Third, the servo circuit analysis

 

 

1, the focus servo circuit :

During playback , the focus of the laser beam is only accurate at all times to play the track on information , in order to effectively read information from the disc . Can not swing when the rotation of the disc so that the information track is maintained in a plane , a focus servo mechanism to dynamically adjust the vertical position of the focal point of the laser beam , upper and lower tracks of the disc information correcting jitter. A, B, C, D four photodiode electrical conversion through A + C and B + D are fed to the mixing CXA2550 (4), (5) feet, after amplification ( 13 ) output from the focus error CXA2550 signal into CXD3068 section ( 39 ) feet by a / D converter to focus a digital signal to the servo logic controller , digital error calculation . The focus servo logic controller or PWM modulation signal by the output control circuit ( 33 ) , ( 34 ) pin output from CXD3068, fed BA6392 (19), (20) feet, the focus servo control voltage into a defocus state in contrast , proportional to the magnitude of the drive current from BA6392 (16), (17) pin output is applied to both ends of the focus coil , the magnetic force generated by driving the objective lens moves up and down , to achieve the purpose of focusing .

2, the tracking servo circuit :

Sensitive receivers E, F receives the electrical signal generated by the two auxiliary light , were sent to CXA2550 (7), (8) after subtraction amplifier ( 11 ) feet tracking error signal output from CXA2550, from CXD3068 (40) feet fed to the internal a / D converter generates a digital signal tracking . After processing into a PWM signal PWM circuit (31 ) , ( 32 ) feet out from CXD3068, fed BA6392 (9 ) , ( 10 ) feet processed into orbit in the opposite direction from , the current correction of equal size from BA6392 (12) ( 13 ) output , corrected by tracking coil so the focus track .

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