtain a high gain factor. The circuit shown to the right of the figure represents the analogue equivalent of the PDM circuit. This corresponds to an inver