AK4637 Datasheet, PDF (46/96 Pages) Asahi Kasei Microsystems – 24bit Mono CODEC with MIC - SPK-AMP

fs: Sampling Frequency
fc: Cutoff Frequency
Register Setting (Note 33)
LPF: F2A[13:0] bits =A, F2B[13:0] bits =B
(MSB=F2A13, F2B13; 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 must be set as below.
fc/fs  0.05 (fc min = 2400Hz at 48kHz)
[AK4637]
(3) 4-band Equalizer & 1-band Equalizer after ALC
This block can be used as equalizer or Notch Filter. 4-band equalizers (EQ2~EQ5) are switched ON/OFF
independently by EQ2, EQ3, EQ4 and EQ5 bits. EQ1 bit controls ON/OFF switching of the equalizer after
ALC (EQ1). When the equalizer is OFF, the audio data passes this block by 0dB gain. E1A15-0 bits,
E1B15-0 bits and E1C15-0 bits set the coefficient of EQ1. E2A15-0 bits, E2B15-0 bits and E2C15-0 bits
set the coefficient of EQ2. E3A15-0 bits, E3B15-0 bits and E3C15-0 bits set the coefficient of EQ3.
E4A15-0 bits, E4B15-0 bits and E4C15-0 bits set the coefficient of EQ4. E5A15-0 bits, E5B15-0 bits and
E5C15-0 bits set the coefficient of EQ5. The EQn (n=1, 2, 3, 4 or 5) coefficient must be set when EQn bit
= “0” or PMPFIL bit = “0”. EQn starts operation 4/fs(max) after when EQn = PMPFIL bit = “1” is set.
Each EQ2 ~ 5 blocks have a gain controller (EQ2G ~ EQ5G) independently after the equalizer. EQnG5-0
bits (n = 2~5) setting is reflected by writing “1” to EQCn bit (n = 2~5). EQnG5-0 bits and EQCn bit (n=2~5)
can be set during operation (EQn =PMPFIL bit= “1”).
fs: Sampling Frequency
fo₁ ~ fo₅: Center Frequency
fb₁ ~ fb₅: Band width where the gain is 3dB different from the center frequency
K₁ ~ K₅: Gain (1  K_n < 3)
Register Setting (Note 33)
EQ1: E1A[15:0] bits =A₁, E1B[15:0] bits =B₁, E1C[15:0] bits =C₁
EQ2: E2A[15:0] bits =A₂, E2B[15:0] bits =B₂, E2C[15:0] bits =C₂
EQ3: E3A[15:0] bits =A₃, E3B[15:0] bits =B₃, E3C[15:0] bits =C₃
EQ4: E4A[15:0] bits =A₄, E4B[15:0] bits =B₄, E4C[15:0] bits =C₄
EQ5: E5A[15:0] bits =A₅, E5B[15:0] bits =B₅, E5C[15:0] bits =C₅
(MSB=E1A15, E1B15, E1C15, E2A15, E2B15, E2C15, E3A15, E3B15, E3C15, E4A15, E4B15,
E4C15, E5A15, E5B15, E5C15 ; LSB= E1A0, E1B0, E1C0, E2A0, E2B0, E2C0, E3A0, E3B0,
E3C0, E4A0, E4B0, E4C0, E5A0, E5B0, E5C0)
A_n = K_n x
tan (fb_n/fs)
1 + tan (fb_n/fs)
(n = 1, 2, 3, 4, 5)
, B_n = cos(2 fo_n/fs) x
2
1 + tan (fb_n/fs)
, ^{Cn =}
1  tan (fb_n/fs)
1 + tan (fb_n/fs)
015010680-E-00
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2015/09