JPH05273272A - Timing-difference measuring system - Google Patents

Abstract

PURPOSE:To accurately measure the timing difference of signals. CONSTITUTION:A timing-difference measuring apparatus is constituted of an E-O measuring device 110 and a waveform storage and operation device 210. The E-O measuring device 110 samples electric signals of a device 101 under test by means of strobe light PS, and measures signal waveforms. Its time resolution is very high and its optical system is simplified by using a laser diode as a light source. The device is made small-sized. The waveform storage and operation device 210 stores electric-signal waveforms measured by means of the E-O measuring device 110 as digital values; it computes the mutual correlation of two stored electric-signal waveforms in a mutual correlation computation part 230; it detects a peak value of the mutual correlation and sets the peak value as the timing difference of signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a timing difference measuring system for detecting a temporal relationship between signals (timing difference between signals) such as a temporal difference between two signals.

[0002]

2. Description of the Related Art An oscilloscope (including a storage oscilloscope) is usually used to measure the time difference between two signals.
It is made by using a device for displaying a signal waveform. This is briefly explained as follows. These signal waveforms are displayed on the display surface of the device, and the time difference (timing difference) is obtained by obtaining the difference on the time axis of the display surface. For example, in the case of signal waveforms having peaks, focusing on the peak positions of those waveforms, the difference on the time axis is taken as the time difference.

Further, in the IC tester, a pulse signal having a fast rising edge is applied to each pin, and the delay in the input / output of the signal is measured. At this time, if there is a deviation in the distance from the pulse signal source to each pin, there will be a time deviation in the pulse signal at each pin (if the speed of the electric signal is the same as that of light, a deviation of 10 ps will occur at 3 mm). Therefore, it is necessary to calibrate the time lag of this pulse signal in advance,
It is done as follows. A pulse signal is put in a comparator near each pin to obtain a time difference across a certain threshold level, and the timing from each pulse signal source is adjusted so that the time difference becomes zero. After this calibration, similarly, a comparator is used to measure the input / output timing difference by the time difference across the threshold level.

[0004]

When a device for displaying a signal waveform as described above is used, if there is noise in the signal,
Because the part to compare becomes unclear due to noise,
The time difference cannot be measured accurately. In addition, there is always a visual error due to visual inspection. Furthermore, if the waveform is distorted, it is difficult to specify the portion to be compared, and different values can be obtained depending on the measurer.

The same problem occurs when measuring the time difference at the threshold level. If there is noise, the threshold level is erroneously detected due to the noise, and if the waveform is distorted,
The time difference across the threshold level is no longer a signal time difference.

As described above, there is a limit in accurately measuring the time difference between two signals.

A first object of the present invention is to provide a means for accurately measuring the time difference between two signals with higher resolution. The second purpose is to enable a measurement without a visual error even when a portion to be compared becomes unclear due to noise. A third object is to achieve the above object with a device that is simple to use.

[0008]

In order to solve the above-mentioned problems, the timing difference measuring system of the present invention stores the waveforms of the signals, and the first means for measuring the waveforms of two or more signals. Second means for detecting a timing difference between the signals by performing a predetermined calculation on the waveform of the stored signal.

The first means has an optical system for converting an electric field of a signal into an optical signal by optical modulation for detection, and a measuring system for measuring a waveform of the signal from the electric field of the detected signal. Also good.

The optical system can be arranged near the signal path,
It may be configured to include a probe having an electro-optic effect, a light source that outputs light to the probe, and a detector that detects light optically modulated by the probe.

The light modulated by the probe may be reflected by the reflection film formed on the bottom surface of the probe and detected by the detector.

The light source may be a laser light source capable of outputting a laser beam of a short pulse.

The measurement system is a control circuit for driving a light source to output light in pulses, and a measurement for lock-in amplifying the detection output of the detector based on the drive timing of the drive circuit to detect the waveform of the signal. It may be characterized in that it is configured to include a section.

The measurement system further includes a drive circuit for outputting a drive signal to the circuit under measurement including a signal path, and the control circuit drives the light source by gradually shifting the timing of the pulse output by the drive circuit. It may be characterized by doing.

The optical system may be characterized by having two systems.

The optical system can be arranged in the vicinity of one of the signals and has a first probe having an electro-optical effect, a first light source for outputting light to the first probe, and a first probe. A first detector that detects the light-modulated light, a second probe that can be arranged in the vicinity of another path of the signal, and has an electro-optical effect, and a first probe that outputs the light to the second probe. Two
And a second detector for detecting the light modulated by the second probe.

The optical system can be arranged in the vicinity of two paths of the signal, and an optical system that applies a probe having an electro-optical effect, a light source for outputting light to the probe, and light of the light source near the two paths of the probe, respectively. First to detect light modulated by a probe in the vicinity of each of the circuit and the path
And a second detector may be included.

The second means may be characterized in that the waveform of the signal is stored as a digital value.

The second means may be characterized by obtaining the cross-correlation of the waveforms of the stored signals and detecting the timing difference from the peak value of the cross-correlation.

The second means obtains the cross-correlation of the waveforms of the signals by Fourier-transforming each of the two stored signal waveforms and applying the inverse Fourier transform to the product of the conjugate function of one of them and the other. May be a feature.

The second means stores one of the signals, then measures the other one of the signals by the first means, and at the same time performs a predetermined calculation on the waveform of the signal to obtain the timing difference of the signal. It may be characterized by detecting.

It may be characterized by further comprising a third means for subjecting the waveform of the signal to a predetermined processing (for example, a low-pass filter, a digital filter, a waveform filter of the signal, etc.).

The first means has a pulse signal source for outputting a pulse signal to the pin of the IC to be measured, and inputs signals through a large number of channels corresponding to the pins connected to the pulse signal source, and outputs those signals. The waveform of the signal may be measured, and the timing of each pulse output from the pulse signal source to the pin may be adjusted based on the timing difference detected by the second means.

[0024]

In the timing difference measuring system of the present invention, first, the waveform of the signal to be measured is measured by the first means, and this waveform is stored by the second means. In the second means, the waveform of the stored signal is subjected to a predetermined calculation (a process of extracting a temporal difference between signals, for example, cross-correlation) to detect a temporal relationship. Where the cross-correlation of the signals,
Alternatively, if the process of extracting the temporal relationship from the phase of the cross spectrum of the waveform is performed, even if there is noise in the signal,
A time difference is detected with high accuracy that cannot be obtained by comparing waveforms. Various processes can be performed by storing the signal waveform.

In particular, when the first means is constituted by using an electro-optic crystal for inputting a signal, it has a very high time resolution, so that the measurement can be performed with higher accuracy.

In the case where the light modulated by the probe is reflected by the probe, an optical system can be formed on one surface of the signal path, and the optical system can be located at a position corresponding to the signal path. The probe may be movable. Therefore, the temporal relationship can be easily measured at various positions in the signal path.

Further, in the case of having the third means, the noise component is removed by filtering the waveform of the signal so that a signal having a predetermined threshold value or less becomes a constant value.

Further, when the first means is constituted by using the pulse signal source for outputting the pulse signal to the pin of the IC to be measured, the timing of the pulse signal to the pin of the IC is adjusted, The timing of the pulse signal to the IC to be measured can be aligned.

[0029]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of the first embodiment of the present invention.
This timing difference measuring system is based on the EO measuring device 11
0 and a waveform storage arithmetic device 210.

The EO measuring apparatus 110 measures the signal waveform by sampling the electric signal of the device under test 101 with the strobe light P _S, and has a very high time resolution. In addition, this device is characterized in that a laser diode is used as a light source to simplify the optical system and downsize the device.

The optical system of the E-O measuring device 110 includes an LD pulse light source 130 using a laser diode and a polarizer 12.
0c, EO probe 120b made of electro-optic crystal,
Half mirror 120e, analyzer 120d, photodetector 14
It consists of zero. The EO probe 120b is shown in FIG.
As shown in the, for detecting the vertical direction of the electric field in the figure, the electro-optic crystal in the glass block 120b ₁ (L
iNbO ₃ , GaAs, ZnTe, CdTe, BSO)
120b ₂ is attached and configured. The bottom surface of the electro-optic crystal 120b ₂ is coated with a dielectric multilayer film for reflecting the strobe light P _S. A transparent electrode of ITO is provided at the other end, and a side electrode 120b ₃ for applying a voltage to this electrode is attached.

The operation of the optical system of the EO measuring apparatus 110 will be briefly described as follows. The strobe light P _S from the LD pulse light source 130 is emitted from the EO probe 12.
It is guided to 0b, reflected at its tip and returns. EO
The device under test 10 is provided near the tip of the probe 120b.
1 is arranged, and when a voltage is applied to the device under test 101, the electro-optic crystal 120b is generated according to the voltage.
The refractive index of ₂ changes, and as a result, the polarization state of the strobe light P _S changes. This strobe light P _S is transmitted to the analyzer 120.
After passing through d, the change in the polarization state is detected by the photodetector 140 as a change in the detected light amount (light modulation). FIG. 3 shows a change in the detected light amount depending on the position, which is caused by the electric field of the electrodes (ground electrode, signal electrode) on the device to be measured 101.

The measurement / control system of the EO measuring device 110 is
It is composed of a drive circuit 170, a control unit 150, a measuring unit 160, and a display unit 180. The drive circuit 170 provides a pulse signal (drive pulse) to the device under test 101. As an example, a comb generator (33002A manufactured by HP Co.) is used to provide an impulse-like measurement signal as shown in FIG. The control unit 150 causes the LD pulse light source 130 to output the impulse strobe light P _S as shown in FIG. 5 according to the drive timing of the drive circuit 170, and
The reference signal is output to the measurement unit 160 according to the timing at which the strobe light P _S is output. The measuring unit 160 has a lock-in amplifier built therein and determines the waveform of the electric signal from the control unit 150.
Lock-in amplification is detected by the signal of.

The operation of the E-O measuring device 110 will be described below. It is assumed that the drive circuit 170 sequentially outputs drive pulses, and the waveform of the electric signal of the device under test 101 for one of the drive pulses is a waveform as shown in the first quadrant of FIG. 6. The strobe light P _S is output with a predetermined timing offset from the drive pulse, and the electric signal of the device under test 101 is sampled and detected by the optical system by the strobe light P _S. Here, the strobe light P _S is at the position a for a predetermined time with reference to the point a in FIG.
It is turned on and then turned on at the position b for a predetermined time, which is repeated.

Then, the lighting at the position c instead of the position b is repeated in the same manner, and hereinafter, with reference to the point a, the position c,
Change the position to d, e ... The measuring unit 160 outputs voltages B, C, D, E ... With reference to the voltage A. In this way, the E-O measuring apparatus 110 measures the waveform of the electric signal of the device under measurement 101. Here, since the laser diode is used as the light source to electrically turn on the light, the lighting timing is electrically controlled, and the optical system for optical delay is not required and is simple. The time resolution of the electric signal waveform measured by the E-O measuring device 110 is about the pulse width of the strobe light P _S.

The waveform storage / calculation device 210 includes the waveform storage unit 2
20, a cross-correlation calculation unit 230, a peak detection unit 240, and a timing change display unit 250, and is specifically configured by using a computer, its software, and peripheral devices such as an A / D converter. Waveform storage unit 220
Stores an electric signal waveform measured by the EO measuring device 110 as a digital value after A / D conversion. The cross-correlation calculation unit 230 calculates the cross-correlation between the two electric signal waveforms stored in the waveform storage unit 220. Peak detector 240
Detects the peak value of the cross-correlation calculated by the cross-correlation calculation unit 230 and sets the time at this peak value as the temporal difference between these signals. The timing change display section 250
The results of the cross-correlation calculation unit 230 and the peak detection unit 240 are displayed.

The calculation of the cross correlation will be described as follows. Letting f (t) and g (t) be the two electric signal waveforms stored in the waveform storage unit 220, the cross-correlation I (τ) between them is expressed by the following equation 1.

[0038]

[Equation 1]

Here, if f (t) and g (t) have the same waveform and are deviated by time t ₀ , it can be written as g (t) = f (t + t ₀ ). At this time, the cross-correlation I (τ) is expressed by the following Expression 2.

[0040]

[Equation 2]

This represents the autocorrelation of f (t), which is the maximum value (peak value) when t ₀ + τ = 0, that is, t ₀ = -τ. Therefore, by obtaining τ at which the cross-correlation I (τ) has the maximum value, the temporal change t ₀ can be obtained.

The cross-correlation I (τ) may be obtained by an algorithm based on "Equation 2", but it may be modified by using Fourier transform as shown below. By processing with the algorithm based on Equation 3, the speed becomes higher.

[0043]

[Equation 3]

As an algorithm for calculating Fourier transform at high speed, FFT using butterfly calculation is widely known. Here, a cross spectrum is obtained by using it, and inverse Fourier transform is performed to obtain the cross-correlation I (τ).

The temporal change t ₀ can be directly obtained from the phase of the cross spectrum which is a complex number.

Next, the measurement of the temporal relationship using this system will be described.

A drive pulse to the device under test 101 is a pulse having a peak voltage of 1 Volt and a full width at half maximum of 150 ps, and a microstrip line is used for the device under test 101. Then, the drive circuit 170 and the device under test 10
Between 1 and 1, a variable length waveguide (not shown) is provided to delay the drive pulse, so that the drive pulse is artificially changed with time. FIG. 7A is an output waveform of the EO measuring apparatus 110 when the delay of the variable length waveguide is zero, and FIG.
Is the output waveform when delay is given. The full scale in the figure is 1024 ch, which is 550 ps. By comparing these waveforms, it can be easily understood that there is a temporal change because the output waveforms are deviated, but it is difficult to accurately determine how much the change is. This is because the output waveform contains noise and the true waveform is hidden.

FIG. 7 (c) shows the result of the cross-correlation of the waveforms of FIGS. 7 (a) and 7 (b) obtained by the waveform storage / calculation device 210, which has a peak at 155ch. The time 83.3 ps corresponding to this peak shows the temporal change amount. 7 (a) and 7 (b) had a waveform containing noise, the waveform of FIG. 7 (c) obtained from them had very little noise, which is noteworthy. That is. It is considered that the noise disappears because the noise in the output waveform is averaged by obtaining the cross-correlation. Therefore, the peak of cross-correlation can be obtained with high accuracy. As a result, the change over time can be obtained with extremely high accuracy.

Next, in order to evaluate the measurement accuracy, the variation of the measurement result is measured. The delay of the variable length waveguide was fixed and multiple measurements were performed. The output waveform of the E-O measuring device 110 is different every measurement. For example, FIG. 8A shows the result of three measurements. When the number of times of measurement increases, it becomes something with a certain width as shown in FIG. 8B (FIG. 8B is measured 9 times). A simple comparison of the output waveforms of the E-O measuring device 110 shows that the measurement limit is larger than this width. The standard deviation σ of the temporal change obtained by cross-correlation using these output waveforms is 2.
It was 8 ps. The range 4σ in which 95% of the data is included is 1
This is 1.2 ps, which is a great improvement in accuracy. In the optical system of the E-O measuring device 110, although the pulse width of the LD pulse light source 130 is 30 ps,
The apparatus of the present embodiment is capable of measuring temporal changes with higher accuracy than this.

As described above, the system of this embodiment is capable of accurately measuring the temporal change of the high-speed electric signal waveform, and therefore can be applied in various ways. For example, measurement of propagation characteristics (velocity, attenuation, distortion, etc.) on high-frequency transmission lines,
Calibration for matching the timing of waveforms from multiple signal sources, gate delay characteristics of semiconductors such as transistors, etc. In such applications, the time relationship of electric signals is measured by changing the measurement target or changing the setting conditions.

FIG. 9 shows an application to measurement of gate delay characteristics of semiconductors such as transistors. In general,
In many cases, the input terminal and the output terminal of the gate do not have the same output level or waveform. In such a case, simply comparing the waveforms does not show how much the delay occurs. For example, it is a case where the signal having the waveform shown in FIG. 10A is input and the output is shown in FIG. in this case,
Since the apparatus of this embodiment measures from the peak of the cross-correlation of these waveforms, it is possible to measure the temporal change even with such a distorted waveform. This shows that the delay characteristics can be measured not only for digital devices but also for analog devices.

The reason why a distorted waveform can be measured is considered as follows. In Equation 1, when the input signal component (true signal component) and the distortion component are considered separately, the distortion component is
It is considered that the noise is averaged and becomes very small, like the noise component described above. Therefore, since the distortion component is represented by the series sum of the harmonics of the true signal component, it is possible to measure the time difference with higher accuracy by passing it through a filter before obtaining the cross-correlation. To construct this filter, there is a method of providing a low-pass filter at the output of the EO measuring device 110, or a method of providing a digital filter in the waveform storage / calculation device 210. Since these are realized by a known method, detailed description will be omitted.

Further, by using a comparator or the like to obtain the cross-correlation for the output waveform of the EO measuring apparatus 110 within the predetermined threshold value, it becomes possible to measure the time difference with higher accuracy. For example, in the waveform of FIG. 10B, overshoot and undershoot occur,
They are removed depending on whether they are within a predetermined threshold. Also in this case, a method is provided in which a comparator is provided at the output of the E-O measuring device 110, data processing is performed in the waveform storage arithmetic device 210, and the like.

An IC tester is applied to the two measurements of the calibration for synchronizing the timings of the waveforms from a plurality of signal sources and the measurement of the gate delay characteristic described above.

The IC tester has terminals corresponding to the pins of the IC, and the number thereof reaches 512 at maximum. These pins need to be given a well-timed drive pulse, but they are actually cables, socket boards and ICs.
The delay time and the stray capacitance vary depending on the wiring length of the socket and the mechanical arrangement, and the timing of the drive pulse at each pin of the IC also varies. This becomes an error factor in the measurement of gate delay characteristics and the measurement of logic skew.
FIG. 11 is one of the proposals when applied to the timing calibration and the timing correction of the IC tester, and is a conceptual diagram thereof.

In this system, reference numeral 300 is the same as in FIG.
Of the input signal, a measuring device 370 for measuring the signal waveform of the input signal, a storage device 340 for storing the measured signal as a digital value, and a cross-correlation from the digital value stored in the storage device 340. Calculation device 3 for calculation
50 and a display device 360 that displays the result. Further, the voltage detected by the measuring device 370 is switched by the changeover switch 330. And
The output from the arithmetic unit 350 is the delay setting circuit 320.
driver 3 connected to a, b, c ...
The delay time of 10a, b, c ... Can be changed. The measurement of the gate delay characteristic using this device is as follows.

First, when calibrating the drive pulse timing, the changeover switch 330 is set to the uppermost position on the A side, and the drive pulse is given from the driver 310a. The waveform of this drive pulse near the pin of the device under measurement 101 is measured by the measuring device 3
The measurement is performed at 70 and is stored in the storage device 340. Next, the changeover switch 330 is set to the second position from the upper side, and the waveform of the drive pulse is captured in the same manner. Next, the arithmetic unit 350 detects the difference in timing between the first captured waveform and the second captured waveform. The delay setting circuit 320b is adjusted according to the detected timing difference, and the drive pulse from the driver 310b is adjusted by the driver 31b.
Align with 0a. Then, the changeover switch 330 is sequentially changed over from the third position on the A side, and the waveform of the drive pulse is aligned with the first one in the same manner.

When the gate delay characteristic is measured, the driver 3
Drive pulses with uniform timing are applied to the device under test 101 from 10a, b, c ...
Are sequentially switched from the B side to sequentially measure the device under test 1
The waveform of the output pin 01 is captured and the gate delay characteristic is measured as described above. In this way, it is considered that delay time measurement can be performed accurately not only for digital ICs but also for analog ICs.

FIG. 12 shows a block diagram of the second embodiment. In this figure, the same reference numerals as those in FIG. 1 are used, and the same EO measuring device 110 is used. Waveform storage arithmetic unit 21
1 is basically the same, but the changeover switch 260 is provided, and the electric signal waveform previously measured by the EO measuring device 110 is stored as a digital value and then compared with the electric signal waveform measured later. I'm trying to get it.

First, the changeover switch 260 is set to the waveform storage section 2
20 side and E as in the case of the embodiment of FIG.
The -O measuring device 110 measures the electric signal waveform of the device under test 101. Then, this waveform is stored in the waveform storage unit 220. After that, the changeover switch 260 is set to the cross-correlation calculation unit 230 side. The electric signal waveform is changed from the setting condition, the measurement position is changed from the input of the gate of the device under test 101 to the output, or the measurement target is changed. Then, in the same manner, the electrical signal waveform is measured by the E-O measuring device 110, and at the same time, the electrical signal waveform from the E-O measuring device 110 and the previously stored waveform are mutually interrelated. Calculate the correlation. The peak value of the cross-correlation is detected by the peak detection unit 240, and the timing change display unit 2
At 50, the time difference is displayed.

By doing so, it is not necessary to store two waveforms, so that the memory is small and the peak value can be detected quickly.

FIG. 13 shows a block diagram of the third embodiment. In this embodiment, two optical systems of the EO measuring apparatus 110 are prepared, and the electric signal waveform of the device under test 101 can be measured at different positions at the same time. Also in this figure, the same reference numerals as those in FIG. 1 are used.

One optical system of the EO measuring device 110 is the same as that of FIG. 1, and is for detecting the electric field at the measuring point A. An optical system equivalent to this (LD pulse light source 1
32, a polarizer 122c, an EO probe 122b made of an electro-optic crystal, a half mirror 122e, and an analyzer 122.
d, a photodetector 142) is provided, and this optical system is for detecting the electric field at the measurement point B. The LD pulse light source 132 is driven together with the LD pulse light source 130, and outputs pulsed light having an equivalent shape. The measurement unit 162 is also the same as the measurement unit 160, and detects the waveform of the electric signal at the measurement point B by lock-in amplification. These measurement points A and B
Each of the optical systems can independently move the device under test 101.

The waveform storage operation device 212 is basically the same, but since the measuring section 160 and the measuring section 162 are input at the same time, an extra A / D converter is provided as the interface, and the cross-correlation calculating section 230 is Measuring unit 1
The electric signal waveforms of the measurement points A and B from 60 and the measuring unit 162 are temporarily stored, and then the cross-correlation is calculated.

First, the above optical systems are aligned with the positions on the device to be measured 101 to be measured, that is, measurement points A and B. Then, the electric signal waveforms at the measurement points A and B are detected by the E-O measuring device 110 in the same manner as in the embodiment of FIG. 1 described above, and the timing difference between these waveforms is measured by the waveform storage / arithmetic device 212 by cross correlation. To do. By doing so, it is possible to measure two waveforms at the same time, so that the time difference can be measured more quickly than in FIG.

FIG. 14 shows a block diagram of the fourth embodiment. This embodiment also has two optical systems of the E-O measuring device 110 as in FIG. 13, but is characterized in that the optical system is simply configured. This embodiment also makes it possible to measure the electric signal waveform of the device under test 101 at different positions at the same time. Also in this figure,
The same symbols as those in FIG. 1 are used for the same reference numerals.

In the optical system of this EO measuring device 110,
The LD pulse light source 130, the polarizer 120c, and the EO probe 120b made of an electro-optic crystal are commonly used. The light of the LD pulse light source 130 is branched by the half mirror 124, one of which is given to the optical system of the measurement point A and the other of which is given to the optical system of the measurement point B. The optical system at the measurement point A includes an LD pulse light source 130, a polarizer 120c, an EO probe 120b made of an electro-optic crystal, a half mirror 120e, an analyzer 120d, and a photodetector 140. Measurement point B
The optical system includes an LD pulse light source 130 and a total reflection mirror 12
5, polarizer 120c, EO probe 120b made of electro-optic crystal, half mirror 122e, analyzer 122
d, a photodetector 142. The waveform storage / calculation device 212 is basically equivalent to the above, and the cross-correlation calculation unit 230 calculates the cross-correlation of the electric signal waveforms at the measurement points A and B from the measurement units 160 and 162. FIG.
The time difference is measured in the same manner as.

In this embodiment, the EO probe 120b
The measurement points A and B are different from those in FIG.
Although it lacks flexibility in setting, there is an advantage that the number of optical components is reduced.

The present invention is not limited to the above-described embodiment, but various modifications can be made.

For example, the waveform storage / calculation device 210 is not limited to a computer, but may be a DSP (Digital signal
processer), a memory device, or the like. Also,
In the measurement by the IC tester, the changeover switch 330 was changed over from the top on the A side, but the changeover order may not be this order. Further, in FIG. 11, the E-O measuring device 110 of FIG. 1 may be used. in this case,
Since the optical system of the E-O measuring device 110 can be downsized and can be manufactured integrally, the optical system of the E-O measuring device 110 is moved by an actuator or the like to be input to the E-O measuring device 110. You should do so.

When the waveforms to be measured are mutually inverted, the cross-correlation calculation has linearity, so that FIG.
The waveform of will be inverted. Therefore, in such a case, the smallest value is the time difference.

In the embodiment described above, the EO measuring device 11
0 is for measuring the signal waveform by sampling with the strobe light from the pulse light source, but the present invention is not limited to this. That is, a non-sampling method may be used in which the light source is a CW light source and a light speed photodetector is used. At this time, the time resolution of the EO measuring device is
Limited by photodetector and measurement. If a high-speed pin-PD or APD is used as the photodetector and a high-speed digital oscilloscope is used as the measuring unit, a working area of 1 GHz or higher can be obtained. Even in this case, the tie-sync difference can be accurately measured by using the waveform storage operation device as in the above-described embodiment.

[0073]

As described above, according to the timing difference measuring system of the present invention, since the waveform of signals is subjected to a predetermined calculation by the second means to detect a temporal relationship, it is more preferable than visual inspection of waveforms. It is possible to detect a more accurate temporal difference, and it is possible to detect a more accurate temporal relationship even if there is noise depending on the processing method.

In particular, when the first means is constituted by using an electro-optic crystal for inputting a signal, it has a very high time resolution, so that the measurement can be performed with higher accuracy.

Further, when the first means is constructed by using the pulse signal source for outputting the pulse signal to the pin of the IC to be measured, the timing of the pulse signal to the IC to be measured can be aligned. Therefore, the timing change of the IC to be measured can be measured more accurately.

Further, when the third means is further provided,
Since the noise component is removed, a more precise temporal relationship can be detected.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is a block diagram of an EO probe.

FIG. 3 is a graph showing an example of the detection result of the E-O measuring device.

FIG. 4 is a diagram showing a waveform of a drive pulse.

FIG. 5 is a diagram showing a waveform of strobe light.

FIG. 6 is a diagram showing an outline of processing of a measurement / control system of the EO measuring apparatus.

7 is a diagram showing an example of measurement results of the apparatus of FIG.

FIG. 8 is a diagram showing how measurement results of the apparatus of FIG. 1 vary.

FIG. 9 is an explanatory diagram of measurement of gate delay characteristics of a semiconductor device.

10 is a diagram showing an example of input / output waveforms to / from a semiconductor element in the measurement of FIG.

FIG. 11 is a conceptual diagram of an application example to an IC tester.

FIG. 12 is a configuration diagram of a second embodiment.

FIG. 13 is a configuration diagram of a third embodiment.

FIG. 14 is a configuration diagram of a fourth embodiment.

[Explanation of symbols]

110 ... EO measuring device, 120b, 122b ... EO
Probe, 120c, 122c ... Polarizer, 120d, 1
22d ... Analyzer, 120e, 122e ... Half mirror,
140, 142 ... Photodetector, 130, 132 ... LD pulse light source, 220 ... Waveform storage section, 230 ... Cross-correlation calculation section, 310a, b, c ... Driver, 320a, b, c ...
Delay setting circuit, 260, 330 ... Changeover switch.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isuke Hirano 1 126-1, Nomachi, Hamamatsu City, Shizuoka Prefecture Hamamatsu Photonics Co., Ltd.

Claims (17)

[Claims] 1. A first means for measuring waveforms of two or more signals; storing the waveforms of the signals; and performing a predetermined operation on the stored waveforms of the signals to obtain a timing difference between the signals. A timing difference measuring system comprising: a second means for detecting. 2. The optical system for converting the electric field of the signal into an optical signal by optical modulation for detection, and the measuring system for measuring the waveform of the signal from the electric field of the detected signal. The timing difference measurement system according to claim 1, further comprising: 3. The optical system, which can be arranged in the vicinity of the path of the signal, has a probe having an electro-optical effect, a light source for outputting light to the probe, and detection for detecting light optically modulated by the probe. 3. The timing difference measuring system according to claim 2, wherein the timing difference measuring system comprises: 4. The timing difference measuring system according to claim 3, wherein the light modulated by the probe is reflected by a reflective film formed on the bottom surface of the probe and detected by the detector. 5. The light source is a laser light source capable of outputting laser light with a short pulse.
The described timing difference measurement system. 6. The control system includes a control circuit for driving the light source to output light in a pulsed form, and lock-in amplification of a detection output of the detector based on a drive timing of the drive circuit, 4. A measuring section for detecting a waveform of a signal, the measuring section being included.
The described timing difference measurement system. 7. The measurement system further includes a drive circuit that outputs a drive signal to a circuit under measurement including the path of the signal, and the control circuit controls the timing of the pulse output by the drive circuit. 7. The timing difference measuring system according to claim 6, wherein the light source is driven with a gradual shift. 8. The timing difference measuring system according to claim 2, wherein the optical system has two systems. 9. The first optical probe, which can be arranged near one path of the signal and has an electro-optical effect, and a first light source that outputs light to the first probe, A first detector that detects light modulated by the first probe; a second probe that can be arranged near another path of the signal and has an electro-optical effect; 9. A second light source that outputs light to the probe of 1), and a second detector that detects the light modulated by the second probe are included. Timing difference measurement system. 10. The optical system can be arranged in the vicinity of two paths of the signal and has a probe having an electro-optical effect, a light source for outputting light to the probe, and a light of the light source for the probe. 6. An optical circuit which is provided in the vicinity of each of the paths, and first and second detectors which respectively detect the light modulated by the probe in the vicinity of each of the paths. 8. The timing difference measurement system described in 8. 11. The timing difference measuring system according to claim 1, wherein the second means stores the waveform of the signal as a digital value. 12. The timing difference according to claim 1, wherein the second means obtains the cross-correlation of the waveforms of the stored signals and detects the timing difference from the peak value of the cross-correlation. Measuring system. 13. The second means stores the stored two
13. The timing difference measurement according to claim 12, wherein each of the two signal waveforms is Fourier-transformed, and the product of the conjugate function of one of them is subjected to an inverse Fourier transform to obtain the cross-correlation of the waveforms of the signals. system. 14. The second means is one of the signals.
2. After storing one of the signals, another one of the signals is measured by the first means, and at the same time, a predetermined operation is performed on the waveform of the signal to detect the timing difference between the signals. The described timing difference measurement system. 15. The timing difference measuring system according to claim 1, further comprising third means for performing a predetermined process on the waveform of the signal. 16. The timing difference measuring system according to claim 15, wherein the third means processes the waveform of the signal by filtering the waveform of the signal. 17. The first means has a pulse signal source for outputting a pulse signal to a pin of an IC to be measured, and the signal is provided in a large number of channels corresponding to the pin connected to the pulse signal source. Is input, the waveforms of those signals are measured, and the timing of each pulse output from the pulse signal source to the pin is adjusted based on the timing difference detected by the second means. The timing difference measuring system according to claim 1.