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.1999 Jun 17 27 Philips Semiconductors Product specificationDigital servo processor and Compact DiscSAA7325decoder with integrated DAC (CD10)handbook, full pagewidthSATELLITE SATELLITE SATELLITEDIODE R1 DIODE R1 DIODE R1D1D1 D2 D1D2D3D3D2 D4 D3D4SATELLITE SATELLITE SATELLITEDIODE R2 DIODE R2 DIODE R2single Foucault astigmatic focus double FoucaultMBG422Fig.20 Detector arrangement.7.14.3 FOCUS SERVO SYSTEM 7.14.3.2 Focus position control loopThe focus control loop contains a digital PID controller7.14.3.1 Focus start-upwhich has 5 parameters which are available to the user.Five initially loaded coefficients influence the start-upThese coefficients influence the integrating (foc_int),behaviour of the focus controller.The automaticallyproportional (foc_lead_length, part of foc_parm3) andgenerated triangle voltage can be influenced bydifferentiating (foc_pole_lead, part of foc_parm1) action of3 parameters; for height (ramp_height) and DC offsetthe PID and a digital low-pass filter (foc_pole_noise, part(ramp_offset) of the triangle and its steepnessof foc_parm2) following the PID.The fifth coefficient(ramp_incr).foc_gain influences the loop gain.For protection against false focus point detections twoparameters are available which are an absolute level on 7.14.3.3 Dropout detectionthe CA-signal (CA_start) and a level on the FEn signalThis detector can be influenced by one parameter(FE_start).When this CA level is reached the FOK signal(CA_drop).The FOK signal will become false and thebecomes true.integrator of the PID will hold if the CA signal drops belowIf the FOK signal is true and the level on the FEn signal is this programmable absolute CA level.When the FOKreached, the focus PID is enabled to switch on when the signal becomes false it is assumed, initially, to be causednext zero crossing is detected in the FEn signal.by a black dot.1999 Jun 17 28 Philips Semiconductors Product specificationDigital servo processor and Compact DiscSAA7325decoder with integrated DAC (CD10)7.14.3.4 Focus loss detection and fast restart 7.14.4.3 Tracking controlWhenever FOK is false for longer than approximately The actuator is controlled using a PID loop filter with user3 ms, it is assumed that the focus point is lost.A fast defined coefficients and gain.For stable operationrestart procedure is initiated which is capable of restarting between the tracks, the S-curve is extended over 0.75 ofthe focus loop within 200 to 300 ms depending on the the track.On request from the microcontroller, S-curveprogrammed coefficients of the microcontroller.extension over 2.25 tracks is used, automatically changingto access control when exceeding those 2.25 tracks.7.14.3.5 Focus loop gain switchingBoth modes of S-curve extension make use of atrack-count mechanism.In this mode, track countingThe gain of the focus control loop (foc_gain) can beresults in an automatic return-to-zero track , to avoidmultiplied by a factor of 2 or divided by a factor of 2 duringmajor music rhythm disturbances in the audio output fornormal operation.The integrator value of the PID isimproved shock resistance.The sledge is continuouslycorrected accordingly.The differentiating (foc_pole_lead)controlled, or provided with step pulses to reduce poweraction of the PID can be switched at the same time as theconsumption using the filtered value of the radial PIDgain switching is performed.output.Alternatively, the microcontroller can read theaverage voltage on the radial actuator and provide the7.14.3.6 Focus automatic gain control loopsledge with step pulses to reduce power consumption.The loop gain of the focus control loop can be correctedFilter coefficients of the continuous sledge control can beautomatically to eliminate tolerances in the focus loop.preset by the user.This gain control injects a signal into the loop which is usedto correct the loop gain.Since this decreases the optimum7.14.4.4 Accessperformance, the gain control should only be activated forThe access procedure is divided into two different modesa short time (for example, when starting a new disc).(see Table 13), depending on the requested jump size.7.14.4 RADIAL SERVO SYSTEMTable 13 Access modes7.14.4.1 Level initializationACCESS ACCESSDuring start-up an automatic adjustment procedure is JUMP SIZE(1)TYPE SPEEDactivated to set the values of the radial error gain (re_gain),Actuator jump 1 - brake_distance decreasingoffset (re_offset) and satellite sum gain (sum_gain) for TPIvelocitylevel generation.The initialization procedure runs in aradial open loop situation and is d"300 ms.This start-upSledge jump brake_distance - 32768 maximumtime period may coincide with the last part of the motorpower tostart-up time period:sledge(1)" Automatic gain adjustment: as a result of thisNoteinitialization the amplitude of the RE signal is adjusted to1.Microcontroller presettable.within ±10% around the nominal RE amplitude" Offset adjustment: the additional offset in RE due to theThe access procedure makes use of a track countinglimited accuracy of the start-up procedure is less thanmechanism, a velocity signal based on a fixed number of±50 nmtracks passed within a fixed time interval, a velocity set" TPI level generation: the accuracy of the initializationpoint calculated from the number of tracks to go and a userprocedure is such that the duty factor range of TPIprogrammable parameter indicating the maximum sledgebecomes 0.4 [ Pobierz caÅ‚ość w formacie PDF ]
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.1999 Jun 17 27 Philips Semiconductors Product specificationDigital servo processor and Compact DiscSAA7325decoder with integrated DAC (CD10)handbook, full pagewidthSATELLITE SATELLITE SATELLITEDIODE R1 DIODE R1 DIODE R1D1D1 D2 D1D2D3D3D2 D4 D3D4SATELLITE SATELLITE SATELLITEDIODE R2 DIODE R2 DIODE R2single Foucault astigmatic focus double FoucaultMBG422Fig.20 Detector arrangement.7.14.3 FOCUS SERVO SYSTEM 7.14.3.2 Focus position control loopThe focus control loop contains a digital PID controller7.14.3.1 Focus start-upwhich has 5 parameters which are available to the user.Five initially loaded coefficients influence the start-upThese coefficients influence the integrating (foc_int),behaviour of the focus controller.The automaticallyproportional (foc_lead_length, part of foc_parm3) andgenerated triangle voltage can be influenced bydifferentiating (foc_pole_lead, part of foc_parm1) action of3 parameters; for height (ramp_height) and DC offsetthe PID and a digital low-pass filter (foc_pole_noise, part(ramp_offset) of the triangle and its steepnessof foc_parm2) following the PID.The fifth coefficient(ramp_incr).foc_gain influences the loop gain.For protection against false focus point detections twoparameters are available which are an absolute level on 7.14.3.3 Dropout detectionthe CA-signal (CA_start) and a level on the FEn signalThis detector can be influenced by one parameter(FE_start).When this CA level is reached the FOK signal(CA_drop).The FOK signal will become false and thebecomes true.integrator of the PID will hold if the CA signal drops belowIf the FOK signal is true and the level on the FEn signal is this programmable absolute CA level.When the FOKreached, the focus PID is enabled to switch on when the signal becomes false it is assumed, initially, to be causednext zero crossing is detected in the FEn signal.by a black dot.1999 Jun 17 28 Philips Semiconductors Product specificationDigital servo processor and Compact DiscSAA7325decoder with integrated DAC (CD10)7.14.3.4 Focus loss detection and fast restart 7.14.4.3 Tracking controlWhenever FOK is false for longer than approximately The actuator is controlled using a PID loop filter with user3 ms, it is assumed that the focus point is lost.A fast defined coefficients and gain.For stable operationrestart procedure is initiated which is capable of restarting between the tracks, the S-curve is extended over 0.75 ofthe focus loop within 200 to 300 ms depending on the the track.On request from the microcontroller, S-curveprogrammed coefficients of the microcontroller.extension over 2.25 tracks is used, automatically changingto access control when exceeding those 2.25 tracks.7.14.3.5 Focus loop gain switchingBoth modes of S-curve extension make use of atrack-count mechanism.In this mode, track countingThe gain of the focus control loop (foc_gain) can beresults in an automatic return-to-zero track , to avoidmultiplied by a factor of 2 or divided by a factor of 2 duringmajor music rhythm disturbances in the audio output fornormal operation.The integrator value of the PID isimproved shock resistance.The sledge is continuouslycorrected accordingly.The differentiating (foc_pole_lead)controlled, or provided with step pulses to reduce poweraction of the PID can be switched at the same time as theconsumption using the filtered value of the radial PIDgain switching is performed.output.Alternatively, the microcontroller can read theaverage voltage on the radial actuator and provide the7.14.3.6 Focus automatic gain control loopsledge with step pulses to reduce power consumption.The loop gain of the focus control loop can be correctedFilter coefficients of the continuous sledge control can beautomatically to eliminate tolerances in the focus loop.preset by the user.This gain control injects a signal into the loop which is usedto correct the loop gain.Since this decreases the optimum7.14.4.4 Accessperformance, the gain control should only be activated forThe access procedure is divided into two different modesa short time (for example, when starting a new disc).(see Table 13), depending on the requested jump size.7.14.4 RADIAL SERVO SYSTEMTable 13 Access modes7.14.4.1 Level initializationACCESS ACCESSDuring start-up an automatic adjustment procedure is JUMP SIZE(1)TYPE SPEEDactivated to set the values of the radial error gain (re_gain),Actuator jump 1 - brake_distance decreasingoffset (re_offset) and satellite sum gain (sum_gain) for TPIvelocitylevel generation.The initialization procedure runs in aradial open loop situation and is d"300 ms.This start-upSledge jump brake_distance - 32768 maximumtime period may coincide with the last part of the motorpower tostart-up time period:sledge(1)" Automatic gain adjustment: as a result of thisNoteinitialization the amplitude of the RE signal is adjusted to1.Microcontroller presettable.within ±10% around the nominal RE amplitude" Offset adjustment: the additional offset in RE due to theThe access procedure makes use of a track countinglimited accuracy of the start-up procedure is less thanmechanism, a velocity signal based on a fixed number of±50 nmtracks passed within a fixed time interval, a velocity set" TPI level generation: the accuracy of the initializationpoint calculated from the number of tracks to go and a userprocedure is such that the duty factor range of TPIprogrammable parameter indicating the maximum sledgebecomes 0.4 [ Pobierz caÅ‚ość w formacie PDF ]