JPH08146050A - Measuring instrument using differential amplifier - Google Patents

Abstract

PURPOSE: To use a differential amplifier which operates with a single power supply in a measuring instrument using the differential amplifier. CONSTITUTION: The measuring instrument is provided with first and second amplifiers 4 and 5 which operate with a single power supply and amplify an input voltage according to the same amplification rate and a differential amplifier 6 which operates with a single power supply and outputs a voltage corresponding to the differential value of the output values of the first and second amplifiers 4 and 5 to measure a measurement value indicated by the input voltage according to the output voltage of the differential amplifier 6. And also, it is provided with a voltage source for applying a reference voltage to either one of the input terminals of the differential amplifier 6, where the reference voltage sets the output voltage of the differential amplifier 6 to non-zero value. Further, it is provided with a means 9 for storing the output voltage value of the differential amplifier 6 when the input voltage is equal and a means 10 for calculating the differential value between the storage value and the output voltage value of the differential amplifier 6 to measure a measurement value indicated by the input voltage according to the calculation value of the calculation means 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device using a differential amplifier for measuring a physical quantity using a differential amplifier,
In particular, it relates to a measuring device using a differential amplifier that enables the use of a differential amplifier that operates with a single power supply.

In a measuring device for measuring a physical quantity, a circuit may be constructed using a differential amplifier. Since the differential amplifier used at this time and the two amplifiers at the previous stage connected to it generate an offset voltage, a structure is constructed to realize a highly accurate measurement process without being affected by the offset voltage. Need to go.

[0003]

2. Description of the Related Art A differential amplifier operating with a + power supply cannot output a negative output voltage. On the contrary, −
The differential amplifier operated by the power supply cannot output the + side output voltage. That is, the differential amplifier that operates with a single power supply does not have the offset voltage zero adjustment function.

Against this background, as a differential amplifier incorporated in a measuring device, a differential amplifier using both the + and-power supplies as voltage sources is usually used. That is, the differential amplifier incorporated in the measuring device is usually required to output both the + side voltage and the − side voltage, which is why the differential amplifier using both the + power source and the − power source as voltage sources. Is used. Even when only the voltage on one side is required to be output, if the differential amplifier operating with one power supply is used, the original output voltage may enter the opposite side due to the generation of the offset voltage. However, it cannot output it.

[0005]

However, if a differential amplifier operating with a single power supply is used, the power supply device to be prepared becomes simple and the cost is low. Therefore, in a device such as a portable electronic device, a single power supply is used. There is a strong demand for using a differential amplifier that operates in.

However, according to the prior art,
When it is required to output both the + side voltage and the − side voltage, it is not possible to use a differential amplifier that operates with one power supply. Further, even when it is required to output only the voltage on one side, if the influence of the offset voltage cannot be ignored, the differential amplifier operating with one power source cannot be used.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a measuring apparatus using a new differential amplifier that enables the use of a differential amplifier operating with one power source.

[0008]

FIG. 1 shows the principle configuration of the present invention. In the figure, reference numeral 1 denotes a measuring device equipped with the present invention, which detects a physical quantity by detecting a voltage value according to a physical quantity of a measurement target and a voltage value detected by the detection circuit 2. And a computing mechanism 3 for specifying.

The detection circuit 2 includes a first amplifier 4, a second amplifier 5 and a differential amplifier 6. The first amplifier 4 operates with a single power supply and amplifies the first input voltage detected from the physical quantity to be measured. The second amplifier 5 is
It operates with a single power supply and amplifies the second input voltage detected from the physical quantity to be measured with the same amplification factor as that of the first amplifier 4. The differential amplifier 6 operates with a single power supply,
The output of the first and second amplifiers 4 and 5 is input, and a voltage corresponding to the difference value between the inputs is output. To realize the present invention, either one of the two input terminals is output. A configuration including a voltage source 7 for adding a reference voltage is adopted.

On the other hand, the arithmetic mechanism 3 comprises a reading means 8, a storage means 9, a calculating means 10 and a converting means 11.
The reading means 8 reads the voltage value detected by the detection circuit 2. The storage unit 9 stores the detected voltage value of the detection circuit 2 when the first and second input voltages have the same value. The calculation means 10 calculates the difference value between the stored value of the storage means 9 and the detected voltage value of the detection circuit 2. The conversion unit 11 specifies the physical quantity from the calculated value of the calculation unit 10.

[0011]

In the present invention, when the difference value between the first input voltage and the second input voltage may be positive or negative, the reference voltage generated by the voltage source 7 becomes the first and second reference voltages. The output voltage of the differential amplifier 6 is set to a non-zero value within the input range of the input voltage. According to this configuration, the differential amplifier 6 operates so as to always output a non-zero value voltage even if it operates with a single power supply.

In response to the detection processing of the detection circuit 2, the reading means 8 is, for example, prior to the start of measurement, the first and second reading means 8.
The output voltage value of the differential amplifier 6 when the input voltages are equal to each other is stored in the storage means 9, and when the measurement is started, the output voltage value of the differential amplifier 6 is output to the calculation means 10.

Then, when the calculating means 10 receives the output voltage value of the differential amplifier 6 from the reading means 8, the calculating means 10 calculates the difference value between the stored value of the storing means 9 and the received output voltage value of the differential amplifier 6. Then, in response to this, the conversion unit 11 specifies the physical quantity from the calculated value of the calculation unit 10.

In the present invention, the first input voltage and the second input voltage
Output voltage of the differential amplifier 6 when the reference voltage generated by the voltage source 7 has the same value as the first and second input voltages. Is set to zero value. According to this configuration, the differential amplifier 6 operates so as to always output an accurate voltage by having a function of adjusting the offset voltage even if it operates with one power supply.

In response to the detection processing of the detection circuit 2, the reading means 8 outputs the output voltage value of the differential amplifier 6 to the converting means 11 when the measurement is started, and in response to this, the converting means 11 receives the output voltage value. Specifies the physical quantity from the received output voltage value.

In this way, according to the measuring apparatus 1 of the present invention, when it is required to output both the + side voltage and the − side voltage to the differential amplifier 6 according to the physical quantity to be measured. Also, it becomes possible to use a differential amplifier 6 that operates with a single power supply. Even when it is required to output either the + side voltage or the − side voltage to the differential amplifier 6 and the magnitude of the offset voltage cannot be ignored, the differential Amplifier 6
It is possible to use a device that operates with a single power source.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to an embodiment applied to a process for detecting a battery remaining amount of a portable electronic device.

FIG. 2 illustrates an example of the device configuration of the portable electronic device 20. As shown in this figure, a portable electronic device 20 includes a display 21, a data processing circuit 22 that executes specified data processing, a rechargeable battery 23 that supplies power to the data processing circuit 22, and an AC adapter. Two
4, the charging circuit 25 for charging the battery 23, the charging / discharging current detecting circuit 26 for detecting a voltage value corresponding to the charging / discharging current of the battery 23, and the charging / discharging current detecting circuit 2
A / D converter 27 for converting the voltage value detected by 6 from analog to digital, and a program,
A battery remaining amount detection mechanism 28 that detects the remaining amount of the battery 23 from the output value of the A / D converter 27; a first switch 29 that controls the opening and closing of the power supply path between the charging circuit 25 and the battery 23;
A second switch 30 for controlling opening / closing of a power supply path between the data processing circuit 22 and the battery 23 is provided.

FIG. 3 shows an embodiment of the charge / discharge current detection circuit 26 constructed according to the present invention. As shown in this figure, the charge / discharge current detection circuit 26 includes a resistor R1 for detecting the charge / discharge current of the battery 23, and a resistor R2 connected in series between the end of the resistor R1 on the battery 23 side and the ground. And R4 and the charging circuit 25 of the resistor R1 (data processing circuit 2
2) A resistor R connected in series between the side end and the ground
3 and R5, a first operational amplifier 40 for detecting the potential of the resistor R1 on the side of the battery 23, and a second operational amplifier 40 for detecting the potential of the resistor R1 on the side of the charging circuit 25 (data processing circuit 22). And the differential amplifier 42 that outputs the difference value between the output voltage value of the first operational amplifier 40 and the output voltage value of the second operational amplifier 41.

The first operational amplifier 40 operates with the + power supply, inputs the voltage divided by the resistors R2 and R3 to the + terminal, and the − terminal of the second operational amplifier 41 via the resistor R6. A feedback resistor R8 is provided between the output terminal and the-terminal while being connected to the-terminal. In addition, the second operational amplifier 41 operates with a + power supply, inputs the voltage divided by the resistors R3 and R5 to the + terminal, and the-terminal of the first operational amplifier 40 via the resistor R6. And a feedback resistor R7 is provided between the output terminal and the-terminal.

According to this structure, if the potential of the end of the resistor R1 on the side of the battery 23 is represented by V1, + of the first operational amplifier 40 is obtained.
The terminal has

[0022]

[Equation 1]

The voltage represented by is input, and upon receipt of this input, the first operational amplifier 40 is

[0024]

[Equation 2]

The voltage value represented by is output. If the potential of the resistor R1 on the charging circuit 25 (data processing circuit 22) side is represented by V2, the positive terminal of the second operational amplifier 41 has

[0026]

(Equation 3)

The voltage represented by is input, and upon receipt of this input, the second operational amplifier 41 is

[0028]

[Equation 4]

The voltage value represented by is output. here,
"R2 = R3, R4 = R5, R7 = R8" is assumed. On the other hand, the differential amplifier 42 operates with the + power supply, inputs the output voltage of the first operational amplifier 40 to the + terminal via the resistor R10, and outputs the output voltage of the second operational amplifier 41 via the resistor R9. Is input to the − terminal, a feedback resistor R11 is provided between the output terminal and the − terminal, and the + terminal and the ground are connected via the resistor R12 and the voltage source 43 connected in series. Here, the resistors R9, R10, R
Since 11 and R12 have the same impedance, the differential amplifier 42 constitutes an existing voltage follower circuit.

The voltage source 43 connected to the + terminal of the differential amplifier 42 is characteristic of the present invention, and the reason for providing it is as follows. That is, the charging circuit 25
Is provided, a charging current in addition to the discharging current flows through the resistor R1, and when the discharging current flows, “V1> V
The relational expression “2” is established, and conversely, when the charging current flows, the relational expression “V1 <V2” is established. Therefore, the differential amplifier 42, when the discharge current flows through the resistor R1,
Since the voltage value input to the + terminal is larger than the voltage value input to the − terminal, the voltage value on the + side is output, and when the charging current flows through the resistor R1, it is input to the − terminal. Since the voltage value is larger than the voltage value input to the + terminal, the negative voltage value is output. From this, it is impossible to use the differential amplifier 42 operating with the + power supply as it is.

Therefore, in the present invention, the voltage source 43 is connected to the + terminal of the differential amplifier 42 so that the differential amplifier 42 has a voltage of, for example, 4 V even when no current flows through the resistor R1. By adopting a configuration in which both a discharge current and a charge current can be measured by outputting a large + voltage and swinging the output voltage with reference to that.

Further, when the charging circuit 25 is not provided, only the discharge current flows through the resistor R1. Therefore, the relational expression "V1>V2" is always established. Therefore, the differential amplifier 42 is always in the + side. Since it is required to output the voltage value of, it is possible to use the differential amplifier 42 operating with the + power supply. However, the impedance of the resistor R1 becomes a very small value in order to suppress the power loss, and from this, the offset voltage of the first operational amplifier 40 and the second operational amplifier 41 (about ± 10 m in a general-purpose IC).
The influence of (about V) cannot be ignored. For example, −
When an offset voltage of 10 mV exists, the first operational amplifier 40, the second operational amplifier 41, and the differential amplifier 4
If the amplification factor determined by the input resistance of 2 is 20 times, the differential amplifier 42 must output a voltage of −200 mV, but if the differential amplifier 42 operating with the + power supply is used, This value is suppressed to 0V.
Therefore, when the voltage output from the differential amplifier 42 has a small value due to the small impedance of the resistor R1, the discharge current cannot be accurately measured.

Therefore, in the present invention, the voltage source 43 is connected to the + terminal of the differential amplifier 42 so that the differential amplifier 42 outputs 0 V when no current flows through the resistor R1. By doing so, the discharge current can be accurately measured even if the differential amplifier 42 operating with the + power supply is used. To explain with the above example, +2
The voltage source 43 that outputs a voltage of 00 mV is connected to the differential amplifier 42.
It will be connected to the + terminal of.

FIG. 4 shows an embodiment of a processing flow executed by the battery remaining amount detecting mechanism 28. Next, this processing flow will be described. Here, this processing flow is executed when the charging circuit 25 is provided, and therefore, in the voltage source 43, even when the current does not flow in the resistor R1, the differential amplifier 42 sets the differential amplifier 42 to, for example, 4V. It is controlled to output such a large + voltage.

When the user instructs to turn on the power, the remaining battery level detecting mechanism 28, as shown in the processing flow of FIG.
First, in step 1, the output voltage output from the charge / discharge current detection circuit 26 is read. At this time, the first and second
Since the switches 29 and 30 are off, no current flows through the resistor R1 of the charging / discharging current detection circuit 26. Therefore, the output voltage read at this time is given by the voltage source 43. For convenience of explanation, the read output voltage is set to 4V.

Then, in step 2, the read output voltage of 4 V is written in a prescribed memory area. continue,
In step 3, the first switch 29 that controls the opening and closing of the power supply path between the charging circuit 25 and the battery 23 is turned on to set the battery 23 in the chargeable state. Subsequently, in step 4, the second switch 30 that controls the opening and closing of the power supply path between the data processing circuit 22 and the battery 23 is turned on, thereby setting the battery 23 in the dischargeable state.

When the processing of step 4 is completed, the data processing circuit 22 can be supplied with power from the battery 23, so that the execution of data processing is started. When the AC adapter 24 is attached, regardless of whether the second switch 30 is ON or OFF, A
Since power can be supplied from the C adapter 24, it is possible to immediately start execution of data processing.

In accordance with the start of operation of the data processing circuit 22, a charging current or a discharging current starts to flow through the resistor R1 of the charging / discharging current detecting circuit 26, so that the battery remaining amount detecting mechanism 28 subsequently determines in step 5 the prescribed value. The output voltage output from the charge / discharge current detection circuit 26 is read in accordance with the cycle. As shown in FIG. 5, the output voltage read at this time has a voltage value of 4 V or more centering around 4 V when the discharge current flows through the resistor R1 and 4 V when the charging current flows through the resistor R1.
The following voltage values will be shown.

Subsequently, in step 6, 4V stored in the specified memory area is read, a difference value between the voltage read in step 5 and the read 4V is obtained, and the charge / discharge current detection circuit 26 is amplified. By taking the rate into consideration and dividing by the resistance value of the resistor R1, the magnitude of the current flowing through the resistor R1 and whether it is the charging current or the discharging current are obtained.

Subsequently, in step 7, the charge / discharge current obtained in step 6 is added / subtracted to / from the integrated value obtained in the previous cycle, whereby the remaining amount of the battery 23 (here, "current × time" is left). The method for obtaining the quantity is used) and the data processing circuit 22 is notified of it. Here, upon receiving this notification, the data processing circuit 22 performs processing to display an alarm on the display 21 as necessary. Then, in the following step 8, it is determined whether or not the user has instructed to turn off the power. When it is determined that the instruction has been issued, the entire process is ended, and when it is determined that the instruction has not been issued, the process returns to step 5. .

In this way, the charge / discharge current of the battery 23 can be detected even when the differential amplifier 42 operating with the + power supply is used, so that the remaining amount of the battery 23 can be detected. .

In the processing flow of FIG. 4, it is assumed that both the charging current and the discharging current flow through the resistor R1 of the charging / discharging current detection circuit 26, but when only the discharging current flows, the voltage source 43 causes the resistor R1 to flow. A configuration is adopted in which the differential amplifier 42 is controlled so as to output 0 V when no current is flowing in. With this configuration, the battery remaining amount detection mechanism 28
Can read the output voltage of the charging / discharging current detection circuit 26 without being affected by the offset voltage, and then directly obtain the discharging current. When only the charging current flows, the divided voltage of the resistors R3 and R5 is input to the + terminal of the first operational amplifier 40, and the resistor R2 is input to the + terminal of the second operational amplifier 41.
Similarly, by inputting the divided voltage of the resistor R4, it is possible to obtain the same.

On the other hand, according to the conventional technique,
Both the charging current and the discharging current of the battery 23 cannot be detected by using the differential amplifier 42 operating with the + power supply. Further, as shown in FIG. 6, when only the discharge current flows through the resistor R1, the output voltage of the differential amplifier 42 is always on the + side. Therefore, the discharge current is changed by using the differential amplifier 42 operating with the + power supply. There is a possibility that it can be measured, but its accuracy is not good because it is affected by the offset voltage. Further, when detecting the charging current, as shown in FIG. 7, the voltage input to the first operational amplifier 40 and the second operational amplifier 4 are input.
There is also a problem that the voltage input to 1 must be exchanged.

[0044]

As described above, according to the measuring apparatus of the present invention, both the + side voltage and the-side voltage are output to the differential amplifier constituting the detection circuit according to the physical quantity to be measured. Even when required, it is possible to use a differential amplifier that operates with a single power supply. Then, there are times when it is required to output either the + side voltage or the − side voltage to the differential amplifier,
Even when the magnitude of the offset voltage cannot be ignored, a differential amplifier that operates with a single power supply can be used.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is an example of a device configuration of a portable electronic device.

FIG. 3 is an example of a charge / discharge current detection circuit.

FIG. 4 is an example of a processing flow executed by a battery remaining amount detection mechanism.

FIG. 5 is an explanatory diagram of an output voltage of a charge / discharge current detection circuit.

FIG. 6 is an explanatory diagram of a conventional technique.

FIG. 7 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measuring device 2 Detection circuit 3 Arithmetic mechanism 4 1st amplifier 5 2nd amplifier 6 Differential amplifier 7 Voltage source 8 Reading means 9 Storage means 10 Calculation means 11 Conversion means

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Tsutomu Suzui 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (2)

[Claims] 1. A first amplifier which operates with a single power supply and amplifies a first input voltage, and a second amplifier which operates with a single power supply and has the same amplification factor as that of the first amplifier. And a second amplifier for amplifying the input voltage of the
And a differential amplifier that outputs a voltage according to a difference value of the input, and measures a measured value indicated by the first and second input voltages according to the output voltage of the differential amplifier. In a measuring device using a differential amplifier having the configuration, a configuration is provided in which a voltage source that adds a reference voltage to one of the two input terminals of the differential amplifier is adopted, and the reference voltage generated by this voltage source is A measuring apparatus using a differential amplifier, characterized in that the differential amplifier is configured to set the output voltage to a zero value when the first and second input voltages have the same value. 2. A first amplifier which operates with a single power supply and amplifies a first input voltage, and a second amplifier which operates with a single power supply and has the same amplification factor as that of the first amplifier. And a second amplifier for amplifying the input voltage of the
And a differential amplifier that outputs a voltage according to a difference value of the input, and measures a measured value indicated by the first and second input voltages according to the output voltage of the differential amplifier. In a measuring device using a differential amplifier having the configuration, a configuration is provided in which a voltage source that adds a reference voltage to one of the two input terminals of the differential amplifier is adopted, and the reference voltage generated by this voltage source is When the output voltage of the differential amplifier is set to a non-zero value within the input range of the first and second input voltages, and when the first and second input voltages have the same value, The storage device stores the output voltage value of the differential amplifier, the storage device stores the storage voltage stored in the storage unit, and the calculation unit that calculates the difference value between the output voltage value of the differential amplifier. According to the first and second A measuring device using a differential amplifier, characterized in that it is arranged to measure the measured value of the input voltage.