AK4950 Datasheet, PDF (42/106 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK/Cap-less VIDEO-AMP & mini DSP

[AK4950]
(2) Low Pass Filter (LPF)
This is composed with 1st order LPF. 09H, 0AH, 0CH (3-wire mode, COEW bit = “1”) and 89H~8AH and 8CH (I²C
mode) 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”. The LPF starts operation 2/fs (max) after when
LPF bit =PMPFIL bit= “1” is set.
fs: Sampling Frequency
fc: Cutoff Frequency
Register Setting (Register Map 2) (Note 37)
1
A0: Register Addr = 09H(3-wire mode), 89H(I²C mode)
A1: Register Addr = 0AH(3-wire mode), 8AH(I²C mode)
B1: Register Addr = 0CH(3-wire mode), 8CH(I²C mode)
1
1 / tan (πfc/fs) − 1
A0 = A1 =
, 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 ≥ 0.05 (fc min = 2205Hz at 44.1kHz)
Setting Example) When fc=15kHz @ fs=44.1kHz (I²C mode)
A0 = 0A53F3 (hex): Addr. 89H
A1 = 0A53F3 (hex): Addr. 8AH
B1 = FB581A (hex): Addr. 8CH
MS1320-E-00
- 42 -
2011/10