LA9240M Datasheet, PDF (8/20 Pages) Sanyo Semicon Device – Analog Signal Processor (ASP) for CD players

LA9240M
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^− (pin 42); if necessary, this
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^− (pin 21).
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 amplifier 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, 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^− (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^− (pin6) and TE (pin7).
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
amplifier 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.)
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^− (pin 30) and SL⁺ (pin 31); specifically, the pins are connected to the microprocessor output ports via resistors,
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^− (pin 30) and SL⁺ (pin 31), an offset will arise in the SLD output.
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 39) and CV⁺ (pin 40) and sets the equalizer characteristics through SP
(pin 23), SP^− (pin 26), and SPD (pin 27), which are output to SPD (pin 27). The 12-cm mode amplifier gain is set by the
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.
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