JPH11174022A - Blood-glucose level measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a temperature compensation even if a blood-glucose level measuring device has the temperature characteristics of a converting circuit obtained by combining a resistance with an operational amplifier when a current output from a sensor is converted into a voltage. SOLUTION: A current from a sensor 1 is converted into a voltage in proportion to a resistance 4 with a reference voltage generating part 3 taken as a reference. The voltage is converted again to a current by a VI converting part 5. A switch 7 integrates that data and a current output from a current source 6 with respect to an integrating part 8. Because a calculation part 9 calculates the integrated data from the integrating part 8 together with the condition of the switch 7, a blood-glucose level can be known. Then the resistance 4 and a temperature variation rate at the reference voltage generating part 3 are aligned with each other so as to obtain a blood-glucose level measuring device no affected by the temperature variation even if temperature compensation is not performed in a calculation processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blood sugar level measuring apparatus for performing an intermediate conversion to a time interval.

[0002]

2. Description of the Related Art Conventionally, a temperature measuring unit is used as a blood glucose measuring device when a correction is made for a change in measuring conditions with respect to temperature, as in a blood glucose measuring device disclosed in Japanese Patent Application Laid-Open No. 62-83645. It is common to make corrections on the calculation. FIG. 7 shows the configuration diagram.

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

[0004] The operation of the blood sugar level measuring device thus configured will be described. The microcomputer 76 measures the ambient temperature using the temperature measuring unit 73, the multiplexer 74, and the A / D converter 75, and calculates the completion time of the reaction between glucose and the enzyme if the temperature is within the operating temperature range. The result is displayed on the display unit 77 to inform the measurer. When the measurer presses the switch section 78, the microcomputer 76 determines the start of measurement based on the signal of the switch section 78. Then, it subtracts 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.

[0005] By the above-described temperature correction processing, the blood glucose level is measured while eliminating the influence of the temperature change.

[0006]

In this conventional blood sugar level measuring device, when the response current detecting section 72 converts the current output from the sensor 70 into a voltage, the current is usually converted by a circuit combining a resistor and an operational amplifier. However, when this circuit is incorporated in an 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.

[0007] The present invention provides a current-
It is an object of the present invention to provide a blood glucose level measuring device that is not affected by a change in temperature even if a resistor has a temperature characteristic in voltage conversion even if temperature compensation is not performed in arithmetic processing.

[0008]

According to a first aspect of the present invention, there is provided a sensor for outputting a current signal corresponding to a blood glucose level, and an input current from the sensor based on a predetermined reference voltage. An IV converter that converts the voltage output from the IV converter into a current, a VI converter that converts the voltage output by the IV converter into a current, a current source that outputs a constant current, an output current of the VI converter, and the current A switch for switching the current output from the source, an integration unit for integrating the current output from the switch, and a calculation unit for controlling the switch and performing a calculation process, wherein the reference voltage of the IV conversion unit is: It has the same temperature change rate characteristics as the first resistor.

According to a second aspect of the present invention, there is provided a sensor for outputting a current signal corresponding to a blood glucose level, and an input current from the sensor is converted into a voltage proportional to a first resistance based on a predetermined reference voltage. An IV converter, a VI converter having a second resistor for converting a voltage output from the IV converter into a current, a current source outputting a constant current, an output current of the VI converter, and the current A switch for switching the current output from the source, an integration unit for integrating the current output from the switch, and a calculation unit for controlling the switch and performing a calculation process. The second resistor of the VI converter has the same rate of temperature change as the first resistor.

[0010]

FIG. 1 is a block diagram showing a blood sugar level measuring apparatus 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 sugar level to an operational amplifier 2. The operational amplifier 22 is also connected to the output terminal of the reference voltage generator 3 that supplies a voltage that serves as a reference for current-voltage conversion. The feedback resistor 4 is a first resistor serving 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.
The output of the converter is provided to the VI converter 5 and is again proportionally converted to the current. The current source 6 outputs a constant current I1. Switch 7 is VI
The output current of the conversion unit 5 and the current output by the current source 6 are switched. The integrator 8 integrates the current output from the switch 7. The calculation unit 9 determines the switching of the switch 7, calculates the integration data output by the integration unit 8 in consideration of the state of the switch, and outputs the calculation result.
The display unit 10 displays a calculation result output from the calculation unit 9.

The configuration and operation of each part of the blood sugar level measuring device configured as described above will be described in further detail. First, a current to be measured is output from the sensor 1 and converted into a voltage by an IV conversion unit including an operational amplifier 2, a reference voltage generation unit 3, and a resistor 4. The current output from the sensor 1 represents the blood sugar level to be measured, and this current value is expressed as Iin
And Assuming that 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 without variation in the output current value due to the power supply voltage or temperature. Resistance 22 is resistance 4
This is a resistor created under exactly the same conditions. The reference voltage output terminal 23 outputs a voltage generated by the current source 21 and the resistor 22. In 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 is generated under the same conditions as the resistor 4.
Is a voltage having a change rate characteristic equal to the temperature change rate characteristic. 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 according to the temperature characteristics of the resistor 4. When 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 the voltage may be passed through the buffer. In addition, it is easy to form the resistor 22 and the resistor 4 under the same conditions if they are formed 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 unit 5 will be described with reference to FIG. In FIG. 3, a voltage input terminal 3
1, a voltage to be subjected to current conversion is input. The operational amplifier 32 performs a voltage-current conversion operation, and its output is supplied to an NPN transistor 34. The resistor 33 is a second resistor serving as a voltage-current conversion coefficient. The transistor 34 supplies a feedback voltage to the input of the operational amplifier 32 by applying a current to 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 in which the current converted from the input voltage flows and outputs the converted current from the current output terminal 39.

Next, the operation of the VI converter 5 will be described. First, the operational amplifier 32 and the NPN transistor 34 supply a current to the resistor 33 by the voltage input to the voltage input terminal 31. The voltage generated by this is the operational amplifier 3
The input voltage of the NPN transistor 34 is supplied to the input terminal 2 and the voltage of the NPN transistor 34 becomes equal to the voltage input to the voltage input terminal 31 by the voltage feedback to the operational amplifier 32. 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, assuming that 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 is Va / R2. This current is P
The current is output from a current output terminal 39 via a current mirror circuit including NP transistors 35 and 36 and resistors 37 and 38. Here, assuming that 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 expressed by the following equation. Ia = (Iin × R1 + V1) / R2 × M (2)

In FIG. 3, the output current is supplied to a current output terminal 39.
Although the description has been made with reference to the circuit flowing out of the PNP transistor 26, the collector current of the PNP transistor 26 may be configured so as to absorb the output current by adding another mirror circuit. With the above operation, the VI conversion unit 5 converts the input voltage into a current and outputs the current.

Next, the switch 7 selects and outputs the output current Ia of the VI conversion section 5 and the output current I1 of the current source 6 according to an external switching signal. The VI conversion unit 5
The operation of the switch 7 can be realized even if only one of the current source 6 and the current source 6 is operated, and the current output terminal 39 and the output of the current source 6 are short-circuited.

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

The operation of the integrator 8 configured as described above will be described. The current input from the integration current input terminal 41 is integrated by the capacitor 42. Here, the current input from the integration current input terminal 41 is Ib,
Assuming that the capacitance of No. 2 is C and the time interval during which the current is input from the integration current input terminal 41 is ΔT, the voltage change of the capacitor 42 during the time 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.
2 is prevented from decreasing. Incidentally, the integrated voltage output terminal 4
The buffer 43 can be omitted if the input impedance of the circuit connected to the switch 4 is sufficiently high, or if the input current can be neglected to the extent that the bias current has no effect.

Therefore, the voltage change when the current Ia output from the VI converter 5 is integrated is expressed by the following equation from the equation (2). On the other hand, a voltage change when the output current I1 of the current source 6 is integrated is expressed by the following equation from Ib = I1. (I1 × ΔT) / C (4) By the operation described above, the integrator 8 integrates the input current and outputs integrated data.

Next, the operation unit 9 will be described. FIG. 5 shows the configuration of the calculation unit 9. In FIG. 5, an integral data input terminal 51 receives the integral data output from the integrator 8.
52 is a reference voltage source that outputs the 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 a comparison result. The counter 54 measures time based on a predetermined reference clock. The control circuit 55 performs overall control management in the arithmetic processing and outputs count data obtained from the counter 54. The switching signal output from 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 a calculation result from a calculation result output terminal.

The operation of the arithmetic unit 9 configured as described above will be described. First, the integration data output from the integration unit 8 is input to the integration data input terminal 51. By comparing the integration data with the reference voltage source 52 by the comparator 53, the control circuit 55 determines that the voltage of the integration data is low. Whether the voltage is higher or lower than the reference voltage source can be detected. Further, the control circuit 55 can control the switch 7 via the switching signal output terminal 56, and can control the counter 54 and output a time measurement result from the count data of the counter 54.

Here, the relationship between the integration data input from the integration data input terminal 51, the comparison result, the switching signal output by 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 integration data, the comparison result, and the switching signal with respect to time.

In FIG. 6, (a) shows the integration data input to the integration data input terminal 51, (b) shows the comparison result output from the comparator 53, and (c) shows the output from the switching signal output terminal 56. FIG.

As a condition, the voltage value of the reference voltage source 52 is V3, if 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 current output terminal 39 by the VI converter 5 is in the discharge direction, and the current output from the current source 6 is in the sink direction. The direction can be determined by a configuration such as the current mirror circuit shown in FIG. In this case, if the switching signal is L, the voltage increases with time in the integrator 8, and if the switching signal is H,
In the integrator 8, the voltage decreases with time. Further, when the integral data is higher than V3, the comparison result is H
And L in the opposite case. FIG. 6 is a schematic diagram under the above conditions.

First, the switching signal is H until time t0,
It is assumed that the integral 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 higher, 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 the time has reached t2, the control circuit 55 switches the switching signal from L to H. The time measurement of ΔT1 is performed using the counter 54, and the control circuit 55 resets the data of the counter 54 at t1, and measures the time by detecting that the value of the counter 54 reaches the value indicating ΔT1.

Then, the control circuit 55 detects that the integrated data has reached V3 when the comparison result changes from H to L, and measures the time ΔT2 from t2 to t3 with the time at this time as t3. The time measurement of this ΔT2 is also ΔT1
Similarly to the above, the control is performed by controlling the counter 54.

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 of the periods ΔT1 and ΔT2. Therefore, from the relationship between the amount of change in the integral data due to the current output from the VI converter 5 and the amount of change in the integral data due to the current output from the current source 6, the following equation (5) is established.

(Equation 1) Thus, 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 the other values are constants. Therefore, from the time measurement result output from the control circuit 55, the calculation processing circuit 57 calculates Iin using the above equation, converts it into a blood sugar level, and outputs data indicating the blood sugar level from the calculation result output terminal 58.

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

Here, A = I1 × R2 / (M × R1 × Δ
T1), if 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 determined. However, when R1 has a temperature characteristic, it is understood that V1 needs 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 with temperature. Also, R1 is included in the denominator of A,
Since R2 having the same temperature change rate characteristic is multiplied by the numerator, the temperature characteristic of R1 is canceled for A.

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

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

Further, the circuit type in which the current is integrated by the capacitor has been described. However, the same effect can be obtained by using a circuit for performing the integration operation in the same manner and calculating the input current from the change of the integration data with time. It is obvious.

[0034]

As described above, according to the present invention, even when a temperature change occurs, the input current can be calculated by using a reference voltage having the same temperature characteristic as that of the resistor and fixing the calculation formula. Further, highly accurate current measurement that is not affected by temperature changes can be realized without using a temperature measurement circuit or the like, and the configuration of the blood sugar level measurement device can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram in one embodiment of a blood sugar level measuring device of the present invention.

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

FIG. 3 is a circuit diagram illustrating a configuration of a VI conversion unit according to the present embodiment.

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

FIG. 5 is a block diagram illustrating a configuration of a calculation unit according to the present embodiment.

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

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sensor 2 operational amplifier 3 reference voltage generator 4 resistor 5 VI converter 6 current source 7 switch 8 integrator 9 arithmetic unit 10 display unit

Claims (2)

[Claims] A sensor that outputs a current signal corresponding to a blood glucose level; an IV converter that converts an input current from the sensor into a voltage proportional to a first resistance based on a predetermined reference voltage; A VI converter for converting a voltage output from the IV converter to a current, a current source for outputting a constant current, a switch for switching between an output current of the VI converter and a current output from the current source, and the switch And an operation unit for controlling the switch and performing a calculation process. The reference voltage of the IV conversion unit has the same temperature change rate characteristic as that of the first resistor. A blood sugar level measuring device comprising: 2. A sensor that outputs a current signal according to a blood glucose level; an IV converter that converts an input current from the sensor into a voltage proportional to a first resistance based on a predetermined reference voltage; A VI converter having a second resistor for converting a voltage output from the IV converter into a current, a current source for outputting a constant current, and an output current of the VI converter and a current output from the current source. A switching unit, an integration unit that integrates a current output from the switch, and a calculation unit that controls the switch to perform a calculation process, wherein a reference voltage of the IV conversion unit and a second voltage of the VI conversion unit are provided. The blood glucose level measuring device, wherein the resistance has the same rate of temperature change as the first resistance.