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參數(shù)資料
| 型號： | OQ8868 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 模擬信號調(diào)理 |
| 英文描述： | Digital Servo Integrated Circuit Silent DSICS |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PQFP44 |
| 文件頁數(shù)： | 8/20頁 |
| 文件大小： | 106K |
| 代理商： | OQ8868 |
1997 Feb 12
8
Philips Semiconductors
Product specification
Digital Servo Integrated Circuit Silent
(DSICS)
OQ8868
F
OCUS START
-
UP
Five initially-loaded coefficients influence the start-up
behaviour of the focus controller. The automatically
generated triangle voltage can be influenced by three
parameters for the height (ramp_height) and DC-offset
(ramp_offset) of the triangle and its steepness (ramp_inc).
For protection against false focus point detections, two
parameters are available, these being 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 this 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.
F
OCUS POSITION CONTROL LOOP
The focus control loop contains a digital PID controller,
which has five parameters available to the user. These
coefficients influence the integrating (foc_int), proportional
(foc_prop) and differentiating (foc_pole_lead) action of this
PID and a digital low-pass filter (foc_pole_noise) following
the PID. The fifth coefficient (foc_gain) influences the loop
gain.
D
ROPOUT DETECTION
This detector can be influenced by one parameter
(CA_drop). The FOK signal will become false and the PID
integrator will hold if the CA signal drops below this
programmable absolute CA level. When the FOK signal
becomes false, it is assumed initially that this is caused by
a black dot.
F
OCUS LOSS DETECTION AND FAST RESTART
Whenever FOK is false 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 to 300 ms, depending on the
microprocessor-programmed coefficients.
F
OCUS LOOP GAIN SWITCHING
The gain of the focus control loop (foc_gain) can be
multiplied by a factor of 2 or divided by 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 when gain
switching is performed.
F
OCUS 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 that is used
to correct the loop gain. Since this decreases the optimum
performance, the gain control should only be activated
briefly, e.g. when starting a new disc.
Radial control
The DSICS digital controller includes the following radial
servo functions:
1.
Level initialization
2.
Sledge home
3.
Tracking control
4.
Access
5.
Radial automatic gain control loop.
L
EVEL INITIALIZATION
During start-up, an automatic adjustment procedure is
activated, to set the values of the radial error gain
(RE_gain), offset (RE_offset) and satellite sum signal gain
(Sum_gain) for TPI level generation. The initialization
procedure runs in a radial open loop situation and is
≤
300 ms. This start-up time period may coincide with the
last part of the turntable motor start-up time period.
Automatic gain adjustment:
As a result of this
initialization, the amplitude of the RE signal is adjusted
within
±
10% around the nominal RE amplitude.
Offset adjustment:
The additional offset in RE due to the
limited accuracy of the start-up procedure is less than
±
50 nm.
TPI level generation:
The accuracy of the initialization
procedure is such that the duty cycle range of TPI
becomes 0.4 < duty cycle < 0.6. Duty cycle definition:
TPI-HIGH/TPI-period).
S
LEDGE HOME
The sledge moves to a reference position
(end_stop_switch) at the inner side of the disc with
user-defined voltage.
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