AK4648 Datasheet, PDF (49/119 Pages) Asahi Kasei Microsystems – Stereo CODEC with MIC/HP/SPK-AMP

[AK4648]
3) EQ
fs: Sampling frequency
fc₁: Pole frequency
fc₂: Zero-point frequency
f: Input signal frequency
K: Filter gain [dB] (Maximum +12dB)
Register setting
EQA[15:0] bits =A, EQB[13:0] bits =B, EQC[15:0] bits =C
(MSB=EQA15, EQB13, EQC15; LSB=EQA0, EQB0, EQC0)
1 + 1 / tan (πfc₂/fs)
A = 10^K/20 x
,
1 + 1 / tan (πfc₁/fs)
1 − 1 / tan (πfc₁/fs)
B=
,
1 + 1 / tan (πfc₁/fs)
1 − 1 / tan (πfc₂/fs)
C =10^K/20 x
1 + 1 / tan (πfc₁/fs)
Transfer function
H(z) =
A + Cz ^−1
1 + Bz ^−1
M(f) =
Amplitude
A² + C² + 2ACcos (2πf/fs)
1 + B² + 2Bcos (2πf/fs)
Phase
(AB−C)sin (2πf/fs)
θ(f) = tan ^−1
A + BC + (AB+C)cos (2πf/fs)
[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.
[Filter Coefficient Setting Example]
1) FIL1 Block
Example: HPF, fs=44.1kHz, fc=100Hz
F1AS bit = “0”
F1A[13:0] bits = 01 1111 1100 0110
F1B[13:0] bits = 10 0000 0111 0100
2) EQ block
Example: fs=44.1kHz, fc₁=300Hz, fc₂=3000Hz, Gain=+8dB
Gain[dB]
+8dB
fc₁
fc₂
EQA[15:0] bits = 0000 1001 0110 1110
EQB[13:0] bits = 10 0001 0101 1001
EQC[15:0] bits = 1111 1001 1110 1111
Frequency
MS0625-E-01
- 49 -
2007/06