JP3165873B2 - Electric signal measuring method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric circuit for supplying a drive signal to a circuit under test, and sampling an electric signal under test in the circuit under test driven by the drive signal with a pulse signal (for example, laser pulse light). The present invention relates to a signal measuring method and apparatus.

[0002]

2. Description of the Related Art When an electro-optical material is brought close to a circuit to be measured in an operating state, a leakage electric field due to an operation electric signal in the circuit to be measured is coupled with the electro-optical material. The birefringence of the electro-optic material changes according to the strength of the coupled electric field. When the laser beam is irradiated to the electro-optic material in this state, the polarization of the laser beam changes due to a change in the birefringence. The change in the polarization of the laser light can be converted into a change in the intensity of the laser light by passing the laser light through an appropriate polarizer. The light intensity change is converted into an electric signal by a photodetector. By measuring this electric signal, it is possible to measure the electric field coupled to the electro-optical material, that is, the operating electric signal (measured electric signal) propagating at the measurement point inside the circuit under test.

[0003] This electric signal measuring technique is divided into a measuring method according to a technique for controlling the timing of sampling an electric signal to be measured with laser pulse light (timing control technique) and a technique for detecting a weak signal (signal processing technique). Can be The timing control technology includes a beat method in which a beat frequency is set so that a beat frequency is generated between the repetition frequency of the electric signal to be measured and the laser pulse light, and a timing method in which both phases are changed using a phase shifter. And a phase shift method for controlling the phase shift. The signal processing technology includes a method of modulating a signal to be detected into a band with little noise and measuring the band with a lock-in amplifier in a narrow band (lock-in narrow band detection method).
And a method of fetching the detected signal many times and performing an averaging process (averaging process). FIG. 4 shows the measurement methods used so far as conventional methods 1, 2, and 3. FIGS. 5, 6, and 7 show block diagrams of electric signal measuring devices according to the conventional methods 1, 2, and 3, respectively. As will be described later, the present invention employs a measurement method combining the phase shift method and the averaging method as shown in FIG. 4 in comparison with the conventional methods 1, 2, and 3.

[Conventional method 1] In FIG. 5, 1 is a signal generator for generating a drive signal for the circuit under test 2, 6 is a pulse generator, 7 is a laser for generating laser pulse light, and 9 is an electro-optic material. A probe head 8 comprising: a laser beam detector for detecting a change in the polarization of the laser pulse light emitted from the laser 7 in the probe head 9; 11: an amplitude modulator for amplitude-modulating a drive signal generated by the signal generator 1; 13
Is a signal generator for generating a reference signal to the pulse generator 6,
Reference numeral 12 denotes a reference signal generator for generating reference signals to the signal generators 1 and 13, and reference numeral 14 denotes a lock-in amplifier. In this electric signal measuring device, a driving signal to the circuit under test 2 (repetition frequency f _{si g)} amplitude modulated at a low frequency by the amplitude modulator 11, the lock-in amplifier 1 and the modulation frequency fm
4 is detected in a narrow band as a reference signal. In this method, the circuit under test 2 may operate abnormally due to the input of the modulation signal, so that applicable circuits are limited.

[Conventional method 2] In FIG. 6, reference numeral 4 denotes a phase shifter,
Reference numeral 15 denotes a signal generator for generating a timing control signal to the phase shifter 4, and the same reference numerals as those in FIG. 5 denote the same or equivalent components. In this electric signal measuring apparatus, a rectangular wave (timing control signal) based on a zero level is supplied to a phase shifter 4, and a point of a phase difference corresponding to a level difference of the rectangular wave and a reference point are alternately sampled (FIG. 8), the difference between the sampled voltage levels is detected in a narrow band using the repetition frequency fr of the rectangular wave as the reference signal of the lock-in amplifier 14. Here, the leading value of the rectangular wave is V _P , the repetition frequency of the output signal of the signal generator 13 is f _L , the voltage-phase shift amount conversion coefficient of the phase shifter 4 is α, the phase difference between the reference point and the sampling point. Let Δφ be the timing difference and Δt be the timing difference. The _{Δφ = α · V P Δt =} Δφ / 2πf L = α · V P / 2πf L which, by changing the V _P, and controls the phase difference i.e. timing difference, to measure the waveform of the electrical signal to be measured ing. In this method, the point of the phase difference corresponding to the level difference of the rectangular wave and the reference point are alternately sampled, so that at the measurement point where the timing difference is large, the error in the timing of capturing the electric signal to be measured becomes large, and the waveform measurement is performed. Accuracy decreases.

[Conventional method 3] In FIG. 7, reference numeral 10 denotes an averaging device, and the same reference numerals as those in FIG. 5 denote the same or equivalent components. In the electric signal measuring device, the polarization change of the laser pulse light detected by the laser light detecting device 8 in the probe head 9, that is, the waveform value of the sampled electric signal to be measured is added and averaged by the averaging device 10. In this method, the reference signals of the signal generator 1 for driving the circuit under test and the signal generator 13 for driving the laser are made the same as in the conventional methods 1 (FIG. 5) and 2 (FIG. 6). Need to synchronize the phase, the repetition frequency f of the drive signal
_Assuming that a slight frequency shift between _sig and the repetition frequency f _L of the laser pulse light is Δf, n is a natural number, the relations expressed by f _sig = n · f _L + Δf in the conventional methods 1 and 3, and the conventional method Then, there is a frequency limitation that the relationship represented by f _sig = n · f _L must be set.

[0007]

As described above, in the conventional electric signal measuring apparatus, "the circuit under test abnormally operates by inputting the modulated signal to the circuit under test", and "the timing at which the phase shift amount is large". The error in the timing of capturing the electrical signal under test is large and the waveform measurement accuracy is degraded. "," The circuit under test is synchronized with the reference signal of the laser driving synthesizer, and the natural number of the repetition frequency of the laser pulse light It is necessary to set a frequency that is twice as small as the frequency shift as the repetition frequency of the drive signal ", and it has not been possible to measure a measured electrical signal having an arbitrary repetition frequency with high accuracy.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and an object of the present invention is to provide an electric signal measuring method and an electric signal measuring method capable of measuring an electric signal to be measured having an arbitrary repetition frequency with high accuracy. It is to provide a device.

[0009]

In order to achieve such an object, the first and second inventions (Claims 1 and 2)
The invention according to the present invention) divides the repetition frequency of one of the drive signal to the circuit under test and the signal output from the circuit under test by a natural number, and changes the phase of the divided signal by a fixed amount. A pulse signal is generated using the signal thus obtained as a reference signal, and the electric signal under test sampled with the pulse signal is subjected to an averaging process. Further, the third and fourth inventions (inventions according to claims 3 and 4)
Is a signal obtained by dividing the repetition frequency of one of the drive signal to the circuit under test and the signal output from the circuit under test by a natural number, and changing the phase of the divided signal by a fixed amount. A laser pulse light is generated as a reference signal, and an electric signal to be measured sampled with the laser pulse light is subjected to an averaging process.

[0010]

Therefore, according to the present invention, in the first and second inventions, the repetition frequency of the drive signal to the circuit under test (or the signal output from the circuit under test) is divided by a natural number, and A pulse signal is generated using a signal obtained by changing (increasing or decreasing) the phase of the frequency-divided signal by a constant amount as a reference signal, and the electric signal to be measured sampled with the pulse signal is subjected to an averaging process. In the third and fourth inventions, the repetition frequency of the drive signal to the circuit under test (or the signal output from the circuit under test) is divided by a natural number, and the phase of the frequency-divided signal is kept constant. Laser pulse light is generated with the signal changed (increased or decreased) by an amount as a reference signal, and the measured electric signal sampled with the laser pulse light is subjected to an averaging process.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. FIG. 1 is a block diagram showing an electric signal measuring apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a signal generator for generating a drive signal to the circuit under test 2, and SW denotes a drive signal to the circuit under test 2 (input signal to the circuit under test 2) and output from the circuit under test 2. A switch for inputting a signal (output signal) and selecting one of them; a frequency divider for dividing a repetition frequency of a signal given via a switch SW to a natural number (n) by 1; A phase shifter for changing the phase of the frequency-divided signal divided by the frequency divider 3 and outputting the signal; a signal generator for generating a timing control voltage signal for controlling the phase shifter 4; a pulse generator 6; Reference numeral 7 denotes a laser for generating laser pulse light, 9 denotes a probe head made of an electro-optical material, 8 denotes a laser light detecting device for detecting a change in polarization of the laser pulse light emitted from the laser 7 in the probe head 9, and 10 denotes laser light. Signal output from detector 8 An averaging device for processing averaging the. In this embodiment, the switch SW is set to a switching mode in which a drive signal for the circuit under test 2 is branched and applied to the frequency divider 3.

In this electric signal measuring device, the signal generator 1
Is supplied to the circuit under test 2 while
It is also provided to the frequency divider 3 via the switch SW. Divider 3
_Divides the repetition frequency f _sig of the drive signal supplied via the switch SW by a natural number, and shifts the resulting frequency- _divided signal of the repetition frequency f _L (f _L = f _sig / n). Give to phaser 4. This frequency-divided signal completely matches the phase of the electric signal under test in the circuit under test 2. Here, the same measurement is possible even if the frequency divider 3 is replaced with a trigger countdown.

In this state, when the laser pulse light is generated from the laser 7 through the pulse generator 6 and the electric signal to be measured is sampled, the same point of the waveform of the electric signal to be measured is always measured. That is, the electric signal under measurement having an arbitrary repetition frequency and the laser pulse light can be synchronized without being aware of the repetition frequency of the circuit under measurement 2.

The phase of the frequency-divided signal output from the frequency divider 3 is changed by the phase shifter 4 in order to change the timing for capturing the electric signal to be measured. For a slight voltage change ΔV, the time change Δt at the sampling point is represented by Δt = Δφ / 2πf _L = α, where α is the voltage-phase shift amount conversion coefficient of the phase shifter 4 and Δφ is the phase shift amount for ΔV. · Expressed as ΔV / 2πf _L.

Here, in the present embodiment, as the phase shifter 4,
The amount of phase shift is proportional to the control voltage, and a phase shifter capable of high-speed control is used. As the timing control voltage signal from the signal generator 5, a signal (sawtooth wave) whose voltage changes in proportion to time and returns at a certain point in time is used. As a result, the phase of the frequency-divided signal changes by a fixed amount (Δφ), that is, the generation timing of the laser pulse light becomes a fixed amount (Δt).
By changing (see FIG. 2), the maximum timing difference _{Δt MAX = α · V P /} 2πf corresponding to the top value V _P of the sawtooth
After changing to _L , the phase difference returns to the original state again, and the waveform of the measured electric signal is repeatedly sampled.

In this embodiment, since the phase shifter 4 which can be controlled at high speed is used, it is possible to perform sampling 1000 times or more per second. By performing the high-speed averaging process in the averaging device 10, the S / n ratio is improved, and the electric signal to be measured can be measured with high accuracy. If the linearity of the phase shift amount that determines the time accuracy is calibrated from the control voltage and the measured data of the phase shift amount, picosecond accuracy can be easily obtained.

In the present embodiment, the drive signal to the circuit under test 2 is divided and applied to the frequency divider 3. However, the switching mode of the switch SW is changed to provide the frequency divider 3 with the drive signal. An output signal from the electric signal under measurement 2 may be given. Also in this case, the frequency-divided signal output from the frequency divider 3 completely matches the phase of the measured electric signal in the circuit-under-measurement 2.

Further, in the present embodiment, the intensity of the electric field coupled to the probe head 9 is sampled by irradiating the probe head 9 with laser pulse light. Alternatively, another method may be adopted as long as the method measures the electrical signal under measurement with a pulse signal.
FIG. 3 shows a block diagram of the electric signal measuring device in this case.

[0019]

As is apparent from the above description, according to the present invention, in the first and second inventions, the repetition frequency of the drive signal to the circuit under test (or the signal output from the circuit under test) is used. Is divided by a natural number, and the phase of the divided signal is changed by a fixed amount (increase or decrease).
A pulse signal is generated using the signal thus obtained as a reference signal, and the electric signal to be measured sampled with the pulse signal is subjected to an averaging process. In the third and fourth aspects of the present invention, the circuit to be measured is The repetition frequency of the drive signal (or the signal output from the circuit under test) is divided by a natural number, and a signal obtained by changing (increasing or decreasing) the phase of the divided signal by a fixed amount at a time is used as a reference signal. A pulse light is generated, and the electric signal to be measured sampled by the laser pulse light is subjected to an addition averaging process. The electric signal to be measured having an arbitrary repetition frequency is subjected to a high-speed averaging process to obtain an S / N ratio. In addition to the improvement, the measurement can be performed with high accuracy.

[Brief description of the drawings]

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

FIG. 2 is a timing chart for explaining the operation of the electric signal measuring device.

FIG. 3 is a block diagram of an electric signal measuring device when a method of sampling a measured electric signal with a pulse signal including irradiation of laser pulse light is adopted.

FIG. 4 is a diagram showing a comparison between the conventional methods 1, 2, 3 and the electric signal measuring method of the present invention.

FIG. 5 is a block diagram of an electric signal measuring device according to Conventional Method 1.

FIG. 6 is a block diagram of an electric signal measuring device according to Conventional Method 2.

FIG. 7 is a block diagram of an electric signal measuring device according to Conventional Method 3.

FIG. 8 is a timing chart for explaining the operation of the electric signal measuring device according to the conventional method 2.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 signal generator SW switch 3 divider 4 phase shifter 5 signal generator 6 pulse generator 7 laser 9 probe head 8 laser light detector 9 probe head 10 averaging device

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01D 1/00 G01R 29/12

Claims (4)

(57) [Claims] 1. An electric signal measuring method for applying a drive signal to a circuit under test and sampling an electric signal under test in the circuit under test driven by the drive signal with a pulse signal, wherein the drive signal to the circuit under test is provided. And the repetition frequency of one of the signals output from the circuit under test is divided by a natural number, and the pulse signal is generated using a signal obtained by changing the phase of the divided signal by a constant amount as a reference signal. And
An electric signal measuring method, wherein the electric signal under measurement sampled with the pulse signal is subjected to an averaging process. 2. An electric signal measuring apparatus which supplies a drive signal to a circuit under test, and samples an electric signal under test in the circuit under test driven by the drive signal with a pulse signal, wherein the drive signal to the circuit under test is provided. A frequency dividing means for dividing one of the repetition frequencies of the signal output from the circuit under test to a natural number, and changing the phase of the frequency-divided signal divided by the frequency dividing means by a fixed amount. A phase shifter for generating a signal generated by the phase shifter, a pulse signal generator for generating the pulse signal using the signal generated by the phase shifter as a reference signal, and a pulse signal generated by the pulse signal generated by the pulse signal generator. An electric signal measuring device, comprising: addition averaging processing means for performing averaging processing of the measured electric signal. 3. A drive signal is supplied to a circuit under test, and an electric signal under test in the circuit under test driven by the drive signal is coupled to the electro-optical material by irradiating the electro-optical material with laser pulse light. In an electric signal measuring method for detecting and sampling the intensity of an electric field, a frequency of a repetition frequency of one of a driving signal to the circuit to be measured and a signal output from the circuit to be measured is divided by a natural number, The laser pulse light is generated using a signal obtained by changing the phase of the frequency-divided signal by a fixed amount as a reference signal, and the measured electric signal sampled with the laser pulse light is subjected to an averaging process. Electrical signal measurement method. 4. A drive signal is supplied to a circuit under test, and an electric signal under test in the circuit under test driven by the drive signal is coupled to the electro-optical material by irradiating the electro-optical material with laser pulse light. An electric signal measuring device for detecting and sampling the intensity of an electric field, wherein the frequency of one of a repetition frequency of a drive signal to the circuit under test and a signal output from the circuit under test is divided by a natural number. Frequency dividing means, phase shifting means for generating a signal in which the phase of the frequency-divided signal divided by the frequency dividing means is changed by a fixed amount, and the laser pulse light using the signal generated by the phase shifting means as a reference signal And an averaging process for averaging the electric signal under measurement sampled with the laser pulse light generated by the pulse light generating device. Electrical signal measuring apparatus characterized by comprising a means.