Reducing EMI in Class D audio applications by spread-spectrum modulation techniques

McCulley, Bill; Higashi, Royce
January 2007
Portable Design;Jan2007, Vol. 13 Issue 1, p12
The article discusses several techniques on how to reduce electromagnetic interference (EMI) or radio frequency interference in Class D audio applications. One technique to reduce EMI is to slow down the edges of the square wave. Using inductor plus capacitor filters also reduce EMI, as well as placing ferrite beads in series with the loudspeaker close to the amplifier. Another technique to reduce EMI is the use of spread spectrum to adjusts the switching frequency of the output bridge in a band around a center switching frequency. Spread-spectrum modulation technique improves EMI performance because of lower radiated noise peaks and reduces or eliminates the EMI filters in Class D applications.


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