JPH03180772A - Measuring device for characteristic of electrostatic capacitance to voltage - Google Patents

Abstract

PURPOSE:To enable an accurate measurement at low cost by forming a closed loop with a DC adder circuit, sinewave eliminating circuit, voltage comparator and deviation amplifier, and superimposing a DC voltage on the sinewave by a feedback operation of this loop. CONSTITUTION:The sinewave outputted from a sinewave generating device 1 is added to the DC voltage outputted from a DC voltage generating device 13 by the DC adder circuit 3 and converted to a sinewave signal superimposed on the DC voltage, then impressed to an electrostatic capacitance 5 to be measured. This voltage is taken out to the sinewave eliminating circuit 11 to eliminate the sinewave, and the DC voltage supplied to the electrostatic capacitance to be measured is taken out. The voltage is compared with the DC voltage outputted from the device 13 by the voltage comparator 12 to obtain a deviation voltage and amplified by the deviation amplifier 14, then supplied to the input terminal of DC voltage in the DC adding circuit 3. By the feedback operation of this closed loop, the DC voltage is superimposed on the sinewave. That is, the device can be made at low cost since a floating type DC voltage generating device is not used, and the accurate measurement can be performed with restraining the generation of noise.

Description

Detailed Description of the Invention "Industrial Application Field" This invention measures the capacitance value generated between the electrodes of an active element such as a transistor, and also measures the capacitance value due to changes in DC voltage. The present invention relates to a capacitance versus voltage characteristic measuring device that measures how the capacitance changes with respect to the capacitance.

"Prior Art" Figure 3 shows a conventional capacitance versus voltage characteristic measuring device. In the figure, l indicates a sine wave generator. This sine wave generator is I
A sine wave V having a frequency range of about Hz to several M) (Hz) is generated.The frequency ω is set by frequency setting data Dω given from the controller 8.

A sine wave V output from the sine wave generator 1 is amplified by a bumper amplifier 2 and provided to a DC adder circuit 3. In the DC adding circuit 3, the DC voltage V given from the DC voltage generator 4 is added, and as shown in FIG.
This is a voltage signal in which a sine wave V is superimposed on the sine wave V. The DC voltage generator 4 generates a DC voltage of, for example, +IOV to -10V,
A DC voltage within this voltage range is applied to the capacitance to be measured 5.

A current 1 flowing through the PIk measurement capacitance 5 is applied to a capacitance measuring device 6, and the imaginary component of the current i is measured in the capacitance measuring device 6 to obtain an analog voltage corresponding to the value of the capacitance C. This analog voltage is applied to the AD converter 7 to obtain a digital value corresponding to the capacitance C.

The digital signal output from the AD converter 7 is sent to the controller 8.
The data is taken in and stored in a memory or the like, and is also output to the display 9.

The controller 8 can be constituted by, for example, a microcomputer, and sequentially changes the voltage setting data Dv given to the DC voltage generator 4 to determine the capacitance C at each DC voltage value. DC voltage V.

The capacitance C measured for each DC voltage value when changing is loaded into the memory, and by reading this memory, the display 9 displays the capacitance vs. DC voltage characteristic as shown by the curve Cv.

"Problem to be Solved by the Invention" In a conventional device of this type, the DC adding circuit 3 has a capacitor 3A for passing the sine wave and blocking the DC voltage.
and an inductor 3B that is connected between the DC voltage generator 4 and both ends of the capacitor 3A to block the entry of sine waves and output only the DC component. DC voltage ■ is added to the sine wave V. FIG. 5 shows an equivalent circuit of the connection relationship between the sine wave generator 1, the DC voltage generator 4, and the capacitance to be measured 5 and the capacitance measuring device 6.

As is clear from this equivalent circuit, the DC voltage generator 4 is a so-called floating type DC voltage generator that is electrically insulated from the common potential point AS of the entire device.

Since the common potential point of this floating type DC voltage generator cannot be connected to the common potential point AS of the entire device, the structure is complicated and expensive due to insulation.

Further, since the device cannot be installed at a common potential point AS of the entire device, noise is likely to occur, and measurement accuracy cannot be improved.

Furthermore, the DC voltage generator 4 is required to change the voltage with high precision and high speed. In order to change the output voltage at high speed, it is necessary to lower the output impedance of the DC voltage generator 4.

To reduce the output impedance, the current capacity that can be output must be increased. In this respect as well, it has the disadvantage of being expensive.

An object of the present invention is to provide an apparatus for measuring capacitance versus voltage characteristics that is inexpensive and capable of performing highly accurate measurements.

"Means for Solving the Problems" The present invention proposes a configuration in which a DC voltage is superimposed on a sine wave without using a floating DC voltage generator.

In other words, the present invention includes: a sine wave generator that generates a sine wave to be applied to a capacitance to be measured; a DC voltage generator to generate a DC voltage to be applied to the capacitance to be measured; and the sine wave generator. A DC voltage adding circuit that adds a DC voltage corresponding to the DC voltage output from the DC voltage generator to the sine wave output from the device, and a DC voltage adding circuit that removes the sine wave applied to the capacitance to be measured and adds only the DC voltage. a sine wave removal circuit that extracts the sine wave removal circuit; a voltage comparator that compares the DC voltage extracted by the sine wave removal circuit with the DC voltage output from the DC voltage generator and outputs a deviation signal; It is equipped with a deviation amplifier that amplifies the deviation value of the DC voltage and applies it to the DC voltage input terminal of the DC voltage addition circuit, and a synchronous detector, and outputs a sine wave current flowing through the capacitance to be measured from the sine wave generator. Synchronous detection is performed using a reference signal that has a phase that differs by 90 degrees from the phase of the sine wave to be detected,
A capacitance versus voltage characteristic measuring device is constructed by a capacitance measuring device that measures the current value of the imaginary part to measure the capacitance.

According to the configuration of the present invention, the sine wave output from the sine wave generator is added to the DC voltage output from the DC voltage generator in the DC voltage adding circuit, and converted into a sine wave signal superimposed on the DC voltage to be measured. Fp electric charge is applied.

The voltage applied to the capacitance to be measured is taken out to a sine wave removal circuit, the sine wave is removed in this sine wave removal circuit, and the DC voltage applied to the capacitance to be measured is taken out. This DC voltage is compared with the DC voltage output from the DC voltage generator using a voltage comparator to obtain a deviation voltage.

This deviation voltage is amplified by a deviation amplifier and applied to a DC voltage input terminal of a DC adding circuit.

In the end, the DC adding circuit, the sine wave removing circuit, the voltage comparator, and the deviation amplifier form a closed loop, and the feedback operation of this closed loop causes the DC voltage to be superimposed on the sine wave.

Therefore, according to the present invention, there is no need to use a floating type DC voltage generator, so it can be manufactured at low cost.

Moreover, since the DC voltage is generated by the feedback operation, the generation of noise can be suppressed. Therefore, highly accurate measurement can be performed.

Embodiment] FIG. 1 shows an embodiment of the present invention. 1 in the figure is a sine wave V
, shows a sine wave generator that outputs . sine wave generator l
The sine wave ■1 outputted from the DC adder circuit 3 is input to the DC adder circuit 3. The DC adding circuit 3 can be configured by an operational amplifier, and a sine wave v1 is input to one input terminal 3A.
A DC voltage V is applied to the other input terminal 3B.

Therefore, on the output side of the DC adder circuit 3, a voltage signal is obtained in which the sine wave v1 is superimposed on the DC 2it voltage V shown in FIG. This voltage signal is amplified by buffer amplification H2 and applied to capacitance to be measured 5.

A current i flowing through the capacitance to be measured 5 is extracted by applying a voltage signal, and this current i is applied to the capacitance measuring device 6. The capacitance measuring device 6 synchronously detects the sine wave component of the current i using a reference signal whose phase differs by 90 degrees from the reference phase (the phase of the sine wave output from the sine wave generator 1).
Take out the imaginary part of current i. By determining the imaginary part of the current i, a value corresponding to the capacitance of the capacitance to be measured 5 can be obtained.

By calibrating the relationship between the imaginary part of the current i and the capacitance value using a standard capacitor, the capacitance value can be calculated from the imaginary part of the current i.

The analog voltage having the value of the imaginary part of the current i is sent to the AD converter 7.
is input to the controller 8 through an AD converter, and each time the controller 8 changes the DC voltage, the value corresponding to the capacitance is fetched from the AD converter 7, stored in the memory, and displayed on the display. 9, and the capacitance vs. DC voltage characteristic Cv
Display.

Here, in this invention, the voltage signal applied to the capacitance to be measured 5 is taken out to the sine wave removal circuit 11, and the sine wave removal circuit 11 applies a sine wave V'8 to the capacitance to be measured 5.
is removed and only the DC voltage V' is taken out.

For this purpose, a sine wave removal circuit 1 is operated by an operational amplifier, a voltage signal to be applied to the capacitance to be measured 5 is input to one input terminal 11A of the operational amplifier, and a sine wave is applied to the other input terminal 11B. A sine wave ■ is given from the generator 1.

The sine wave V' included in the voltage signals applied to the input terminals 11A and IIB is subtracted and canceled by the sine wave V1. Therefore, the output side of the sine wave removal circuit 11 has a DC voltage V
′, is output.

The DC voltage v′ output from the sine wave removal circuit 11 is input to the voltage comparator 12. The voltage comparator 12 can also be constituted by an operational amplifier, and one input terminal receives the DC voltage v' output from the sine wave removal circuit 11,
A DC voltage V is applied to the other input terminal from the DC voltage generator 13.
. give.

This DC voltage generator 13 is controlled by the controller 8, for example, +
It is possible to output any voltage within the range of 10V to -10V, and for example, it is controlled to change sequentially from -1OV to +10VO at a pitch of about 10mV, and for each voltage value, the controller 8 The capacitance value output from the converter 7 is taken in.

The voltage comparator 12 is directly connected to the sine wave removal circuit 11! A deviation signal V between the DC voltage V' given from the voltage generator 13 and vbh is output. This deviation signal ■.

is amplified by the deviation amplifier 14 and applied to the DC voltage input terminal 3B of the DC adding circuit 3.

In this circuit structure, if the gain A of the deviation amplifier 14 is a sufficiently large value, a sine wave V is output from the sine wave generator l and a DC voltage v is output from the DC voltage generator 13.
bb is applied to the capacitance to be measured 5 at its apparent value, regardless of the value of the gain A of the deviation amplifier I4.

This situation will be explained using the equivalent circuit shown in FIG. The reference numerals of each part shown in FIG. 2 are the same as the reference numerals of each part shown in FIG.

If the output of the sine wave generator l is X, the output of the DC voltage generator 13 is y, and the voltage applied to the capacitance to be measured 5 is 2, then Z I A 1+AX
1+A 1+A I+A, and x=z is maintained regardless of the value to the gain of the deviation amplifier 14.

Moreover, it becomes y1+A. Therefore, if A is a sufficiently large value, 2=y is maintained and a DC voltage can be stably applied to the capacitance 5 to be measured.

"Effects of the Invention" As explained above, according to the present invention, the DC voltage generator 13 does not need to be a floating type DC power supply, and can be connected to the same potential AS as the common potential AS of the device. Therefore, a normal power supply circuit can be used and it can be manufactured at low cost.

Further, since the common potential of the DC voltage generator 13 can be connected to a common potential point of the entire device, noise generation can be suppressed. Therefore, a highly accurate DC potential can be generated.

Further, according to the present invention, a closed loop is configured and the DC voltage V
, is added to the sine wave V, so that changes in the DC voltage V' applied to the capacitance to be measured 5 can be tracked at high speed in response to changes in the DC voltage vbb output from the DC voltage generator 13. can be done. Therefore, there is an advantage that the voltage characteristics of one capacitance to be measured can be measured in a short time.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram for explaining the operation of FIG. 1, FIG. 3 is a block diagram for explaining the conventional technology, and FIG. 3 is a waveform diagram for explaining the operation of FIG. 3, and FIG. 5 is an equivalent circuit diagram for explaining the operation of FIG. 3. 1: Sine wave generator, 3: DC adder circuit, 5: Capacitance to be measured, 6-Capacitance measuring device, 7: AD converter, 8:
Controller, 9: Display, 11: Sine wave removal circuit, 12. Voltage comparator, 13: DC voltage generator.

Claims (1)

[Claims] (1) A. A sine wave generator that generates a sine wave to be applied to the capacitance to be measured; B. A DC voltage generator to generate a DC voltage to be applied to the capacitance to be measured; C. D. A DC voltage adding circuit that adds a DC voltage corresponding to the DC voltage output from the DC voltage generator to the sine wave output from the sine wave generator; A sine wave removal circuit that removes and extracts only the DC voltage; E. A voltage comparator that compares the DC voltage extracted by this sine wave removal circuit with the DC voltage output from the DC voltage generator and outputs a deviation signal. and F, a deviation amplifier that amplifies the deviation value of the DC voltage output from the voltage comparator and applies it to the DC voltage input terminal of the DC voltage adding circuit; G, a synchronous detector equipped with the electrostatic detector to be measured An electrostatic capacitor that synchronously detects the sinusoidal current flowing through the capacitor using a reference signal that has a phase 90° different from the phase of the sinusoidal wave output from the sine wave generator, and measures the current value of the imaginary part to measure the capacitance. A capacitance measuring device and a capacitance versus voltage characteristic measuring device composed of.