AK4646EZ Datasheet, PDF (37/78 Pages) Asahi Kasei Microsystems – Stereo CODEC with MIC/SPK-AMP

[AK4646EZ]
(5) 5-band Notch
This block can be used as Equalizer or Notch Filter. 5-band Equalizer (EQ1, EQ2, EQ3, EQ4 and EQ5) is selected
ON/OFF independently by EQ1, EQ2, EQ3, EQ4 and EQ5 bits. 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. The EQx (x=1∼5)
coefficient should be set when EQx bit = “0” or PMADL=PMADR= PMDAC bits = “0”.
fs: Sampling frequency
fo₁ ~ fo₅: Center frequency
fb₁ ~ fb₅: Band width where the gain is 3dB different from center frequency
K₁ ~ K₅: Gain (−1 ≤ K_n ≤ 3)
Register setting (Note 36)
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 + h₁(z) + h₂(z) + h₃(z) + h₄(z) + h₅(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. When it is used as notch filter, central frequency of a real
notch filter deviates from the above-mentioned calculation, if its central frequency of each band is near. The control soft
that is attached to the evaluation board has functions that revise a gap of frequency and calculate the coefficient. When its
central frequency of each band is near, the central frequency should be revised and confirm the frequency response.
Note 36. [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.
MS0630-E-00
- 37 -
2007/06