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 microprocessor.

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 ±3 dB, 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

resistance is also used for 3T compensation for the EFM signal.

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 is 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

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

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, and a focus search signal composition function and is completed in about

560 ms. Focus search 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

FSC (pin 46) is for smoothing the focus search ramp waveforms, and a capacitor is connected between FSC and REF.

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

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. Furthermore, this

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.)

6.

Sled servo

The response characteristics are set by SLEQ (pin 28). The amplifier positioned after SLEQ (pin 28) has a mute function that

is applied either when SLOF (pin 38) goes high or the SLED OFF command is issued. The sled is moved by inputting

current to SL

and the movement gain is set by the resistance value of that resistor. It is important to note that if there is a deviation in the

resistance values for SL

7.

Spindle servo

This configures the servo circuit, which maintains the linear velocity of the disc at a constant speed, along with the DSP. This

circuit accepts signals from the DSP through CV

(pin 24), SP

resistor connected between SPG (pin 25) and the reference voltage. In 8-cm mode, this amplifier serves as an internal buffer,

and SPG (pin 25) is ignored. Note that the gain setting is made for 8-cm mode first, and then 12-cm mode. If SPG (pin 25)

is left open, the gain is forcibly set for 8-cm mode, regardless of whether 8-cm or 12-cm mode is in effect.

LA9241M

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