saa7803 NXP Semiconductors, saa7803 Datasheet - Page 54

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

Philips Semiconductors
9397 750 13695
Objective data sheet
6.7.5.5 Access
6.7.5.6 Radial automatic gain control loop
6.7.6 Off-track counting
The access procedure is divided into two different modes (see
the requested jump size.
Table 14:
[1]
The access procedure makes use of a track counting mechanism, a velocity signal based
on a fixed number of tracks passed within a fixed time interval, a velocity set point
calculated from the number of tracks to go and a user programmable parameter indicating
the maximum sledge performance.
If the number of tracks remaining is greater than the brake_distance then the sledge jump
mode should be activated or, the actuator jump should be performed. The requested jump
size together with the required sledge breaking distance at maximum access speed
defines the brake_distance value.
During the actuator jump mode, velocity control with a PI controller is used for the
actuator. The sledge is then continuously controlled using the filtered value of the radial
PID output. All filter parameters (for actuator and sledge) are user programmable.
In the sledge jump mode, maximum power (user programmable) is applied to the sledge
in the correct direction while the actuator becomes idle (the contents of the actuator
integrator leaks to zero just after the sledge jump mode is initiated). The actuator can be
electronically damped during sledge jump. The gain of the damping loop is controlled via
the hold_mult parameter.
The fast track jumping circuitry can be enabled or disabled via the xtra_preset parameter.
The loop gain of the radial control loop can be corrected automatically to eliminate
tolerances in the radial loop. This gain control injects a signal into the loop which is used
to correct the loop gain. Since this decreases the optimum performance, the gain control
should only be activated for a short time (for example, when starting a new disc).
This gain control differs from the level initialization. The level initialization should be
performed first. The disadvantage of using the level initialization without the gain control is
that only tolerances from the front-end are reduced.
The Track Position Indicator (TPI) is a flag which is used to indicate whether the radial
spot is positioned on the track, with a margin of
the Radial Polarity flag (RP) the relative spot position over the tracks can be determined.
These signals can have uncertainties caused by:
Access type
Actuator jump
Sledge jump
•
•
Microprocessor presettable.
Disc defects such as scratches and fingerprints
The HF information on the disc, which is considered as noise by the detector signals.
Access types
Rev. 01 — 19 April 2005
Jump size
brake_distance
brake_distance - 32768
[1]
1
4
of the track-pitch. In combination with
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Access speed
decreasing velocity
maximum power to sledge
One chip CD audio device
Table
14), depending on
SAA7803
54 of 74