AK4950 Datasheet, PDF (45/106 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK/Cap-less VIDEO-AMP & mini DSP

2) When EQ0 = Low boost Filter
fs: Sampling Frequency
fc: Cutoff Frequency
β = A/Q
A = boost gain. Example) Boost gain = +12dB (A = 10 ^{Gain [dB] / 40} ) when A=2.
Gain =20 log (Q)[dB] for fs. Normally Q should be set to 0.7071.
Register Setting (Register Map 2) (Note 37)
1
A0: Register Addr = 19H(3-wire mode), 99H(I²C mode)
A1: Register Addr = 1AH(3-wire mode), 9AH(I²C mode)
A2: Register Addr = 1BH(3-wire mode), 9BH(I²C mode)
B1: Register Addr = 1CH(3-wire mode), 9CH(I²C mode)
B2: Register Addr = 1DH(3-wire mode), 9DH(I²C mode)
A0 =
A × ((A+1) + (A–1) × cos (2πfc/fs) + β × sin (2πfc/fs))
(A+1) + (A–1) × cos (2πfc/fs) + β × sin (2πfc/fs)
A1 =
2A × ((A+1) – (A+1) × cos (2πfc/fs)
(A+1) + (A–1) × cos (2πfc/fs) + β × sin (2πfc/fs)
A2
=
–A × ((A+1) – (A–1) × cos (2πfc/fs) – β ×
(A+1) + (A–1) × cos (2πfc/fs) + β × sin
sin (2πfc/fs))
(2πfc/fs)
B1 =
–2 × ((A–1) – (A+1) × cos (2πfc/fs))
(A+1) + (A–1) × cos (2πfc/fs) + β × sin (2πfc/fs)
B2 =
(A+1) + (A–1) × cos (2πfc/fs) – β × sin (2πfc/fs))
(A+1) + (A–1) × cos (2πfc/fs) + β × sin (2πfc/fs)
Transfer Function
H_x (z) =
A₀ + A₁ z ^−1 + A₂z ^−2
1 − B₁z ^−1− B₂z ^−2
The cut-off frequency must be set as below.
fc₁ / fs < 0.497
Gain
fc
F requenc y
Figure 38. EQ0 Frequency Response (Low –boost)
[AK4950]
MS1320-E-00
- 45 -
2011/10