SAA7806H NXP [NXP Semiconductors], SAA7806H Datasheet - Page 54

• Manufacturer Part Number: SAA7806H
• Description: One chip automotive CD audio device
• Manufacturer: NXP [NXP Semiconductors]

Philips Semiconductors
9397 750 13697
Objective data sheet
6.7.5.6 Radial automatic gain control loop
6.7.6 Off-track counting
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:
In order to determine the spot position with sufficient accuracy, extra conditions are
necessary to generate a Track Loss signal (TL) and an off-track counter value. These
extra conditions influence the maximum speed and this implies that, internally, one of the
following three counting states is selected:
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Disc defects such as scratches and fingerprints
The HF information on the disc, which is considered as noise by the detector signals.
Protected state; used in normal play situations; a good protection against false
detection caused by disc defects is important in this state
Slow counting state; used in low velocity track jump situations; in this state a fast
response is important rather than the protection against disc defects (if the phase
relationship between TL and RP of
direction cannot be determined accurately)
Fast counting state; used in high velocity track jump situations; highest obtainable
velocity is the most important feature in this state.
Rev. 01 — 20 June 2005
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radians is affected too much, then the
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One chip automotive CD audio device
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of the track-pitch. In combination with
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
SAA7806
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