AK4636 Datasheet, PDF (46/105 Pages) Asahi Kasei Microsystems – 16-Bit Mono CODEC with ALC & MIC/SPK/Video-AMP

[AK4636]
(3) 4-band Equalizer and Equalizer after ALC
This block can be used as Equalizer or Notch Filter. ON/OFF 5-band Equalizer (EQ2, EQ3, EQ4 and EQ5) can be
controlled independently by EQ2, EQ3, EQ4 and EQ5 bits. The Equalizer after ALC (EQ1) can be ON/OFF by EQ1 bit.
When Equalizer is OFF, the audio data passes this block by 0dB gain. E1A15-0, E1B15-0 and E1C15-0 bits set the
coefficient of EQ1. E2A15-0, E2B15-0 and E2C15-0 bits set the coefficient of EQ2. E3A15-0, E3B15-0 and E3C15-0
bits set the coefficient of EQ3. E4A15-0, E4B15-0 and E4C15-0 bits set the coefficient of EQ4. E5A15-0, E5B15-0 and
E5C15-0 bits set the coefficient of EQ5. Each EQ coefficient setting should be made when the corresponding EQ bit is
“0” or PMPFIL bit “0”.
fs : The Sampling frequency
fo₁ ~ fo₅ : The Center frequency
fb₁ ~ fb₅ : The Band width where the gain is 3dB different from center frequency
K₁ ~ K₅ : The 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 (πfb_n/fs)
1 + tan (πfb_n/fs)
(n = 1, 2, 3, 4, 5)
, B_n = cos(2π fo_n/fs) x
2
1 + tan (πfb_n/fs)
, ^{Cn =}
1 − tan (πfb_n/fs)
1 + tan (πfb_n/fs)
Transfer Function
H(z) = ( 1 + h₂(z) + h₃(z) + h₄(z) + h₅(z) ) x {1 + h₁(z)}
h_n (z) = A_n
1 − z ^−2
1− B_nz ^−1− C_nz ^−2
(n = 1, 2, 3, 4, 5)
The center frequency should be set as below
fo_n / fs < 0.497
When gain of K is set to “−1”, the equalizer becomes notch filter. The central frequency of a real notch filter deviates from
the above calculation, if the central frequency of each band is near. The control soft that is attached to the evaluation board
has a function that revises a gap of frequency, and calculates the coefficient. When the central frequency of each band is
near, revise the central frequency and confirm the frequency response.
Note 33.
[Translation the filter coefficient calculated by the equations above from real number to binary code (2’s complement)]
X = (Real number of filter coefficient calculated by the equations above) x 2¹³
X should be rounded to integer, and then should be translated to binary code (2’s complement).
MSB of each filter coefficient setting register is sine bit.
MS1012-E-01
- 46 -
2010/08