Specifications

2000 Jun 26 28
Philips Semiconductors Product specification
Digital servo processor and Compact Disc
decoder with integrated DAC for video CD (CD7 II)
SAA7327
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.20 Detector arrangement.
7.14.3 FOCUS SERVO SYSTEM
7.14.3.1 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 FE
n
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 FE
n
signal is
reached, the focus PID is enabled to switch on when the
next zero crossing is detected in the FE
n
signal.
7.14.3.2 Focus position control loop
The focus control loop contains a digital PID controller
which has 5 parameters which 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.
7.14.3.3 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.