AK4633 Datasheet, PDF (41/82 Pages) Asahi Kasei Microsystems – 16-Bit Mono CODEC with ALC & MIC/SPK-AMP

ASAHI KASEI
[AK4633]
„ Digital Programmable Filter
The AK4633 have 2steps of 1st order HPF and 2 band Equalizer for recording and playback path (Figure 32).
(1) High Pass Filter (HPF)
Normally, this HPF is used for a Wind-Noise Reduction Filter. This is composed with 2 steps of 1st order HPF. The
coefficient of both HPF is same and should be set by F1A13-0 bits and F1B13-0 bits. The HPF of ADC could be ON/OFF
by HPFAD bit, and the HPF before 2 band EQ could be ON/Off by setting HPF bit. When the HPF is OFF, the audio data
passes this block by 0dB . The coefficient should be set when HPFAD bit = HPF bit = “0” or PMADC bit = PMPFIL bit
= “0”. After changing the coefficient, the HPF starts with 3/fs (max) delay time after (HPFAD bit and PMADC bit) or
(HPF bit and PMPFIL bit) are set to “1”. The waiting time is not necessity for setting HPFAD bit, HPF bit, PMADC bit
and PMPFIL bit to “1” after setting the coefficient.
fs: Sampling frequency
fc: Cut-off frequency
Register setting (Note 29)
HPF: F1A[13:0] bits =A, F1B[13:0] bits =B
(MSB=F1A13, F1B13; LSB=F1A0, F1B0)
1
A=
, B=
1 + tan (πfc/fs)
1− tan (πfc/fs)
1 + tan (πfc/fs)
The cut-off frequency should be set as below.
fc/fs ≥ 0.0001 (fc min = 1.6Hz at 16kHz)
(2) 2 band Equalizer
This could be used as Equalizer or notch filter. 2 band Equalizer (EQ1 and EQ2) are ON/OFF independently by EQ1 bit
and EQ2 bit. When Equalizer is OFF, the audio data passes this block by 0dB. The coefficient of EQ1 should be set by
E1A15-0 bits, E1B15-0 bits and E1C15-0 bits, the coefficient of EQ2 should be set by E2A15-0 bits, E2B15-0 bits and
E2C15-0 bits. The EQ1 coefficient should be set when EQ1 bit = “0” or PMPFIL bit = “0”, the EQ2 coefficient should be
set when EQ2 bit = “0” or PMPFIL bit = “0”. After changing the coefficient, the Equalizer starts with 3/fs (max) delay
time after (EQ1 bit and PMPFIL bit) or (EQ2 bit and PMPFIL bit) are set to “1”. The waiting time is not necessity for
setting EQ1 bit, EQ2 bit and PMPFIL bit to “1” after setting the coefficient.
fs: Sampling frequency
fo: Center frequency
fb: Band width of 3dB gain difference from center frequency
K : Gain ( -1 ≤ K < 3 )
Register setting(Note 29)
EQ1: E1A[15:0] bits =A, E1B[15:0] bits =B, E1C[15:0] bits =C
EQ2: E2A[15:0] bits =A, E2B[15:0] bits =B, E2C[15:0] bits =C
(MSB=E1A15, E1B15, E1C15, E2A15, E2B15, E2C15 ; LSB= E1A0, E1B0, E1C0, E2A0, E2B0, E2C0)
A= K x
tan (πfb/fs)
1 + tan (πfb/fs)
, B = cos(2π fo/fs) x
2
,
1 + tan (πfb/fs)
1 − tan (πfb/fs)
C= −
1 + tan (πfb/fs)
The center frequency should be set as below.
fo/fs < 0.497
MS0447-E-03
- 41 -
2006/04