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SAF784X_2
NXP B.V. 2008. All rights reserved.
Product data sheet
Rev. 02 — 9 May 2008
55 of 93
NXP Semiconductors
SAF784x
One chip CD audio device with integrated MP3/WMA decoder
6.6.4.3
Dropout detection
This detector can be influenced by one parameter (CA_drop). Focus will be lost and the
integrator of the PID will hold if the CA signal drops below this programmable absolute
CA level. When focus is lost it is assumed, initially, to be caused by a black dot.
6.6.4.4
Focus loss detection and fast restart
Whenever focus is lost 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 ms to 300 ms depending on the programmed coefficients of the
microcontroller.
6.6.4.5
Focus loop gain switching
The gain of the focus control loop (foc_gain) can be multiplied by a factor of 2 or divided
by a factor of 2 during normal operation. The integrator value of the PID is corrected
accordingly. The differentiating (foc_pole_lead) action of the PID can be switched at the
same time as the gain switching is performed.
6.6.4.6
Focus automatic gain control loop
The loop gain of the focus control loop can be corrected automatically to eliminate
tolerances in the focus loop. This gain control injects a signal into the loop which is used to
correct the loop gain. Since this decreases the optimum performance, the gain control
should only be activated for a short time (for example, when starting a new disc).
6.6.5
Radial servo system
6.6.5.1
Radial PID - on-track mode
When the radial servo is in On-track mode (normal play mode), a PID controller is active
for the fast actuator, while the sledge is steered using either a PI or pulsed-mode system.
A simplified diagram of the radial PID system is given in
Figure 32
.
An explanation of the different radial PID parameters are given in
Table 13
. The system
frequency response is given in
Figure 33
.
Fig 32. Block diagram of radial PID system
001aag343
j
ω
/
ω
3
1 + j
ω
/
ω
3
ω
4
scaled
radial error
satellite 1
satellite 2
internal
sledge error signal
external
I
P
G
radial
actuator
G
E
D
zero on
defect
or drop out
1 / j
ω
ω
1
ω
2
/
ω
3
NORMALIZER