JPH11230995A - Waveform measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a waveform measuring apparatus in which a proper DC component in every device to be tested can be extracted and removed even when a DC component in a signal, to be measured, which is output by a device to be tested is changed by a method wherein the DC component is extracted from the signal to be measured, the DC component is subtracted from the signal to be measured and an AC component is obtained. SOLUTION: A signal Si, to be measured, which is input to an input terminal 11 is supplied to a filter 17, and a DC component V0 which is contained in the signal Si to be measured is extracted by the filter 17. The DC component V0 is input to an analog computing unit 16 after its polarity is inverted through a buffer 18 for polarity inversion as required, and the DC component V0 is subtracted from the signal Si, to be measured, in the analog computing unit 16. Consequently, only an AC component SAC in the signal Si to be measured can be extracted on the output side of the analog computing unit 16. As a result, when the AC component VAC is amplified properly by a variable gain amplifier 12, it can be given to an A/D converter 13 as a signal at an amplitude which becomes maximum as far as possible in an allowable input range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform measuring apparatus suitable for application to, for example, an IC testing apparatus for testing an IC including an analog circuit.

[0002]

2. Description of the Related Art Conventionally, when testing an IC including an analog circuit, the quality of an analog waveform such as an amplitude value or a distortion rate of an analog signal output from the analog circuit is measured, and the analog circuit operates normally. Is determined. In order to automatically measure the amplitude value, distortion rate, or the like of an analog signal output from an IC under test, it is easier to convert the signal to be measured into a digital signal and process the digital signal with a digital signal processing circuit.

For this reason, conventionally, a signal under test Si is inputted to an input terminal 11 shown in FIG. 3, and the signal under test Si inputted to this input terminal 11 is amplified by a variable gain amplifier 12 to obtain an AD.
The A / D conversion is performed by the converter 13 and input to the digital signal processor 14 to automatically measure the amplitude value or the waveform distortion rate of the signal under test Si. However in many cases the measured signal Si, a DC component V ₀ which offset voltage such as shown in FIG. 4 are outputted in superposition. If the DC component V ₀ is input to the AD converter 13 while being superimposed, the DC component V ₀ is also amplified by the variable gain amplifier 12, so that the AC component S _AC in the target signal Si under test is amplified. Are input allowable values CV _max , −CV of the AD converter 13 as shown in FIG.
It shifted, for example, the upper limit CV _max near range _max, there is a disadvantage that can not be accurately measured.

For this reason, conventionally, a DA converter 15 is provided,
Voltage -V corresponding to the DC component V ₀ In this DA converter 15
_Then , the voltage -V _O is supplied to the analog computing unit 16, and the DC component V ₀ is subtracted from the signal to be measured Si and input to the variable gain amplifier 12. With this circuit structure, only the AC component S _AC is input to the variable gain amplifier 12 as shown in FIG. 4B, so that the signal shown in FIG. 4C can be input to the AD converter 13. The input allowable range CV of the AD converter 13 around the common potential OV
AC component S _AC by fully utilizing the range between _max and -CV _max
Can be AD-converted, so that highly accurate measurement can be performed.

[0005]

With the circuit configuration shown in FIG. 3, the DA converter 15 supplies a voltage -V ₀ corresponding to the DC component V ₀ included in the signal Si to be measured output from the IC under test. Must be input to generate the set value X. The set value X differs for each device, and for this purpose, it has to be manually set, so that there is a drawback that the test is troublesome.

An object of the present invention is to provide a waveform measuring apparatus capable of automatically removing a DC component output from a device.

[0007]

According to the present invention, a signal to be measured is supplied to a filter, a DC component is extracted by the filter, and the DC component contained in the signal to be measured is subtracted from the signal to be measured. The present invention proposes a waveform measuring device configured to remove the waveform. According to the waveform measuring apparatus of the present invention, the DC component can be automatically extracted from the signal under measurement. Therefore, the DC component is removed from the signal under measurement using this DC component, and only the AC component is extracted. be able to.

Accordingly, the amplitude of the AC component is amplified to an amplitude that becomes the maximum value within the allowable input range of the AD converter, and the amplitude of the AD component is increased.
By providing the signal to the converter, it is possible to perform AD conversion with high accuracy, thereby providing a waveform measuring device capable of measuring the quality of the waveform with high accuracy.

[0009]

FIG. 1 shows an embodiment of a waveform measuring apparatus according to the present invention. Parts corresponding to those in FIG. 3 are denoted by the same reference numerals. In the present invention, the signal under test Si input to the input terminal 11 is supplied to the filter 17 and
Extracts the DC component V ₀ included in the signal under measurement Si.
This DC component V ₀ is converted into a polarity inversion buffer 1 as necessary.
By polarity inverting input to the analog calculator 16 through 8, in which a configuration of subtracting the DC component V ₀ from the measured signal Si in the analog calculator 16.

Accordingly, since the output side of the analog calculator 16 can extract only the alternating current component S _AC in the input signal Si, as shown in FIG. 2B, the AC component S _AC variable gain amplifier 12 By appropriately amplifying, the AD converter 13 has an allowable input range CV _{max as} shown in FIG. 2C.
It can be given as the maximum amplitude signal serving as possible in the ~-CV _max.

[0011]

As described above, according to the present invention, to extract the DC component V ₀ from the measured signal Si according to the present invention, has a configuration for obtaining an AC component S _AC to the DC component is subtracted from the measured signal Si From the device under test S output from the device under test
Even if the value of the DC component V ₀ in i changes, an appropriate DC component V ₀ can be extracted and removed for each device.

As a result, it is possible to automatically remove the DC component V ₀ from the signal under test Si, to automate the test of the analog IC, and to obtain the advantage of improving the measurement accuracy.

[Brief description of the drawings]

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

FIG. 2 is a waveform chart for explaining the operation of FIG.

FIG. 3 is a connection diagram for explaining a conventional technique.

FIG. 4 is a waveform chart for explaining the operation of FIG. 3;

FIG. 5 is a waveform chart for explaining the operation of FIG. 3;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Input terminal 12 Variable gain amplifier 13 A / D converter 14 Digital signal processor 16 Analog operation unit 17 Filter 18 Polarity inversion buffer Si Signal under test V ₀ DC component S _AC AC component

Claims (1)

[Claims] 1. A. First Embodiment An AD converter; B. a variable gain amplifier for amplifying the amplitude of the signal under measurement to be AD-converted by the AD converter to an optimum input state of the AD converter; D. a filter for extracting a DC component from the signal under measurement; A waveform measuring device comprising: an analog calculator for adding and subtracting the DC component extracted by the filter to the signal under measurement.