saa7803 NXP Semiconductors, saa7803 Datasheet - Page 50

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

Philips Semiconductors
9397 750 13695
Objective data sheet
6.7.4.1 Focus start-up
6.7.4.2 Focus position control loop
6.7.4 Focus servo system
Five initially loaded coefficients influence the start-up behavior 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
When this CA level is reached then focus has been achieved.
When focus is achieved and the level on the FE
enabled to switch on when the next zero crossing is detected in the FE
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.
Figure 30
determine the behavior.
A simplified block diagram of the focus PID system is given in
Fig 30. Bode diagram of focus PID system
Amplitude
foc_gain
(dB)
shows the transfer function of the controller, and the coefficients which
foc_int_strength
5
Rev. 01 — 19 April 2005
I
foc_int
1
P
foc_lead_length
2
D
n
foc_pole_lead
signal is reached, the focus PID is
3
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
foc_pole_noise
One chip CD audio device
Figure
4
n
signal (FE_start).
31.
SAA7803
n
signal.
Frequency
001aab773
(log Hz)
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