AK4145 Datasheet, PDF (13/27 Pages) Asahi Kasei Microsystems – Digital BTSC Stereo Encoder

[AK4145]
■ Input Level to BTSC Encoder
The AK4145 is designed to be 100% modulation of L+R signal when L=R= 50% (approx. -6dBFS) signal data is input. In
addition to this -6dBFS, the BTSC standard contains the pre-emphasis filter. To prevent the clipping in a BTSC encoder
of the AK4145, following maximum input levels are recommended. The input data can be attenuated by controlling the
Stereo Volume Control registers (L7-0, R7-0 bits).
Frequency[Hz]
Maximum Input Level
to BTSC Encoder[dBFS]
20~1000
-7
2500
-10
5000
-14
8000
-15
13000
-22
Table 7. Maximum Input Level to BTSC Encoder
■ Stereo Volume Control (DVOL)
The AK4145 has a stereo digital volume control (DVOL. 256 levels, 0.5dB step, Mute). The L7-0, R7-0 bits control the
gain. The gain ranges from +31.0dB to –96.0dB, or MUTE. When the VOLC bit = “1” (default), the L7-0 bits control gain
for both Lch and Rch. When the VOLC bit = “0”, the L7-0 bits control gain for Lch and R7-0 bits control gain for Rch.
This volume has a soft transition function. When changing levels, transitions are executed in soft changes; thus no
switching noise occurs during these transitions. The transition time of 1 level and all levels are shown in Table 8. In
parallel control mode, volume control is fixed to 0dB.
DVOL Transition Time
1 Level
0dB to -96dB +31.0dB to -96dB
4LRCK
768LRCK
1016LRCK
Table 8. DVOL Transition Time
L7-0
00H
01H
:
3DH
3EH
3FH
FDH
FEH
FFH
Gain
+31.0dB
+30.5dB
:
+0.5dB
0dB
-0.5dB
:
-95.5dB
-96.0dB
MUTE (-∞)
Table 9. Lch Digital Volume
(default)
R7-0
00H
01H
:
3DH
3EH
3FH
FDH
FEH
FFH
Gain
+31.0dB
+30.5dB
:
+0.5dB
0dB
-0.5dB
:
-95.5dB
-96.0dB
MUTE (-∞)
Table 10. Rch Digital Volume
(default)
MS0982-E-01
- 13 -
2010/09