AK4691 Datasheet, PDF (38/80 Pages) Asahi Kasei Microsystems – 4ch ADC + 2ch DAC with MIC/HP/SPK-AMP

[AK4691]
3) EQ
fs: Sampling frequency
fc₁: Pole frequency
fc₂: Zero-point frequency
f: Input signal frequency
K: Filter gain [dB] (Maximum +12dB)
Register setting for ADC1
EQA[15:0]A bits =A, EQB[13:0]A bits =B, EQC[15:0]A bits =C
(MSB=EQA15A, EQB13A, EQC15A; LSB=EQA0A, EQB0A, EQC0A)
Register setting for ADC2
EQA[15:0]B bits =A, EQB[13:0]A bits =B, EQC[15:0]B bits =C
(MSB=EQA15B, EQB13B, EQC15B; LSB=EQA0B, EQB0B, EQC0B)
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
Amplitude
Phase
H(z) =
A + Cz ^−1
1 + Bz ^−1
M(f) =
A² + C² + 2ACcos (2πf/fs)
1 + B² + 2Bcos (2πf/fs)
θ(f) = tan ^−1
(AB−C)sin (2πf/fs)
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) FIL1Ablock
Example: HPF, fs=44.1kHz, fc=100Hz
F1ASAbit = “0”
F1A[13:0]A bits = 01 1111 1100 0110
F1B[13:0]A bits = 10 0000 0111 0100
2) EQA block
Example: fs=44.1kHz, fc₁=300Hz, fc₂=3000Hz, Gain=+8dB
Gain[dB]
+8dB
fc₁
fc₂
EQA[15:0]A bits = 0000 1001 0110 1110
EQB[13:0]A bits = 10 0001 0101 1001
EQC[15:0]A bits = 1111 1001 1110 1111
Frequency
MS0672-E-00
- 38 -
2007/11