Application Report
SNAA050A–November 2007–Revised May 2013
AN-1737 Managing EMI in Class D Audio Applications
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ABSTRACT
Electromagnetic interference (EMI) is an unwanted disturbance caused in an electrical circuit by
electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or
otherwise degrade the effective performance of the circuit.
Contents
1 EMI - The Basics ............................................................................................................ 2
2 The Class D Audio Amplifier .............................................................................................. 3
3 Countering EMI .............................................................................................................. 4
4 References ................................................................................................................... 6
List of Figures
1 Wavelength as a Function of Frequency ................................................................................ 2
2 Common Antennas ......................................................................................................... 2
3 Unintended Antennas in PCBs............................................................................................ 3
4 The Class D Audio Amplifier PWM ....................................................................................... 4
5 Resistance and Inductance as a Function of Frequency.............................................................. 5
6 Comparison of Fixed-Frequency and Spread-Spectrum Modulation................................................. 5
7 LM48511 - A Spread-Spectrum Modulated Class D Amplifier........................................................ 6
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SNAA050A–November 2007–Revised May 2013 AN-1737 Managing EMI in Class D Audio Applications
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