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S3.3.1 Sensor Output/LED Control
The relationship between these subsections is shown in the LCD PCB block
diagram, Figure S3-3.
To/from CPU PCB
Raw +10 Vdc
Raw -5 Vdc
V ref
Printer
LED signal
LCD clock
LCD data
LCD enable
LCD light enable
Beeper drive
Analog sensor
signal
Analog circuit
control signals
Figure S3-3: LCD PCB Block Diagram
The SpO
analog circuitry provides control of the red and IR LEDs such that
2
the received signals are within the dynamic range of the input amplifier.
Because excessive current to the LEDs will induce changes in their spectral
output, it is sometimes necessary to increase the received signal channel
gain. To that point, the CPU controls both the current to the LEDs and the
amplification in the signal channel.
Technical Supplement
+10Vdc
Power
conditioning
-5 Vdc
LCD
driver
Red
channel
IR
channel
LED
drive
To/from patient sensor
LED drive
RSENS
Photodiode
Printer
IR LED
LCD
LCD
backlight
Beeper
Sensor
D-connector
S-13
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