SAA7806H NXP [NXP Semiconductors], SAA7806H Datasheet - Page 24

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

Philips Semiconductors
9397 750 13697
Objective data sheet
Together with the noise filter on the peak detector this prevents noise occurring on the RF
which would result in volatile gain regulation. To decrease volatile behavior even further a
hysteresis window with a width of one gain step has been added between the integrator
and G2. The bandwidth of the gain loop will determine how fast it reacts on fingerprints
and scratches, and can be programmed via register AGCIntegBW. It is also possible to
limit the range of G2 by programming a maximum and minimum boundary (in register
AGCGainBound).
AOC control:
order HPF with 3 dB point around 3.6 kHz). The remaining offset (mainly introduced by
the analog frontend itself), can be removed by adding or subtracting a fixed offset in the
analog part. This offset subtraction or addition has a range of 32 steps in each direction,
with approximately 1.4 LSBs per step (referenced to the RF-ADC). This leads to a full
correction range of 42 LSB steps (more then the whole ADC range). This offset
compensation value can be programmed via register OffsetComp, and will be regulated in
hardware as soon as the AOC is turned on.
The AOC will regulate the offset compensation value such that the measured offset stays
within a programmed window (OffsetBound). If offset is above this window,
OFFSETCOMPVALUE will decrease; if it is below, it will increase. If an inversion occurs
on the RF signal between analog and digital, this reaction of the loop can be inverted by
programming OffsetBound(OffsetInv).
These offset changes are not sent to the analog offset subtraction directly, but are
integrated over time. Only if on average an offset increase or decrease is requested, this
will result in a real offset increase or decrease on the analog addition (can also be read
back via register OffsetComp). Together with the noise filter on the peak detector this
prevents noise occurring on the RF which would result in a volatile offset regulation. To
decrease volatile behavior even further a hysteresis window with a width of one offset step
has been added between the integrator an OffsetCompValue. The bandwidth of the offset
loop will determine how fast it reacts on fingerprints and other defects, and can be
programmed via register OffsetIntegBW. It is also possible to limit the range of the
OFFSETCOMPVALUE by programming a maximum and minimum boundary (in register
OffsetCompBoundHi and OffsetCompBoundLo).
AGC and AOC in general and rules of thumb:
loops can be enabled and disabled separately by register AGCAOCControl. This register
also allows the use of a slow AGC and / or AOC loop. In that case the programmed loop
bandwidth is decreased with an extra factor of 128. In this mode the loops will be too slow
to react on defects, but can be used for a slow software-like gain and / or offset regulation
to regulate the average gain and offset over the disc nicely within a specified range.
An important feature is the AGCAOCControl(DISHOLDNOLOCK) bit, which disables
holding of the AGC and AOC loops during defects (triggered by the defect detector, see
Section “Defect
lockups of the loops caused by a small amplitude triggering the defect detector, which in
turn would hold the AGC loop.
As rule of thumb, the following should be taken into account:
The amplitude thresholds should be programmed not too close to each other, to allow at
least 2 gain steps (1.6 dB) to go from lower to higher boundary and vice versa. This is to
avoid a volatile AGC.
Most RF-offset at the ADC input will be removed by the analog HPF (first
Detector”) while the HF-PLL is not in lock. This feature avoids permanent
Rev. 01 — 20 June 2005
One chip automotive CD audio device
The AGC and AOC hardware regulation
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
SAA7806
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