JPS5828544B2 - Voltage applied current measurement circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a voltage applied current measuring circuit.

The present invention was made in order to provide a voltage applied current measuring circuit with a simple configuration.

Further, the present invention has been made to provide a voltage applied current measuring circuit with improved shielding effect of a measuring cable.

This invention uses an operational amplifier circuit in which an inverting input terminal is used as a measurement terminal, a non-inverting terminal is used as a setting voltage terminal, and a resistor is connected between the inverting input terminal and the output terminal. It is intended to be detected as the voltage difference between the output terminal and the output terminal.

EXAMPLES The present invention will be specifically explained below with reference to Examples.

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

The inverting input terminal (to) of the operational amplifier 1 is used as a measurement terminal, and is connected to the object to be measured RL via a cable l.

A voltage Eo is applied using the non-inverting input terminal (G) as a set voltage terminal.

Then, a resistor R1 is connected between the inverting input terminal (→ and the output terminal).
Connect.

All of the current flowing through the object to be measured RL flows through the resistor Rt.

This is because the input impedance of the operational amplifier is very high and the input current can be ignored.

In order to detect the current flowing through the measurement object RL as a voltage drop across the resistor Rt, the voltage difference between the voltage at the non-inverting input terminal (G) and the output terminal is calculated by a subtraction circuit 6 constituted by an operational amplifier 8. demand.

The circuit 5 constituted by the operational amplifier 2 is an inverting circuit and is used to perform the above-mentioned subtraction operation.

Therefore, the differential voltage detection circuit may be a high input impedance differential amplifier circuit.

According to this embodiment circuit, since each voltage is stabilized so that the voltage difference between the input terminals (A) and (@) of the operational amplifier 1 becomes zero, the voltage between the non-inverting input terminal (A) and the output terminal The difference is
It is equal to the voltage difference between the inverting input terminal (→) and the output terminal, and measuring the former voltage difference measures the voltage drop across the resistor R1.

In other words, it measures the current flowing through the load.

Since the measurement circuit connected to this resistor Rt is an input to the operational amplifier 3, its impedance is extremely large, so the current flowing to the object to be measured RL will all flow to the resistor Rt, resulting in poor accuracy. High current measurement becomes possible.

For this reason, the voltage applied current measurement circuit is used to measure leakage current in semiconductor integrated circuits or C-MOS (complementary MO8
It is mainly used to measure minute currents such as power consumption of FET circuits.

In the embodiment circuit having the above configuration, the operational amplifier 14 constituting the ratio vane impedance conversion circuit can be omitted from the conventionally widely used voltage applied current measuring circuit shown in FIG. 2, so that the circuit configuration can be simplified. .

That is, the circuit shown in the figure requires the operational amplifier 4 that prohibits current from flowing into the measuring circuit through the resistor RM in order to measure the voltage drop across the resistor RM.

In contrast, in this embodiment circuit, the inverting input terminal of the operational amplifier 1 is used as the measurement terminal, the non-inverting input terminal is used as the setting voltage terminal, and the non-inverting input terminal and the output terminal are used as the measurement terminal. This allows one impedance conversion circuit to be omitted.

Further, it is connected to the object to be measured RL via a shielded cable l.

In this case, in the circuit shown in FIG. 2, when the shield line is grounded, a charging operation is performed on the parasitic capacitance between the signal line and the ground, so that measurement cannot be performed until the charging operation is completed.

When measuring minute currents such as leakage current measurements, this charging time becomes considerably long and is not efficient.

For this reason, it is conceivable to connect the above-mentioned shielding line to the output terminal of the operational amplifier 4, which has the same potential as the signal line, but in this case, the above-mentioned output terminal fluctuates due to noise induced in the signal line, so the shielding effect is becomes worse.

In contrast, as in this example circuit, by connecting the shielding line to the non-inverting input terminal (G), it is possible to maintain the same stable potential as the signal line, improving the shielding effect. be able to.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of the prior art. 1 to 4... operational amplifier, 5... inverting circuit, 6...
Differential voltage detection circuit.

Claims (1)

[Claims] 1. Voltage difference between an operational amplifier in which the inverting input terminal is the measurement terminal, the non-inverting input terminal is the setting voltage terminal, and a resistor is connected between the inverting input terminal and the output terminal, and the non-inverting input terminal and the output terminal. 1. A voltage applied current measuring circuit comprising: a high input impedance high voltage output circuit for detecting a high input impedance;