AK4679EG Datasheet, PDF (92/220 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with DSP and MIC/RCV/HP/SPK/LINE-AMP

[AK4679]
(2-2) Low Pass Filter (LPF)
This is composed with 1st or 2nd order LPF. DLLA13-0 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 54. 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 (πfc/fs)
1 − 1 / tan (πfc/fs)
B=
1 + 1 / tan (πfc/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 = 2205Hz at 44.1kHz)
MS1402-E-06
- 92 -
2013/02