JPH051824Y2 - - Google Patents

Description

[Detailed explanation of the invention] "Industrial field of application" This invention is applicable, for example, to measuring temperature by measuring the resistance value of a resistance temperature detector, or to measuring the DC resistance between the terminals of an IC element. This invention relates to a four-wire resistance measuring device used in various cases.

``Prior Art'' Figure 3 shows a conventional four-wire resistance measuring device. In the figure, 1 indicates the resistor to be measured. This resistor to be measured 1
can be, for example, a side temperature resistor or a resistance between terminals of the IC under test. A resistance measuring device 2 is connected to the resistor 1 to be measured. Between the resistance measuring device 2 and the resistor to be measured 1 are four conductive wires 3A,
Connected by 3B, 3C, and 3D. Constant current source 4 is connected to two of the four conductors 3A to 3D, 3A and 3B.
A constant current I is supplied from the constant current source 4 to the resistor 1 to be measured. One end of the constant current source 4, in this example the connection side of the conductive wire 3B, is connected to the common potential point 5 of the resistance measuring device 2. Therefore, the conductors 3A and 3B are generally called current supply lines. Conductive wires 3C and 3D are called voltage detection wires and switch elements 6A and 6
A common connection is made via B, and connected to the input terminal A of the high input impedance circuit 7. The high input impedance circuit 7 uses an operational amplifier with high input impedance, and is used to create a structure that does not take in current from the constant current source 4 via the voltage detection lines 3C and 3D.

For example, in the subsequent stage of the high input impedance circuit 7,
An AD converter 8 is provided, and the AD converter 8 performs AD conversion on the voltage value given from the high input impedance circuit 7.The AD conversion output is given to the data processor 9, where the data is processed and the temperature is It is used to convert into a value, etc. and display the temperature value. The data processor 9 also has a control function,
By applying the control signals P ₁ and P ₂ shown in FIG. 4A and B to the two switch elements 6A and 6B, these two switch elements 6A and 6B are turned on alternately.
OFF control is performed to apply voltages at one end (point B) and the other end (point C) of the resistor to be measured 1 to the high input impedance circuit 7.

In this way, by adopting a structure in which the voltages at points B and C of the resistor to be measured 1 are applied to the AD converter 8 using the high input impedance circuit 7, the voltage detection line 3
Even if C and 3D become longer, the potential difference between both ends of the resistor 1 to be measured can be accurately measured without being affected by the line resistance.

``Problem that the invention attempts to solve'' By the way, if there is a stray capacitance C at the input terminal A of the high input impedance circuit 7, when the switch element 6B is turned on, the input terminal A is connected to the common input terminal A through the switch element 6B. Connected to potential point 5. Switch 6B-conducting wire 3 formed at this time
D-3B- Since the path of the common potential point 5 has low impedance, the charging/discharging time constant of the stray capacitance C is small. Therefore, almost at the same time as switch 6B turns on, the potential of input terminal A changes to C of resistor 1 to be measured.
It becomes equal to the potential at the point.

On the other hand, when the switch 6A is turned on, the charging/discharging current path for the stray capacitance C becomes a path from the common potential point 5 to the conductor 3B to the resistor to be measured 1 to the conductor 3C to the switch element 6A. In this way, since the resistor 1 to be measured is inserted in series in the charging/discharging path of the stray capacitance C, when the resistance value of the resistor 1 to be measured is large, the charging/discharging time constant for the stray capacitance C becomes large. As shown in Figure 2, it takes time _t1 for the potential at input terminal A to stabilize to the potential at point B.

As a result, the AD converter 8 must perform AD conversion after time _t1 has elapsed and the potential at the input terminal A has stabilized. Therefore, as shown in FIG. 4D in the conventional case, when the switch element 6A is turned on, the AD conversion timing is
It is set after the time t ₁ has elapsed from the time when is turned on.

Since only the time _t1 has to be maintained in this way, the time TA for which the switch 6A is kept on becomes longer. In particular, when the resistance value of the resistor 1 to be measured is high, the waiting time t ₁ becomes a considerably large value. Furthermore, the fourth
In the figure, E indicates the timing of AD conversion output. The AD conversion output _D1 is an AD conversion output when the switch element 6A is turned on. This corresponds to the potential at point B of the resistor 1 to be measured. Also AD conversion output
_D2 is the AD conversion output when the switch element 6B is on. This corresponds to the potential at point C of the resistor 1 to be measured.

"Means for solving the problem" In this invention, a constant current is passed through the resistor under test, and the voltage generated at one end and the other end of the resistor under test is extracted through a high input impedance circuit. In a four-wire resistance measuring device configured to determine the potential difference that occurs between both ends of the resistor to be measured and calculate the resistance value of the resistor to be measured from that potential difference, the voltage on the non-grounded side of the resistor to be measured is increased. The input terminal of the high input impedance circuit is connected to the non-grounded side of the resistor under test via the impedance conversion circuit for a short period of time at the beginning of the timing applied to the input impedance circuit.

(Function) According to the configuration according to this invention, at the beginning of the timing when the non-grounded end of the resistor to be measured is connected to the input terminal of the high input impedance circuit, the input terminal of the high input impedance circuit is connected to the input terminal of the high input impedance circuit via the impedance converter. is connected to the non-grounded terminal of the resistor to be measured, so even if a stray capacitance C exists at the input terminal of the high input impedance circuit, the stray capacitance is rapidly charged through the impedance converter.

As a result, the potential at the input point of the high input impedance circuit rapidly changes to the potential at the point to be measured at the timing when the potential on the non-grounded side of the resistor 1 to be measured is taken in. Therefore, even if the resistance value of the resistor 1 to be measured is high, the AD conversion operation can be performed with a short waiting time.

``Example'' Figure 1 shows an example of this invention. This first
Most of the configuration in the figure is the same as a conventional four-wire resistance measuring device. The feature of this invention is that a series circuit consisting of an impedance converter 11 and a switch element 12 is connected in parallel with the switch element 6A.

The impedance converter 11 uses an impedance conversion circuit with high input impedance and low input impedance by applying feedback to an operational amplifier so that it becomes an amplifier with a gain of "1".

The switch element 12 is controlled to be turned on for a short time at the beginning of the timing when the switch element 6A is turned on, as shown in FIG. 2C.

With this configuration, the switch element 1
At the same time that 2 turns on, the floating capacitance C is charged and discharged through the impedance converter 11, so the potential at point A immediately changes to the potential at point B of resistor 1 to be measured.

Therefore, the timing of AD conversion by the AD converter 8 can be set a short time after the switch element 6A is turned on, that is, immediately after the switch element 12 is turned off, as shown in FIG. 2E. can. In particular, since a charging/discharging current is applied to the stray capacitance C through the impedance converter 11, even if the resistance value of the resistor 1 to be measured is large, the voltage of the stray capacitance C can be changed from point B in a short time without being affected by it. It can be changed to voltage.

"Effect of the invention" As described above, according to this invention, even if the resistance value of the resistor under test 1 is large, the potential of the input terminal A of the high input impedance circuit 7 can be applied almost simultaneously when the switch element 12 is turned on. The potential can be changed to the potential at point B of the non-grounded terminal of the measuring resistor 1.
Therefore, it is not necessary to significantly delay the timing of AD conversion, and the measurement period can be set to a short time. As a result, it is possible to capture measurement data at high speed while following temperatures that are subject to severe changes.

Furthermore, when testing an IC, there is an advantage that the test time can be shortened and the number of test pieces per unit time can be increased.

[Brief explanation of drawings]

Figure 1 is a connection diagram for explaining one embodiment of this invention, Figure 2 is a waveform diagram for explaining the operation of the four-wire resistance measuring device according to this invention, and Figure 3 is a conventional four-wire resistance measuring device. A connection diagram for explaining the resistance measuring device, and FIG. 4 is a waveform diagram for explaining the operation of the conventional four-wire resistance measuring device. 1... Resistor to be measured, 2... Resistance measuring device, 3
A, 3B... Current supply line 3C, 3D... Voltage detection line, 4... Constant current source, 5... Common potential point, 6A,
6B, 12... Switch element, 7... High input impedance circuit, 8... AD converter, 9... Data processor, C... Stray capacitance, 11... Impedance converter, A... High input impedance circuit input terminal, B...non-grounded terminal of the resistor under test,
C... Ground side terminal of the resistor to be measured.

Claims (1)

[Claims for Utility Model Registration] A. A constant current source that applies a constant current to the resistor under test through a pair of current supply lines, one end of which is connected to a common potential point, and B. A voltage generated across the resistor under test. A pair of voltage detection lines for taking in the voltage, C A pair of switch elements for alternately time-sharing the voltage detected by the pair of voltage detection lines and taking it out to the input terminal of the high input impedance circuit, D The above. An AD converter that sequentially AD converts two voltages input into a high input impedance circuit; a data processor that calculates the resistance value of the resistor under test from F, a terminal on the non-ground side of the resistor under test connected between the non-ground terminal of the resistor under test and the common terminal Immediately after the switch element connected to is controlled to be on, the potential of the non-grounded terminal of the resistor under test is changed to the above high level with low impedance through the switch element that is controlled to be on and this switch element. A four-wire resistance measuring device comprising: an impedance conversion circuit that applies to an input terminal of an input impedance circuit;