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參數(shù)資料
| 型號： | LA9242M |
| 廠商： | Sanyo Electric Co.,Ltd. |
| 英文描述： | Analog Signal Processor ASP for CD Players |
| 中文描述： | 模擬信號處理器的ASP CD播放機 |
| 文件頁數(shù)： | 7/20頁 |
| 文件大小： | 150K |
| 代理商： | LA9242M |
LA9242M
No.7097–7/20
Description of Operation
1. APC (auto laser power control)
This circuit controls the pickup laser power. The laser is turned on and off by commands from the microcontroller.
2. RF amplifier (eye pattern output)
The pickup photodiode output current (A+C) is input to FIN2 (pin 1), and (B+D) is input to FIN1 (pin 2). The
current that is input is converted to the voltage, passes through the AGC circuit, and is then output from the RFSM
amplifier output RFSM (pin 41). The internal AGC circuit has a variable range of
±
3dB, and the time constant can
be changed through the external capacitor connected to PH1 (pin 60). In addition, this circuit also controls the
bottom level of the EFM signal (RFSM output), and the response can be changed through the external capacitor
connected to BH1 (pin 61). The center gain setting for the AGC variable range is set by the resistance between
RFSM (pin 41) and RFS
–
(pin 42) ; if necessary, this resistance is also used for 3T compensation for the EFM
signal. If RW disc is detected, input signal gain is set high by RW (pin 38) which accepts Low from the DSP.
3. SLC (slice level control)
The SLC sets the duty ratio for the EFM signal that is input to the DSP to 50%. The DC level determined by
integrating the EFMO signal output from the DSP to determine the duty factor.
4. Focus servo
The focus error signal is derived by detecting the difference between (A+C) and (B+D), which is (B+D) – (A+C),
and is then output from FE (pin 20). The focus error signal gain is set by the resistance between FE (pin 20) and
FE
–
(pin 21). If RW disc is detected, input signal gain is set high by RW (pin 38) which accepts Low from the DSP.
Offset cancellation is performed by the FE amplifier. “Offset cancellation” cancels the offset for the IC’s internal
IV amplifier, etc. Adjustment is initiated by the FOCUS-OFFSET ADJUST START command, and terminates after
about 30 ms. The FOCUS-OFFSET ADJUST OFF command is used to return to the state before offset
cancellation.The FA amplifier is the pickup phase compensation amplifier, and the equalizer curve is set by the
external capacitor and resistance. Furthermore, this amplifer has a mute function which is applied when V
CC
is
turned on, when the F-SERVO OFF command is sent, and during F-SEARCH. In order to turn the focus servo on,
send either the LASER ON command or the F-SERVO ON command.
The FD amplifier has a phase compensation circuit, a focus search signal composition function and is completed in
about 560 ms. Focus seach is initiated by the F-SEARCH command, and a ramp waveform is generated by the
internal clock. This waveform is used for focus detection (focus zero cross) with the focus error signal and then
turn the focus servo on. The ramp waveform amplitude is set by the resistance between FD (pin 16) and FD
–
(pin
17). FSC (pin 46) is for smoothing the focus search ramp waveforms, and a capacitor is connected between FSC
and REF. FSS (pin 55) is the focus search mode switching pin. If FSS is shorted with V
CC
, the “+ search” is set ; if
FSS is left open or is shorted with GND, the “
±
search” is set.
5. Tracking servo
The pickup photodiode output current is input to E (pin 3) and F (pin 4). The current that is input is converted to
the voltage, passes through the balance adjustment VCA circuit and then the VCA circuit that follows the gain in
the RFAGC circuit, and is then output from TE (pin 7). The tracking error gain is set by the resistance between TE
–
(pin 6) and TE (pin 7). If RW disc is detected, input signal gain is set high by RW (pin 38) which accepts Low
from the DSP.
Offset cancellation is performed by the TE amplifier. Offset cancellation terminates after about 30 ms. The
TRACK-OFFSET ADJUST OFF command is used to return to the state before the offset.
The TH amplifier alters the servo response characteristics according to the THLD signal, etc., generated internally
after detection of the TGL signal from the DSP or the JP signal. When a defect is detected, the THLD mode goes
into effect internally. To avoid this, short DEF (pin 49) to L=GND. By inserting an external bandpass filter to
remove the shock component from the tracking error signal at SCI (pin 9), the gain is automatically boosted when
a defect is detected.
The TA output (pin 11) has a built-in resistance to allow configuration of a low-pass filter.
The TD amplifier performs servo loop phase compensation ; the characteristics are set by external CR. Further-
more, this amplifer has a mute function, which is applied when V
CC
is turned on or the TRACK-SERVO OFF
command is issued. The muting function is released by the TRACK-SERVO ON command.
The TOFF amplifier that is positioned immediately after TD (pin 13) functions to turn off the servo in response to
the TOFF signal from the DSP.
The TO amplifier has a JP pulse composition function. The JP pulse is set by JP (pin 14). (THLD detection is
performed internally.)
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