GE B30 Technical Reference Manual page 52

B30 Patient Monitor
Figure 22
Pulse oximetry measurement section
LED control signals
The D/A converters of the microcontroller on the STP board set the LED intensity adjustment
values for the infrared and red LEDs of the SpO
switches ON (to the adjusted intensity) and OFF the SpO
predetermined sequence.
LED driving circuit
Differential amplifiers measure the LED currents (LED current indication) of the SpO
the shunt resistors placed in the LED current paths. The LED driving voltages (LED voltage
indication) are measured from the driver circuitry. The LED driving circuits also have MOSFET
transistor matrix to enable the use of different probe configurations.
Measured signal preamplification
The preamplifier is a bipolar/single-ended current-to-voltage converter with adjustable gain. A
higher gain is used for measuring thin tissue. The preamplification stage has also ambient light
reduction and a second amplifier stage.
1-38
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Document no 2044677-001
Vin
Pressure
transducer
Vout
Pressure measurement principle
Current
G
measurement
Instrum entation
amplifier
G
Input filter
to A D converter
probe. The microcontroller on the STP board
2
probe LEDs according to the
2
to AD converter
2
probe over