Medical Applications User Guide (pdf) - Freescale Semiconductor
Medical Applications User Guide (pdf) - Freescale Semiconductor
Medical Applications User Guide (pdf) - Freescale Semiconductor
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6.2<br />
Test Strip<br />
A test strip consists of an electrode with<br />
chemical elements where a blood sample is<br />
deposited. The elements present in the strip<br />
generate a reaction and an electric current is<br />
sent to a transimpedance amplifier that converts<br />
the current into voltage. The output voltage is<br />
proportional to the input current, following the<br />
equation of the transimpedance amplifier.<br />
The transimpedance amplifier embedded on<br />
the Kinetis MK50 and the Flexis MM MCUs<br />
(S08MM and MCF51MM) allows the user to<br />
acquire the current generated by the glucose’s<br />
chemical reaction to the enzyme. The external<br />
components are used to configure the desired<br />
gain value of the amplifier. The transimpedance<br />
module is called TRIAMPV1 and it is managed<br />
through the values of the TIAMPCO register.<br />
The TIAMPEN bit of this register enables the<br />
transimpedance module and the LPEN bit<br />
enables low-power mode (LPEN = 1) and<br />
high-speed mode (LPEN = 0). Low-power<br />
mode is commonly used for battery-dependent<br />
systems, but it compromises the response<br />
speed of the system.<br />
The TRIOUT pin of this module must be<br />
connected with an external resistor (gain<br />
resistor) to the VINN pin, which is the inverting<br />
input of the operational amplifier. The VINP pin<br />
must be connected to ground.<br />
A general block diagram of the test strip is<br />
shown in Figure 6-4.<br />
The basic sensor for a glucometer is an enzymatic<br />
strip. These are based on the detection of<br />
hydrogen peroxide formed in the course of<br />
enzyme-catalyzed oxidation of glucose.<br />
Glucose GOD gluconolactone hydrogen<br />
peroxide<br />
C6H12O6 → C6H10O6 + H2O2<br />
These strips are amperometric sensors that<br />
use a three-electrode design. This approach<br />
is useful when using amperometric sensors<br />
because of the reliability of measuring voltage<br />
and current in the same chemical reaction.<br />
The three-electrode model uses a working<br />
electrode (WE), reference electrode (RE) and<br />
counter electrode (CE).<br />
Home Portable <strong>Medical</strong><br />
Figure 6-1: Blood Glucose Monitor (BGM) General Block Diagram<br />
Blood Glucose Monitor (BGM)<br />
Wireless<br />
Comm<br />
Keypad<br />
MCU/MPU<br />
DAC<br />
ADC<br />
opAmp<br />
Power<br />
Management<br />
<strong>Freescale</strong> Technology Optional<br />
Figure Figure 6-2: 6-2: Equivalent Equivalent Circuit Circuit with with Rv Equal Rv Equal to Blood to Blood Conductivity Conductivity<br />
Figure 6-3: Basic Transimpedance Amplifier<br />
Figure 6-3: Basic Transimpedance Amplifier<br />
freescale .com/medical 35<br />
Vi<br />
li<br />
R<br />
R V<br />
Vo =-li x Rf<br />
R2<br />
U1<br />
Display<br />
Test Strip<br />
Vo=Vi Rv<br />
R+Rv<br />
Figure 6-4: Test Strip Basic Block Diagram Using Flexis MM<br />
Figure 6-4: Test Strip Basic Block Diagram Using Flexis MM<br />
Blood<br />
Sample<br />
Reactive<br />
Electrode<br />
External<br />
Components<br />
Vo<br />
Vo<br />
Embedded<br />
Transimpedance<br />
Amplifier<br />
MCU/MPU<br />
PWM<br />
Embedded<br />
ADC
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