JP3369084B2 - Electro-optic sampling probe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electro-optical sampling probe used for measuring an electric signal having a high frequency of, for example, 5 GHz flowing in a conductive path.

[0002]

2. Description of the Related Art In a high-speed information communication system or the like, for inspection, maintenance, measurement, etc., the potential of a high frequency circuit signal is measured with high accuracy without disturbing the circuit under test. There is a need. On the other hand, the previous F
Instead of the ET probe, a handy type high impedance probe has already been proposed, which can measure the potential of a circuit signal having a frequency exceeding 5 GHz, for example, without disturbing the circuit to be measured.

In this high impedance probe, a metal needle to be contacted with, for example, a microstrip line to which an electric signal to be measured is applied is attached to one end of an electro-optical material such as BSO (Bi12SiO20) to which a dielectric mirror is attached. It consists of the attached ones. Then, in this high impedance probe, an electric signal on the microstrip line obtained through the metal needle is detected as a potential difference at both ends of the electro-optical material, and further according to a change in electric field strength obtained as the potential difference, The light birefringence of the electro-optic material is changed.

Therefore, when a laser beam is incident on the electro-optical material, the laser beam undergoes a deflection change due to a change in the birefringence index, and is deflected to each photodiode as polarized light beams orthogonal to each other and having opposite phases. It is incident. Then, each of these deflected lights is converted into an electric signal by these photodiodes, input to a differential amplifier or the like and processed, and measurement data corresponding to the conductor potential can be output.

[0005]

However, in such a conventional high-impedance probe, the high-frequency electric signal obtained through the electro-optic material has its DC component removed by the low-cut action for removing low-frequency noise. Therefore, only the signal corresponding to the change in the signal potential on the conductor is output, and as a result, there is a problem that the signal voltage including the DC component cannot be correctly measured.

The present invention solves the above-mentioned conventional problems. By utilizing the direct current component of the electric signal obtained directly from the conductor, the direct current component of the electric signal obtained through the electro-optical material is reproduced. Therefore, it is an object of the present invention to provide an electro-optical sampling probe capable of measuring a high frequency signal voltage on the conductor with high accuracy and stability while compensating for the drawbacks of the conventional sampling oscilloscope.

[0007]

[Means for Solving the Problems] To achieve the above object,
The electro-optical sampling probe according to the invention of claim 1 includes a DC level detector for detecting a DC level of an electric signal applied to a conductive path, and an AC component of the electric signal detected by the electro-optical material from the conductive path. Is provided so that the data synthesizing means synthesizes and outputs the respective detection data of the AC component detector and the DC level detector.

The electro-optical sampling probe according to the invention of claim 2 is characterized in that the data synthesizing means outputs an electric signal detected by the electro-optical material from the conductive path,
A comparator for comparing with the direct current level detected by the direct current level detector, and an electric signal detected by the electro-optical material based on the output of the comparator, at the direct current level detected by the direct current level detector. It is composed of a DC level correction circuit for correction.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an electro-optic sampling probe of the present invention. In FIG. 1, reference numeral 1 denotes a metal needle as a contact for measurement, which is a tip with respect to a conductive path 3 on a printed board 2 to be measured. It is said that the touch operation is free. An electric signal to be measured is applied to the conductive path 3, and the other end is terminated.

Reference numeral 4 is BSO (Bi12SiO2) to which an electric field obtained from the conductive path 3 through the metal needle 1 is coupled.
0) or the like, which receives the electric field and exhibits a birefringence according to the electric field strength due to the Bockels effect as the electro-optical effect. Reference numeral 5 denotes a light source that makes laser light incident on the electro-optical material 4, and 6 receives deflected light of laser light that changes according to the birefringence index, and converts this into an electric signal to center the AC component. It is a light detecting means as an AC component detector for outputting as an electric signal.

Further, 7 is a direct current level detector connected to the metal needle 1, which detects the direct current level of the electric signal applied to the conductive path 3. This DC level detector 7
Is composed of, for example, an operational amplifier 7a to which a high cut inductor 7b and a signal integrating capacitor 7c are connected as shown. Further, 8 is the conductive path 3
Is a comparator for comparing the electric signal detected by the electro-optic material 4 with the DC level detected by the DC level detector 7, which is, for example, an operational amplifier 8a and a feedback resistor 8b.
And a capacitor 8c connected as shown.

Reference numeral 9 denotes an adder as a DC level correction circuit, which is based on the output of the comparator 8 and detects an AC electric signal detected by the electro-optical material and a predetermined level detected by the DC level detector 7. It functions to add a level DC electric signal, correct the AC electric signal at the DC level, and generate a normal AC signal biased by the DC component. Then, the adder 9 and the comparator 8 constitute data synthesizing means 10 for synthesizing the respective detection data of the level detector 7 and the light detecting means 6.

In the electro-optic sampling probe having such a structure, in measuring the electric signal of the object to be measured on the conductive path 3, the tip of the metal needle 1 which is a contact for measurement is brought into contact with the conductive path 3. Therefore, an electric field corresponding to the change of the electric signal acts on the electro-optical material 4 through the metal needle 1, and the electro-optical effect corresponds to the optical signal corresponding to the electric field intensity and the optical signal according to the electro-optical effect as in the conventional case. The obtained electric signal is obtained from the light detecting means 6, and this electric signal is used as a signal corresponding to the potential on the conductive path 3 and the data synthesizing means 10
Is output to. That is, the signal from the light detection means 6 is
As described above, the signal is mainly an AC component, does not include a DC component, and is directly input to one input terminal of the adder 9.

On the other hand, the electric signal on the conductive path 3 is input to the DC level detector 7 through the metal needle 1. Here, the AC component of the signal to be measured is cut by the inductor 7b serving as an AC cut filter, further integrated by the capacitor, the remaining ripple is removed and smoothed, and only the DC component electric signal is output. It

Then, the electric signal of the direct current component and the electric signal of the alternating current component obtained through the photo-detecting means 6 are inputted to the comparator 8 and are compared with each other, and a voltage of a predetermined level corresponding to an error amount due to the comparison is obtained. It is input to the other input terminal of the adder 9. As a result, the adder 9 combines the AC electric signal obtained through the photodetector 6 with the DC level detected by the DC level detector 7 and outputs the combined voltage to the voltage measuring device 11.

As a result, as shown in FIG. 2, the voltage input to the voltage measuring device 11 corresponds to the DC level Vd detected by the DC level detector 7 of the electric signal Va obtained through the light detecting means 6. The voltage becomes a biased voltage, and the voltage measuring device 11 can stably and faithfully measure this as an electric signal containing a DC component. It should be noted that the synthesizing process of the DC data and the AC data by the data synthesizing means 10 including the comparator 8 and the adder 9 may be arbitrarily executed by an arithmetic process by a microprocessor. This execution process can be realized by synthesizing the DC data and the AC data on the waveform display.

Further, if the DC level detector 7 is always connected to the metal needle 1, the high frequency characteristics when the AC component is being measured by the photodetector 6 deteriorates, so that the metal needle 1 and the DC level detector are detected. A switch may be provided between the container 7 and the container 7. This switch connects between the DC level detector 7 and the metal needle 1 only when the DC level detector 7 measures the DC level. Further, this switch is composed of a photoconductive switch, a transistor, or the like.

[0018]

As described above, according to the present invention, the DC level detector for detecting the DC level of the electric signal applied to the conductive path, and the electric signal of the electric signal detected by the electro-optical material from the conductive path. An AC component detector for detecting an AC component is provided, and the data synthesizing means is configured to synthesize and output each detection data of the AC component detector and the DC level detector. The direct current component of the electric potential signal can reproduce the direct current component of the electric signal obtained through the electro-optic material, and thus the high-frequency signal electric potential of the conductor can be measured with high accuracy, which could not be performed by the conventional sampling oscilloscope. The effect that it can be realized stably is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an electro-optic sampling probe according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an output waveform of the data synthesizing means in FIG.

[Explanation of symbols]

3 conductive paths 4 Electro-optical material 6 Light detection means (AC component detector) 7 DC level detector 8 comparator 9 Adder (DC level correction circuit) 10 Data synthesizer

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Kikuchi 4-19-7 Kamata, Ota-ku, Tokyo Ando Electric Co., Ltd. (72) Yoshio Endo 4-19-7 Kamata, Ota-ku, Tokyo Ando Electric Incorporated (72) Inventor Mitsuru Shinagawa 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Tadao Nagatsuma 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Telegraph and Telephone Corporation (72) Inventor Ichiyoshi Matsuhiro 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nihon Telegraph and Telephone Corporation (56) Reference JP-A-8-262117 (JP, A) ( 58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 13/40 G01R 15/24 G01R 19/00 G01R 31/302-31/304

Claims (2)

(57) [Claims] 1. A DC level detector for detecting a DC level of an electric signal applied to a conductive path, and an AC component detector for detecting an AC component of the electric signal detected by an electro-optic material from the conductive path. An electro-optic sampling probe, comprising: a data synthesizing means for synthesizing and outputting each detection data of the AC component detector and the DC level detector. 2. A comparator for comparing the electric signal detected by the electro-optical material from the conductive path with a DC level detected by the DC level detector, and the data synthesizing means based on an output of the comparator. And a DC level correction circuit for correcting the electric signal detected by the electro-optical material with the DC level detected by the DC level detector. Optical sampling probe.