CS43131 datasheet(62/156 Pages) CIRRUS

62 / 156 page

DS1155F1

CS43131

4.14 Programmable Filter

In the CS43131, there are a series of programmable filters which is open for user's customization. The filter coefficients

can be programmed for altering frequency response or other characteristics to fit the design intention. The filter runs at the

input sample rate as set by xSP. This feature is intended to be used for normal PCM playback under single-, double-, and

quad-speed settings. (If operating at 192 kHz, MCLK_INT is required to be at 24.576 MHz.) For WBF mode and impedance

measurement mode, the filter should be properly turned off.

The filter series are composed of 1 first-order IIR system (FOS) and 3 second-order IIR system (SOS), which effectively

is a seventh-order system. FOS and SOS structures are illustrated as in Fig. 4-35 and Fig. 4-36, respectively. Any filter

stage can be chosen to be either utilized or bypassed through coefficient settings. Each stage is represented by filter

coefficients, which is accessed through I2C writes. The filter coefficients are located in register address 0x09 000C to

0x09 0041. Each coefficient is comprised of a most-significant byte, a least-significant byte, and a sign byte.

Figure 4-35. First-Order IIR System

Figure 4-36. Second-Order IIR System

The filter can only be programmed when PDN_HP is set. Program the filter coefficients when PDN_HP is cleared will result

in non-expected behavior.

To properly enable each filter's coefficients, after the coefficients is programmed in control port, user enable the control

port filter coefficients through registers Programmable Filter Control 1 and Programmable Filter Control 2. When user not

using the programmable filters, the filter should be disabled properly.

‐1

‐a1

X[n]

Y[n]

‐1

X[n]

Y[n]

‐1

‐a2

‐a1

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