AK4695 Datasheet, PDF (55/107 Pages) Asahi Kasei Microsystems – 24bit 4ch CODEC with MIC/HP/SPK/LINE-AMP

[AK4695]
(2-2) Low Pass Filter (LPF)
This is composed with 1st or 2nd order LPF. DMLA13-0 bits and DMLB13-0 bits set the coefficient of LPF. DMLPF1-0
bits controls ON/OFF of the LPF. When the LPF is OFF, the audio data passes this block by 0dB gain. The coefficient must
be set when DMLPF1-0 bits = “00” or PMDRC bit = “0”. The LPF starts operation 4/fs(max) after when DMLPF1-0 bits
= “01” or “10” and PMDRC bit = “1” are set.
DMLPF1 bit DMLPF0 bit
Mode
0
0
Bypass
(default)
0
1
1st order LPF
1
0
2nd order LPF
1
1
N/A
Table 52. DMLPF Mode Setting (N/A: Not Available)
fs: Sampling frequency
fc: Cut-off frequency
Register setting
LPF: DMLA[13:0] bits =A, DMLB[13:0] bits =B
(MSB=DMLA13, DMLB13; LSB=DMLA0, DMLB0)
1
A=
,
1 + 1 / tan (fc/fs)
1  1 / tan (fc/fs)
B=
1 + 1 / tan (fc/fs)
Transfer function (1st order)
1 + z ^1
H(z) = A
1 + Bz ^1
Transfer function (2nd order)
1 + z ^1
1 + z ^1
H(z) = A
xA
1 + Bz ^1
1 + Bz ^1
The cut-off frequency should be set as below.
fc/fs  0.05 (fc min = 2400Hz at 48kHz)
MS1463-E-01
- 55 -
2014/12