SAA7348GP Datasheet, PDF (15/60 Pages) NXP Semiconductors – All Compact Disc Engine ACE

Philips Semiconductors
All Compact Disc Engine (ACE)
Preliminary specification
SAA7348GP
7.3.2 Focus control
The SAA7348 performs the following focus servo function:
• Focus start-up
• Focus position control loop
• Drop-out detection
• Focus loss detection and fast restart
• Focus loop gain switching
• Focus automatic gain control loop.
7.3.3 RADIAL CONTROL
The SAA7348 performs the following radial servo
functions:
• Level initialization
• Radial position control loop
• Sledge control
• Tracking control
• Access with or without track loss information
• Radial automatic gain control loop.
7.3.4 OFF-TRACK COUNTING
The track position signal (TPI) is a flag used to indicate
whether the radial spot is positioned on the track with a
margin of ±0.25 of the track pitch. One of the following
three counting states is selected:
• Protected state
• Slow counting state
• Fast counting state.
7.3.5 OFF-TRACK DETECTION
The Off-Track Detection (OTD) signal flags off-track
conditions; the polarity of this signal is programmable.
7.3.6 SHOCK DETECTION
A shock detector can be switched on during normal track
following. Within an adjustable frequency range, it detects
whether disturbances in the radial spot relative to the track
exceed a programmable level. Every time the Radial
tracking Error (RE) exceeds this level, the radial control
bandwidth is switched to twice its original bandwidth and
the loop gain is increased by a factor of 4.
switched off, applied only to focus control, or applied to
both focus and radial controls under software control.
The actions of the circuit can be monitored on the DEFO
pin (active HIGH).
An external defect detector can be added by removing the
connection between DEFO and DEFI (normal operation)
and inserting the necessary circuitry.
7.3.8 DRIVER INTERFACE
The control signals (pins RA, FO and SL) for the
mechanism actuators are pulse density modulated.
The modulating frequency can be set to either
s----e---r--v---o--8---c---l-o----c---k- _or s----e---r--v---o--4---c---l-o----c---k- _{MHz. An analog representation}
of the output signals can be generated by connecting a first
order low-pass filter to the outputs.
During reset (i.e. RST pin held HIGH) the RA, FO and SL
pins are high impedance.
7.3.9 LASER INTERFACE
The LDON pin (open-drain output) is used to turn the laser
on and off. When the laser is on, the output is high
impedance. The action of the LDON pin is controlled by the
xtra_preset parameter; the pin is automatically driven if the
focus control loop is active.
7.4 Subcode interface
There are two subcode interfaces:
• One which conforms to “EIAJ CP-2401” (using SBSY,
SFSY, RCK and SUB) and can be configured as either
a 3- or 4-wire interface. The interface formats are
illustrated in Fig.6.
• An RS232 like format on SUBQW as illustrated in Fig.7.
The subcode sync word is formed by a pause of ^{2----0n---0--} µs
minimum. Each subcode byte starts with a 1 followed by
7 bits (Q to W). The gap between bytes can vary
between ^{1----1-n--.--3--} and ^9--n--0-- µs. Note that SUBQW is not
valid in lock-to-disc mode (includes QLLV).
The subcode data is also available at the EBU output
(DOBM).
7.3.7 DEFECT DETECTION
A defect detection circuit is incorporated into the
SAA7348. If a defect is detected, the circuit can hold all
radial and focus controls. The defect detector can be
1997 Jul 11
15