AK4955 Datasheet, PDF (43/117 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK/Cap-less VIDEO-AMP/ LDO & DSP

[AK4955]
■ Digital Programmable Filter Circuit
(1) High Pass Filter (HPF3)
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 HPF3. When the HPF3 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 HPF3 starts operation 4/fs (max) after when HPF bit=PMPFIL bit= “1” is
set.
fs: Sampling Frequency
fc: Cutoff Frequency
Register Setting (Note 42)
HPF: F1A[13:0] bits =A, F1B[13:0] bits =B
(MSB=F1A13, F1B13; LSB=F1A0, F1B0)
1 / tan (πfc/fs)
A=
,
1 + 1 / tan (πfc/fs)
1 − 1 / tan (πfc/fs)
B=
1 + 1 / tan (πfc/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.
fs: Sampling Frequency
fc: Cutoff Frequency
Register Setting (Note 42)
LPF: F2A[13:0] bits =A, F2B[13:0] bits =B
(MSB=F2A13, F1B13; LSB=F2A0, F2B0)
1
A=
,
1 + 1 / tan (πfc/fs)
1 − 1 / tan (πfc/fs)
B=
1 + 1 / tan (πfc/fs)
Transfer Function
1 + z ^−1
H(z) = A
1 + Bz ^−1
The cut-off frequency must be set as below.
fc/fs ≥ 0.05 (fc min = 2400Hz at 48kHz)
MS1343-E-00
- 43 -
2011/12