JPH08160110A - Electric signal measuring instrument - Google Patents

Abstract

PURPOSE: To measure electric signals to be measured with high accuracy at a high speed by providing a harmonic generator which electrically generates harmonic signals from laser reference signals. CONSTITUTION: A first laser reference signal 15 from a first power splitter 3 is inputted to a laser light source 5 and the light source 5 emits a pulsed laser beam 20. A second laser reference signal 16 is inputted to a harmonic generator 6 and electrically converted into a signal containing a high-order harmonic component having a frequency which is natural-number of times as high as that of the reference signal 16. A circuit 22 to be measured is operated by a signal from a signal generator 8 and an electric field 21 leaks out when a signal to be measured is propagated through a signal line 23 and coupled with an electrooptic material 9. The index of birefringence of the material 9 varies in accordance with the intensity of the coupled electric field. When the laser beam 20 is made incident on the material 9, the polarized state of the beam 20 varies due to the variation of the birefringence and a polarization detector 10 detects the variation of the polarized state. Therefore, a waveform fetching signal having a stabilized amplitude and the same frequency as the pulse repetition frequency of the signal to be measured is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric signal measuring device for measuring a high-speed electric signal propagating through a wiring in a circuit operating at high speed with a laser beam with high accuracy.

[0002]

2. Description of the Related Art An electric signal measuring technique using this type of electro-optical material and laser light is widely known as EO sampling. In EO sampling, the phases of the two synthesizers are usually synchronized, the frequency of the signal generated from the first synthesizer, which is the reference of the pulse repetition frequency of the laser light, is f ₁ , and the second synthesizer is the reference of the repetition frequency of the signal under measurement. the frequency of the signal generated from the f _2,
By setting f ₁ and f ₂ in the relationship of the following equation, a beat frequency is generated between them.

F ₂ = n × f ₁ + Δf (1) where n is a natural number and Δf is the beat frequency of f ₁ and f ₂ .

When the frequency is set in this way, the repetition frequency f _{2 of the} signal under measurement is down-converted to the beat frequency Δf by EO sampling. In order to capture the down-converted signal with a waveform measuring device with high accuracy, a waveform capturing reference signal having the same frequency as the beat frequency is required.

As a conventional electric signal measuring apparatus using EO sampling, there is a conventional method 1 shown in FIG. 2, for example. In the conventional method 1, the reference signal for waveform acquisition is obtained by the method described below.

In FIG. 2, the pulsed laser light output from the laser light source 5 is branched by a beam splitter 31, one of which is used as a sampling pulse light incident on the electro-optical material 9, and the other is a high-speed photoelectric converter 30. Is converted into an electric signal with. Since the electric signal after photoelectric conversion is a signal obtained by converting the laser pulse light generated with the first synthesizer 1 as a reference, the harmonic component m × f ₁ (m = 1, m = 1, _{1 of the} signal frequency output from the first synthesizer 1 2, 3, ...
m) is included. When this signal and the signal f ₂ output from the second synthesizer 2 are input to the mixer 11, the mixer 11 outputs

## EQU1 ## A signal having a frequency component of Δf + (f ₁ + Δf) + (2 × f ₁ + Δf) + (3 × f ₁ + Δf) (2) is output. Here, if the bandpass filter 12 is set so that only the beat frequency Δf component of the first term passes, a signal having the same frequency as the signal under measurement whose repetition frequency is down-converted to the beat frequency by EO sampling is obtained. You can The signal to be measured is measured by using this signal as a reference signal for waveform acquisition of the waveform measuring device 14.

Further, there is a method using a third synthesizer 40 synchronized with the first synthesizer 1 and the second synthesizer 2, as in the conventional method 2 shown in FIG. A signal having the same frequency as the beat frequency is output from the third synthesizer 40, and the measured signal is measured as a reference signal for waveform acquisition of the waveform measuring device 14.

[0008]

Among the above-mentioned conventional electric signal measuring devices, in the device of the conventional method 1 shown in FIG. 2, the laser light generally causes excess noise components and fluctuations of the light emission due to the light emission thereof. Mixer 1 because it is in the low frequency band
The amplitude of the signal output from 1 fluctuates. If this signal is used as the reference signal for waveform acquisition, an error will occur in the trigger timing when the digital oscilloscope is used in the waveform measuring instrument 14, or when the lock-in amplifier is used, the synchronization with the reference signal is likely to be lost and the phase is lost. There is a problem that the measurement accuracy deteriorates.

In the conventional method 2 shown in FIG. 3, the frequency difference between the first and second synthesizers is 5
A low frequency beat frequency separated by more than one digit is synthesized and generated by a synthesis method. The time accuracy Δt of the synthesizer is expressed by the following equation as is generally known.

[0010]

[Equation 2] f _c is the frequency of the signal output by the synthesizer, L (f)
Is the phase noise characteristic near that frequency. From the above formula,
The third synthesizer 40 has the same time accuracy at a frequency lower than that of the first and second synthesizers 1 and 2 by five digits or more,
That is, a phase noise characteristic lower by 10 digits or more is required. It is generally known that the lower the frequency of the signal output from the synthesizer, the lower the phase noise characteristic is. However, as described above, the phase noise does not decrease by more than 10 digits.
Therefore, in the conventional method 2, the phase noise having the same time accuracy as that of the first and second synthesizers cannot be obtained from the third synthesizer. If this signal is used as the reference signal for waveform acquisition, an error will occur in the trigger timing when the digital oscilloscope is used in the waveform measuring instrument 14, and when the lock-in amplifier is used, the synchronization with the reference signal tends to be lost and the phase There is a problem that the measurement accuracy deteriorates.

The present invention has been made in view of the above,
It is an object of the invention to provide an electric signal measuring device capable of measuring a high speed electric signal to be measured with high accuracy.

[0012]

In order to achieve the above object, the electrical signal measuring apparatus of the present invention has a birefringence index which varies depending on the strength of an electric field to be coupled, and which is propagated through a wiring of a circuit under measurement in an electro-optical material. An electric field caused by an electric signal is coupled, the electro-optic material is irradiated with laser light, and the laser light that has undergone polarization change due to a change in birefringence of the electro-optic material is converted into a low-speed electric signal by a polarization detector. In the electric signal measuring device for measuring the electric signal under measurement by measuring the low-speed electric signal with a waveform measuring device, a first synthesizer that repeatedly generates a signal and a signal output from the first synthesizer are branched. A first power splitter that outputs a first laser reference signal and a second laser reference signal, a laser light source that generates laser light from the first laser reference signal, and the second laser A harmonic generator that electrically generates a harmonic signal from a quasi-signal and a phase that is in phase with the first synthesizer, and has a low beat frequency that is a natural number multiple of the frequency of the signal output by the first synthesizer. A second synthesizer that generates a signal of a frequency to which is added, a second power splitter that branches a signal output from the second synthesizer, and outputs a first circuit reference signal and a second circuit reference signal, and the first circuit From a signal generator that generates a signal for driving the circuit under test from a reference signal, and a signal output from the second circuit reference signal and the harmonic generator, a signal having a sum frequency and a difference frequency of both signals. A mixer that generates
A bandpass filter that allows only a signal having the beat frequency to pass among the signals output from the mixer and outputs a reference signal for capturing a waveform of the waveform measuring device.

The electrical signal measuring apparatus of the present invention is characterized in that the harmonic generator has a non-linear type device for distorting an input signal.

Further, the electrical signal measuring apparatus of the present invention is characterized in that the harmonic generator has a pulse generator for converting an input signal into a pulse wave.

The electrical signal measuring device of the present invention is characterized by having an IF amplifier for amplifying the signal output from the band pass filter.

Further, the gist of the electrical signal measuring apparatus of the present invention is to have an RF amplifier for amplifying the second circuit reference signal output from the second power splitter.

[0017]

In the electric signal measuring apparatus of the present invention, the harmonic generator that electrically converts a signal obtained by branching the output of the first synthesizer for generating a signal serving as a reference for laser driving into a signal having a higher harmonic component. The signal obtained by inputting
Generates a signal that is in phase with the first synthesizer and that is a natural frequency multiple of the frequency of the signal output by the first synthesizer plus a low beat frequency. The signal that splits the output of the two synthesizer is input to the mixer, and a signal with a beat frequency is obtained by connecting an appropriate bandpass filter to the signal output from the mixer, and the reference signal for waveform acquisition of the waveform measuring instrument. Used as.

In the electric signal measuring apparatus of the present invention, the harmonic generator is composed of a non-linear type device, and the non-linear type device distorts the input signal.

Further, in the electric signal measuring device of the present invention, the harmonic generator is composed of a pulse generator, and the input signal is converted into a pulse wave by the pulse generator.

In the electric signal measuring device of the present invention, the output signal of the band pass filter is amplified by the IF amplifier.

In the electric signal measuring device of the present invention, the output signal of the second power splitter is amplified by the RF amplifier.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an electric signal measuring apparatus according to an embodiment of the present invention. In the figure, 1 and 2 are a first synthesizer and a second synthesizer which generate signals. The two synthesizers synchronize the phases of the output signals by making the master clocks for synthesizing the frequencies the same, and the first synthesizer 1 serving as the reference of the pulse repetition frequency of the laser light.
F ₁ the frequency of the signal generated from the frequency of the signal generated from the second synthesizer 2 serving as a reference for the repetition frequency of the measured signal and f _2, the f ₁ and f _2, the frequency shown in equation (1) Set in a relationship.

Reference numeral 3 is a first power splitter which branches the signal output from the first synthesizer 1 and outputs a first laser reference signal 15 and a second laser reference signal 16. The first laser reference signal 15 is input to the laser light source 5 to generate pulsed laser light 20. The second laser reference signal 16 is input to the harmonic generator 6 and is electrically converted into a signal having a high-order harmonic component that is a natural multiple of the frequency of the second laser reference signal. The harmonic generator 6 uses, for example, a non-linear device such as a step recovery diode or a pulse generator such as a comb generator.

Reference numeral 7 is a second power splitter for branching the signal output from the second synthesizer 2 and outputting a first circuit reference signal 17 and a second circuit reference signal 18. The first circuit reference signal 17 is input to the signal generator 8 and a signal for driving the circuit under test 22 is output. As the signal generator 8, for example, a pattern generator is used, or the signal generator 8 is removed when a sine wave is required, and the second power splitter 7 is used.
The output of 1 may be directly input to the circuit under test 22.

Two ground lines 24 on the circuit under test 22
When the signal line 23 is wired between the two, the circuit under measurement 22 is operated by the signal output from the signal generator 8 and the signal under measurement propagates through the signal line 23 in the circuit under measurement 22 to generate the electric field 21. Leak and bond to the electro-optic material 9. The birefringence of the electro-optic material 9 changes according to the strength of the coupled electric field 21. When the laser light 20 enters the electro-optical material 9 in this state, the polarization state of the laser light 20 changes due to the change in birefringence of the electro-optical material 9. Reference numeral 10 is a polarization detector that detects a change in polarization of the laser light 20. The polarization detector 10 often used in EO sampling is configured by combining a polarizer, a polarization beam splitter, a wave plate, and optical components such as a photodiode.

Reference numeral 11 denotes a mixer for mixing the second circuit reference signal 18 and the signal output from the harmonic generator 6 and outputting the difference frequency and the sum frequency of the frequency components of the two signals. Amplitude of second circuit reference signal 18 and harmonic generator 6
Depending on the output signal amplitude from, the RF amplifier 4 may be used before inputting to the mixer 11 to adjust the amplitude so that the mixer 11 operates normally. Of the signal components output from the mixer 11, the pass frequency of the band pass filter 12 is set so that only the beat frequency passes. If the amplitude of the signal having the beat frequency that has passed through the bandpass filter 12 is small, it causes an error in the waveform measuring device 14, so the output of the bandpass filter 12 is amplified by the IF amplifier 13 and the waveform of the waveform measuring device 14 is amplified. Input as a reference signal for acquisition.

The signal obtained as described above has a very stable amplitude and has the same frequency as the repetition frequency of the signal under measurement down-converted by EO sampling. Therefore, a digital oscilloscope is used for the waveform measuring instrument 14. In this case, if this signal is input as a trigger signal, and if a lock-in amplifier is used, as a reference signal, it is possible to perform high-accuracy measurement with the time accuracy deterioration and phase accuracy deterioration that occur during waveform acquisition minimized.

[0029]

As described above, according to the present invention,
Based on the output signal of the reference synthesizer for driving the laser and the reference synthesizer for driving the circuit under measurement, the repetition frequency of the measured signal down-converted by EO sampling by an electrical method using a harmonic generator and a mixer. A reference signal for waveform acquisition that has the same frequency and stable amplitude can be easily obtained, and high-accuracy high-speed electrical signal measurement that suppresses the deterioration of time accuracy and phase accuracy that occurs during waveform acquisition can be performed. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an electric signal measuring device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional electric signal measuring device.

FIG. 3 is a block diagram showing another configuration of a conventional electric signal measuring device.

[Explanation of symbols]

 1 1st synthesizer 2 2nd synthesizer 3 1st power splitter 4 RF amplifier 5 laser light source 6 harmonic generator 7 2nd power splitter 8 signal generator 9 electro-optic material 10 polarization detector 11 mixer 12 bandpass filter 13 IF amplifier 14 waveform measuring instrument 22 circuit under measurement 23 signal line 24 ground line

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/66 C 7735-4M

Claims (5)

[Claims] 1. An electric field caused by an electric signal to be measured propagating through a wiring of a circuit to be measured is coupled to the electro-optical material whose birefringence changes depending on the strength of the electric field to be coupled, and the electro-optical material is irradiated with laser light. , Converting the laser light that has undergone polarization change due to a change in birefringence of the electro-optic material into a low-speed electrical signal with a polarization detector, and measuring the low-speed electrical signal with a waveform measuring device to obtain the measured electrical signal. In an electric signal measuring device for measuring, a first synthesizer that generates a repetitive signal, a first power splitter that branches a signal output from the first synthesizer and outputs a first laser reference signal and a second laser reference signal, A laser light source that generates laser light from the first laser reference signal, a harmonic generator that electrically generates a harmonic signal from the second laser reference signal, and the first system. A second synthesizer that is phase-synchronized with the synthesizer and that generates a signal having a frequency obtained by adding a low-frequency beat frequency to a frequency that is a natural multiple of the frequency of the signal output by the first synthesizer, and is output from the second synthesizer. A second power splitter that splits a signal that outputs a first circuit reference signal and a second circuit reference signal, a signal generator that generates a signal that drives the circuit under test from the first circuit reference signal, and A mixer that generates a signal of a sum frequency and a difference frequency of both signals from a two-circuit reference signal and a signal output from the harmonic generator, and has the beat frequency in the signal output from the mixer An electric signal measuring device, comprising: a band pass filter that allows only a signal to pass through and outputs a reference signal for waveform acquisition of the waveform measuring device. 2. The harmonic generator has a non-linear device that distorts an input signal.
The electrical signal measuring device described. 3. The electrical signal measuring device according to claim 1, wherein the harmonic generator includes a pulse generator that converts an input signal into a pulse wave. 4. The electric signal measuring device according to claim 1, further comprising an IF amplifier that amplifies a signal output from the band pass filter. 5. The electric signal measuring device according to claim 1, further comprising an RF amplifier that amplifies the second circuit reference signal output from the second power splitter.