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SAA7824 Datasheet(PDF) 31 Page - NXP Semiconductors |
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SAA7824 Datasheet(HTML) 31 Page - NXP Semiconductors |
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31 / 89 page  2003 Oct 01 31 Philips Semiconductors Product specification CD audio decoder, digital servo and filterless DAC with integrated pre-amp and laser control SAA7824 handbook, full pagewidth D3 D1 D2 SATELLITE DIODE R1 SATELLITE DIODE R2 D1 D3 D2 D4 SATELLITE DIODE R1 SATELLITE DIODE R2 D1 D2 D3 D4 SATELLITE DIODE R1 SATELLITE DIODE R2 single Foucault astigmatic focus double Foucault MBG422 Fig.21 Detector arrangement. 7.16.3 FOCUS SERVO SYSTEM 7.16.3.1 Focus start-up Five initially loaded coefficients influence the start-up behaviour of the focus controller. The automatically generated triangular voltage can be influenced by 3 parameters; for height (ramp_height) and DC offset (ramp_offset) of the triangle and its steepness (ramp_incr). For protection against false focus point detections two parameters are available which are an absolute level on the CA signal (CA_start) and a level on the FEn signal (FE_start). When this CA level is reached the FOK signal becomes true. If the FOK signal is true and the level on the FEn signal is reached, the focus PID is enabled to switch-on when the next zero crossing is detected in the FEn signal. 7.16.3.2 Focus position control loop The focus control loop contains a digital PID controller which has 5 parameters that are available to the user. These coefficients influence the integrating (foc_int), proportional (foc_lead_length, part of foc_parm3) and differentiating (foc_pole_lead, part of foc_parm1) action of the PID and a digital low-pass filter (foc_pole_noise, part of foc_parm2) following the PID. The fifth coefficient foc_gain influences the loop gain. 7.16.3.3 Dropout detection This detector can be influenced by one parameter (CA_drop). The FOK signal will become false and the integrator of the PID will hold if the CA signal drops below this programmable absolute CA level. When the FOK signal becomes false it is assumed, initially, to be caused by a black dot. 7.16.3.4 Focus loss detection and fast restart Whenever FOK is false for longer than approximately 3 ms, it is assumed that the focus point is lost. A fast restart procedure is initiated which is capable of restarting the focus loop within 200 to 300 ms depending on the programmed coefficients of the microcontroller. |
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