AK4584_01 Datasheet, PDF (33/53 Pages) Asahi Kasei Microsystems – 24Bit 96kHz Audio CODEC with DIT/DIR

ASAHI KASEI
[AK4584]
„ Input Volume
The AK4584 includes two channel-independent analog volumes (IPGA), each with 37 levels in 0.5dB increments. These
are located in front of the ADCs while digital volume controls (IATT) with 128 levels (including MUTE) are located after
the ADCs. Control of both of these volumes setting is handled the same register address. When the MSB of the register is
“1”, the IPGA changes and when the MSB = “0” the IATT changes.
The IPGA is an analog volume control that improves the S/N ratio compared with digital volume controls (Table 19).
Level changes only occur during zero-crossings to minimize switching noise. Channel independent zero-crossing detection
is used. If there is no zero-crossings, then the level will change after a time-out. The time-out period scales with fs. The
periods of 256/fs, 512/fs, 1024/fs and 2048/fs are selected by ZTM1-0 bits in normal speed mode. If new value is written
to the IPGA register before IPGA changes at the zero crossing or time-out, the previous value becomes invalid. The timer
(channel independent) for time-out is reset and the timer restarts for new IPGA value. The ZCEI bit in the control register
enable zero-crossing detection.
The IATT is a pseudo-log volume that is linear-interpolated internally. When changing the level, the transition between
ATT values has 8031 levels and is done by soft changes (zero crossings), eliminating any switching noise.
Input Gain Setting
0dB
+6dB
fs=44.1kHz, A-weight
100dB
98dB
Table 19. PGA+ADC S/N
+18dB
90dB
ZTM1
0
0
1
1
ZTM0
Normal Speed Double Speed
0
256/fs
512/fs
1
512/fs
1024/fs
0
1024/fs
2048/fs
1
2048/fs
4096/fs
Table 20. Zero Crossing Timeout
Default
„ De-emphasis Control
The DAC includes the digital de-emphasis filter (tc=50/15µs) by IIR filter. This filter corresponds to three frequencies
(32kHz, 44.1kHz, 48kHz). This setting is done via control register (DEM1-0 bits). This filter is always OFF at double
speed and quad speed modes.
DEM1 DEM0
Mode
0
0
44.1kHz
0
1
OFF
Default
1
0
48kHz
1
1
32kHz
Table 21. De-emphasis Control
„ Output Volume
The AK4584 includes channel independent digital output volumes (ATT) with 256 levels at 0.5dB steps including MUTE.
These volumes are in front of the DAC and can attenuate the input data from 0dB to −127dB and mute. When changing the
level, the transitions are executed by soft changes (zero crossings), eliminating any switching noise.
MS0118-E-00
- 33 -
2001/11