Rev. 0.1 11/12

Copyright © 2012 by Silicon Laboratories

AN726

AN726

1. Introduction

Class-D is a switching power amplifier architecture that uses high-frequency Pulse-Width Modulation (PWM) to

generate the output waveform. The transistors are fully on or fully off, which means this architecture can reach very

high efficiency levels, resulting in significant power savings. However, the translation from the input signal to PWM

and the PWM itself can cause more distortion on the output than other amplifier architectures. Figure 1 shows a

very basic Class-D signal diagram.

Figure 1. Class-D Power Amplifier Signal Diagram

Because the Class-D amplifier transistors are fully on or fully off, the transistors lose less energy in the form of

heat. This architecture, therefore, lends itself to small, cheap MOSFETs. The Class-D amplifier can be

implemented in either analog or digital form.

An analog Class-D amplifier is non-trivial and typically consists of a comparator, triangle waveform generator, and

several blocks to condition the input signal before transferring to the output MOSFETs.

A digital Class-D amplifier requires the following:

the input signal

Since the Silicon Labs Precision32™ SiM3U1xx/SiM3C1xx 32-bit MCUs have peripherals and features capable of

meeting all of these requirements, these MCUs are uniquely suited to a utility Class-D power amplifier application

without using many external components by directly driving the speaker using the high drive I/O.

In addition to providing a development platform for Class-D applications, the Class-D ToolStick board serves as a

lower-cost, general-purpose development platform for the SiM3U1xx USB MCUs.

2. Relevant Documents

This document provides a hardware and software overview for the Class-D ToolStick. Additional documentation on

the Precision32 tools and MCUs can be found on the Silicon Labs website: www.silabs.com/32bit-appnotes,