16
3-2. Focus Servo for CD/DVD
Focus Servo for CD/DVD is based on focus error signal generated from RF AMP (TA1254F). It standardizes the
laser beam (CD:A, B, DVD:A, B, C, D) radiated from the pick-up.
Each other focus gain or path is made at the TA1254F (IC201) according to the disc, Focus Error signal
output from the FEO terminal and input to Servo IC (IC301 TC9461F).
After the first amplification of this signal, the signal is converted to A/D and input to Digital Equalizer Block
assigned the most important part at the Focus Servo, and generates the focus servo with coefficient value
set at the µ -COM through the Digital Filter.
At this Digital Equalizer, auto adjustment for Focus Balance or Focus Loop Gain occurs and the basic offset
value for pick-up is accepted on the balance mode, and set the focus standard level to this value.
After the signal for Focus Servo is converted to the D/A and output through FOO (IC301 TC9461F ).
This signal is amplified to gain through OP AMP (IC605), drives Focus Actuator through the Focus Drive IC
(IC604:BA6792Y).
3-3. Tracking Servo for CD/DVD
For Tracking Servo, CD uses 3 Beam method (E-F), DVD uses DPD (Differential Phase Detect) method
(phase difference for A+C signal and B+D signal).
According to the disc, Tracking Error is set at TA1254F, Gain or Path differs from each other, and the
generated signal output through the TEO terminal.
This signal input to TEI of IC301, after the first amplification, and converted to A/D.
The signal converted to A/D input to the Digital Equalizer assigned the most important part at the Tracking
Servo, Tracking Servo Gain is generated with Digital Filter coefficient value set according to the disc at the
µ-COM.
*
Tracking balances at this digital equalizer automatically, adjusted balance input to pin TEB terminal of
IC201 through the pin (TEBC) of IC301. Tracking Error Balance is adjusted, and the reference level for
the balance sets offset value to produce differently according to CD/DVD at the first disc drive.
Tracking signal is converted to D/A through the pin TRO terminal of IC301 and output and amplified at
IC605 (OP AMP), and input to IC604 (BA6792-Y) tracking drive.
This drive drives the tracking actuator actually.
Also, DVD controls the DPDB for the balance by differential DPD Error signal according to the pit shape
type of disc. It controls the delay volume for A, B, C and D in the DPD TE generating mode, is adjusted
by a µ-COM, outputs PWM with the pin of IC401 (TC90A41F), and input to the pin DPDB of IC201
and is controlled.
3-4. Sled Servo (Feed Servo) for CD/DVD
Sled servo operates related with a tracking servo basically
It goes with the progressive track speed according to the disc rotation speed.
Sled drive voltage is generated with a accumulated capacity of tracking error signal and is applied sled
movement voltage according to the track movement capacity, and this voltage outputs to the pin FOO of
IC301. This value is amplified at IC610 (OP AMP) and the sled motor drove by the IC630 (Sled drive:
BA6792Y). But, the shift speed for pick-up is not controlled and broke with a only sled servo, itself, in the
data access mode, and the feedback is used according to the sled shift speed at this time.
So, the accurated shift speed for the pick-up is controlled added to the sleed signal.
The hall sensor is used in the feedback and DA0 (84) output at the µ
-COM (IC501) is used with it in the
sled kick or break.
41
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