• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Electrical Engineering News and Products

Electronics Engineering Resources, Articles, Forums, Tear Down Videos and Technical Electronics How-To's

  • Products / Components
    • Analog ICs
    • Connectors
    • Microcontrollers
    • Power Electronics
    • Sensors
    • Test and Measurement
    • Wire / Cable
  • Applications
    • Automotive/Transportation
    • Industrial
    • IoT
    • Medical
    • Telecommunications
    • Wearables
    • Wireless
  • Resources
    • DesignFast
    • Digital Issues
    • Engineering Week
    • Oscilloscope Product Finder
    • Podcasts
    • Webinars / Digital Events
    • White Papers
    • Women in Engineering
  • Videos
    • Teschler’s Teardown Videos
    • EE Videos and Interviews
  • Learning Center
    • EE Classrooms
    • Design Guides
      • WiFi & the IOT Design Guide
      • Microcontrollers Design Guide
      • State of the Art Inductors Design Guide
    • FAQs
    • Ebooks / Tech Tips
  • EE Forums
    • EDABoard.com
    • Electro-Tech-Online.com
  • 5G

Sound design considerations for Class D amps

June 16, 2020 By Jeff Shepard

The first two FAQs in this series, “Class D Amplifiers for High-Efficiency Switched-Mode Sound” and “Class D Audio – Why Now?” focused on basic Class D amplifier topologies, modulation techniques, general component and technology advancements that have made Class D amplifiers an increasingly viable option, and the evolving tradeoffs between silicon and GaN power devices. This final installment in this three-part FAQ series will delve into design and specification considerations when using Class D amplifiers.

Class D amplifier reference design with GaN FETs from Efficient Power Conversion (Image: Renesas)

Eradicating EMI

Expecting to eradicate electromagnetic interference (EMI) may be overly optimistic for a high-frequency power switching Class D amplifier design. But managing and controlling EMI is possible, and can also be very important for noise-sensitive environments such as automotive audio systems. EMI can be controlled in several ways when dealing with Class D amplifiers.

At the system level, it is important to keep the connection from the amplifier to the speakers as short as possible. Any circuit board traces or a wiring harness will act as an antenna. Minimizing the length of these antennae will also minimize the radiated EMI. Particularly in the case of filterless Class D amplifiers, those connections between the amplifier and the speaker are likely to be the primary source of radiated EMI. As always, when dealing with switching power converters, good overall EMI design practices such as paying attention to the location of ground planes, the use of properly placed decoupling capacitors, and including ferrite beads on the output leads, are wise measures.

In addition, the application of spread-spectrum technology to Class D amplifiers can help mitigate EMI. With this approach, the switching frequency of the amplifier is randomized (or dithered), typically over about a 10% range. In a fixed-frequency design, the spectral energy is concentrated at the switching frequency and its harmonics. The use of spread-spectrum modulation effectively spreads the RF energy of the output signal. While the total amount of RF energy (EMI) in the output remains the same, the energy is redistributed over a much wider bandwidth, reducing the energy peaks. This reduces the density of the energy and simplifies filtering.

The wideband output spectrum is shown for the MAX9700 using a fixed switching frequency, (source Maxim Integrated Products)

The wideband output spectrum is shown for the MAX9700 using a fixed switching frequency (Image: Maxim Integrated Products)

Dealing with distortion

Major sources of distortion in Class D amplifiers are the deadtime in the output stage, nonlinearities in the modulation scheme, and non-optimal feedback mechanisms. Deadtime protects against the slight differences in switching characteristics between the power switches in the output and the variances in the respective drive circuits, which could inadvertently result in simultaneously turning both devices on. But adding deadtime also adds a nonlinear timing error, which results in cross-over distortion of the audio content in the signal. The shortest deadtime that prevents shoot-through also minimizes the associated distortion.

Feedback is used in both traditional linear amplifiers and Class D amplifiers to clean up the sound and reduce THD. THD is measured under static conditions, and there is a tradeoff between THD and dynamic response. Music, in particular, is dynamic, and too much feedback reduces the dynamic response of the amplifier. As a result, there is a balance to be achieved between low THD and the needed level of dynamic response.

This is an instance where using GaN switching devices can be beneficial. GaN provides higher linearity in the open loop and needs less feedback to achieve a given level of THD. As a result, GaN-based Class D amplifiers can more easily deliver low THD and high dynamic response, resulting in richer-sounding music.

Sound protection

As with all electronic power systems, Class D amplifiers require comprehensive protective functions to ensure reliable operation. A summary of the most critical output protection functions includes:

  • Thermal shutdown – thermal sensing in the power stage can be implemented that shuts down the amplifier at elevated temperatures. Or, the control circuitry may reduce the output power (volume of the sound) to reduce power dissipation and keep the temperature within acceptable limits.
  • Overcurrent protection – current sensing on the output of the power transistors is necessary. As with thermal protection, this can take the form of a complete shutdown in the case of excessive currents, or in more complex designs, it can act as a current limit enabling continuous operation of the amplifier by limiting short-duration high-current transients.
  • Undervoltage protection – also called undervoltage lockout, this function disables operation when the voltage drops below a preset level to protect the amplifier from damage. This can be especially important in battery-powered applications.
  • Deadtime protection – sometimes called “break-before-make” this controls the turn-on timing of the output transistors to prevent conduction overlap, which would result in shoot-through currents and could result in transistor overheating, damage, or even destruction. This is an important design consideration. Too much deadtime can result in on-linearities in the output, degrading the audio quality of the amplifier.

References

3-in-1 Audio System Reference Design, Renesas
Class D audio amplifiers: what, why and how, Analog Devices
Class D Audio Amplifiers, Efficient Power Conversion
Fundamentals of Class D Amplifiers, Maxim Integrated Products
Managing EMI in Class D Audio Applications, Texas Instruments

 

 

You may also like:


  • Class D audio – Why now?

  • Class D amplifiers for high-efficiency switched-mode sound
DesignFast Banner version: 03eceadf

Filed Under: Amplifiers, Analog IC Tips, Analog ICs, FAQ, Featured Tagged With: FAQ

Primary Sidebar

EE Training Center Classrooms

EE Classrooms

Featured Resources

  • EE World Online Learning Center
  • CUI Devices – CUI Insights Blog
  • EE Classroom: Power Delivery
  • EE Classroom: Building Automation
  • EE Classroom: Aerospace & Defense
  • EE Classroom: Grid Infrastructure
Search Millions of Parts from Thousands of Suppliers.

Search Now!
design fast globle

R&D World Podcasts

R&D 100 Episode 7
See More >

Current Digital Issue

April 2022 Special Edition: Internet of Things Handbook

How to turn off a smart meter the hard way Potential cyber attacks have a lot of people worried thanks to the recent conflict in Ukraine. So it might be appropriate to review what happened when cybersecurity fi rm FireEye’s Mandiant team demonstrated how to infiltrate the network of a North American utility. During this…

Digital Edition Back Issues

Sponsored Content

Positioning in 5G NR – A look at the technology and related test aspects

Radar, NFC, UV Sensors, and Weather Kits are Some of the New RAKwireless Products for IoT

5G Connectors: Enabling the global 5G vision

Control EMI with I-PEX ZenShield™ Connectors

Speed-up time-to-tapeout with the Aprisa digital place-and-route system and Solido Characterization Suite

Siemens Analogue IC Design Simulation Flow

More Sponsored Content >>

RSS Current EDABoard.com discussions

  • Smallest header needed to support PCB vertically above main PCB
  • What base emitter resistors are inside Darlington
  • Simulation of resonator in HFSS
  • series connection of power audio amplifier
  • Sampling with MOS transistor and cap

RSS Current Electro-Tech-Online.com Discussions

  • software PWM
  • ASM - Enhanced 16F and long calls - how?
  • Ampro 16mm Stylist projector woes.
  • Will Header and socket hold this PCB OK?
  • Passthrough charging-simple but impossible to achieve?

Oscilloscopes Product Finder

Footer

EE World Online

EE WORLD ONLINE NETWORK

  • 5G Technology World
  • Analog IC Tips
  • Battery Power Tips
  • Connector Tips
  • DesignFast
  • EDABoard Forums
  • Electro-Tech-Online Forums
  • Engineer's Garage
  • Microcontroller Tips
  • Power Electronic Tips
  • Sensor Tips
  • Test and Measurement Tips
  • Wire & Cable Tips

EE WORLD ONLINE

  • Subscribe to our newsletter
  • Lee's teardown videos
  • Advertise with us
  • Contact us
  • About Us
Follow us on TwitterAdd us on FacebookConnect with us on LinkedIn Follow us on YouTube Add us on Instagram

Copyright © 2022 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy