WM9082

Production Data

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PD, August 2012, Rev 4.1

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Figure 4 Speaker Connection Losses

The Class D output requires external filtering in order to recreate the audio signal. This may be

implemented using a 2

internal inductance provides the required filter response. An LC filter should be used if the

loudspeaker characteristics are unknown or unsuitable, or if the length of the loudspeaker connection

is likely to lead to EMI problems.

A suitable LC filter implementation is illustrated in Figure 5.

Figure 5 Class D Output Filter Components

A simple equivalent circuit of a loudspeaker consists of a serially connected resistor and inductor, as

shown in Figure 6. This circuit provides a low pass filter for the speaker output. If the loudspeaker

characteristics are suitable, then the loudspeaker itself can be used in place of the filter components

described earlier. This is known as ‘filterless’ operation.

Figure 6 Speaker Equivalent Circuit for Filterless Operation