SAMA5D2 Series

54.6.2.4 Low Pass Filter

The PDMIC includes a sixth-order IIR filter that performs a low pass transfer function and decimates by 2 the output of the sinc filter. The coefficients are computed for a decimated sampling rate of 48 kHz and optimize the 0 to 20 kHz band flatness while rejecting the aliasing of the PDM microphone by at least 60 dB in the 28 to 48 kHz band.

If the decimated sampling rate is modified, the frequency response of this filter is scaled proportionally to the new frequency.

Figure 54-7 and Figure 54-8 are drawn for an output sampling frequency of 48 kHz.

Figure 54-7. Low Pass Filter Spectral Mask

Figure 54-8. Low Pass Filter Ripple in the 0 to 20 kHz Band

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