saa7803 NXP Semiconductors, saa7803 Datasheet - Page 48

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

Philips Semiconductors
9397 750 13695
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
From a system perspective, the simplest configuration provides an LF path that is
equivalent to the hardware servo (DSICS) of the other audio devices such as SAA7826,
which uses the onboard hardware servo controller logic. However, an alternative setup will
provide additional fine DC-offset compensation (in addition to the coarse compensation
already found in the analog ADCs) and the potential for full software servo control via the
ARM microprocessor.
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
FE
n
=
natural duration of
20.
---------------------
IRQ cycle time of ~60 s
D1 D2
D1
IRQ (~45 s)
+
int #1
–
D2
–
---------------------
D3
D3 D4
–
+
Rev. 01 — 19 April 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
IRQ #3 cleared by
inreq_clr
IRQ cycle time of ~60 s
int #3
pulse
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
One chip CD audio device
SAA7803
001aab772
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