AK4950 Datasheet, PDF (41/106 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK/Cap-less VIDEO-AMP & mini DSP

[AK4950]
■ Digital Programmable Filter Circuit
(1) High Pass Filter (HPF2)
Normally, this HPF is used for Wind-Noise Reduction. This is composed 1st order HPF. The coefficient of HPF is set by
03H, 04H, 06H (3-wire mode, COEW bit = “1”) and 83H, 84H and 86H (I²C mode). 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”. The HPF2 starts operation 2/fs (max) after when HPF bit=PMPFIL bit= “1” is set.
fs: Sampling Frequency
fc: Cutoff Frequency
Register Setting (Register Map 2) (Note 37)
1
A0: Register Addr = 03H(3-wire mode), 83H(I²C mode)
A1: Register Addr = 04H(3-wire mode), 84H(I²C mode)
B1: Register Addr = 06H(3-wire mode), 86H(I²C mode)
1 / tan (πfc/fs)
1 / tan (πfc/fs) − 1
A0 =
, A1 = − A0, B1 =
1 + 1 / tan (πfc/fs)
1 / tan (πfc/fs) + 1
Transfer Function
1 − z ^−1
H(z) = A0
1 − B1 z ^−1
The cut-off frequency must be set as below.
fc/fs ≥ 0.0001 (fc min = 4.41Hz at 44.1kHz)
Setting Example) When fc=150Hz @ fs=44.1kHz (I²C mode)
A0 = 0FD4B1 (hex): Addr. 83H
A1 = F02B4F (hex): Addr. 84H
B1 = 0FA963 (hex): Addr. 86H
MS1320-E-00
- 41 -
2011/10