Principles of Operation
2-9
2.2.4 SpO
2
Module
2.2.4.1 General
The SpO
2
module provides the function of measuring the Pulse Oxygen Saturation (SpO
2
).
2.2.4.2 Principle diagram
Figure 7 Operation principle of the SpO2 module
2.2.4.3 Principle
The SpO
2
measurement principle:
1. Collecting the light signal of the red light and infrared transmitting through the
finger or toe which is pulsing;
2. Processing the collected signal to get the measured result.
The drive circuit of the LED and the gain of the amplifying circuit should be controlled
according to the different perfusions and transmittances of the tested object.
2.2.4.3.1 Led Drive Circuit
This circuit supplies the LED with the drive current, which can be regulated.
2.2.4.3.2 SPO2 Signal Process Network
The pre-amplifying circuit converts the photoelectric signal to the voltage signal and conducts
the primary amplification.
The gain adjusting and amplifying circuit conducts the secondary signal amplification and
adjusts the gain.
The biasing circuit adjusts the dynamic range of the signal, and sends it to the A/D conversion
part.
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