Since 1991 we have been experimenting with various Class-D driver- and inverter-concepts, for generating analog power with a bandwidth from DC to 100kHz, to replace power-wasting Class-B amps .
A very simple DIY Class-D amplifier for low power portable devices has been published in EWW.
In 2003 we finished the a class D project LPC1, originally designed for making efficient high audio power till 1kW,
and later on optimized for higher quality, for replacing conventional amplifiers in studio- or home-systems.
The LPC1 was meant as a demonstration-project in where many analog challenges, like Precision Audio, RF, Fast-Switching Power-electronics, and EMC are combined in one device.
The demands on speed and accuracy in parts of the LPC1 are similar to HDR-electronics.
In the LPC1, power is generated by modulating the duty-cycle ratio of a constant frequency square-wave signal from a switching inverter, with power-mosfets in a half- bridge. The duty-cycle ratio results in a low-frequency-component (after filtering) with the same maximum power-level in respect to supply-voltage as Class A or B, but with an efficiency of 90%.