SAA7824 Datasheet, PDF(31/89 Page) NXP Semiconductors – CD audio decoder, digital servo and filterless DAC with integrated pre-amp and laser control (PhonIC)

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SAA7824 Datasheet, PDF (31/89 Pages) NXP Semiconductors – CD audio decoder, digital servo and filterless DAC with integrated pre-amp and laser control (PhonIC)

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Philips Semiconductors

CD audio decoder, digital servo and ï¬lterless

DAC with integrated pre-amp and laser control

Product speciï¬cation

SAA7824

handbook, full pagewidth

SATELLITE

DIODE R1

SATELLITE

DIODE R2

single Foucault

SATELLITE

DIODE R1

D2 D1

D4 D3

SATELLITE

DIODE R2

astigmatic focus

SATELLITE

DIODE R1

SATELLITE

DIODE R2

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.

2003 Oct 01

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