AK4648 Datasheet, PDF (47/119 Pages) Asahi Kasei Microsystems – Stereo CODEC with MIC/HP/SPK-AMP

[AK4648]
■ Digital EQ/HPF/LPF
The AK4648 performs wind-noise reduction filter, stereo separation emphasis, gain compensation and ALC (Automatic
Level Control) by digital domain for A/D converted data (Figure 34). FIL1, FIL3 and EQ blocks are IIR filters of 1^st
order. The filter coefficient of FIL3, EQ and FIL1 blocks can be set to any value. Refer to the section of “ALC operation”
about ALC.
When only DAC is powered-up, digital EQ/HPF/LPF circuit operates at playback path. When only ADC is powered-up
or both ADC and DAC are powered-up, digital EQ/HPF/LPF circuit operates at recording path. Even if the path is
switched from recording to playback, the register setting of filter coefficient at recording remains. Therefore, FIL3, EQ,
FIL1 and GN1-0 bits should be set to “0” if digital EQ/HPF/LPF is not used for playback path.
PMADL bit, PMADR bit PMDAC bit LOOP bit
Status
Digital EQ/HPF/LPF
00
0
x
Power-down
Power-down
1
x
Playback
Playback path
0
x
Recording
Recording path
01, 10 or 11
1
0
Recording & Playback
Recording path
1
Recording Monitor Playback Recording path
Note 55. Stereo separation emphasis circuit is effective only at stereo operation.
Table 24. Digital EQ/HPF/LPF Circuit Setting (x: Don’t care)
(default)
FIL3 coefficient also sets the attenuation of the stereo separation emphasis.
The combination of GN1-0 bit (Table 25) and EQ coefficient set the compensation gain.
FIL1 and FIL3 blocks become HPF when F1AS and F3AS bits are “0” and become LPF when F1AS and F3AS bits are
“1”, respectively.
When EQ and FIL1 bits are “0”, EQ and FIL1 blocks become “through” (0dB). When FIL3 bit is “0”, FIL3 block become
“MUTE”. When each filter coefficient is changed, each filter should be set to “through” (“MUTE” in case of FIL3).
When MIX bit = “1”, only FIL1 is available. In this case, EQ and FIL3 bits should be set to “0”.
Wind-noise reduction
FIL1
Stereo separation emphasis
FIL3
Gain compensation
EQ
Gain
ALC
An y coefficient
F1A13-0
F1B13-0
F1AS
An y coefficient 0dB _∼ -10dB
F3A13-0 MUTE
F3B13-0 (set by
F3AS
FIL3 coefficient)
An y coefficient
EQA15-0
EQB13-0
EQC15-0
+12dB ∼ 0dB
GN1-0
+24/+12/0dB
Figure 34. Digital EQ/HPF/LPF
GN1
GN0
Gain
0
0
0dB
(default)
0
1
+12dB
1
x
+24dB
Table 25. Gain select of gain block (x: Don’t care)
MS0625-E-01
- 47 -
2007/06