AK4679EG Datasheet, PDF (82/220 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with DSP and MIC/RCV/HP/SPK/LINE-AMP

[AK4679]
3. EQ5: 1st order High Pass Filter
<High Pass Filter>
fs: Sampling frequency
fc: Cut-off frequency
k: Filter gain
Register setting (Note 78)
5E5A[13:0] bits =A, 5E5B[13:0] bits =B
(MSB=5E5A13, 5E5B13; LSB=5E5A0, 5E5B0)
1 / tan (πfc/fs)
A=k x
,
1 + 1 / tan (πfc/fs)
1 − 1 / tan (πfc/fs)
B=
1 + 1 / tan (πfc/fs)
Transfer Function
1 − z ^−1
h_5H (z) = A
1 + Bz ^−1
The cut-off frequency should be set as below.
fc/fs ≥ 0.0001 (fc min = 4.41Hz at 44.1kHz)
Note 78. [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.
Total Transfer Function:
H(z) = K₁ x h_1L(z) + K₂ x h₂(z) + K₃ x h₃(z) + K₄ x h₄(z) + K₅ x h_5H(z)
K₁ ~ ₅: EQ Gain (+12 ~ -12dB, 0.5dB step). This value is changed by control register.
K₁: 5EQ1G5-0 bits (Addr=6AH)
K₂: 5EQ2G5-0 bits (Addr=6BH)
K₃: 5EQ3G5-0 bits (Addr=6CH)
K₄: 5EQ4G5-0 bits (Addr=6DH)
K₅: 5EQ5G5-0 bits (Addr=6EH)
Default Center Frequency (Sampling Frequency = 44.1kHz):
EQ1: fc=100Hz
EQ2: fo₂=250Hz (fb₂=50Hz)
EQ3: fo₃=1kHz (fb₃=200Hz)
EQ4: fo₄=3.5kHz (fb₄=700Hz)
EQ5: fc=10kHz
MS1402-E-06
- 82 -
2013/02