SAA7806H NXP [NXP Semiconductors], SAA7806H Datasheet - Page 51

• Manufacturer Part Number: SAA7806H
• Description: One chip automotive CD audio device
• Manufacturer: NXP [NXP Semiconductors]

Philips Semiconductors
9397 750 13697
Objective data sheet
6.7.4.3 Dropout detection
6.7.4.4 Focus loss detection and fast restart
6.7.4.5 Focus loop gain switching
6.7.4.6 Focus automatic gain control loop
6.7.5.1 Radial PID - on-track mode
6.7.5 Radial servo system
Table 12:
[1]
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.
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.
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.
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).
When the radial servo is in on-track mode (i.e. 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
Parameter
G
G
1
2
3
4
3
5
E
/
= (
Refer to Table 3 of the HSI specification .
2
1
.
2
/
Focus PID parameters
3
)
Controlled by
-
-
foc_parm1
foc_parm2
foc_parm3
foc_int_strength
foc_gain
end stage gain
Rev. 01 — 20 June 2005
[1]
Comment
focus integrator bandwidth
beginning of focus lead
foc_pole_lead; end of focus lead (differentiating part)
foc_pole_noise; low-pass function following PID
foc_lead_length; lead length (proportional part)
integrator strength
focus loop gain
defined as peak-to-peak voltage swing over focus
actuator
One chip automotive CD audio device
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Figure
SAA7806
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