SBAS884A March 2020 – June 2020 PCM6240-Q1 , PCM6260-Q1 , PCM6340-Q1 , PCM6360-Q1
PRODUCTION DATA.
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:
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.
PROGRAMMABLE BIQUAD FILTER | RECORD OUTPUT CHANNEL ALLOCATION USING P0_R108_D[6:5] REGISTER SETTING | ||
---|---|---|---|
BIQUAD_CFG[1:0] = 2'b01
(1 Biquad per Channel) |
BIQUAD_CFG[1:0] = 2'b10 (Default)
(2 Biquads per Channel) |
BIQUAD_CFG[1:0] = 2'b11
(3 Biquads per Channel) |
|
SUPPORTS ALL 8 CHANNELS | SUPPORTS UP TO 6 CHANNELS | SUPPORTS UP TO 4 CHANNELS | |
Biquad filter 1 | Allocated to output channel 1 | Allocated to output channel 1 | Allocated to output channel 1 |
Biquad filter 2 | Allocated to output channel 2 | Allocated to output channel 2 | Allocated to output channel 2 |
Biquad filter 3 | Allocated to output channel 3 | Allocated to output channel 3 | Allocated to output channel 3 |
Biquad filter 4 | Allocated to output channel 4 | Allocated to output channel 4 | Allocated to output channel 4 |
Biquad filter 5 | Not used | Allocated to output channel 1 | Allocated to output channel 1 |
Biquad filter 6 | Not used | Allocated to output channel 2 | Allocated to output channel 2 |
Biquad filter 7 | Not used | Allocated to output channel 3 | Allocated to output channel 3 |
Biquad filter 8 | Not used | Allocated to output channel 4 | Allocated to output channel 4 |
Biquad filter 9 | Allocated to output channel 5 | Allocated to output channel 5 | Allocated to output channel 1 |
Biquad filter 10 | Allocated to output channel 6 | Allocated to output channel 6 | Allocated to output channel 2 |
Biquad filter 11 | Not used | Allocated to output channel 5 | Allocated to output channel 3 |
Biquad filter 12 | Not used | Allocated to output channel 6 | Allocated to output channel 4 |
Table 17 shows the biquad filter coefficients mapping to the register space.
PROGRAMMABLE BIQUAD FILTER | BIQUAD FILTER COEFFICIENTS REGISTER MAPPING | PROGRAMMABLE BIQUAD FILTER | BIQUAD FILTER COEFFICIENTS REGISTER MAPPING |
---|---|---|---|
Biquad filter 1 | P2_R8-R27 | Biquad filter 7 | P3_R8-R27 |
Biquad filter 2 | P2_R28-R47 | Biquad filter 8 | P3_R28-R47 |
Biquad filter 3 | P2_R48-R67 | Biquad filter 9 | P3_R48-R67 |
Biquad filter 4 | P2_R68-R87 | Biquad filter 10 | P3_R68-R87 |
Biquad filter 5 | P2_R88-R107 | Biquad filter 11 | P3_R88-R107 |
Biquad filter 6 | P2_R108-R127 | Biquad filter 12 | P3_R108-R127 |