saa7803 NXP Semiconductors, saa7803 Datasheet - Page 51

• Manufacturer Part Number: saa7803
• Description: Saa7803 One Chip Cd Audio Device
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 13695
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
By using a zero error signal, the actuator position can be held. This action is taken if a
defect or shock is encountered. The PID is followed by a low-pass filter to reduce audible
noise in the control loop.
The desired frequencies for the loop (
Full tables are given in the Hardware Software Interface (HSI) specification . An
explanation of the parameters in these diagrams is given in
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
microprocessor.
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.
Parameter
G
G
Fig 31. Functional diagram of focus PID system
1
2
3
4
3
5
focus error,
FE
zero on
defect
or shock
E
/
= (
n
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
P
I
D
Rev. 01 — 19 April 2005
1/j
[1]
1 j /
1
j /
1
3
3
to
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
4
) are used to calculate the coefficient values.
2
/
3
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Table
One chip CD audio device
4
12.
SAA7803
G
68 FO
G
E
001aab774
actuator
51 of 74
focus