TDA1301 Philips Semiconductors, TDA1301 Datasheet - Page 5

• Manufacturer Part Number: TDA1301
• Description: Digital servo processor DSIC2
• Manufacturer: Philips Semiconductors

Philips Semiconductors
In the event of single Foucault focusing method, the DSIC2
signal conditioning can be switched under software control
so that the signal processing conforms to that given in
equation (4).
The FE
proportional integral and differential filter section (PID).
A focus OK flag (FOK) is generated by means of the
central aperture signal and an adjustable reference level.
This signal is used to provide extra protection for the
Track-Loss (TL) generation, the focus start-up procedure
and the drop-out detection. The radial or tracking error
signal is generated by the satellite detector signals R1 and
R2. The radial error signal (RE) can be formulated as per
equation (5).
Where the index ‘s’ indicates the automatic scaling
operation which is performed on the radial error signal.
This scaling is necessary to avoid non-optimum dynamic
range usage in the digital representation and, also, to
reduce radial bandwidth spread. The radial error signal will
also be released from offset during disc start-up. The four
signals from the central aperture detectors, together with
the satellite detector signals, generate a track position
signal (TPI) which can be formulated as per equation (6).
Where the weighting factor Sum_gain is generated
internally in the DSIC2 during initialization.
Focus control
The following focus servo functions are incorporated in the
DSIC2 digital controller.
F
Five initially loaded coefficients influence the start-up
behaviour of the focus controller. The automatically
generated triangular voltage can be influenced by
3 parameters, for the height (ramp_heigth) and DC-offset
(ramp_offset) of the triangle and its steepness (ramp_inc).
To protect against false focus point detections two
parameters are available. One is an absolute level on the
CA signal (CA_start) and the other is an absolute level on
the FE
March 1994
FE
RE
TPI
OCUS START
Digital servo processor (DSIC2)
n
s
=
=
=
n
n
–
2
sin
signal (FE_start). When the CA_start level is
+
thus obtained is further processed by a
R1 R2
R1
D1 D2
--------------------- -
D1
R1
-
–
D1
UP
+
+
–
+
R2
D2
R2
+
D2
RE_gain
+
Sum_gain
RE_offset
D3
+
D4
(4)
(5)
(6)
6
reached, the FOK signal becomes true. If the FOK signal
is true when the level on the FE
focus PID is enabled and switches on when the next zero
crossing is detected in the FE
F
The focus control loop contains a digital PID controller
which has 5 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 the digital low-pass filter (foc_pole_noise) which
follows the PID. The fifth coefficient (foc_gain) influences
the loop gain.
D
This detector can be influenced by one parameter
(CA_drop). The FOK signal will become false and the
integrator of the PID will hold if the CA signal drops below
the programmed absolute CA level. When the FOK signal
becomes false it is assumed, initially, to be caused by a
black dot.
F
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
programmed coefficients set by the microcontroller.
F
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.
Radial control
The following radial servo functions are incorporated in
the DSIC2 digital controller.
L
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
last part of the turn table motor start-up time period.
EVEL INITIALIZATION
300 ms. This start-up time period may coincide with the
OCUS POSITION CONTROL LOOP
OCUS LOSS DETECTION AND FAST RESTART
OCUS LOOP GAIN SWITCHING
ROP
-
OUT DETECTION
n
signal.
n
signal is reached the
Product specification
TDA1301T