JPH04219949A - Measuring device of voltage signal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to voltage signal measuring devices, particularly LSI (large scale integrated)
d circuit).

[0002] Generally, circuits that have been simulated in the design process are passed on to the manufacturing process, and in this manufacturing process prototype ICs are created as engineering samples.
is made. A circuit designer obtains this IC and tests and evaluates whether its functions are correct (so-called prototype testing).

In prototype testing, input vectors from a workstation's logic simulation are applied to the IC under test (hereinafter referred to as UUT), and while the UUT is actually operating, the output signal vector and output expected value vector obtained from the UUT are calculated. A malfunctioning UUT is determined by comparing the UUTs.

[0004] In such prototype tests, it is important not only to test using external terminals, but also to observe voltage signals of internal circuits of wafers and chips. This is because the cause of failure cannot often be determined by testing only from external terminals.

In this case, a metal probe is applied to a desired node on the wafer or chip of the UUT to extract an output vector from the internal circuit, and this output vector is compared with the expected value vector of logic simulation at the workstation. Find errors in logic design and malfunctions in manufacturing.

By the way, in such a metal probe method, the insulating coating on the surface of the wafer or chip must be removed using a solution or the like. Further, in order to reduce the contact resistance of the metal probe, it is necessary to press it strongly, and the wafer or chip surface is easily damaged by the tip of the probe. It has the disadvantage of easily causing damage to the UUT.

[0007]

2. Description of the Related Art Therefore, a laser probe method has been proposed that uses an electro-optic effect that causes less damage to the UUT. FIG. 3 is a diagram showing the configuration of its main parts.

The laser beam P1 from the light source 10 passes through a quarter wavelength element 11 and a first beam splitter (beam splitter: BS) 12, is guided to a crystal body 13, and is emitted from the back surface 13B of this crystal body 13. The reflected light P3 is extracted. This reflected light P3 is transmitted to the first beam splitter 12
After the optical path is bent by
The beam splitter 14 divides the light beam into two directions with light intensity depending on the polarization state of the light beam. The signals are then converted into voltage signals Sa and Sb by the first photoelectric conversion element 15 and the second photoelectric conversion element 16, respectively, and the voltage difference signal Sc between Sa and Sb is extracted by the deviation detection circuit 17. Note that the range surrounded by the broken line represents the optical system.

Here, the polarization state of the light propagating inside the crystal 13 depends on the strength of the "electric field" applied to the crystal 13. For this reason, the laser beam (P
1) and the polarization state of the laser beam (P3) after reflection and round trip change depending on the magnitude of the applied electric field. As a result, the intensity of the two lights divided by the second beam splitter 14 changes depending on the applied electric field.

[0010] Therefore, the signal of the UUT can be observed from the difference in intensity between the two distributed light beams. In this way, the laser probe method measures the "electric field" of the electrical signal to be measured, so there is no need to remove the insulation coating from the measurement site, and there is no need to make strong contact with it, compared to the metal probe method. , it has the advantage of causing extremely little damage to the UUT.

[0011]

[Problem to be Solved by the Invention] However, in such conventional voltage signal measuring devices, consideration is not given to the temperature characteristics of the optical system, and measurement errors especially when the environmental temperature changes cannot be ignored. There were some problems.

[0012] Accordingly, the present invention aims to suppress measurement errors particularly when the environmental temperature changes by heating or cooling the optical system so that the temperature of the optical system is constant.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a light source, a light beam from the light source guided to a predetermined crystal body, and a light beam propagated inside the crystal body. a first optical system that guides the light beam to the second optical system; a second optical system that separates the light beam based on the polarization state and guides the light beam to the first and second photoelectric conversion elements; A voltage signal measuring device comprising a signal difference output circuit that extracts and outputs a difference between an output voltage and an output voltage of a second photoelectric conversion element, wherein the temperature of the first optical system and/or the second optical system temperature measuring means for measuring the temperature; deviation direction signal output means for comparing the measurement result of the temperature measuring means with a predetermined value and outputting a signal representing the direction of the deviation; and a current source based on the deviation direction signal. A current direction control means for controlling the direction of the generated current, and a cooling means for heating or cooling the first optical system and/or the second optical system according to the direction of the current from the current source. Preferably, a deviation amount signal output means for comparing the measurement result of the temperature measuring means with a predetermined value and outputting a signal representing the amount of deviation; and a current source based on the deviation amount signal. A current amount control means for controlling the amount of current generated.

[0014]

[Operation] In the present invention, the first optical system and/or the second optical system
The temperature of the first optical system and/or the second optical system is controlled such that the deviation between the temperature measurement value of the optical system and the predetermined value becomes zero.

[0015] Therefore, the temperature of the first optical system and/or the second optical system is maintained constant regardless of changes in the environmental temperature, and measurement errors are suppressed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings. 1 and 2 are diagrams showing an embodiment of a voltage signal measuring device according to the present invention.

For explanation of the configuration of the optical system in this embodiment, reference is made to FIG. 3 used in the conventional explanation. That is, in FIG. 3, the 1/4 wavelength element 11 and the first
A beam splitter (BS) 12 guides the light beam P1 from the light source 10 to a predetermined crystal body 13, and also guides the light beam P3 propagated inside the crystal body to a second optical system H2. , and the second beam splitter 14 splits the light beam P3 propagated inside the crystal body 13 into
A second optical system H2 that distributes and guides the light beam P3 to the first and second photoelectric conversion elements 15 and 16 according to the polarization state.
Further, the deviation detection circuit 17 includes a signal difference output circuit that extracts and outputs a difference signal Sc between the output voltage Sa of the first photoelectric conversion element 15 and the output voltage Sb of the second photoelectric conversion element 16. is forming.

In FIG. 1, the optical element 20 is at least one element included in the first optical system or the second optical system, and is, for example, an element included in the first beam splitter 12 or the second beam splitter 14. be. Optical element 20
The circled x mark described above represents the incident (or exit) point of the light beam, and the light beam passes through this point in the vertical direction of the page. A temperature sensor (temperature measuring means) 21 in contact with the lower surface of the optical element 20 measures the surface temperature Ts of the optical element 20, and a Peltier effect element (cooling means) 22 in contact with the upper surface of the optical element 20 measures the surface temperature Ts of the optical element 20. The surface of the optical element 20 is heated or cooled with an amount of heat depending on the applied current Ic. The distinction between heating and cooling is determined by the direction (polarity) of the current Ic, and here it is assumed that heating occurs when the polarity is positive (+Ic), and cooling occurs when the polarity is negative (-Ic).

Note that the optical element 20 and the temperature sensor 21
is surrounded by a heat insulating member 23, and a radiation fin 22a is attached to the Peltier effect element 22. On the other hand, 30 is a temperature control circuit, and the temperature control circuit 30 includes a setting circuit 31 that sets a reference temperature To, and a deviation ±± between this To and the above Ts (surface temperature of the optical element 20).
Deviation detection circuit 3 that detects ΔT (±ΔT=To-Ts)
2, a polarity extraction circuit 33 that extracts the direction of ±ΔT (polarity +/-), and a current polarity determination circuit that determines the polarity of the current Ic generated by the current source 34 according to the extracted polarity (+/-). 35, and preferably the deviation ±
A current amount control circuit 36 is provided that controls the amount of current Ic generated by the current source 34 based on the amount of ΔT (absolute value |ΔT|).

Here, the above deviation detection circuit 32 and polarity extraction circuit 33 detect the measurement result (Ts) of the temperature sensor 21.
and a predetermined value (To) and outputs a signal representing the direction (+/-) of the deviation (±ΔT). ) also functions as a deviation amount signal output means for outputting a signal representing the amount (|ΔT|). Further, the current polarity determining circuit 35 functions as a current direction control means for controlling the direction of the current (Ic) generated in the current source 34 based on the deviation direction signal (+/-), and also The amount control circuit 36 functions as a current amount control means that controls the amount of current (Ic) generated by the current source 34 based on the deviation amount signal (|ΔT|).

Next, the operation will be explained. FIG. 2 is a diagram showing the temperature characteristics of the optical system (see FIG. 3) when the temperature control circuit 30 is not operated.

In FIG. 2, the vertical axis is temperature (° C.), the horizontal axis is time (t), Ts is the temperature of the optical element 20, Sa is the output signal from the first photoelectric conversion element 15, and SaAV is the average of Sa. value, Sb is the output signal from the second photoelectric conversion element 16,
SbAV is the average value of Sb.

From this characteristic diagram, it can be seen that when Ts changes downward (or upward), Sa and Sb follow this and increase (increase).
or downward) changes are observed. For example, 27℃
Sa increases from Sa27 to Sa26 during the temperature drop from 26°C to 26°C.

[0024] Such temperature dependence is caused by each element forming the optical system, such as a beam splitter (BS or PBS).
This is due to the fact that the physical structure of the substance changes minutely as the environmental temperature changes. For example, thermal expansion of the main body (glass) of the optical element affects the interference effect, or change in film thickness of the optical element main body affects wavelength dependence. Therefore, in this embodiment, when the temperature control circuit 30 is operated with To set at 27°C, for example, the difference between Ts at that time (29°C, for example) and To (27-29=-2
℃) is obtained, and the direction of the deviation, that is, the polarity is negative (-), so in this case, a negative polarity current Ic is applied to the Peltier effect element 22, so the optical element continues to flow until the deviation between Ts and To becomes zero. 20 is cooled. Alternatively, if the direction of the deviation is positive (Ts is lower than To), a positive current Ic is applied to the Peltier effect element 22, and the optical element 20 is heated.

Therefore, the temperature of the optical element 20 is kept constant (To
), and measurement errors can be suppressed. Note that the current (Ic) varies depending on the magnitude of the deviation (ΔT).
It is preferable to control the amount of , since the response delay time of the control system can be shortened. That is, even if the optical element 20 is heated or cooled, the temperature Ts does not change immediately, but changes after a predetermined time delay determined by the thermal conductivity, heat capacity, etc. of the optical element 20, resulting in insufficient control responsiveness. It is.

[0026] Therefore, the absolute value of the deviation (ΔT) (|ΔT|
) is controlled such that the larger the current amount (Ic) is, the larger the current amount (Ic) is. That is, the gain of the control system is increased when the deviation is large. Thereby, responsiveness can be improved. Note that when the deviation is small, it is desirable to reduce the gain of the control system. This is because overheating or overcooling can be avoided and the convergence of the control system can be accelerated.

[0027]

[Effects of the Invention] As described above, according to the present invention, the temperature of an optical element is measured, and the optical element is heated or cooled so that the deviation between the measured temperature and a predetermined temperature becomes zero. Therefore, the temperature of the optical element can be kept constant, and measurement errors especially when the environmental temperature changes can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of main parts of an embodiment.

FIG. 2 is a temperature characteristic diagram of the optical system when temperature control is not performed.

FIG. 3 is a configuration diagram of an optical system common to the conventional example and one embodiment.

[Explanation of symbols]

H1...first optical system, H2...second optical system, 10...
...Light source, 13...Crystal, 15...First photoelectric conversion element, 16...Second photoelectric conversion element, 17...Difference detection circuit (signal difference output circuit), 21...Temperature sensor (temperature measurement means), 22... Peltier effect element (cooling means), 32...
... Deviation detection circuit (deviation amount signal output means, deviation direction signal output means), 33 ... Polarity extraction circuit (deviation direction signal output means), 34 ... Current source, 35 ... Current polarity determining circuit (current direction control means) ), 36... Current amount control circuit (current amount control means).

Claims (2)

[Claims] 1. A light source, a first optical system that guides a light beam from the light source to a predetermined crystal body, and guides a light beam propagated inside the crystal body to a second optical system, and the light beam. a second optical system that separates the light based on the polarization state and guides it to the first and second photoelectric conversion elements, and detects the difference between the output voltage of the first photoelectric conversion element and the output voltage of the second photoelectric conversion element. A voltage signal measuring device comprising: a signal difference output circuit for extracting and outputting a signal; a temperature measuring means for measuring the temperature of the first optical system and/or the second optical system; a deviation direction signal output means for comparing the deviation direction with a predetermined value and outputting a signal representing the direction of the deviation; a current direction control means for controlling the direction of the current generated in the current source based on the deviation direction signal; 1 optical system and/or the second optical system
A voltage signal measuring device comprising: a cooling means for heating or cooling the optical system according to the direction of current from the current source. 2. Deviation amount signal output means for comparing the measurement result of the temperature measuring means with a predetermined value and outputting a signal representing the amount of deviation; and a current generated in a current source based on the deviation amount signal. 3. The voltage signal measuring device according to claim 2, further comprising current amount control means for controlling the amount of current.