SAA7806H NXP [NXP Semiconductors], SAA7806H Datasheet - Page 25

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

Philips Semiconductors
9397 750 13697
Objective data sheet
Defect Detector:
white dots in the RF-stream, and to freeze some signal conditioning and bit recovery logic
during these defects. This will prevent the control loops drifting away from their optimal
point of operation whilst there is no RF present, so they can recover quickly when good
RF is present again.
The detection of a defect is based on amplitude. The amplitude is measured via a set of
peak detectors with decay, as described in
programming of the decay bandwidth and noise filter bandwidth is done by register
DefectDetPeakBW.
Two thresholds can be programmed. A low threshold will trigger a ’defect-detected’ signal
as soon as amplitude goes below this threshold. A high threshold will clear this
’defect-detected’ signal again as soon as amplitude goes above this threshold. Together
these thresholds add an hysteresis to the defect detection, which avoids a jittery
’defect-detected’ signal (switching on/off many times) when amplitude is on the edge.
Thresholds are programmed in register DefectDetThres.
The defect-detected signal can be used to hold the PLL, slicer, AGC, AOC and HPF
during a defect. Which feature(s) will be held can be programmed in register
DefectDetEnables. The same register can be used via software to force the PLL, slicer
and HPF into hold mode. The AGC and AOC can be held in software by just disabling the
loops in register AGCAOCControl.
Two special features exist on the defect detector:
The detection of the beginning or end of a defect, with and without start and stop delays,
can be used to generate an interrupt. This is programmed in register InterruptEnable1.
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The offset boundary should be programmed not too tight, 8 is a good value. This is to
avoid a volatile AOC.
The BW of the loops should never be programmed too high (’fast’) with respect to the
peak detector measurement window, to avoid an unstable loop. If the PDwindow = 2
sysclk’s wide, the BW of the loops should never be higher than 2
It is possible to delay the enabling and disabling of hold features at the beginning and
end of a defect. This can be done by programming a start and / or stop delay (in
number of sysclks) via register DefectDetStartStopDelay. Whenever the defect
detector detects the start of a defect, the detector will wait for the start delay before
triggering a defect-detected-processed signal. When the defect detector detects the
end of a defect, the detector will wait for the programmed stop delay before clearing
the defect-detected-processed signal again. This also means that defects which are
smaller than the start delay are ignored and, that if the defect contains zones with
good RF amplitude but smaller than the stop delay, they are ignored as well. In reality
all hold features are triggered by the defect-detected-processed signal, rather than the
defect-detected signal; but after rest of the decoder, both delays are zero, so both
signals are equal.
It is possible to program a time-window after the end of a defect, during which higher
PLL and / or slicer bandwidths can be used (to speed-up the recovery of these loops
after the defect). This window can be programmed via register
DefectDetHighBWDelay, the programming of the bandwidths is explained in
6.6.5.2 “Bit detector” on page
The purpose of the defect detector is to detect the presence of black or
Rev. 01 — 20 June 2005
26.
Section “Peak detectors” on page
One chip automotive CD audio device
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
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