LA9242M 데이터 시트보기 (PDF) - SANYO -> Panasonic

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LA9242M

Analog Signal Processor (ASP) for CD Players

SANYO -> Panasonic 

LA9242M

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 VCC 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 VCC, 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 VCC 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.)

No.7097–7/20

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