AK4637EN Datasheet, PDF (45/96 Pages) Asahi Kasei Microsystems – 24bit Mono CODEC with MIC/SPK-AMP

[AK4637]
■ Digital HPF1
A digital High Pass Filter (HPF) is integrated for DC offset cancellation of the ADC input. The cut-off
frequencies (fc) of the HPF1 are set by HPFC1-0 bits. It is proportional to the sampling frequency (fs) and
the default value is 3.7Hz (@fs = 48kHz). HPFAD bit controls the ON/OFF of the HPF1 (HPF ON is
recommended).
HPFC1
bit
0
0
1
1
HPFC0
fc
bit
fs=8kHz fs=16kHz fs=48kHz
0
0.62Hz
1.2Hz
3.7Hz
1
2.47Hz
4.9Hz
14.8Hz
0
19.7Hz
39.5Hz
118.4Hz
1
39.5Hz
78.9Hz
236.8Hz
Table 25. HPF1 Cut-off Frequency
(default)
■ Digital Programmable Filter Circuit
(1) High Pass Filter (HPF2)
This is composed 1st order HPF. The coefficient of HPF is set by F1A13-0 bits and F1B13-0 bits. HPF bit
controls ON/OFF of the HPF2. When the HPF2 is OFF, the audio data passes this block by 0dB gain. The
coefficient must be set when PMPFIL bit = “0” or HPF bit = “0”. The HPF2 starts operation 4/fs (max) after
when HPF bit = PMPFIL bit = “1” is set.
fs: Sampling Frequency
fc: Cutoff Frequency
Register Setting (Note 33)
HPF: F1A[13:0] bits =A, F1B[13:0] bits =B
(MSB=F1A13, F1B13; LSB=F1A0, F1B0)
1 / tan (fc/fs)
A=
,
1 + 1 / tan (fc/fs)
1  1 / tan (fc/fs)
B=
1 + 1 / tan (fc/fs)
Transfer Function
1  z ^1
H(z) = A
1 + Bz ^1
The cut-off frequency must be set as below.
fc/fs  0.0001 (fc min = 4.8Hz at 48kHz)
(2) Low Pass Filter (LPF)
This is composed with 1st order LPF. F2A13-0 bits and F2B13-0 bits set the coefficient of LPF. LPF bit
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 PMPFIL bit = “0” or LPF bit = “0”. The LPF starts operation 4/fs (max) after
when LPF bit =PMPFIL bit= “1” is set.
015010680-E-00
- 45 -
2015/09