8.3.6.5 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. As described in Table 18, 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 TLV320ADCx140 Programmable Biquad Filter Configuration and Applications application report for further details.

Table 19 shows the biquad filter coefficients mapping to the register space.