JP2010217116A - Probe and system for measurement of electric signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a probe for measuring an electric signal, capable of measuring an accurate signal waveform without receiving an effect of reflection waves (reflection signals) without adding excessive transmission wires. <P>SOLUTION: The probe for measuring the electric signal includes: a tip 4 for allowing an RF probe 30 (the probe for measuring the electric signal) to be brought into contact with the surface of the transmission wire 11 of a planar circuit and taking-in the electric signal propagating transmission wires 11; and an electrooptical crystal 1 for input of a laser beam. The electrooptical crystal 1 is brought into contact with the surface of the tip 4 or arranged in the neighborhood of the above surface so that an electromagnetic wave generated by electromagnetic induction of the electric signal propagating the tip 4 is incident on itself. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention is an electrical signal measuring probe suitable for use in measuring a high-speed electrical signal output from an integrated circuit or a device on a circuit board by utilizing the electro-optic effect of a pulse laser beam and an electro-optic crystal. And an electrical signal measurement system.

  A technique called electro-optic sampling is widely used as means for measuring the waveform of a high-speed electrical signal with less disturbance and high time resolution (see, for example, Patent Document 1). This technique uses an electro-optic crystal having a property of changing the birefringence by an electric field as an electric field sensor. That is, as shown in FIG. 5, the electro-optic crystal 1 is arranged (adhered or arranged with a gap) on a transmission line 11 through which an electric signal propagates. When the electro-optic crystal 1 is irradiated with pulsed laser light (incident light), the polarization state of the laser light (emitted light) returned from the electro-optic crystal 1 changes according to the intensity of the electric signal (electric field signal). To do. Since this polarization change can be converted into light intensity by the polarizing plate, the magnitude of the electric signal can be measured as the light intensity after all. In this way, by using pulsed laser light, it is possible to measure an electrical signal that changes over time with a resolution of pulse width (usually 1 picosecond or less).

  In addition, FIG. 5 is a figure explaining the electric signal measurement method as background art of this invention. The electric signal measurement system shown in FIG. 5 includes a circuit under test 9 made of an electronic device such as LSI (Large Scale Integration) on a circuit board 10 and a transmission line 11 for transmitting input / output electric signals of the circuit under test 9. It is installed. A tip 4 is connected to the transmission line 11, and an electrical signal to be supplied to the measuring line (not shown) or from the measuring instrument to the transmission line 11 is input / output via the coaxial cable 5 and the coaxial connector 6. On the transmission line 11, as described above, the electro-optic crystal 1 irradiated with the laser light is disposed. When the electromagnetic wave induced from the transmission line 11 acts on the electro-optic crystal 1, the polarization state of the laser light output from the electro-optic crystal 1 changes. By detecting this change in the polarization state as a change in the intensity of the laser beam, the waveform of the electric signal energized in the transmission line 11 can be observed.

  In addition, this method can measure the electrical signal on the circuit board 10 where the electrical signal is generated, so there is no problem of signal loss and distortion compared to the method of connecting the signal to the sampling oscilloscope using a coaxial cable. It is the only one that can measure the signal waveform.

Japanese Patent Laid-Open No. 5-72299

  However, while the electric signal measurement using electro-optic sampling has the above-described excellent features, there are problems related to the following reflected wave and problems to be solved.

  To explain this, a normal measurement procedure is described. First, as shown in FIG. 5, in order to supply power to a circuit under test (device) 9 and to electrically terminate the circuit 9, a probe 20 called a radio frequency (RF) probe is signaled. One end of the transmission line 11 is contacted. The RF probe 20 has a contact terminal (usually three, consisting of two ground terminals and a signal terminal therebetween) at one end of the coaxial cable 5, and the other is connected to the coaxial connector 6. It has become. The characteristic impedance of the coaxial cable 5 in the transmission line 11 and the RF probe 20 is set to 50Ω. Next, the electro-optic crystal 1 is placed in the vicinity of the circuit 9 to be measured, and the electrical signal waveform is optically measured by the electro-optic sampling described above.

  However, when the tip 4 of the RF probe 20 is brought into contact with the transmission line 11 on the circuit board 10, since the connection from the planar circuit to the three-dimensional circuit is made, reflection of 10% or more usually occurs at the contact point. The reflected wave (reflected signal) due to this reflection returns to the electro-optic crystal 1 side and is superimposed on the signal waveform with a time delay as shown in FIG.

  FIG. 6 shows an example in which the pulse waveform is measured. As shown in FIG. 6B, the second pulse having a small amplitude is measured. The polarity of the second pulse may be negative depending on the tip 4 contact situation. When the waveform (a) in the case of no reflection is as shown in (c), the reflected wave overlaps the original signal waveform, and the two cannot be separated. The time for the reflected wave to reach is given by 2 L / v, where L is the distance between the RF probe 20 and the electro-optic crystal 1. v is the speed of the signal on the transmission line 11 and varies depending on the type of the circuit board 10 (Si, GaAs, InP, etc.), but is about 150 μm per picosecond. For example, measurement of a pulse waveform having a bandwidth of 30 GHz (10 picoseconds each for rise and fall times) needs to be “reflected wave free” over a time region of at least 20 picoseconds. For that purpose, the distance of the transmission line 11 of 1.5 mm is required. Normally, a margin about twice that (and hence 3mm) is set, which is significantly larger than the chip size (0.5mm square) of general circuits and devices.

  In order to perform measurement taking advantage of the ability to measure signals on the circuit board 10, it is necessary to add an extra transmission line 11 to the device 9 as described above. This space of several millimeters of the transmission line 11 is a useless space on the circuit board 10, and in general, there are limited cases in which measurement is performed until such a transmission line 11 is added.

  The present invention has been made in consideration of the above circumstances, and an electric signal that enables accurate signal waveform measurement without being affected by a reflected wave (reflected signal) without adding an extra transmission line. An object is to provide a measurement probe and an electric signal measurement system.

  In order to solve the above-mentioned problems, the invention according to claim 1 includes a tip portion that contacts the surface of a transmission line of a planar circuit and takes in an electric signal that propagates through the transmission line, and an electro-optic crystal to which laser light is input. The electro-optic crystal is disposed in contact with or near the surface of the tip portion so that an electromagnetic wave generated by electromagnetic induction of an electric signal propagating through the tip portion is incident on the electro-optic crystal. This is a probe for measuring an electric signal.

  According to a second aspect of the present invention, in the electrical signal measurement probe according to the first aspect, the laser light is input to the electro-optic crystal through an optical fiber via a condenser lens. This is a measurement probe.

  The invention according to claim 3 is the electrical signal measurement probe according to claim 1, the laser light source for supplying laser light to the electrical signal measurement probe, and the electro-optic crystal of the electrical signal measurement probe. An electrical signal measurement system comprising: means for converting a change in the polarization state of the laser light output from the laser light into a change in the intensity of the laser light; and a means for measuring the change in the intensity of the laser light.

  According to the above configuration, since the electro-optic crystal is arranged in the tip portion, no extra transmission line is added to measure the waveform of the high-speed electrical signal output from the integrated circuit or device on the circuit board. However, an accurate signal waveform can be measured without the influence of the reflected wave (reflected signal). In addition, it is not necessary to place the electro-optic crystal on the circuit to be measured (or in the vicinity thereof) for each measurement, and the time spent for the total measurement is reduced. Furthermore, calibration of the signal voltage amplitude is facilitated.

It is a figure which shows the structure of the electrical signal measurement probe concerning this invention. It is a figure which shows the detailed structure of the electric signal measuring probe concerning this invention. It is a figure which shows the structure of the other electric signal measurement probe concerning this invention. It is a figure which shows the structure of the other electric signal measurement probe concerning this invention. It is a figure explaining the electric signal measuring method as background art of the present invention. It is a figure for demonstrating the influence of a reflected wave when a to-be-measured signal is a pulse waveform.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram for explaining a basic configuration of an electrical signal measurement probe (RF probe 30) according to the present invention. FIG. 1 (a) shows a transmission line (or signal line) on the circuit board 10 as shown in FIG. ) Is a side view showing the case of contact with 11, and (b) is a side view showing the RF probe 30. FIG. FIG. 2 is a perspective view showing a detailed configuration example of the RF probe 30 shown in FIG.

  The electro-optic crystal 1 shown in FIG. 1 is disposed on the tip 4 of the RF probe 30, and laser light is introduced into the electro-optic crystal 1 through the optical fiber 3. Tip 4 is inclined, and when the RF probe 30 is brought into contact with the transmission line (or signal line) 11 on the circuit board 10, the position and inclination of the electro-optic crystal 1 change. To introduce. As shown in FIG. 2, a collimator lens 2 may be inserted between the optical fiber 3 and the electro-optic crystal 1 in order to efficiently guide the light from the optical fiber 3 to the electro-optic crystal 1. it can.

  FIG. 2 shows the positional relationship between the electro-optic crystal 1 and the tip 4 of the RF probe 30 in detail. The electro-optic crystal 1 is disposed on the signal line 4b of the tip 4, and a reflection film 7 for reflecting the laser light is applied to the bottom surface thereof. The reflective film 7 may be a dielectric or a metal.

  Further, a coaxial connector 6 is connected to the tip 4 via a coaxial cable 5. A measuring instrument (not shown) is connected to the coaxial connector 6 via another coaxial cable (not shown). In the configuration example shown in FIG. 1, the tip 4, the coaxial cable 5, and the coaxial connector 6 are held in the package housing 12.

  In FIG. 2, the configuration corresponding to the tip 4 in FIG. 1 includes three tips 4a, 4b, and 4c. In this case, the tips 4a and 4c on both sides are ground terminals, and the tip 4b between them is a signal terminal. Further, in FIG. 2, the coaxial cable 5 in FIG. 1 is divided into a coaxial cable 5a (shield line portion) serving as a ground line and a coaxial cable 5b serving as a central conductor. In this case, the coaxial cable 5a is connected to the tips 4a and 4c, and the coaxial cable 5b is connected to the tip 4b.

  In this embodiment, when the tip 4 of the RF probe 30 is brought into contact with the transmission line 11 and the circuit under test 9 is turned on, an electrical signal is output from the transmission line 11. A part of the electric signal is taken into the tip 4 and terminated at a termination portion (not shown) connected to the tip of the tip 4. Due to this termination, the reflection of the electric signal captured at the tip 4 is suppressed.

  That is, the RF probe 30 according to the embodiment of the present invention is in contact with the surface of the transmission line 11 of the circuit board 10 (planar circuit) on which the circuit 9 to be measured 9 is mounted, and captures an electric signal propagating through the transmission line 11. (Tip portion) and electro-optic crystal 1 to which laser light is input are provided as constituent elements. However, a terminal part (not shown) for terminating the electrical signal taken in from the tip 4 (tip part) can be provided as a component. In this case, the electro-optic crystal 1 is in contact with the surface of the tip 4 (tip portion) so that an electromagnetic wave generated by electromagnetic induction of an electric signal propagating through the tip 4 (tip portion) is incident on the electro-optic crystal 1. (Or near the surface).

  In the present embodiment, the electric signal flowing through the tip 4 emits an electromagnetic wave by electromagnetic induction. When this electromagnetic wave is incident on the electro-optic crystal 1 arranged so as to be in contact with the tip 4 (or located in the vicinity), the birefringence of the electro-optic crystal 1 is changed, and the laser incident on itself. Change the polarization state of light. In the laser light output from the electro-optic crystal 1 with the polarization state changed, the polarization state change is converted into an intensity change by an external polarizer (not shown), for example. This laser light intensity change is converted into electrical signal intensity using a photodiode, etc., and then measured using a lock-in amplifier, etc., so that the waveform of the electrical signal propagating through tip 4 is output from the circuit 9 under test. The waveform of the electric signal propagating through the transmission line 11 can be measured. That is, using the RF probe 30 (or RF probes 30a and 30b) of the present embodiment or the following embodiment, laser light is supplied from the laser light source to the electro-optic crystal 1, and the polarization of the laser light output from the electro-optic crystal 1 is polarized. By converting the change in the state into the change in the intensity of the laser light and measuring the change in the intensity of the laser light, an electric signal measurement system that measures the waveform of the electric signal propagating through the tip 4 can be configured.

  The following describes how the influence of the reflected wave is reduced by this configuration. On the tip 4 of the RF probe 30, a signal taken into the tip 4 from the transmission line 11 is measured. The signal is reflected at the portion of the coaxial connector 6 on the upper surface of the RF probe 30, but since the distance to that is usually 5 mm or more, even if reflection occurs, there is no problem. Further, the reflection due to the connection between the connectors 6 is originally smaller than the reflection at the contact point between the transmission line 11 and the tip 4 of the RF probe 30. On the other hand, the signal reflected at the contact point between the tip 4 of the RF probe 30 and the transmission line 11 is reflected once again on the circuit under test (device) 9 side and propagates again onto the tip 4 of the RF probe 30. However, the reflection on the circuit under test (device) 9 side is not completely (100%) due to the influence of the input capacitance and resistance even if it is a single device such as a photodiode (30-50 at most) %degree). For this reason, since the intensity of the reflected wave on the tip 4 of the RF probe 30 is reduced, it is not a problem in many cases. More generally, since impedance matching is achieved, for example, by providing an output resistance (usually 50Ω) in the circuit under test (device) 9, such multiple reflections are not often a problem.

  FIG. 3 shows an improvement in the performance and function of the electrical signal measurement probe (RF probe 30) shown in the above embodiment. That is, the RF probe 30a has a configuration in which the electro-optic crystal 1 and the optical fiber 3 are arranged in the package housing 12, and an optical fiber, an electro-optic crystal, etc. around the contact portion with the transmission line 11 of the tip 4 The parts are not exposed, and the contact portion of the tip 4 with the transmission line 11 can be easily observed from above. As a result, the tip 4 can be easily positioned on the transmission line 11. In addition, for example, since the electro-optic crystal 1 can be arranged at a distance of 3 mm or more from the tip of the tip 4, the influence of the reflected wave from the circuit to be measured (device) 9 can be completely avoided. Is possible. However, in this example, since the electro-optic crystal 1 is disposed obliquely, it is desirable that the tip is as small as possible.

  FIG. 4 is a schematic view showing another embodiment of the electrical signal measurement probe of the present invention. The RF probe 30b shown in FIG. 4 includes a right-angle prism 8 inserted after the collimator lens 2 to which the optical fiber 3 is connected in order to facilitate handling of the optical fiber in the RF probe 30a shown in FIG. This is an example in which light is introduced into the electro-optic crystal 1 by bending the optical path by 90 degrees.

  In the embodiment shown in FIGS. 1 to 4, there is another practically important merit. That is, since the measurement sensitivity is constant regardless of the circuit (device) 9 to be measured, the voltage amplitude can be calibrated. Conventionally, when the electro-optic crystal 1 is disposed on (or in the vicinity of) the circuit (device) 9 to be measured as shown in FIG. Changes. Therefore, in order to know the voltage amplitude, the voltage amplitude needs to be calibrated for each circuit pattern, but the present invention does not have such a problem.

  The embodiment of the present invention is not limited to the above-described ones. For example, an optical system lens is further added to the optical path of the laser beam, or changes such as changing the shape and number of tips 4 are appropriately performed. Can do.

30, 30a, 30b RF probes
1 Electro-optic crystal
2 Lens
3 Optical fiber
4, 4a, 4b, 4c tips
7 Reflective film
8 Right angle prism
9 Circuit under test (planar circuit)
10 Circuit board (planar circuit)
11 Transmission line (planar circuit)

Claims (3)

A tip portion that contacts the surface of the transmission line of the planar circuit and captures an electrical signal propagating through the transmission line;
An electro-optic crystal to which laser light is input,
The electro-optic crystal is disposed in contact with or near the surface of the tip portion so that an electromagnetic wave generated by electromagnetic induction of an electric signal propagating through the tip portion is incident on the electro-optic crystal. A probe for measuring electrical signals. The electrical signal measuring probe according to claim 1,
The laser signal is input to the electro-optic crystal by an optical fiber through a condenser lens. The electrical signal measuring probe according to claim 1 or 2,
A laser light source for supplying laser light to the electrical signal measuring probe;
Means for converting a change in the polarization state of the laser beam output from the electro-optic crystal of the probe for measuring the electric signal into a change in intensity of the laser beam;
An electrical signal measurement system comprising: means for measuring an intensity change of the laser beam.

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