JP4097447B2 - Test circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a test circuit for measuring the electrical characteristics of a two-terminal pair circuit, and is suitable for application to, for example, a test circuit for a transmission line or a subscriber line.
[0002]
[Prior art]
Prior art documents: Oikawa et al., “New Simple Media Testing Method Using Subscriber Circuit”, IEICE Transactions BI Vol. J80-BI No. 4 pp. 161-168 April 1997
In order for telecommunications carriers to provide communication services, it is necessary to test the status of transmission lines, subscriber lines and terminal devices connected to them in order to isolate problems at the time of failure and to confirm normality. It is.
[0003]
The prior art document shows a test circuit for this purpose.
[0004]
What should be tested includes external voltage, insulation resistance, and capacitance between wires (time constant). As shown in FIG. 4, FIG. 8, and FIG. The test circuit was configured with resistors and switches, and the voltage was monitored for testing. The test object is a circuit having two terminals, and measures the characteristics of an electric circuit formed between the two terminals and between each terminal and the ground. The final purpose is to determine a normal state or an abnormal state from a measurement result by providing a certain reference value.
[0005]
(1) External voltage
Measure the voltage generated at the two terminals of the object under test with reference to the ground. There are a DC voltage and an AC voltage. In the case of an AC voltage, there is also voltage generation due to capacitive coupling. An abnormal condition is determined when the voltage is above a certain reference voltage.
[0006]
(2) Insulation resistance
The resistance between the two terminals of the object to be tested and between each terminal and the ground is measured. Each is determined to be in an abnormal state when it is below a certain reference resistance (for example, several hundred kilohms).
[0007]
(3) Line capacitance (time constant)
The presence or absence of capacitance between the two terminals of the test object and the time constant formed by the capacitance and resistance are measured. A line disconnection abnormality is determined, or the type of a device such as a terminal connected to the line is determined.
[0008]
[Problems to be solved by the invention]
In the circuit of the prior art document, the same voltage as the power source of the test circuit may be applied to the test object. For example, in FIGS. 8 and 11 of the prior art document, when the resistance between the two terminal pairs of the test object is large (for example, 1 megaohm), the voltage almost the same as the power supply of the test circuit is 2 of the test object. Applied between terminal pair.
[0009]
Depending on the operating voltage of the object under test, there is a risk that the object under test may malfunction or start up when the same voltage as the power supply of the test circuit is applied. Power consumption becomes large.
[0010]
Therefore, there is a demand for a test circuit that can prevent malfunction and erroneous start of an object to be tested and reduce power consumption during testing.
[0011]
[Means for Solving the Problems]
  A first aspect of the present invention is a test circuit for testing electrical characteristics of a circuit under test of a two-terminal pair connected to a first terminal and a second terminal. (1) A third terminal and a fourth terminal A first voltage detection circuit for measuring a potential difference between the first terminal and (2) between the third terminal and the first terminal.A first switch provided in theBetween the fourth terminal and the second terminalAnd a second switch provided onAn inter-terminal connection control means; (3) a first resistor connected between the first power source and the third terminal; and a second power source and the fourth terminal. A second resistor, a first current source connected to the fourth terminal, and a second current source connected to the third terminal.,The potential difference between the third terminal and the fourth terminal is smaller than the potential difference between the first power supply and the second power supply to the test circuit.DesiredAnd a potential difference setting means for variably setting the value, (4)The potential difference setting means includes the first and second terminals in a state where the inter-terminal connection control means blocks the first terminal and the second terminal from the third terminal and the fourth terminal. The current value of the second current source is set to the first initial value IA1, the detection voltage VIA1 by the first voltage detection circuit at that time is taken in, and the current values of the first and second current sources are set to the second value The initial value IA2 is set, and the detected voltage VIA2 by the first voltage detection circuit at that time is taken in, and the current values IA of the first and second current sources in the first type test are determined according to the equation (A). To set the desired value V34 in the first type of test, (5)Between the third terminal and the fourth terminal set by the potential difference setting meansDesired value V34Applying a potential difference to the first terminal and the second terminal via the inter-terminal connection control means, the circuit under testRun the first type of test onIt is characterized by doing.
    IA = (VIA1-V34) × (IA2-IA1)
          / (VIA1-VIA2) + IA1                    ... (A)
[0012]
  A second aspect of the present invention is a test circuit for testing electrical characteristics of a circuit under test of a two-terminal pair connected to a first terminal and a second terminal. (1) A third terminal and a fourth terminal A first voltage detection circuit that measures a potential difference between the first terminal and the second terminal side, and the third terminal and the fourth terminal side. Inter-terminal connection control means that can be cut off, (3) a second resistor connected between the second power source and the fourth terminal, and a first current source connected to the fourth terminal (4) The inter-terminal connection control means disconnects the first terminal and the second terminal from the third terminal and the fourth terminal.,The potential of the third terminal is changed to the potential of the first power supply to the test circuit.In this state, the current value of the first current source is set to one initial value I11, the detection voltage VI11 by the first voltage detection circuit at that time is taken in, and the current value of the first current source is Is taken as the other initial value I12, and the detected voltage VI12 by the first voltage detection circuit at that time is taken in, the current value I1 of the first current source at the time of the test is determined according to the equation (C), (5) The potential difference setting means sets the current value of the first current source to the current value I1, thereby setting the potential of the fourth terminal to the third terminal having the same potential as the potential of the first power source. Is set to a potential difference VT4 that is smaller than the potential difference between the first power supply and the second power supply to the test circuit, and the fourth terminal is connected to the first or second terminal by the inter-terminal connection control means. Connected to terminal 2 and tested Characterized by testing the road.
    I1 = (VI11−VT4) × (I12−I11)
          / (VI11-VI12) + I11                    ... (C)
[0014]
DETAILED DESCRIPTION OF THE INVENTION
(A) First embodiment
Hereinafter, a first embodiment of a test circuit according to the present invention will be described with reference to the drawings.
[0015]
(A-1) Configuration of the first embodiment
FIG. 1 is a circuit diagram showing a configuration of a test circuit 1A according to the first embodiment, in which a circuit under test (object to be tested) is omitted.
[0016]
In FIG. 1, a circuit under test (not shown) is connected to the test circuit 1A via terminals T1 and T2. The pair of terminals T1 and T2 are connected to, for example, a subscriber line that is a circuit under test.
[0017]
For example, the power sources V1 (FIG. 1 shows that the voltage V1 is zero) and V2 defined by a direct current power source DC or the like supply a test operation power source to the test circuit 1A of the first embodiment. Supply a constant voltage to the qi. In the following description, it is assumed that the power supply V1 has a higher potential than the other power supply V2.
[0018]
The voltage detection circuit VDET1 is provided for measuring the voltage between the two terminal pairs of the circuit under test, and is connected between the terminals T3 and T4. The voltage detection circuit VDET1 has a very high impedance and is preferably considered to be infinite. As such a voltage detection circuit VDET1, an existing one such as one constituted by an operational amplifier and a resistor or one constituted by a current mirror circuit and a resistor can be applied.
[0019]
A resistor R1 is connected between one power supply V1 and the terminal T3, and a resistor R2 is connected between the other power supply V2 and the terminal T4.
[0020]
A control current source I1 is connected between one power source V1 and the terminal T4, and a control current source I2 is connected between the terminal T3 and the other power source V2. Each of the control current sources I1 and I2 is a variable constant current source, and can control a constant current to flow from the outside. As such control current sources (constant current sources) I1 and I2, those configured using bipolar transistors or FETs can be applied.
[0021]
Further, a switch SW1 is connected in series between the terminal T1 and the terminal T3, and a switch SW2 is connected in series between the terminal T2 and the terminal T4. As these switches SW1 and SW2, any of a mechanical switch, an electromagnetic relay, a transistor switch, a MOS switch, a photocoupler, a thyristor switch, and the like can be applied.
[0022]
(A-2) Operation of the first embodiment
Next, the operation of the test circuit 1A according to the first embodiment shown in FIG. 1 will be described.
[0023]
Assuming that the impedance of the voltage detection circuit VDET1 is infinite, the potential difference V34 between the terminals T3 and T4 when the two switches SW1 and SW2 are off can be expressed by the following equation (1).
[0024]
V34 = (V1−R1 × I2) − (V2 + R2 × I1) (1)
Here, for the sake of simplicity, when the resistance values of the resistors R1 and R2 are equal, R1 = R2 = RA, the current values of the control current sources I1 and I2 are equal, and I1 = I2 = IA, (1) From the equation, the potential difference V34 between the terminals T3 and T4 can be expressed by equation (2).
[0025]
V34 = (V1-V2) -2 * RA * IA (2)
From this equation (2), it can be seen that the potential difference V34 between the terminals T3 and T4 can be controlled by controlling the current IA. Then, by turning on the switches SW1 and SW2, the controlled voltage V34 can be applied to the terminals T1 and T2 connected to the circuit under test.
[0026]
For example, if the circuit under test has a resistance component between the terminals T1 and T2, a current flows between the terminals T1 and T2 via the circuit under test, the detection voltage of the voltage detection circuit VDET1 becomes low, and the circuit under test Can be measured.
[0027]
It can be seen from the equation (2) that the potential difference V34 between the terminals T3 and T4 can also be controlled by controlling the resistance value RA, and the potential difference V34 is controlled by controlling the resistance value RA. May be. Further, it can be seen from the equation (2) that the potential difference V34 between the terminals T3 and T4 can also be controlled by controlling the resistance value RA and the control current value IA, and the resistance value RA and the control current value IA are controlled. Thus, the potential difference V34 may be controlled.
[0028]
In the first embodiment, the control current IA is controlled for ease of external control.
[0029]
Here, even if the power supply voltage (V1-V2) and the resistance value RA change due to temperature, secular change, manufacturing variation, etc., the both ends of the voltage detection circuit VDET1 are controlled by the calibration procedure as shown in FIG. The potential difference V34 between the terminals T3 and T4 can be set accurately.
[0030]
Procedure P1: Both switches SW1 and SW2 are turned off, and the circuit under test side is disconnected.
[0031]
Procedure P2: The first initial value IA1 is passed through the control current sources I1 and I2 as the control current IA, and the voltage VIA1 of the voltage detection circuit VDET1 at that time is measured.
[0032]
Procedure P3: The second initial value IA2 is passed as the control current IA to the control current sources I1 and I2, and the voltage VIA2 of the voltage detection circuit VDET1 at that time is measured.
[0033]
Procedure P4: A control current value IA for setting the potential difference between the terminals T3 and T4 to a desired value V34 is obtained by the following equation (3), and the control current IA is supplied to the control current sources I1 and I2.
[0034]
IA = (VIA1-V34) × (IA2-IA1)
/ (VIA1-VIA2) + IA1 (3)
Procedure P5: The set potential difference V34 is applied to the circuit under test by turning on the switches SW1 and SW2.
[0035]
The calculation of the above equation (3) is based on the fact that the currents of the current sources I1 and I2 and the potential difference between the terminals T3 and T4, that is, the detection value of the voltage detection circuit VDET1 can be regarded as linear (interpolation or Extrapolation).
[0036]
For the control current, three or more initial values are changed, the measured value of the voltage detection circuit VDET1 is obtained, the regression line or regression curve is obtained, and the potential difference between the terminals T3 and T4 is set to the desired value V34. The control current value IA may be determined.
[0037]
In the above description, the impedance of the voltage detection circuit VDET1 has been described as being infinite. However, the same procedure can be executed even when the voltage detection circuit VDET1 has a finite impedance, and the above expression (3) can be applied as it is.
[0038]
Further, in the above description, the resistance values of the resistors R1 and R2 are equal and the control currents of the control current sources I1 and I2 are equal. However, they may be different. For example, only the current of one control current source I1 or I2 may be controlled to set the desired potential difference V34 between the terminals T3 and T4.
[0039]
Hereinafter, a specific example of setting the control current IA will be described with numerical values.
[0040]
The power supply V1 is 0 volts, the power supply V2 is -50 volts, and the resistance values of the resistors R1 and R2 are 100 kilohms.
[0041]
After executing the procedure P1 for turning off the switches SW1 and SW2, in the procedure P2, the first initial value 200 microamperes is passed as the control current IA, the voltage of the voltage detection circuit VDET1 is measured, and the measurement result is 10 volts. Got.
[0042]
In procedure P3, a second initial value of 50 microamperes was passed as the control current IA, the voltage of the voltage detection circuit VDET1 was measured, and a measurement result of 40 volts was obtained.
[0043]
Here, if it is desired to set the potential difference V34 between the terminals T3 and T4 to 20 volts, the potential difference V34 is calculated by substituting the various specific values described above into the equation (3) in the procedure P4. A control current value of 150 microamperes is achieved and this control current is passed through the current sources I1 and I2.
[0044]
In step P5, the switches SW1 and SW2 are turned on to apply the set potential difference of 20 volts to the circuit under test.
[0045]
Here, even if −50 volts of the power supply V2 fluctuates or 100 kilohms of the resistors R1 and R2 fluctuate, the potential difference can be accurately set to 20 volts by following the above steps P1 to P5.
[0046]
(A-3) Effects of the first embodiment
According to the test circuit of the first embodiment described above, the voltage applied to the circuit under test can be set without depending on the power supply voltage. Further, the power supply voltage of the test circuit is not applied to the circuit under test as it is, so that the circuit under test can be prevented from malfunctioning or erroneously activated, and power consumption in the circuit under test can also be suppressed. .
[0047]
Here, even when the absolute accuracy of the resistors R1 and R2 for keeping the voltage applied to the circuit under test smaller than the power supply voltage is poor, the voltage applied to the circuit under test can be set accurately. Even if the voltage detection circuit VDET1 has a finite impedance, the accuracy of the voltage applied to the circuit under test is not lowered.
[0048]
Further, when the resistance values R1 and R2 are made equal, the impedance of the test circuit viewed from the connection terminals T1 and T2 with the circuit under test is balanced, and the in-phase signal component induced to the circuit under test is Not easily affected.
[0049]
(B) Second embodiment
Next, a second embodiment of the test circuit according to the present invention will be described with reference to the drawings.
[0050]
(B-1) Configuration of the second embodiment
FIG. 3 is a circuit diagram showing the configuration of the test circuit 1B according to the second embodiment. The same reference numerals are given to the same and corresponding parts as those in FIG. 1 according to the first embodiment. In FIG. 3, the circuit under test (object to be tested) is omitted.
[0051]
As is clear from the comparison between FIG. 3 and FIG. 1, the test circuit 1B of the second embodiment is obtained by adding three switches SW3, SW4, and SW5 to the test circuit 1A of the first embodiment. is there.
[0052]
  switchSW4Is inserted in series between the terminals T1 and T4, and is for switching connection and disconnection between the terminals T1 and T4. Also switchSW3Is inserted in series between the terminals T2 and T3, and is for switching connection and disconnection between the terminals T2 and T3.
[0053]
The switch SW5 is connected in parallel to the resistor R1, and when the switch SW5 is turned on, the resistor R1 is short-circuited, and the potential of the terminal T3 is set to the potential of the power source V1 (ground).
[0054]
As these newly added switches SW3 to SW5, any of mechanical switches, electromagnetic relays, transistor switches, MOS switches, photocouplers, thyristor switches, and the like can be applied.
[0055]
(B-2) Operation of the second embodiment
Next, the operation of the test circuit 1B of the second embodiment shown in FIG. 3 will be described.
[0056]
In FIG. 3, the switches SW1 to SW4 are turned off and the switch SW5 is turned on. At this time, since the resistor R1 is short-circuited, the potential of the terminal T3 becomes the potential of the power supply V1 (ground), and the potential VT4 of the terminal T4 becomes as shown in the following equation (4).
[0057]
VT4 = V2 + R2 × I1 (4)
In this state, when the switch SW2 is turned on, one line of the circuit under test is connected to the terminal T4 via the terminal T2 and the switch SW2, and the terminal T2 and the ground are connected based on the detection voltage of the voltage detection circuit VDET1. Can be measured, or a ground voltage applied to the terminal T2 from the circuit under test can be measured.
[0058]
Here, even if the power supply voltage (V1-V2) and the resistance value R2 change due to temperature, aging, manufacturing variation, etc., the potential VT4 of the terminal T4 is controlled by controlling with the calibration procedure as shown in FIG. The correct potential at the start of measurement can be set.
[0059]
Procedure P11: Switches SW1 to SW4 are turned off and SW5 is turned on.
[0060]
Procedure P12: The first initial value I11 is passed as the control current I1 of the control current source I1, and the voltage VI11 of the voltage detection circuit VDET1 at that time is measured.
[0061]
Procedure P13: The second initial value I12 is passed as the control current I1 of the control current source I1, and the voltage VI12 of the voltage detection circuit VDET1 at that time is measured.
[0062]
Procedure P14: The control current value I1 of the control current source I1 for setting the potential of the terminal T4 to the desired value VT4 is obtained by the following equation (5), and the control current I1 is supplied to the control current source I1.
[0063]
I1 = (VI11−VT4) × (I12−I11)
/ (VI11−VI12) + I11 (5)
Procedure P15: By turning on the switch SW2, the set potential VT4 of the terminal T4 is applied to the terminal T2 to the circuit under test.
[0064]
The calculation of the above formula (5) is based on the fact that the current of the current source I1 and the potential of the terminal T4, that is, the detection value of the voltage detection circuit VDET1 can be regarded as linear (interpolation or extrapolation is performed). ing).
[0065]
For the control current I1, three or more initial values are changed, a measurement value of the voltage detection circuit VDET1 is obtained, a regression line or a regression curve is obtained, and control for setting the potential at the terminal T4 to a desired value VT4. The current value I1 may be determined.
[0066]
  In addition, the above calibration procedure for setting the potential VT4 must be performed for each measurement when fluctuations in the power supply voltage and the resistance value are allowable for the required accuracy.In shortAbsent.
[0067]
In the above description, the voltage detection circuit VDET1 has been described as having an infinite impedance. However, the same procedure can be executed even when the voltage detection circuit VDET1 has a finite impedance, and the above equation (5) can be applied as it is.
[0068]
As described above, when the switch SW2 is turned on and the circuit under test (one line thereof) is connected to the terminal T4 via the terminal T2 and the switch SW2, the following characteristics can be measured or detected. .
[0069]
When there is a resistance component between the terminal T2 and the ground, the voltage detection circuit VDET1 detects that the voltage rises from the potential VT4.
[0070]
When a ground voltage is applied to the terminal T2 from the circuit under test, the voltage detection circuit VDET1 detects that the potential changes with the potential VT4 as a reference.
[0071]
If the switch SW4 is turned on while the switches SW1 to SW4 are turned off and the switch SW5 is turned on, the other line of the circuit under test is connected to the terminal T4 via the terminal T1 and the switch SW4, and voltage detection is performed. Based on the detected voltage of the circuit VDET1, the resistance between the terminal T1 and the ground can be measured, or the external voltage applied to the terminal T1 from the circuit under test can be measured.
[0072]
(B-3) Effects of the second embodiment
According to the second embodiment, the same effect as that of the first embodiment can be obtained.
[0073]
According to the second embodiment, the voltage applied by the test circuit to one line of the circuit under test can be set without depending on the power supply voltage. Even if the absolute accuracy of the resistor R2 constituting the circuit is poor, the potential of the terminal VT4 can be set accurately. Furthermore, even if the voltage detection circuit VDET1 has a finite impedance, the measurement and detection accuracy of characteristics relating to one line of the circuit under test is not reduced.
[0074]
(B-4) Modified embodiment of the second embodiment
If it is not necessary to perform the measurement described in the first embodiment, the resistor R1, the switch SW5, and the control current source I2 may be omitted, and the terminal T3 may be directly connected to the power source V1.
[0075]
In the above, the case where the power source V1 is the ground potential is shown. However, when the power source V2 on the low potential side is the ground potential, the switch SW5 is provided in parallel with the resistor R2, and the same measurement as described above is performed. It is sufficient to execute the operation.
[0076]
(C) Third embodiment
Next, a third embodiment of the test circuit according to the present invention will be described with reference to the drawings.
[0077]
(C-1) Configuration of the third embodiment
FIG. 5 is a circuit diagram showing a configuration of a test circuit 1C according to the third embodiment. The same reference numerals are given to the same and corresponding parts as those in FIG. 3 according to the second embodiment. In FIG. 5, the circuit under test (object to be tested) is omitted.
[0078]
As apparent from the comparison between FIG. 5 and FIG. 3, the test circuit 1C of the third embodiment is obtained by adding a resistor R3 and a switch SW7 to the test circuit 1B of the second embodiment.
[0079]
The resistor R3 and the switch SW7 constitute a series circuit, and this series circuit is connected in parallel to the voltage detection circuit VDET1. Therefore, when the switch SW7 is on, the resistor R3 is connected in parallel to the voltage detection circuit VDET1.
[0080]
As the switch SW7, any of a mechanical switch, an electromagnetic relay, a transistor switch, a MOS switch, a photocoupler, a thyristor switch, and the like can be applied.
[0081]
(C-2) Operation of the third embodiment
Next, the operation of the test circuit 1C according to the third embodiment shown in FIG. 5 will be described.
[0082]
The test circuit 1C of the third embodiment also has a function of determining whether the ground resistance of the circuit under test is larger or smaller than the resistance value of the resistor R3. Hereinafter, the procedure for the determination function will be described with reference to FIG.
[0083]
Procedure P21: The switch SW5 is turned on and the switches SW1 to SW4 and SW7 are turned off.
[0084]
Procedure P22: The switch SW7 is turned on, and the voltage VR3 is measured and recorded by the voltage detection circuit VDET1. The recorded measurement value is a voltage at both ends of the resistor R3, and the potential at one end of the resistor R3 is grounded.
[0085]
Procedure P23: The switch SW7 is turned off, and the resistor R3 is disconnected from the measurement path of the voltage detection circuit VDET1.
[0086]
Procedure P24: The switch SW2 is turned on, the terminal T2 is connected to the terminal T4, and the voltage is measured by the voltage detection circuit VDET1. The measured value is compared with the recorded measured value VR3 at equal time intervals. The number of times that the comparison result is larger than and smaller than the recorded measurement value VR3 is counted.
[0087]
Procedure P25: In a stage where measurement is performed for a certain period, in other words, after a predetermined number of comparisons, it is determined whether the number of times greater or smaller than the recorded measurement value VR3 is greater. If the number of times greater than the recorded measurement value VR3 is large, it is determined that the ground resistance of the terminal T2 is larger than the resistance of the resistor R3, and if the reverse is true, the ground resistance is determined to be smaller than the resistance of the resistor R3.
[0088]
In the above description, the case where it is determined whether or not the ground resistance of the terminal T2 of the circuit under test is larger than the reference resistance (R3) is shown. However, the switch that is turned on in the above-described procedure P24 is changed from the switch SW2 to the switch SW4. In other words, it can be determined whether or not the ground resistance of the terminal T1 of the circuit under test is larger than the reference resistance (R3).
[0089]
(C-3) Effects of the third embodiment
According to the third embodiment, the same effect as that of the second embodiment can be obtained.
[0090]
Even if the accuracy of the power supply voltage and the resistors R1 and R2 is poor, if the accuracy of the resistor R3 is sufficient, an accurate comparison and determination can be made. In particular, when an AC component is superimposed on the circuit under test to induce an AC signal, measurement is made without being affected by the AC component by selecting a multiple of the period of the induced AC signal as the measurement period. It can be performed.
[0091]
(D) Fourth embodiment
Next, a fourth embodiment of the test circuit according to the present invention will be described with reference to the drawings.
[0092]
(D-1) Configuration of the fourth embodiment
FIG. 7 is a circuit diagram showing a configuration of a test circuit 1D according to the fourth embodiment. The same reference numerals are given to the same and corresponding parts as those in FIG. 1 according to the first embodiment. In FIG. 7, the circuit under test (object to be tested) is omitted.
[0093]
As is apparent from the comparison between FIGS. 7 and 1, the test circuit 1D of the fourth embodiment is obtained by adding switches SW3, SW4, and SW6 to the test circuit 1A of the first embodiment.
[0094]
As in the case of the second embodiment, the switch SW3 is inserted in series between the terminals T1 and T4, and is used to switch connection and disconnection between the terminals T1 and T4, and the switch SW4. Is inserted in series between the terminals T2 and T3, and is for switching connection and disconnection between the terminals T2 and T3.
[0095]
The switch SW6 is connected in parallel to the voltage detection circuit VDET1, and is provided for controlling the application and stop of the voltage to the circuit under test.
[0096]
As the switches SW3, SW4, and SW6, any of mechanical switches, electromagnetic relays, transistor switches, MOS switches, photocouplers, thyristor switches, and the like can be applied.
[0097]
(D-2) Operation of the fourth embodiment
Next, the operation of the test circuit 1D of the fourth embodiment shown in FIG. 7 will be described.
[0098]
The capacitance of the circuit under test can be measured by applying a voltage to the circuit under test and observing the voltage rise after a short circuit or opening by the switch (see the above-mentioned prior art document).
[0099]
The test circuit 1D of the fourth embodiment can cope with such a measurement function, that is, can measure the capacitance or time constant between the terminals T1 and T2 of the circuit under test. Hereinafter, the measurement procedure will be described with reference to FIG.
[0100]
  Procedure P31: The switches SW1 to SW4 and SW6 are turned off, and the first embodimentTheoryThe potential difference V34 is set between the terminals T3 and T4 according to the procedure described above.
[0101]
Procedure P32: The switches SW1 and SW2 are turned on, and the voltage V34 is applied between the terminals T1 and T2. By applying this voltage, if the circuit under test has a capacitance, the capacitance between the terminals T1 and T2 of the circuit under test is charged to the voltage V34.
[0102]
Procedure P33: The switch SW6 is turned on for a predetermined time. As a result, the terminals T3 and T4 are short-circuited and the voltage becomes zero, and the electrostatic charge of the circuit under test flows as a current through the terminal T1, the switches SW1, SW6, SW2, and the terminal T2, and is discharged.
[0103]
Procedure P34: The switch SW6 is turned off, and the voltage change after the switch SW6 is turned off is measured by the voltage detection circuit VDET1.
[0104]
Here, when the circuit under test does not have a capacitance, the detection potential of the voltage detection circuit VDET1 rises rapidly and becomes the set voltage V34. On the other hand, when the circuit under test has a capacitance, the detection potential of the voltage detection circuit VDET1 increases according to the time constant determined by the capacitance, and the increase is slow. In this way, the presence or absence of the capacitance of the circuit under test and the time constant can be observed.
[0105]
In the above description, the switch SW6 for detecting the capacitance of the circuit under test is shown. However, one or both of the switches SW3 and SW4 are regarded as the switch SW6 and are controlled to be turned on / off. In this way (switch SW6 is omitted), the capacitance characteristic of the circuit under test can be measured.
[0106]
(D-3) Effect of the fourth embodiment
According to the fourth embodiment, the same effect as that of the first embodiment can be obtained.
[0107]
In addition, the capacitance characteristic of the circuit under test can be measured by observing a change in the voltage applied to the circuit under test while controlling the on / off of the switch SW6.
[0108]
(E) Fifth embodiment
Next, a fifth embodiment of the test circuit according to the present invention will be described with reference to the drawings.
[0109]
(E-1) Configuration of the fifth embodiment
FIG. 9 is a circuit diagram showing a configuration of a test circuit 1E according to the fifth embodiment, in which the same and corresponding parts as those in FIG. 1 according to the first embodiment are denoted by the same reference numerals. In FIG. 9, the circuit under test (object to be tested) is omitted.
[0110]
As is apparent from the comparison between FIG. 9 and FIG. 1, the test circuit 1E of the fifth embodiment has a switch SW6 added to the test circuit 1A of the first embodiment, and the voltage detection circuit VDET1. Instead of this, a resistor R4 is provided, and a voltage detection circuit VDET2 for directly detecting the voltage between the terminals T1 and T2 is provided.
[0111]
The resistor R4 defines the potential difference between the terminals T3 and T4 together with the resistors R1 and R2, the control current sources I1 and I2, and the like.
[0112]
The switch SW6 short-circuits the resistor R4 when turned on, and any of a mechanical switch, an electromagnetic relay, a transistor switch, a MOS switch, a photocoupler, a thyristor switch, and the like can be applied.
[0113]
The voltage detection circuit VDET2 directly detects the voltage between the terminals T1 and T2. Like the voltage detection circuit VDET1 according to the first to fourth embodiments, the voltage detection circuit VDET2 includes an operational amplifier and a resistor. An existing device such as a current mirror circuit and a resistor can be applied.
[0114]
(E-2) Operation of the fifth embodiment
Next, the operation of the test circuit 1E of the fifth embodiment shown in FIG. 9 will be described.
[0115]
Capacitance characteristics of the circuit under test can be measured by applying a voltage to the circuit under test and observing the voltage rise after a short circuit or opening by the switch (see the above-mentioned prior art document).
[0116]
The test circuit 1E of the fifth embodiment can also cope with such a measurement function, that is, it can measure the capacitance or time constant between the terminals T1 and T2 of the circuit under test. Hereinafter, the measurement procedure will be described with reference to FIG.
[0117]
Procedure P41: The switches SW1, SW2 and SW6 are turned off. The potential of the terminals T3 and T4 (potential difference between the terminals T3 and T4) is determined by the potential difference between the power sources V1 and V2, the resistance values of the resistors R1, R2, and R4, and the current values of the control current sources I1 and I2. Considering the resistance value of the resistor R4 as the impedance of the voltage detection circuit VDET1 of the first embodiment, the potential difference between the terminals T3 and T4 is set to a desired one according to the procedure described in the first embodiment. Can do.
[0118]
Procedure P42: The switches SW1 and SW2 are turned on. As a result, a voltage (potential difference) between the terminals T3 and T4 is applied between the terminals T1 and T2, and the capacitance between the terminals T1 and T2 of the circuit under test is charged. The voltage at the end of charging can be measured by the voltage detection circuit VDET2.
[0119]
Procedure P43: The switch SW6 is turned on for a predetermined time. As a result, the terminals T3 and T4 are short-circuited so that the voltage becomes 0, and the electrostatic charge of the circuit under test flows as a current through the terminal T1, the switches SW1, SW6, SW2, and the terminal T2, and is discharged. Note that a potential difference of 0 is observed in the voltage detection circuit VDET2.
[0120]
Procedure P44: The switches SW1 and SW2 are turned off, and the subsequent voltage change is measured by the voltage detection circuit VDET2.
[0121]
Here, when the circuit under test has no capacitance, the detection potential of the voltage detection circuit VDET2 remains zero. Further, when the circuit under test has a capacitance and the time constant formed by the circuit is smaller than the above-described on-time of the switch SW6, there is no residual charge in the capacitance, and the voltage detection circuit VDET2 The detection potential remains 0. Further, when the circuit under test has a capacitance and the time constant formed by it is larger than the above-described on-time of the switch SW6, there is a residual charge in the capacitance, so that the voltage detection circuit VDET2 An increase in potential is detected.
[0122]
As described above, it can be determined that there is a capacitance between the lines of the circuit under test and that the time constant is within a certain range.
[0123]
(E-3) Effect of the fifth embodiment
Also according to the fifth embodiment, it is possible to measure the capacitance characteristics of the circuit under test by observing changes in the voltage applied to the circuit under test while controlling the switches SW1, SW2, and SW6 on and off.
[0124]
Here, the resistor R4 is used, but the voltage applied to the circuit under test by the test circuit can be set without depending on the power supply voltage.
[0125]
Further, during the period when the voltage detection circuit VDET2 is measuring, since the voltage detection circuit VDET2 is disconnected from the power supply of the test circuit, the measurement is hardly affected by disturbance.
[0126]
(F) Sixth embodiment
Next, a sixth embodiment of the test circuit according to the present invention will be described with reference to the drawings.
[0127]
(F-1) Configuration of the sixth embodiment
FIG. 11 is a circuit diagram showing a configuration of a test circuit 1F according to the sixth embodiment, which is the same as or corresponding to FIGS. 1, 3, 5, 7, and 9 according to the above-described embodiments. Are denoted by the same reference numerals. In FIG. 11, the circuit under test (object to be tested) is omitted.
[0128]
The test circuit 1F of the sixth embodiment has a configuration in which the configurations of the first to fifth embodiments described above are merged. Note that the resistor R4 of the fifth embodiment is omitted because the potential difference between the terminals T3 and T4 can be set by other components.
[0129]
(F-2) Operation of the sixth embodiment
In the test circuit 1F of the sixth embodiment, the setting operation of the voltage applied to the circuit under test is the same as that of the first embodiment described above.
[0130]
Further, the measurement of the external voltage to the circuit under test, the measurement operation of the ground resistance of each line of the circuit under test, and the like are the same as in the first embodiment described above.
[0131]
Furthermore, the measurement operation of the insulation resistance of the circuit under test is the same as that in the first, second, and third embodiments described above.
[0132]
Furthermore, the capacitance (line capacitance) of the circuit under test and the time constant measurement operation related thereto are the same as those in the fourth and fifth embodiments described above.
[0133]
(F-3) Effect of the sixth embodiment
According to the sixth embodiment, the voltage applied to the circuit under test by the test circuit can be set without depending on the power supply voltage.
[0134]
Further, according to the sixth embodiment, measurement of external voltage, measurement of insulation resistance, measurement of line capacitance and time constant, etc. can be easily realized with the same test circuit.
[0135]
(G) Other embodiments
The test circuit of the present invention is suitable for use in a subscriber circuit of an electronic exchange, an intra-station line termination circuit of a digital subscriber line transmission system, etc., but is not limited to a communication device and can be applied to a general measuring device.
[0136]
The potentials and polarities of the power supplies V1 and V2 to the test circuit are not limited to those of the above-described embodiments, and can be changed.
[0137]
Further, the output of the voltage detection circuits VDET1 and VDET2 may be input to a signal arithmetic circuit or a filter circuit composed of an operational amplifier or a current mirror circuit, or an analog / digital conversion is performed to the digital arithmetic circuit. You may make it input.
[0138]
Furthermore, the current control of the control current sources I1 and I2 may be controlled from a digital control circuit via a digital / analog conversion circuit. In this case, the numerical calculation of the above-described calculation formula can be performed by digital calculation. Note that the calculation may be performed by a circuit constituted by an operational amplifier, a current mirror circuit, or the like as an analog signal without using a digital calculation.
[0139]
Furthermore, in the sixth embodiment, all of the first to fifth embodiments are combined, but a test circuit is configured by arbitrarily combining the technical ideas of the first to fifth embodiments. You may do it.
[0140]
Further, the calibration procedure and the measurement procedure of each of the above embodiments may be automatically performed by a system element such as a test control circuit, or all or a part of the procedure may be performed by an operator.
[0141]
In the description of the scope of claims, the expression “first, second,...” Is used for easy understanding of the correspondence with each embodiment. However, there is no absolute correspondence with the embodiment. For example, when the potentials and polarities of the power supplies V1 and V2 to the test circuit change from those of the embodiment, the expression “first, second,... No longer supports.
[0142]
【The invention's effect】
As described above, according to the test circuit of the present invention, the first terminal and the second terminal connected to the circuit under test of the two-terminal pair are connected to the test circuit by the potential difference setting means. Since a potential difference that is variably set smaller than the potential difference between the first power source and the second power source is applied, it is possible to prevent malfunction and erroneous start-up of the circuit under test regardless of the test item, and power consumption during testing Can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a test circuit according to a first embodiment.
FIG. 2 is an explanatory diagram illustrating a calibration procedure of a potential difference between terminals T3 and T4 of the first embodiment.
FIG. 3 is a circuit diagram showing a configuration of a test circuit according to a second embodiment.
FIG. 4 is an explanatory diagram illustrating a procedure for measuring a voltage to ground of the circuit under test according to the second embodiment.
FIG. 5 is a circuit diagram showing a configuration of a test circuit according to a third embodiment.
FIG. 6 is an explanatory diagram illustrating a measurement procedure of a magnitude relationship between a ground resistance and a reference resistance of a circuit under test according to a third embodiment.
FIG. 7 is a circuit diagram showing a configuration of a test circuit according to a fourth embodiment.
FIG. 8 is an explanatory diagram showing a procedure for measuring capacitance (line capacitance) characteristics of a circuit under test according to a fourth embodiment.
FIG. 9 is a circuit diagram showing a configuration of a test circuit of a fifth embodiment.
FIG. 10 is an explanatory diagram illustrating a procedure for measuring the capacitance (line-to-line capacitance) characteristics of the circuit under test according to the fifth embodiment.
FIG. 11 is a circuit diagram showing a configuration of a test circuit according to a sixth embodiment.
[Explanation of symbols]
1A to 1F ... test circuit,
VDET1, VDET2, voltage detection circuit,
I1, I2 ... control current source,
R1 to R4: resistors (its resistance value),
SW1-SW7 ... switch,
V1, V2 ... power supply to the test circuit,
T1, T2: Connection terminals with the circuit under test,
T3, T4: terminals for defining the voltage applied to the circuit under test.

Claims (4)

In a test circuit for testing the electrical characteristics of a circuit under test of a two-terminal pair connected to a first terminal and a second terminal,
A first voltage detection circuit for measuring a potential difference between the third terminal and the fourth terminal;
Terminal having a first switch provided between said third terminal and said first terminal, and a second switch provided between the fourth terminal and the second terminal Inter-connection control means;
A first resistor connected between a first power supply and the third terminal; a second resistor connected between a second power supply and the fourth terminal; 4 a first current source connected to the terminals of a second current source connected to the third terminal, the potential difference between the upper Symbol third terminal and the fourth terminal the Potential difference setting means for variably setting to a desired value smaller than the potential difference between the first power source and the second power source to the test circuit;
The potential difference setting means includes the first and second terminals in a state where the inter-terminal connection control means blocks the first terminal and the second terminal from the third terminal and the fourth terminal. The current value of the second current source is set to the first initial value IA1, the detection voltage VIA1 by the first voltage detection circuit at that time is taken in, and the current values of the first and second current sources are set to the second value The initial value IA2 is set, and the detected voltage VIA2 by the first voltage detection circuit at that time is taken in, and the current values IA of the first and second current sources at the time of the first type test are determined according to the equation (A). The desired value V34 at the time of the first type test is set,
The potential difference of the desired value V34 between the third terminal and the fourth terminal set by the potential difference setting means is transferred to the first terminal and the second terminal via the inter-terminal connection control means. A test circuit for applying and performing a first type of test on the circuit under test.
IA = (VIA1-V34) × (IA2-IA1)
/ (VIA1-VIA2) + IA1 (A) The test circuit according to claim 1, wherein resistance values of the first resistor and the second resistor are equal. The inter-terminal connection control means is provided between a third switch provided between the third terminal and the second terminal, and between the fourth terminal and the first terminal. And a fourth switch,
A fifth switch provided in parallel with the first resistor and capable of short-circuiting the first resistor;
The potential difference setting means is configured such that the inter-terminal connection control means disconnects the first terminal and the second terminal from the third terminal and the fourth terminal, and the fifth switch is turned on. In a state where the potential of the third terminal is set to the potential of the first power source, the current value of the first current source is set to a third initial value I11, and the first voltage detection circuit at that time The detection voltage VI11 is captured, the current value of the first current source is set to the fourth initial value I12, the detection voltage VI12 obtained by the first voltage detection circuit at that time is captured, and the second voltage is calculated according to the equation (B). Determine the current value I1 of the first current source during the type of test,
The potential difference setting means sets the current value of the first current source to the current value I1, thereby setting the potential of the fourth terminal to the third terminal having the same potential as the potential of the first power source. Is set to a potential difference VT4 that is smaller than the potential difference between the first power supply and the second power supply to the test circuit, and the fourth terminal is connected to the first or second terminal by the inter-terminal connection control means. The second type of test is performed on the circuit under test by connecting to two terminals.
The test circuit according to claim 1.
I1 = (VI11−VT4) × (I12−I11)
/ (VI11-VI12) + I11 ... (B) In a test circuit for testing the electrical characteristics of a circuit under test of a two-terminal pair connected to a first terminal and a second terminal,
A first voltage detection circuit for measuring a potential difference between the third terminal and the fourth terminal;
An inter-terminal connection control means capable of connecting or blocking between the first terminal and the second terminal side and the third terminal and the fourth terminal side;
A second resistor connected between a second power source and the fourth terminal; and a first current source connected to the fourth terminal;
The inter-terminal connection control means, said first terminal and said second terminal, and cut off from the third terminal and the fourth terminal, the potential of the third terminal to the test circuit first In the state where the potential of the first power source is 1, the current value of the first current source is set to one initial value I11, the detection voltage VI11 by the first voltage detection circuit at that time is taken in, and the first voltage source The current value of the first current source is set to the other initial value I12, the detection voltage VI12 by the first voltage detection circuit at that time is taken in, and the current value I1 of the first current source at the time of the test according to the equation (C) And
The potential difference setting means sets the current value of the first current source to the current value I1, thereby setting the potential of the fourth terminal to the third terminal having the same potential as the potential of the first power source. Is set to a potential difference VT4 that is smaller than the potential difference between the first power supply and the second power supply to the test circuit, and the fourth terminal is connected to the first or second terminal by the inter-terminal connection control means. Test the circuit under test by connecting it to terminal 2
A test circuit characterized by that.
I1 = (VI11−VT4) × (I12−I11)
/ (VI11−VI12) + I11 (C)

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