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Section 3: Functional Block and Circuit Analysis
LED. Drive
Input source selection
Input amplifier and synchronous detector
Demodulator filters and amplifiers
Control signals
Analog to digital converter
Support circuits
LED Drive Circuit
The SAT signal development scheme requires lighting the measurement site
using specific light wavelengths. Nellcor sensors have two LED sources,
infrared (IR) and red. These LED sources are an integral part of each Nellcor
oxygen transducer. The LEDs are alternately pulsed on and off by the
oximetry module microprocessor.
The LED drive bias voltages are developed by dual DAC 01 (figure 3-2).
Initially, both DACs in U1 are directed via the DACBUS to develop
approximately 0.5 VDC on respective outputs (pins 4 and 18) coincident with
the period each LED is selected. The microprocessor alternately closes FET
switches U4A and U4B via control lines IRLED* (U4 pin 16) and REDLED*
(U4A, pin 1). The DAC outputs are gated by these signals and output on pin 2
and pin 15 of U4.
'
LED
+4V:
Drive
ov
0.5V- 1818
1 -4V
LED
ov
3
Voltage with
+
1
Pocket Tester
2
USA
Attached
LED
Drive
-
Feedback
FT
jpe
R29
| REDLED ov- LI
5v-
IRLED
ME
ンジ
osv RIR
Bs,
oV-
.
.
ov
4.
ав
v
TP2 with Pocket
Dual
Lt
va
Tester Attached
Ur
161
|
R2
pa
>Y
U4B
3
o
2
1 や
U4A
RED
N-185/040
Figure 3-2:
Oximetry Module LED Driver Circuit
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Table of Contents
Troubleshooting
