JPH0136362Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to an AD conversion device that can be used in voltage or current measuring instruments, etc.

``Prior Art'' Figure 3 shows a conventional AD converter. In this example, a case of an AD converter for measuring voltage and current used in a DC operation test of an IC tester will be illustrated.

In the figure, 100 indicates a performance board. This performance board 100 has 10 ICs under test.
1 is attached and the DC characteristics of this IC 101 under test are tested.

IC DC characteristic tests can be roughly divided into a current applied voltage measurement mode and a voltage applied current measurement mode.

In current applied voltage measurement mode, a current source is connected between the terminals of the IC under test (one terminal is often a common terminal), and when a specified current is passed between the terminals, a planned voltage is generated between the terminals. Refers to the test mode that tests whether or not the

Further, the voltage application current measurement mode refers to a test mode in which it is determined whether the current value flowing into the IC is a predetermined value while a predetermined voltage is applied between the terminals of the IC under test.

The example shown in the figure shows the connection state in voltage application current measurement mode. In other words, in FIG. 3, 200 is a DA converter, 300 is a voltage generation circuit that applies a predetermined voltage to the IC under test 101, and 400 is the voltage generation circuit 30.
2 shows an AD converter for AD converting the current value flowing from 0 to the IC under test 101.

The DA conversion section 200 converts the digital signal given from the controller 500 and gives the DA conversion output to the voltage generation circuit 300. Voltage generation circuit 30
0 is an amplifier 301, a buffer amplifier 302 connected to the feedback circuit of this amplifier 301, a buffer amplifier 303 that determines the potential of the common potential point CM,
A current detection resistor 304 detects the current value flowing out from the amplifier 301.

Amplifier 301 applies a predetermined voltage between terminals T ₁ and T ₂ via current detection resistor 304 . terminal
The voltages applied to T ₁ and T ₂ are applied to the performance board 100 through the cable 600.
Buffer amplifier 302 extracts the voltage generated between terminals T ₂ and T ₃ at high impedance and returns it to the inverting input terminal of amplifier 301.
It operates to accurately output a voltage corresponding to the voltage given from the DA converter 200. Terminal T ₄
is connected to the common potential point ECM of the power source E and forms a return path for the output current of the amplifier 301.

In this circuit, the potential of the common potential point CM of the circuit network must be held at the same potential as one terminal PCM of the IC 101 under test. cable 600
Since the line is relatively long, there is a slight line resistance there. For this purpose, the buffer amplifier 303 takes in the potential of the terminal PCM at high impedance, and controls the potential of the common potential point CM of the circuit network to be equal to the potential of the terminal PCM without being affected by the DC resistance of the cable. ing. Such a buffer amplifier includes, in addition to the voltage generation circuit 300,
Buffer amplifiers 201 and 401 are also provided in the DA converter 200 and the AD converter 400.

The voltage generated across the current detection resistor 304 in the voltage generation circuit 300 is extracted by the differential amplifier 305 and applied to the AD conversion section 400 .

The AD converter 400 has an input selector switch 402,
403 and buffer amplifiers 404, 405 and AD
A converter 406, an offset data import register 407, a measurement data import register 408,
It is composed of a computing unit 409.

The input selector switch 402 is the buffer amplifier 40
4 input terminal to the common potential point of the AD converter 400
Shows the switch connected to the CM. By turning on this input changeover switch 402, the potential of the common potential point CM is applied to the buffer amplifier 404, and the voltage applied to the AD converter 406 at this time is AD converted. This AD conversion output is output from buffer amplifier 40.
4,405 corresponds to the offset voltage of the AD converter 406, and its AD conversion output is stored in the offset data acquisition register 407.

By turning off the switch 402 and turning on the switch 403, the output voltage of the differential amplifier 305 provided in the voltage generation circuit 300 is applied to the buffer amplifier 404, and the current flows through the current detection resistor 304 in the AD converter 406. The voltage value corresponding to the amount is AD-converted, and the AD-converted output is stored in the measurement data acquisition register 408.

Here, the true measured value is the data value X ₁ stored in the measurement data acquisition register 408 and the data value X ₂ stored in the offset data acquisition register 407.
The value of the difference is X ₁ −X ₂ . This calculation is performed by the calculator 40.
9 to determine the true current measurement.

"Problems that the invention attempts to solve" As mentioned above, the circuits 200, 300, 4 of each part
00 is controlled by the buffer amplifiers 201, 303, and 401 so that the potential of the common potential point CM becomes the potential of the terminal PCM of the IC 101 under test located at a remote point.

In this state, in particular, the common terminal current ICM of the AD converter 406 changes as the AD conversion output changes. This current change is absorbed by the buffer amplifier 401 through the common potential point CM.
Suppresses CM potential fluctuations.

However, if the common terminal current ICM changes at a high speed, the buffer amplifier 401 must also change at a high speed. For this reason, an amplifier capable of high-speed response must be used as the buffer amplifier 401, but an amplifier capable of high-speed response is expensive.

Furthermore, when subtracting the measured value of the offset voltage from the measured value of the voltage to be measured, if there is a large time difference between the measurement time of the offset voltage and the measurement time of the voltage to be measured, there is a drawback that a large error will occur due to the effects of induced noise, etc. .

In other words, as shown in FIG.
Assuming that the induced noise NS is mixed into the offset voltage in step 4, if the offset voltage is measured at time _t1 and then the voltage to be measured is measured at time _t2 , the measurement error between them is small. However, time t ₃
If the voltage to be measured is measured using this method, a large error will occur.

In this way, by reducing the time difference between measuring the offset voltage and measuring the voltage under test, it is possible to accurately measure the voltage under test without being affected by inductive noise.
can be converted.

However, in order to measure the offset voltage and the voltage to be measured in a short time interval, a buffer amplifier 4 is required.
01, an expensive high-speed response amplifier must be used.

"Means for solving the problem" In this invention, the common terminal of the AD converter is connected to the common potential point of the power supply, and the first
and a second buffer amplifier, a switch circuit, an analog arithmetic circuit, and a data processing circuit.

``Example'' FIG. 1 shows an example of a measurement system using an example of the AD converter of this invention, and the components other than the AD converter section 400, which is an example of the AD converter of this invention, are basically shown in FIG. It is the same as the conventional one.

The AD conversion section 400 includes a buffer amplifier 401,
It includes a pair of buffer amplifiers 411 and 412, a switch circuit 420, an analog arithmetic circuit 430, an AD converter 440, and a data processing circuit 450.

The buffer amplifier 401, similar to the one shown in FIG. 3, makes the potential of the common potential point CM of the circuit network the same as the potential of the terminal PCM of the IC under test 101 located at a remote point.

Buffer amplifiers 411 and 412 are each non-inverting amplifiers in the example of FIG.

The switch circuit 420 includes a buffer amplifier 41
switches 421 and 422 that connect the input sides of the switches 1 and 412 to the common potential point CM of the circuit network;
The input side of the buffer amplifier 411 is connected to the voltage generation circuit 3
The switch 423 connected to the output side of the differential amplifier 305 and the input side of the buffer amplifier 412 are connected to the common potential point of the circuit network in the voltage generation circuit 300.
A switch 424 connected to the CM.

In the example of FIG. 1, the analog arithmetic circuit 430 is a subtraction circuit, in which the output side of the buffer amplifier 411 is connected to the inverting input terminal of the differential amplifier 433 via the resistor 431, and the output side of the buffer amplifier 412 is connected to the inverting input terminal of the differential amplifier 433 via the resistor 431. It is connected to the non-inverting input terminal of the differential amplifier 433 via the differential amplifier 433. Note that the non-inverting input terminal side of the differential amplifier 433 is connected to the common potential point ECM of the power source E.

The AD converter 440 is an analog calculation circuit 430
The output voltage of the differential amplifier 433 is AD converted, and its common terminal is connected to the common potential point of the power supply E.
Connect to ECM.

The data processing circuit 450 determines the difference between offset data and measurement data, which will be described later, and is composed of an offset data acquisition register 457, a measurement data acquisition register 458, and an arithmetic unit 459.

In the above configuration, first, the switch 421
and 422 are turned on, switches 423 and 424 are turned off, and buffer amplifier 411
and 412, respectively, the common potential point of the network.
The potential of CM is supplied, and from the AD converter 440,
Buffer amplifiers 411, 412, differential amplifier 43
3 and the offset voltage of AD converter 440 is
AD converted offset data is obtained, and the offset data is taken into the offset data taking register 457.

Next, switches 421 and 422 are turned off, and switches 423 and 424 are turned on, so that buffer amplifier 411 and buffer amplifier 41
2 and the differential amplifier 30 of the voltage generating circuit 300.
The voltage to be measured obtained between the output side of 5 and the common potential point CM of the circuit network is supplied to the AD converter 440.
From this, measurement data is obtained by AD converting the voltage obtained by superimposing the above-mentioned offset voltage on the voltage to be measured, and the measurement data is captured in the measurement data capture register 458.

After that, the arithmetic unit 459 of the data processing circuit 450
The offset data mentioned above is subtracted from the measurement data mentioned above, and true measurement data corresponding to the voltage to be measured mentioned above is obtained from the arithmetic unit 459.

FIG. 2 shows another example of the AD conversion device of this invention, in which the buffer amplifier 411 is a non-inverting amplifier, but the buffer amplifier 412 is an inverting amplifier, and the analog arithmetic circuit 430 is an adder circuit. That is, the buffer amplifier 411
and the output side of 412 is resistor 435 and 436
This is the case where it is connected to the inverting input terminal of the differential amplifier 433 via the inverting input terminal of the differential amplifier 433.

"Effect of the invention" According to this invention, the common terminal of the AD converter 440 is connected to the common potential point ECM of the power supply E, and the common terminal current ICM of the AD converter 440 is directly returned to the power supply E. It is possible to change the common terminal current ICM at high speed without using an expensive high-speed response type as 401.
AD converter 440 can be operated at high speed. Therefore, it is possible to measure the offset voltage and the voltage to be measured in a short time interval.
It is possible to obtain highly accurate measurement results that are not affected by induced noise NS.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing one embodiment of this invention, Fig. 2 is a connection diagram for explaining a modified embodiment of this invention, Fig. 3 is a connection diagram for explaining the prior art, and Fig. 4. is a waveform diagram for explaining the disadvantages of the conventional technology. 400 is an AD conversion unit, 411 and 412 are first and second buffer amplifiers, 420 is a switch circuit, CM is a common potential point of the circuit network, 430 is an analog calculation circuit, 440 is an AD converter, and ECM is a common power supply A potential point 450 is a data processing circuit.

Claims (1)

[Claims for Utility Model Registration] First and second buffer amplifiers;
, the input side of the first buffer amplifier is connected to a terminal to which the voltage to be measured is supplied between the common potential point of the circuit network, and the input side of the second buffer amplifier is connected to the terminal where the voltage to be measured is supplied between the common potential point of the circuit network. a switch circuit that assumes a second switching state connected to a common potential point of the buffer amplifier; An analog arithmetic circuit that adds or subtracts depending on whether one side is an inverting amplifier, and an analog arithmetic circuit that AD converts the output of this analog arithmetic circuit.
AD whose common terminal is connected to the common potential point of the power supply
a converter; output data of the AD converter when the switch circuit takes the first switching state; and output data of the AD converter when the switch circuit takes the second switching state.
An AD conversion device comprising: a data processing circuit that calculates a difference between output data of an AD converter;