JP2698598B2 - Waveform measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for measuring a high-speed signal waveform with high accuracy.

[Technical background of the invention and its problems]

Conventionally, high-speed signal waveforms have been measured directly with a high-speed oscilloscope or sampling scope. However, it is difficult to obtain sufficient accuracy in such a method. Therefore, there has been proposed an apparatus which utilizes the fact that a step signal can be generated relatively easily and sufficiently accurately and corrects a measuring apparatus including a measuring system on the basis of the step signal, thereby measuring the signal under measurement with good precision. Japanese Patent Application No. 62-140614 (Japanese Unexamined Patent Publication No.
This method is described in US Pat.

In the above patent application, a reference pulse wave having a flat crest level is sampled, digitized to obtain reference data, Fourier-transformed based on the reference data, and a Fourier transform of an ideal step wave and a Fourier transform based on the reference data. Thus, the settling characteristics of the measurement system were determined. Specifically, using a point of a certain value of the amplitude (for example, 50%) as a time reference, Fourier transform based on the reference data and Fourier transform of the ideal step wave are normalized to obtain desired measurement system correction data. .

When the timing of the reference pulse wave and the ideal step wave are adjusted by this method, the duty ratio of each signal will be accurate.
Since it is not 50%, higher-order harmonic components are remarkably reduced, causing errors in the correction data. Since the frequency component of the rectangular wave appears on Sin (X) / X as shown in FIG. 3, the amplitude periodically decreases except in the case of an odd-order component having a duty ratio of 50%. In addition, since the value of the amplitude is used as the time-based condition, an error of the measurement system is included.

Furthermore, in this method, the error of the measurement system is obtained by comparing the Fourier transform of the reference data obtained by measuring the reference pulse wave with the Fourier transform of the ideal step wave, but the actual reference pulse has a certain rise and fall time and ringing. Etc. are included. For this reason, the shift between the reference pulse and the ideal step wave increases as the speed increases, and the accuracy deteriorates.

[Object of the invention]

An object of the present invention is to provide an apparatus for performing high-accuracy measurement of a high-speed signal waveform.

[Summary of the Invention]

According to one embodiment of the present invention, a high-speed pulse generator for generating a reference signal, a signal to be measured, and a high-speed measurement system that converts a predetermined level of an input analog signal into a digital signal and outputs the digital signal, A first switch for selectively connecting the signal under measurement and an output of the high-speed pulse generator to an input of the high-speed measurement system;
A parameter extracting device for extracting a parameter such as a temperature; a circuit for simulating a signal of the high-speed pulse generating device based on known circuit parameters of the high-speed pulse generating device and information of the circuit parameters and the parameter extracting device. A simulator, a first digital signal processor (DSP) for performing digital signal processing, a second DSP, and a second switch for selectively connecting the respective inputs of the first and second DSPs to the output of the high-speed measurement system; The characteristic data calculated by the first DSP from the data of the output of the high-speed pulse generator measured by the high-speed measurement system and the output of the circuit simulator is stored, and the output is stored in the second DSP.
The second DSP corrects the error of the high-speed measurement system based on the data measured by the high-speed measurement system and the data from the characteristic data storage device, the second DSP comprising: A measuring device for producing a high-accuracy high-speed measuring output is provided.

(Example of the invention)

FIG. 1 shows a first embodiment of the present invention. In the figure,
First, the switch 2 is connected to the high-speed pulse generator 7 side, and the switch 4 is connected to the DSP 8 side. In this state, the signal of the high-speed pulse generator 7 is measured by the high-speed measurement system 3 (analog input, digital output) via the switch 2. This measurement data is transmitted to DSP 8 via switch 4.
Sent to Parameters such as current and temperature of the high-speed pulse generator 7 are extracted by the parameter extracting device 10 and sent to the circuit simulator 12. The circuit simulator 12 simulates a signal of the high-speed pulse generator 7 based on the information of the circuit parameter 11 which is a known circuit parameter of the high-speed pulse generator 7 and the information of the parameter extracting device 10, and sends the signal to the DSP 8. The DSP 8 calculates the characteristic data of the high-speed measurement system 3 based on these two data and stores it in the characteristic data storage device 9. Next, switch 2 and switch 4
And the high-speed measurement system 3 measures the signal under test 1.
The data thus obtained is sent to the DSP 5 via the switch 4. The DSP 5 corrects an error in the high-speed measurement system 3 based on the characteristic data obtained as described above and outputs a high-precision high-speed measurement output.

FIG. 2 shows a series of signals until the characteristic data is obtained in the above operation. In the figure, the output of the high-speed pulse generator 7 is measured by the high-speed measurement system 3,
Is observed as a signal with rising and falling disturbances like the output of However, these signals use a repetitive signal, and the leading edge and the trailing edge of the signal are always continuous.

The signal measured in this manner is transformed on the frequency axis by a temporary FFT, and pulse position information is extracted from the ratio between the real component and the imaginary component of the fundamental wave component. At the same time, the duty ratio is calculated from the second harmonic component. That is, when the duty ratio is 50%, the even-order component disappears because Sin (X) / X = 0, but attention is paid to the fact that it does not completely disappear when the duty ratio deviates from 50%. When the phase of the second harmonic is obtained by the inverse function of (X) / or Newton's method, the Si
Since n (X) / X is a periodic function using the pulse width as a variable, the duty ratio can be obtained. The output of the high-speed measurement system is standardized based on the position information and the duty ratio information. Specifically, the position correction moves the data of the leading edge and the trailing edge of the output, and the duty ratio correction interpolates and expands and contracts a portion where the transient phenomena of the output rise and fall sufficiently converge.

When the FFT is performed again on the normalized measurement output obtained by the above processing, there is no even-order component and an odd-order component can be obtained to a higher order. When the position of the simulator output is not accurately adjusted and the duty ratio does not become 50%, the same processing as described above is performed to perform FFT to obtain odd-order components up to higher orders. The odd-order components obtained by performing the FFT from the standardized measurement output and the simulator output are compared, and the characteristic data of the high-speed measurement system 3 is obtained. All even-order components are errors of normalization and are not used for characteristic data. Further, when the FFT is calculated with a complex number and the characteristic data is also obtained as a complex number, the gain and phase can be obtained as a relative value from the fundamental wave by orthogonal transform. The fundamental frequency is sufficiently low and accurate. Therefore, the gain and the absolute value of the phase up to the higher order can be obtained by the characteristic data.

Next, switch 2 and switch 4 are switched and the signal under measurement 1
Is measured and corrected with DSP5 along with the characteristic data to obtain a high-accuracy high-speed measurement output. The correction in this case may be multiplied on the frequency axis and converted on the time axis, or the characteristic data may be converted on the time axis in advance and a desired output may be obtained by convolution.

In the above embodiment, without setting the duty ratio to 50%,
The order in which the amplitude decreases may be obtained without standardization as it is and deleted from the characteristic data. In addition, the resolution of the characteristic data is taken to a certain degree of fineness, and the data between the data is obtained by linear approximation, so that it is not necessary to change the measurement condition of the input of the signal under measurement and to collect the characteristic data again.

In addition, the data processing portions denoted by reference numerals 5, 8, 9, and 12 in FIG. 1 can be performed by computer software to simplify the system. Further, the duty ratio may be obtained from another component without obtaining the duty ratio from the second harmonic. Further, it is not necessary to calculate each time characteristic data is obtained by using the result of the circuit simulator as known data.

〔The invention's effect〕

As is clear from the above description, according to the present invention, high-precision measurement of a high-speed measurement system can be performed almost completely and high-precision measurement can be performed. It has tremendous effects such as realizing high speed measurement.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention, FIG. 2 is a view for explaining the operation of the apparatus shown in FIG. 1, and FIG.
It is a figure showing (X) / X. 2, 4: switch, 3: high-speed measurement system 5, 8: DSP, 7: high-speed pulse generator 9: characteristic data storage device, 10: parameter extraction device 11: circuit parameters, 12: circuit simulator

Claims (1)

(57) [Claims] A reference signal generating device for generating a reference signal; a signal to be measured to be measured; a high-speed measuring device for converting a predetermined level of an input analog signal into a digital signal and outputting the digital signal; A first switch for selectively connecting a measurement signal and an output of the reference signal generation device to an input of the high-speed measurement device; a parameter extraction device for extracting parameters such as current and temperature of the reference signal generation device; A known circuit parameter of a reference signal generator, a circuit simulator for simulating a signal of the reference signal generator based on information of the circuit parameter and the parameter extractor, and a first digital signal for performing digital signal processing Processing equipment,
A second digital signal processing device; a second switch for selectively connecting respective inputs of the first digital signal processing device and the second digital signal processing device to an output of the high-speed measurement device; Characteristic data storage for storing characteristic data calculated by the first digital signal processing device from data whose output is measured by the high-speed measuring device and output of the circuit simulator, and sending the output to the second digital signal processing device Wherein the second digital signal processing device corrects the error of the high-speed measuring device based on the data measured by the high-speed measuring device and the data from the characteristic data storage device, A waveform measuring device for generating a high-accuracy high-speed measurement output.