AN726 Datasheet, PDF (1/28 Pages) Silicon Laboratories – UTILITY CLASS-D TOOLSTICK USER’S GUIDE

AN726
UTILITY CLASS-D TOOLSTICK USER ’S GUIDE
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:
PWM output (switching) frequency 10x+ faster than the highest input frequency to adequately reconstruct
the input signal
High-resolution control of the PWM pulse width to reduce output quantization distortion
Method for sampling or receiving the input waveform
Fast core for digital processing and manipulation of data
Pins capable of driving the amplified 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,
www.silabs.com/32bit-software, and www.silabs.com/32bit-mcu.
Rev. 0.1 11/12
Copyright © 2012 by Silicon Laboratories
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