8.3.7.5 Programmable Digital Biquad Filters

The device supports up to 12 programmable digital biquad filters. These highly efficient filters achieve the desired frequence response. In digital signal processing, a digital biquad filter is a second-order, recursive linear filter with two poles and two zeros. Equation 2 gives the transfer function of each biquad filter:

Equation 2.

The frequency response for the biquad filter section with default coefficients is flat at a gain of 0 dB (all-pass filter). The host device can override the frequency response by programming the biquad coefficients to achieve the desired frequency response for a low-pass, high-pass, or any other desired frequency shaping. The programmable coefficients for the mixer operation are located in the Programmable Coefficient Registers: Page = 0x02 and Programmable Coefficient Registers: Page = 0x03 sections. If biquad filtering is required, then the host device must write these coefficients values before powering up any ADC channels for recording. These programmable coefficients are 32-bit, two’s complement numbers. As described in Table 16, these biquad filters can be allocated for each output channel based on the BIQUAD_CFG[1:0] register setting of P0_R108. By setting BIQUAD_CFG[1:0] to 2'b00, the biquad filtering for all record channels is disabled and the host device can choose this setting if no additional filtering is required for the system application. See the PCM6xx0-Q1 Programmable Biquad Filter Configuration and Applications application report for further details.

Table 17 shows the biquad filter coefficients mapping to the register space.