Research: Class
D Amplifier Solutions & Practical Considerations
Fall 2009
OBJECTIVE: To research common switching (class D)
amplifier design techniques and their implementation in various consumer
applications.
RESEARCH SUMMARY: Class-D_amp_research.pdf (21 pages)
NOTE: The above document is only a rough outline summarizing key
information from my research. I had
hoped to produce a well-written report; however, the breadth of my research
would’ve required a 50+ page paper which I regretfully did not have time to
write. Nonetheless, this outline
provides a useful summary of my research on Class D amplifier design and
implementation.
Research
Emphasis:
- Class D amplifier topologies
- Common applications
- Tradeoffs between switching amps
& linear amps
- Practical considerations when
designing & implementing switching amplifier solutions
- Emerging device technologies
Specific Topics:
· Class D history
· Class D topologies & modulation techniques
· Output filter vs. filterless topologies
· Output switching circuits (half-bridge vs. H-bridge)
· Sources of distortion in class D amps
· EMI & noise considerations
· Thermal considerations
· PCB layout considerations
· Power supply requirements & considerations
· Typical class D solutions for:
o Low power mobile applications
o High power applications
o High fidelity applications
REFERENCES: Interested readers are encouraged
to review the extensive list of online references (below) gathered during my
research.
Click HERE for the printable list.
Eli Hughes, resident expert on
switching amplifiers (Penn State University Audio Engineering Society)
NEWS
- Miscellaneous
Class D Amplifiers Empower Mobile Multimedia
http://www.esemagazine.com/index.php?option=com_content&task=view&id=421&Itemid=2
Designing With Class D Amplifier ICs
http://electronicdesign.com/content/print.aspx?topic=designing-with-class-d-amplifier-ics13874
NEWS
http://www.edn.com/article/CA6648691.html?text=class+D+applications
http://www.edn.com/pressRelease/2140344285.html??text=class+D+applications
http://www.edn.com/contents/images/408383.pdf
International
Rectifier
List of IRF application notes on class D
www.irf.com/technical-info/appnotes.htm#audio
Class
D Audio Amplifier Basics
www.irf.com/technical-info/appnotes/an-1071.pdf
A
Class D audio amplifier is basically a switching amplifier or PWM amplifier.
There are a number of different classes of amplifiers. This application note
takes a look at the definitions for the main classifications.
Class
D Audio Amplifier Performance Relationship to MOSFET Parameters
http://www.irf.com/technical-info/appnotes/an-1070.pdf
This
application note discusses key parameters to be considered in the selection of
MOSFETs for class D audio amplifier and their relationship with amplifier’s
performance such as efficiency, EMI, and THD. In addition, benefits and
advantages of IR Digital Audio MOSFETs in class D audio amplifier are
presented.
PCB
Layout with IR Class D Audio Gate Drivers
http://www.irf.com/technical-info/appnotes/an-1135.pdf
…The
layout of a class D amplifier remains the most obscure part of the design
process. The purpose of this application note is to highlight aspects of the
PCB layout which require a designer’s careful attention.
IRS2092(S)
Functional Description
http://www.irf.com/technical-info/appnotes/an-1138.pdf
The
IRS2092(S) is a Class D audio amplifier driver with integrated PWM modulator
and over current protection. Combined with two external MOSFETs and a few
external components, the IRS2092(S) forms a complete Class D amplifier with
dual over current, and shoot-through protection, as well as UVLO protection for
the three bias supplies.
IRS2093M
Functional Description
http://www.irf.com/technical-info/appnotes/an-1146.pdf
The IRS2093M is a four channel Class D audio amplifier
driver with integrated PWM modulators and over current protection. Combined
with eight external MOSFETs and external passive components, the IRS2093M forms
four complete Class D amplifiers.
National Semiconductor
Class D Amplifier FAQ
http://www.national.com/vcm/NSC_Content/Files/en_US/Audio/ClassDAmplifierFAQ.pdf
This FAQ is intended to capture a variety of knowledge
about the selection, application, and measurement of Class D amplifiers. The
emphasis of this FAQ is towards Class D amplifiers in the 0.5W to 2W range
intended for portable media devices such as mobile phones, portable DVD
players, and portable navigation systems. However, the vast majority of this
information can be applied to Class D amplifiers from milliwatts
to kilowatts of output power.
Rane Corporation
Commercializing Class D Amplifier Technologies
http://www.rane.com/pdf/ranenotes/Class%20D%20Amplifier%20Technologies.pdf
The popularity of commercial audio systems having
large numbers of channels has resulted in a growing demand for smaller,
lighter, and less expensive multichannel power amplifier products. This paper
describes how careful integration of power factor corrected switchmode
power supplies, class D power amplifiers, and digital signal processors yields
high power density and especially reliable and electromagnetically quiet
products at a reasonable cost.
Elliott Sound
Products
(Professional results for the Do-It-Yourself
enthusiast)
Class D Audio Amplifiers - Theory and Design
http://sound.westhost.com/articles/pwm.htm
MAXIM
www.maxim-ic.com
Minimize Noise in Audio Channels with Smart PCB Layout
http://pdfserv.maxim-ic.com/en/an/AN4079.pdf
Class D Amplifiers:
Fundamentals of Operation and Recent Developments
http://pdfserv.maxim-ic.com/en/an/AN3977.pdf
Thermal
Considerations for a Class D Amplifier
http://pdfserv.maxim-ic.com/en/an/AN3879.pdf
Reference Design for
a Class-D, 2.1 Channel, Audio Amplifier for an MP3
Player Docking Station
http://pdfserv.maxim-ic.com/en/an/AN4320.pdf
Overview of 2.1
(Satellite/Subwoofer) Speaker Systems
http://pdfserv.maxim-ic.com/en/an/AN4046.pdf
- for 2.1 stereo PC
speakers
Spread-Spectrum-Modulation
Mode Minimizes Electromagnetic Interference in Class D Amplifiers
http://pdfserv.maxim-ic.com/en/an/AN3881.pdf
- no output filter needed
in class D!
Reduce EMI from Class
D Amplifiers Using New Modulation Techniques and Filter Architectures
http://pdfserv.maxim-ic.com/en/an/AN3878.pdf
Feature-Rich,
Complete Audio Record/Playback for GSM/GPRS Cell Phones
http://pdfserv.maxim-ic.com/en/an/AN3573.pdf
Class D Audio
Amplifiers Save Battery Life – 2002
http://pdfserv.maxim-ic.com/en/an/AN1760.pdf
Class D Audio
Amplifier Output Filter Optimization – 2002
http://pdfserv.maxim-ic.com/en/an/AN624.pdf
Amplifier
Considerations in Ceramic Speaker Applications - (pg 3-6)
http://www.maxim-ic.com/appnotes.cfm/an_pk/4164/
http://pdfserv.maxim-ic.com/en/ej/EJ62.pdf
Class G and
Charge-Pump Technologies Maximize Efficiency in Boosted Amplifiers with Minimal
Support Components
http://pdfserv.maxim-ic.com/en/an/AN4121.pdf
- class D cannot drive
ceramic (piezoelectric) speakers
Circuit Refinements
Ensure Quality Audio in Portable Devices
http://pdfserv.maxim-ic.com/en/an/AN2980.pdf
National Semiconductor
www.national.com
Personal Mobile Devices – Selection Guide
http://www.national.com/vcm/NSC_Content/Files/Documents/national_personal_mobile.pdf
Analog Product Guide 2009 Vol
2
http://www.national.com/vcm/NSC_Content/Files/Documents/national_analog_product_selguide.pdf
Filterless Class D Amplifiers
http://www.national.com/an/AN/AN-1497.pdf
Managing EMI in Class D Audio Applications
http://www.national.com/an/AN/AN-1737.pdf
Noise, TDMA Noise, and Suppression Techniques
http://www.national.com/an/AN/AN-1496.pdf
LM49352 - Mono Class D Audio Codec Subsytem with
Ground Referenced Headphone Amplifiers, Earpiece Driver, and Audio DSP from the
PowerWise® Family
http://www.national.com/pf/LM/LM49352.html#Overview
National
Semiconductor Extends Family of Low-Power, Premium Quality Audio Subsystems for
Handheld Devices
http://www.national.com/news/item/0,1735,1390,00.html
App Notes:
http://www.national.com/an/AN/AN-1451.pdf
http://www.national.com/an/AN/AN-1432.pdf
LM48511 - 3W, Ultra-Low EMI, Filterless, Mono, Class D
Audio Power Amplifier with Spread Spectrum
http://www.national.com/pf/LM/LM48511.html#Overview
National
Semiconductor’s New Audio Amplifier with Spread Spectrum and Integrated Boost
Architecture Reduces EMI Sensitivity in Portable Applications
http://www.national.com/news/item/0,1735,1288,00.html
Reference Design 167 - High Efficiency Portable Media
Player (PMP) Docking Station
http://www.national.com/rd/RDhtml/RD-167.html
LM4962 Stereo Ceramic Speaker Driver Application Note
http://www.national.com/an/AN/AN-1440.pdf
- not class D
National
Semiconductor NEWS:
2009 - National Semiconductor’s New Stereo Headphone Amplifier
Doubles Audio Playback Time for Portable Devices
http://www.national.com/news/item/0,1735,1391,00.html
- class G amp
2004 - National Semiconductor Introduces Two High
Efficiency Class D Boomer Audio Amplifiers for Cellular Phones and Flat Panel
Monitors
http://www.national.com/news/item/0,1735,957,00.html
- one of these amps is
obsolete
Analog Devices
www.analog.com
Class D Audio Amplifiers: What, Why, and How
http://www.analog.com/library/analogDialogue/archives/40-06/class_d.pdf
NEWS:
Stereo Audio Codecs Deliver
Best Audio Experience with Lowest Power Dissipation
http://www.analog.com/static/imported-files/solutions_bulletins/consumer01-09/consumer6.html#b
FIRST PULSE DENSITY
MODULATION (PDM) DIGITAL-INPUT CLASS D AUDIO AMPLIFIER
http://www.analog.com/en/press-release/9_25_09_First_Pulse_Density_Modulation_PDM_Digital/press.html
D2Audio
http://www.intersil.com/audio/
D2Audio® DAE-1:
D2-814xx PWM Controllers – The World’s First Intelligent Digital Amplifier Solution
http://www.intersil.com/audio/DAE1/DAE-1%20Product%20Sheet.pdf
Reference Design
D2AUDIO® TXF15-2 – Advanced Audio Processing Solution for Stereo, 2.1 and
Bi-Amp TV’s
http://www.intersil.com/audio/DAE1/TXF15-2%20Product%20Sheet.pdf
Audio Engineering Society
www.aes.org
Call for comment on
reaffirmation of AES17-1998
http://www.aes.org/standards/comments/drafts/aes17-cfc-reaff-091207.pdf