AK4634EN Datasheet, PDF (41/94 Pages) Asahi Kasei Microsystems – 16-Bit Mono CODEC with ALC & MIC/SPK -AMP

[AK4634]
■ Digital Programmable Filter Circuit
The AK4634 has 2 steps of 1^st order HPF, 1^st order LPF and 5-band Equalizer built-in in a recording/playback path.
(1) High Pass Filter (HPF)
Normally, this HPF is used as a Wind-Noise Reduction Filter. This is composed with 2 steps of 1st order HPF. The
coefficient of both HPF is the same and set by F1A13-0 bits and F1B13-0 bits. HPFAD bit controls ON/OFF of the 1st step
HPF and HPF bit controls ON/OFF of the 2nd step HPF. When the HPF is OFF, the audio data passes this block by 0dB
gain. The coefficient should be set when HPFAD = HPF bits = “0” or PMADC = PMPFIL bits = “0”.
fs : Sampling frequency
fc : Cut-off frequency
Register setting (Note 33)
HPF: F1A[13:0] bits = A, F1B[13:0] bits = B
(MSB = F1A13, F1B13; LSB = F1A0, F1B0)
1
1 tan (fc/fs)
A=
, B=
1 + tan (fc/fs)
1 + tan (fc/fs)
Transfer Function
H(z) = A
1  z ^1
1  Bz ^1
The cut-off frequency should be set as below.
fc/fs ≥ 0.0001 (fc min = 1.6Hz at fs=16kHz)
(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 should be set when LPF bit
= “0” or PMPFIL bits = “0”.
fs : Sampling frequency
fc : Cut-off frequency
Register setting (Note 33)
LPF: F2A[13:0] bits =A, F2B[13:0] bits =B
(MSB=F2A13, F1B13; LSB=F2A0, F2B0)
1
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 should be set as below.
fc/fs ≥ 0.05 (fc min = 2205Hz at fs=44.1kHz)
MS0686-E-03
- 41 -
2014/10