SAA7806H NXP [NXP Semiconductors], SAA7806H Datasheet - Page 48

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

Philips Semiconductors
9397 750 13697
Objective data sheet
Fig 28. Function of servo IRQ signal
SRV_FC0
SRV_FC1
inreq_clr
IRQ
6.7.2 Diode signal processing
6.7.3 Signal conditioning
The photo detector in conventional two-stage three-beam compact disc systems normally
contains six discrete diodes. Four of these diodes (three for single foucault systems) carry
the Central Aperture (CA) signal while the other two diodes (satellite diodes) carry the
radial tracking information. The CA signals are summed into an HF signal for the decoder
function and are also differenced (after analog to digital conversion) to produce the low
frequency focus control signals.
The low frequency content of the six (five if single foucault) photodiode inputs are
converted to PDM bit streams by a multiplexed 6-bit ADC followed by a digital PDM
generation circuit. This supports a range of OPUs in voltage mode mechanisms by having
sixteen selectable gain ranges in two sets, one set for D1 to D4 and the other for R1 and
R2.
The digital codes retrieved from the ADC and PDM generator are applied to logic circuitry
to obtain the various control signals. The signals from the central aperture diodes are
processed to obtain a normalized Focus Error (FE) signal:
Figure
In the case of a single foucault focusing method, the signal conditioning can be switched
under software control such that the signal processing is as follows:
The error signal, FE
filter section.
FE
FE
n
n
=
=
natural duration of
29.
---------------------
2
IRQ cycle time of ~60 s
D1 D2
D1
IRQ (~45 s)
+
---------------------
D1
int #1
–
D1 D2
D2
–
+
–
D2
---------------------
D3
D3 D4
n
, is further processed by a Proportional Integral and Differential (PID)
–
+
Rev. 01 — 20 June 2005
D4
where the detector set-up is assumed to be as shown in
cleared by
inreq_clr
IRQ #2
int #2
pulse
IRQ cycle time of ~60 s
One chip automotive CD audio device
IRQ #3 cleared by
inreq_clr
IRQ cycle time of ~60 s
int #3
pulse
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
SAA7806
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