DA7218 datasheet(39/198 Pages) RENESAS

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DA7218

Ultra-Low Power Stereo Codec

Datasheet

Revision 3.4

24-Dec-2021

CFR0011-120-00

39 of 197

The sidetone biquad filter can be used to provide custom filtering, for example microphone frequency

response. Each of the three biquad stages has five 16-bit coefficients a0, a1, a2, b1 and b2 (see

Figure 21). For the three stages, the coefficients are numbered a00, a01 etc. as shown in Figure 14:

-1

a00

a01

a02

-1

b01

b02

-1

a10

a11

a12

-1

b11

b12

-1

a20

a21

a22

-1

b21

b22

-1

x[n]

y[n]

Figure 14: Cascade of Three Biquad Filter Stages

The coefficients are stored using 8-bit registers in a dedicated address space. They are programmed

by first writing the coefficient data value to sidetone_biq_3stage_data and then the coefficient

address to sidetone_biq_3stage_addr. The address location for each of the coefficients is described

in Table 33: Each of the 16-

bit coefficients is two’s complement values that are programmed in the

range of -2 (0x8000) to +2 (0x7FFF). It is the responsibility of the user to ensure that filter transfer

function corresponding to the programmed coefficients is stable.

Table 33: Sidetone 3-Stage Biquad Filter Coefficient Address Map

Address

Name

Description

0x00

SIDETONE_BIQ_A00_LO

Lower byte of a00 coefficient for first sidetone biquad stage

0x01

SIDETONE_BIQ_A00_HI

Upper byte of a00 coefficient for first sidetone biquad stage

0x02

SIDETONE_BIQ_A01_LO

Lower byte of a01 coefficient for first sidetone biquad stage

0x03

SIDETONE_BIQ_A01_HI

Upper byte of a01 coefficient for first sidetone biquad stage

0x04

SIDETONE_BIQ_A02_LO

Lower byte of a02 coefficient for first sidetone biquad stage

0x05

SIDETONE_BIQ_A02_HI

Upper byte of a02 coefficient for first sidetone biquad stage

0x06

SIDETONE_BIQ_B01_LO

Lower byte of b01 coefficient for first sidetone biquad stage

0x07

SIDETONE_BIQ_B01_HI

Upper byte of b01 coefficient for first sidetone biquad stage

0x08

SIDETONE_BIQ_B02_LO

Lower byte of b02 coefficient for first sidetone biquad stage

0x09

SIDETONE_BIQ_B02_HI

Upper byte of b02 coefficient for first sidetone biquad stage

0x0A

SIDETONE_BIQ_A10_LO

Lower byte of a10 coefficient for second sidetone biquad stage

0x0B

SIDETONE_BIQ_A10_HI

Upper byte of a10 coefficient for second sidetone biquad stage

0x0C

SIDETONE_BIQ_A11_LO

Lower byte of a11 coefficient for second sidetone biquad stage

0x0D

SIDETONE_BIQ_A11_HI

Upper byte of a11 coefficient for first sidetone biquad stage

0x0E

SIDETONE_BIQ_A12_LO

Lower byte of a12 coefficient for first sidetone biquad stage

0x0F

SIDETONE_BIQ_A12_HI

Upper byte of a12 coefficient for first sidetone biquad stage

0x10

SIDETONE_BIQ_B11_LO

Lower byte of b11 coefficient for first sidetone biquad stage

0x11

SIDETONE_BIQ_B11_HI

Upper byte of b11 coefficient for second sidetone biquad stage

0x12

SIDETONE_BIQ_B12_LO

Lower byte of b12 coefficient for second sidetone biquad stage

0x13

SIDETONE_BIQ_B12_HI

Upper byte of b12 coefficient for second sidetone biquad stage

0x14

SIDETONE_BIQ_A20_LO

Lower byte of a20 coefficient for third sidetone biquad stage

0x15

SIDETONE_BIQ_A20_HI

Upper byte of a20 coefficient for third sidetone biquad stage

0x16

SIDETONE_BIQ_A21_LO

Lower byte of a21 coefficient for third sidetone biquad stage

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