JP3494564B2 - Blood glucose meter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blood glucose level measuring device for performing intermediate conversion into time intervals.

[0002]

2. Description of the Related Art Conventionally, as a blood glucose level measuring device, a temperature measuring unit has been used when correcting a change in measurement condition with respect to temperature, as in the blood glucose measuring device disclosed in Japanese Patent Laid-Open No. 62-83645. It is common to make corrections on the basis of calculation. The block diagram is shown in FIG.

In FIG. 7, a sensor 70 is a sensor section for reacting glucose and an enzyme, and a reference electrode 70a, a counter electrode 70b and a response current detecting section 72 connected to a sweeping section 71.
Has a measurement electrode 70c connected to the. The sweep unit 71 applies a sawtooth voltage from these electrodes to sweep, and the response current detection unit 72 detects the response current flowing at this time. The response current and the temperature detected by the temperature detector 73 are given to the microcomputer 76 via the multiplexer 74 and the A / D converter 75. Reference numeral 77 is a display section, and 78 is a switch section for performing these operations.

The operation of the blood sugar level measuring device configured as described above will be described. The microcomputer 76 measures the ambient temperature by the temperature measuring unit 73, the multiplexer 74 and the A / D converter 75, and if the temperature is within the operating temperature range, calculates the reaction completion time of glucose and the enzyme. The result is displayed on the display unit 77 to inform the measurer. When the measurer presses the switch unit 78, the microcomputer 76 determines the measurement start from the signal from the switch unit 78. Then, the time is subtracted from the time displayed on the display unit 77, and after the reaction is completed, the sensor 70, the sweep unit 71, the response current detection unit 72, the multiplexer 74, and the A / D converter 75.
The response current is measured via. The blood glucose level is displayed on the display unit 77 by performing temperature correction on the measured temperature.

By the temperature correction processing as described above, the influence of the temperature change is eliminated and the blood glucose level is measured.

[0006]

In this conventional blood glucose level measuring device, when converting the current output from the sensor 70 in the response current detecting section 72 into a voltage, it is usually converted by a circuit combining a resistor and an operational amplifier. However, when this circuit is built in the IC, the voltage converted by the temperature characteristic of the resistor changes depending on the temperature, and it becomes necessary to perform temperature compensation in the subsequent arithmetic processing.

According to the present invention, a current using such a resistor is
It is an object of the present invention to provide a blood glucose level measuring device that is not affected by temperature changes even if temperature resistance is not present in the calculation process even if the resistance has temperature characteristics in voltage conversion.

[0008]

According to a first aspect of the present invention, a sensor for outputting a current signal according to a blood glucose level and a first resistance for an input current from the sensor with a predetermined reference voltage as a reference. An IV conversion unit for converting the voltage output from the IV conversion unit into a current, a current source for outputting a constant current, an output current of the VI conversion unit and the current A switch for switching the current output by the source, an integrating unit for integrating the current output by the switch, and an arithmetic unit for controlling the switch to perform a calculation process, and the reference voltage of the IV conversion unit is It has the same temperature change rate characteristic as that of the first resistor.

According to a second aspect of the present invention, a sensor that outputs a current signal corresponding to a blood glucose level and an input current from the sensor are converted into a voltage proportional to the first resistance with reference to a predetermined reference voltage. An IV conversion unit, a VI conversion unit having a second resistor for converting a voltage output from the IV conversion unit into a current, a current source outputting a constant current, an output current of the VI conversion unit, and the current A switch for switching the current output by the source, an integrating unit for integrating the current output by the switch, and an arithmetic unit for controlling the switch to perform a calculation process. The reference voltage of the IV conversion unit and the The second resistance of the VI conversion unit has the same temperature change rate as the first resistance.

[0010]

1 is a block diagram showing a blood glucose level measuring device according to an embodiment of the present invention. In FIG. 1, a sensor 1 is the same sensor as the conventional example, and outputs a current corresponding to a blood glucose level to an operational amplifier 2. The operational amplifier 22 is also connected to the output terminal of the reference voltage generator 3 which supplies a voltage serving as a reference for current-voltage conversion. The feedback resistor 4 is a first resistor that serves as a conversion coefficient when the operational amplifier 2 performs current-voltage conversion. The operational amplifier 2, the reference voltage generator 3, and the resistor 4 convert the sensor current into a voltage IV
It constitutes a conversion unit, the output of which is given to the VI conversion unit 5 and is again proportionally converted into a current. The current source 6 outputs a constant current I1. Switch 7 is VI
The output current of the converter 5 and the current output by the current source 6 are switched. The integrator 8 integrates the current output by the switch 7. The calculation unit 9 determines switching of the switch 7, calculates the integration data output from the integration unit 8 while considering the state of the switch, and outputs the calculation result.
The display unit 10 displays the calculation result output by the calculation unit 9.

The configuration and operation of each unit of the blood glucose level measuring device configured as described above will be described in more detail. First, the current to be measured is output from the sensor 1 and converted into a voltage by the IV conversion unit including the operational amplifier 2, the reference voltage generation unit 3, and the resistor 4. The current output by the sensor 1 represents the blood glucose level to be measured, and this current value is Iin
And When the voltage value of the reference voltage generator 3 is V1 and the resistance value of the resistor 4 is R1, the output voltage Va of the operational amplifier 2 is expressed by the following equation (1). Va = Iin × R1 + V1 (1)

Next, the reference voltage generator 3 having the same temperature characteristic as that of the resistor 4 will be described. FIG. 2 shows the configuration of the reference voltage generator 3. In FIG. 2, the reference current source 21 is supplied to the resistor 22 on the assumption that the output current value does not change due to the power supply voltage or the temperature. Resistor 22 is resistor 4
It is a resistor created under exactly the same conditions as. The reference voltage output terminal 23 outputs a voltage generated by the current source 21 and the resistor 22. With the configuration shown in FIG. 2, the voltage output from the reference voltage output terminal 23 is proportional to the resistance value of the resistor 22, and since this is created under the same conditions as the resistor 4, the resistor 4
The voltage has a change rate characteristic equal to the temperature change rate characteristic of. Therefore, by using the voltage output from the reference voltage output terminal 23 for the reference voltage generator 3, the output voltage of the operational amplifier 2 also changes in accordance with the temperature characteristic of the resistor 4. If the input impedance of the circuit connected to the reference voltage output terminal 23 is low, a buffer may be added when the voltage is output to the reference voltage output terminal 23 and passed through this buffer. Further, the resistor 22 and the resistor 4 can be easily produced under the same conditions if they are produced as IC elements. That is, it is very advantageous when a part of the device is formed as an IC circuit.

Next, a specific configuration of the VI conversion section 5 will be described with reference to FIG. In FIG. 3, the voltage input terminal 3
A voltage to be current-converted is input to 1. The operational amplifier 32 performs a voltage-current conversion operation, and its output is given to the NPN transistor 34. The resistor 33 is a second resistor that serves as a coefficient for voltage-current conversion. The transistor 34 supplies a feedback voltage to the input of the operational amplifier 32 by flowing a current into the resistor 33. PN
The P transistors 35 and 36 and the resistors 37 and 38 configure a current mirror circuit that changes the direction of the current converted from the input voltage and outputs the converted current from the current output terminal 39.

Next, the operation of the VI conversion section 5 will be described. First, the operational amplifier 32 and the NPN transistor 34 cause a current to flow into the resistor 33 by the voltage input to the voltage input terminal 31. The voltage generated by this is the operational amplifier 3
By the voltage feedback to the operational amplifier 32, the emitter voltage of the NPN transistor 34 becomes equal to the voltage input to the voltage input terminal 31. That is, the current determined by the voltage of the voltage input terminal 31 and the resistor 33 becomes the emitter current of the NPN transistor 34. Here, when the voltage value input to the voltage input terminal 31 is Va and the resistance value of the resistor 33 is R2, the NPN transistor 3
The emitter current of No. 4 becomes Va / R2. This current is P
The signal is output from the current output terminal 39 via the current mirror circuit composed of the NP transistors 35 and 36 and the resistors 37 and 38. When the mirror coefficient of the current mirror circuit is M, the current value Ia output from the current output terminal 39 is Va / R2 × M. From the equation (1), the current value Ia is shown by the following equation. Ia = (Iin × R1 + V1) / R2 × M (2)

Further, in FIG. 3, the output current is supplied to the current output terminal 39.
Although the circuit has been described in the direction in which the output current flows out of the PNP transistor 36 , the collector current in the PNP transistor 36 can be configured to absorb the output current by adding another mirror circuit. Through the above operation, the VI conversion unit 5 converts the input voltage into a current and outputs it. And a control means.

Next, the switch 7 selects and outputs the output current Ia of the VI converter 5 and the output current I1 of the current source 6 by a switching signal from the outside. The VI conversion unit 5
It is possible to realize the operation of the switch 7 even if only the current output terminal 39 and the output of the current source 6 are short-circuited so that only one of the switch 7 and the current source 6 operates.

Next, FIG. 4 shows the configuration of the integrating section 8. In FIG. 4, the output of the switch 7 is connected to the integrated current input terminal 41. The capacitor 42 integrates the current input from the integrated current input terminal 41. The buffer 43 is the capacitor 42
Is held and is output as integrated data from the integrated voltage output terminal 44.

The operation of the integrating unit 8 configured as above will be described. The current input from the integrated current input terminal 41 is integrated by the capacitor 42. Here, the current input from the integrated current input terminal 41 is Ib, and the capacitor 4
When the capacitance of No. 2 is C and the time interval when the current is input from the integrated current input terminal 41 is ΔT, the voltage change of the capacitor 42 at the time of ΔT is (Ib × ΔT) / C. This voltage is output from the integrated voltage output terminal 44 via the buffer 43. The buffer 43 is connected to the capacitor 4 by the input impedance of the circuit connected to the integrated voltage output terminal 44.
Prevent the 2 charge from decreasing. The integrated voltage output terminal 4
The buffer 43 can be omitted if the input impedance of the circuit connected to 4 is sufficiently high, or if it can be ignored to the extent that the bias current does not affect it.

Therefore, the change in voltage when the current Ia output from the VI conversion section 5 is integrated is expressed by the following expression from the expression (2). On the other hand, the voltage change when the output current I1 of the current source 6 is integrated is shown by the following equation from Ib = I1. (I1 × ΔT) / C (4) With the above operation, the integrating unit 8 integrates the input current and outputs the integrated data.

Next, the calculation unit 9 will be described. FIG. 5 shows the configuration of the calculation unit 9. In FIG. 5, the integrated data input terminal 51 receives the integrated data output from the integrating section 8.
A reference voltage source 52 outputs a voltage V3. The comparator 53 compares the integrated data input from the integrated data input terminal 51 with the voltage of the reference voltage source 52 and outputs the comparison result. The counter 54 measures time based on a predetermined reference clock. The control circuit 55 manages the overall control of the arithmetic processing and outputs the count data obtained from the counter 54. The switching signal output by the control circuit 55 is output to the switch 7 via the switching signal output terminal 56. The calculation processing circuit 57 calculates the count data output from the control circuit 55 and outputs the calculation result from the calculation result output terminal.

The operation of the arithmetic unit 9 configured as described above will be described. First, the integrated data output from the integrator 8 is input to the integrated data input terminal 51. The comparator 53 compares the integrated data with the reference voltage source 52, and the control circuit 55 determines that the voltage of the integrated data is It is possible to detect whether it is higher or lower than the reference voltage source. Further, the control circuit 55 can control the switch 7 via the switching signal output terminal 56, and can output the time measurement result from the control of the counter 54 and the count data of the counter 54.

Here, the relationship between the integrated data input from the integrated data input terminal 51, the comparison result thereof, the switching signal output from the control circuit 55, and the count data counted by the counter 54 will be described. FIG. 6 is a schematic diagram showing the relationship between the integrated data, the comparison result, and the switching signal with respect to time.

In FIG. 6, (a) is the integrated data input to the integrated data input terminal 51, (b) is the comparison result output by the comparator 53, and (c) is the output from the switching signal output terminal 56. The switching signal is shown.

As a condition, if the voltage value of the reference voltage source 52 is V3 and the switching signal is H, the switch 7 outputs the output current I1 of the reference current source 6, and if the switching signal is L,
The switch 7 outputs the output current Ia of the VI conversion unit 5. Further, the current output from the VI converter 5 from the current output terminal 39 is in the discharge direction, and the current output from the current source 6 is in the suction direction. The direction can be determined by the configuration of the current mirror circuit shown in FIG. In this case, if the switching signal is L, the voltage increases in the integrating unit 8 with the passage of time, and if the switching signal is H,
In the integrator 8, the voltage decreases with the passage of time. Furthermore, when the integrated data is higher than V3, the comparison result is H
And vice versa. FIG. 6 is a schematic diagram under the above conditions.

First, the switching signal is H until time t0,
It is assumed that the integrated data is lower than V3.
At this time, the comparison result is L. At time t0, when the switching signal becomes L, the integrated data becomes high, and at t1 when V3 is reached, the comparison result changes from L to H. Then, when a predetermined time ΔT1 has elapsed from t1 and reaches t2, the control circuit 55 switches the switching signal from L to H. This time measurement of ΔT1 is performed by using the counter 54, and the control circuit 55 resets the data of the counter 54 at t1 and detects that the value of the counter 54 reaches the value indicating ΔT1 to perform the time measurement.

Then, the control circuit 55 detects that the integrated data has reached V3 when the comparison result changes from H to L, and the time at this time is set to t3, and the time ΔT2 from t2 to t3 is measured. This time measurement of ΔT2 is also ΔT1
Similarly to the above, the counter 54 is controlled.

As described above, the control circuit 55 determines the time measurement result (ΔT2 in FIG. 6). Then, the time measurement result is output to the calculation processing circuit 57.

Next, the operation of the calculation processing circuit 57 will be described. Here, as is apparent from FIG. 6, the absolute value of the voltage change of the integrated data is the same in each period of ΔT1 and ΔT2. Therefore, the following equation (5) is established from the relationship between the amount of change in the integrated data due to the current output by the VI conversion unit 5 and the amount of change in the integrated data due to the current output by the current source 6.

[Equation 1] From this, when the current input from the sensor 1 to the operational amplifier 2 is obtained, the following equation (6) is established.

[Equation 2] In this equation, ΔT2 is a value measured by the counter 54, and is otherwise constant. Therefore, from the time measurement result output by the control circuit 55, the calculation processing circuit 57 calculates Iin using the above equation, converts it into a blood glucose level, and then outputs data indicating the blood glucose level from the calculation result output terminal 58.

The display unit 10 displays the calculation result output terminal 58.
By displaying the data indicating the blood sugar level output from
You can know your blood sugar level.

Here, A = I1 × R2 / (M × R1 × Δ
T1) and B = -V1 / R1, Iin = A × ΔT
2 + B, and Iin is represented by a linear expression of ΔT2.
If A and B are fixed values, ΔT2 to Ii
n can be obtained. However, when R1 has a temperature characteristic, it can be seen that V1 needs to have the same temperature change rate characteristic as R1 in order to keep B at a constant value. This can be realized by using the reference voltage 3 shown in FIG. 2, and the calculation formula B can be fixed even if the resistance value of R1 varies depending on the temperature. The denominator of A also contains R1,
Since the numerator is multiplied by R2 having the same temperature change rate characteristic, the temperature characteristic of R1 for A is canceled.

If the reference voltage is constant irrespective of the temperature, it is necessary to give temperature compensation to B. Therefore, a circuit for measuring the temperature is required, and further, the temperature characteristic of the resistor is calculated. If included in the formula, the formula may become complicated or the calculation accuracy may deteriorate. According to the present invention, since a circuit for measuring temperature is not necessary and the calculation formula is constant, it is possible to obtain a highly accurate measurement result with a simple circuit configuration.

The direction in which the currents output from the VI conversion section 5 and the current source 6 flow can be realized by other than the above embodiment. The arithmetic unit 9 can be easily realized by using a general-purpose microcomputer.

Further, although the circuit form in which the current is integrated by the capacitor has been described, the same effect can be obtained by using the circuit which performs the integration operation in the same manner and calculates the input current from the change of the integrated data with time. It's obvious.

[0034]

As described above, according to the present invention, the input current can be calculated with a fixed calculation formula by using the reference voltage having the same temperature characteristic as the resistance even if the temperature changes. Further, it is possible to realize highly accurate current measurement that is not affected by temperature changes without using a temperature measurement circuit or the like, and it is possible to simplify the configuration of the blood glucose level measuring device.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a blood glucose level measuring device of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a reference voltage generator in the present embodiment.

FIG. 3 is a circuit diagram showing a configuration of a VI conversion unit in the present embodiment.

FIG. 4 is a circuit diagram showing a configuration of an integrating unit in the present embodiment.

FIG. 5 is a block diagram showing a configuration of a calculation unit in the present embodiment.

FIG. 6 is a schematic diagram for explaining an operation of a calculation unit in the present embodiment.

FIG. 7 is a block diagram showing a configuration of a conventional blood glucose level measuring device.

[Explanation of symbols]

1 sensor 2 operational amplifier 3 Reference voltage generator 4 resistance 5 VI converter 6 current source 7 switch 8 integrator 9 Operation part 10 Display

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 27/26-27/49

Claims (2)

(57) [Claims] 1. A sensor that outputs a current signal according to a blood glucose level, an IV conversion unit that converts an input current from the sensor into a voltage proportional to a first resistance with a predetermined reference voltage as a reference, A VI conversion unit that converts the voltage output from the IV conversion unit into a current, a current source that outputs a constant current, a switch that switches between the output current of the VI conversion unit and the current output by the current source, and the switch. And an operation unit that controls the switch and performs a calculation process, and the reference voltage of the IV conversion unit has the same temperature change rate characteristic as that of the first resistor. A blood glucose level measuring device having. 2. A sensor that outputs a current signal according to a blood glucose level, an IV conversion unit that converts an input current from the sensor into a voltage proportional to a first resistance with a predetermined reference voltage as a reference, A VI conversion unit having a second resistor that converts a voltage output from the IV conversion unit into a current, a current source that outputs a constant current, an output current of the VI conversion unit, and a current output from the current source. A switch for switching, an integrator that integrates the current output by the switch, and an arithmetic unit that controls the switch to perform a calculation process. The reference voltage of the IV converter and the second converter of the VI converter are provided. The resistance has the same rate of temperature change as the first resistance, and the blood glucose level measuring device is characterized.