GB2373587A

GB2373587A - Optical output type voltage sensor and IC testing apparatus using it

Info

Publication number: GB2373587A
Application number: GB0214204A
Authority: GB
Inventors: Toshiyuki Okayasu
Original assignee: Advantest Corp
Current assignee: Advantest Corp
Priority date: 1998-02-05
Filing date: 1998-02-05
Publication date: 2002-09-25
Anticipated expiration: 2018-02-05
Also published as: GB2373587B; GB0214204D0

Abstract

A voltage sensor for convening an electric input signal into an optical output signal comprises an interferometric optical modulator (52), including a dielectric substrate. An optical branching portion (52-1) for dividing input light supplied thereto into two parts, an optical coupling portion (52-2), first and second optical waveguides (52-3A, 52-3B) between the optical branching portion and the optical coupling portion, a first electrode (52-5), a second electrode (52-6) and a common electrode (52-4) are formed in the substrate. The first electrode (52-5) and the common electrode (52-4) are arranged as a first electrode pair along opposite sides of the first optical waveguide (52-3A). The second electrode (52-6) and the common electrode (52-4) are arranged as a second electrode pair along opposite sides of the second optical waveguide (52-3B). The sensor generates interference light as the optical output signal outputted by the coupling portion in accordance with the difference between the electric input signal (V<SB>OUT</SB>) and the bias voltage (V<SB>BAS</SB>). The sensor may be used as part of an integrated circuit testing apparatus. The signal V<SB>OUT</SB> from the integrated circuit is converted to an optical signal, allowing optical communication between a test head and a mainframe.

Description

OPTICAL DRIVER, OPTICAL OUTPUT TYPE VOLTAGE SENSOR AND IC TESTING APPARATUS USING THEM TECHNICAL FIELD The present invention relates to an optical driver which is driven by an optical signal to generate a voltage signal for the application of a test pattern signal to an IC under test, an optical

output type voltage sensor which outputs its detected voltage as an A.. L P L LS optical signal for the transmission of an analog amount corresponding to a measured voltage value, and an IC testing apparatus using them.

BACKGROUND ART

Fig. 15 illustrates the general construction of a conventional IC testing apparatus. The IC testing apparatus in common use comprises, as depicted in Fig. 15, a test head THD, a mainframe MIN with the testing device proper stored therein, a cable KBL interconnecting them, and an auto-handler HND for feeding an IC under test 10 to the test head THD on a fully automatic basis.

The illustrated prior art example adopts a system configuration wherein: an IC socket SK is mounted on the test head THD; the IC under test 10 is held in contact with the IC socket SK for electrical connection with the mainframe MIN through the cable KBL; a test pattern signal is applied from the mainframe MIN to the IC under test 10 via the cable KBL; and a response signal of the IC under test 10 is fed via the cable KBL to the mainframe MIN; the response signal and an expectation are subjected to logical comparison in the

mainframe MIN to determine whether the IC under test 10 is in normal operation, thereby conducting its quality evaluation.

In association with the test head THD there is placed the autohandler HND which automatically transfers the IC under test 10.

The auto-handler HND conducts fully automatic operations of engaging the IC under test 10 with the IC socket S, and after

completion of the test, disengaging the tested 1C from the 1C socket SK, then classifying the tested IC 10 as nondefective or defective according to test conclusions, and putting it in the storage cabinet concerned.

Because of the necessity of automatically feeding the IC under test 10 to the test head THD by the auto-handler HND as described

above, the IC testing apparatus is forced to adopt a system configuration that the test head THD is placed apart from the mainframe MIN and electrically connected thereto by the cable KBL.

Fig. 16 depicts a general configuration of an electrical system in the IC testing apparatus. In the mainframe MIN there are housed a pattern generator PG, a timing generator TG, a waveform generator FOM, a logic comparator LOG, and so forth. The pattern generator PG outputs test pattern data PGDT to the waveform generator FOM. The waveform generator FOM generates a test pattern signal PGSIG of a waveform whose H and L logic are defined by the test pattern data PGDT fed from the pattern generator PG and whose rise and fall timing of the H and L logic are defined according to timing data that is provided from the timing generator TG. The test pattern signal PGSIG is generated for each input terminal TIN of the IC under test 10, and is provided via the cable KBL and a driver 12 to every input

terminal TIN of the IC under test 10.

When the IC under test 10 is, for instance, a memory, data is once written in each address of the IC under test 10 using the test pattern signal PGSIG, and then data is read out from each address to an output terminal Tout- The response signal thus read out to the output terminal Tout is decided by comparators 13A and 13B of a

l voltage comparator 13 as to whether it has a predetermined H logic level and a predetermined L logic level, and the decision results are sent as CP1 and CP2 to the mainframe MIN via the cable KBL.

A brief description will be given, with reference to Fig. 17 of operations of the comparators 13A and 13B. Fig. 17A depicts the waveform of a response signal Vout of the IC under test 10 read out to the output terminal Toute The comparators 13A and 13B are supplied with a strobe pulse STR from the mainframe MIN which is

-or T', and output the voltage generated by the timing generator TG, and output the voltage comparison results CP1 and CP"in synchronization with the strobe pulse STR That is, at the conclusion of an elapsed time TDRY from the start of outputting the response signal Vout to the settling of its waveform, the strobe pulse STR is applied to the comparators 13A and 13B to cause it to output the comparison results CP1 and CP2. The comparator 13A is supplied with a comparison voltage Von that defines the normal H logic level. The comparator 13B is supplied with a comparison voltage VOL that defines the normal L logic.

When the H logic of the response signal Vout is further positive than the comparison voltage Von. the comparator 13A outputs, as a test

conclusion, the H-logic comparison result CP1 that represents nondefectiveness. When the L logic of the response signal Vout is I T further negative than the voltage VOL that defines the normal L logic, the voltage comparator 13B outputs the H-logic comparison result CP2 that represents nondefectiveness.

The comparison results CP1 and CP2 provided from the comparators 13A and 13B are sent via the cable KBL to the mainframe MIN and are subjected to a logical comparison with an expectation pattern NPG by means of a logic comparator LOG disposed in the mainframe MIN; the quality of the IC under test 10 is decided, depending on whether a mismatch is found in the logic comparator LOG.

Incidentally, there are connected to the output terminal Tout of the IC under test 10 a terminating resistor TMR for impedance matching use and a DC power supply 14 that has a terminating voltage value VT which is determined by the specifications of the IC under test 10. Fig. 16 depicts the case where the IC under test 10 is an IC of the type having its input terminals TIN and output terminal Tout provided independently of each other, but cases are also often met with that the input terminal and the output terminal share one pin. On this account, as depicted in Fig. 18, the output of each driver DR of the driver 12 and the input terminals of the comparators 13A and 13B of the voltage comparator 13 are connected together to each input/output terminal TIO of the IC under test 10. In this instance, a terminating resistor TMR is connected in series between the output terminal of each driver and its common connection point of the

comparators 13A and 13B ; in a mode in which to read out of the IC under test 10 the test pattern signal (data) written therein, the driver is caused to output a terminating voltage VT, then the potential level of the voltage signal Vout, read out of the IC under test 10 in a state in which the terminating condition of the IC under test 10 is satisfied, is subjected to the comparison by the comparators 13A and 13B, and the comparison results CP1 and CP2 are sent into the mainframe MIN.

It will be understood from the above that the IC testing apparatus has a configuration wherein the test head THD and the mainframe MIN are separated from each other and are electrically connected by the cable KBL.

Incidentally, users of IC testing apparatus call for testing quantities of ICs in a short time. To meet this requirement, the autohandler HND and the test head THD are forced to become large-scale and bulky, and consequently, the length of the cable KBL is on the increase.

With an increase in the length of the longer the cable KBL, electro-magnetically induced noise becomes more likely to get mixed in the signal transmitted over the cable and the signal also becomes more susceptible to a parasitic stray capacitance and a parasitic inductor of the cable KBL--this imposes limitations on the transmission rate (frequency) of signals that can be transmitted between the mainframe MIN and the test head THD; that is, the lengthening of the cable leads to the disadvantage of setting limits on high-speed IC testing. This is an insuperably serious obstacle associated with the use of the configuration that interconnects the

test head THD and the mainframe MIN by an electrical transmission line.

Another problem y arises from the construction that large quantities of electronic circuit elements such as the drivers 12 and the voltage comparators 13 are housed in the narrow space of the test head THD. And there is the recent trend that the number of ICs to be tested at a time increases to 16,32 and 64. As the number of ICs to be tested at a time increases, the calorific value per unit space in the test head THD increases and the temperature also rises remarkably--this requires devising a method for heat radiation and involves additional costs therefor.

A first object of the present invention is to propose an IC testing apparatus which permits dramatic improvements in the test speed, and an optical output type voltage sensor and an optical driver that are used to implement the IC testing apparatus.

A second object of the present invention is to propose an IC testing apparatus which reduces the calorific value in the test head and hence avoids the expenditure for heat radiation, and an optical output type voltage sensor and an optical driver that are used to implement the IC testing apparatus.

According to a first aspect of the present invention there is provided an optical output type voltage sensor as defined in claim 1.

In embodiments of the present invention an optical driver interconnects the test head and the mainframe by an optical waveguide and sends a test pattern signal as an optical signal to the test head for applying the test pattern signal to the IC under test after conversion to an electric signal. An optical output type voltage sensor is used to convert the response signal from the IC under test to an optical signal and send the optical signal to the mainframe.

According to a second aspect of the present invention there is provided an IC testing apparatus as defined in claim 4.

Thus, in embodiments of the present invention, the test head and the mainframe are interconnected by an optical waveguide. The optical

waveguide is free from the possibility of an electro-magnetically induced noise or similar electrical noise getting mixed thereinto. Further, since there is no influence of an electrostatic capacitance or parasitic inductor even if the optical waveguide is long, the frequency of the signal that is transmitted over the optical waveguide can make a dramatic leap upward as compared with the signal frequency in the IC testing apparatus using the electrical transmission line. Therefore, it is possible to realize the IC testing apparatus capable of highspeed testing.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a connection diagram for explaining an embodiment of an IC testing apparatus that uses an optical driver.

Fig. 2 is a connection diagram for explaining an embodiment of an IC testing apparatus that uses the optical output type voltage sensor according to the present invention.

Fig. 3 is a plan view for explaining the configuration and operation of an optical modulator used in the embodiment of Fig. 2.

Fig. 4 is a waveform diagram for explaining the operation of the optical modulator depicted in Fig. 3.

Fig. 5 is a plan view depicting an example of a concrete structure of the optical output type voltage sensor used in the embodiment of Fig. 2.

Fig. 6 is a connection diagram for explaining a modification of the optical output type voltage sensor as being applied to an IC testing apparatus.

Fig. 7 is a connection diagram for explaining another modification of the optical output type voltage sensor as being applied to an IC testing apparatus.

Fig. 8 is a connection diagram for explaining a modified form of the IC testing apparatus depicted in Fig. 2.

Fig. 9 is a waveform diagram for explaining the operation of the modification shown in Fig. 8.

Fig. 10 is a waveform diagram similar to Fig. 9.

Fig. 11 is a connection diagram illustrating an embodiment of an IC testing apparatus that uses both the optical output type voltage sensor according to the present invention and an optical driver.

Fig. 12 is a connection diagram depicting a modified form of the Fig. 11 embodiment.

Fig. 13 is a connection diagram depicting another modification of the Fig.

11 embodiment.

Fig. 14 is a perspective view illustrating still another modification of the Fig. 11 embodiment.

Fig. 15 is a diagram for explaining the general configuration of a conventional if testing apparatus.

Fig. 16 is a block diagram for explaining the general electrical system of

the conventional) C testing apparatus.

Fig. 17 is a waveform diagram for explaining the operation of the Fig. 16 apparatus.

Fig. 18 is a block diagram for explaining another example of the conventional IC testing apparatus depicted in Fig. 16 BEST MODE FOR CARRYING OUT THE INVENTION Fig. 1 illustrates an embodiment of the optical driver according to the present invention. The embodiment depicted in Fig. 1 is a three-value driver capable of outputting the terminating voltage VT that is determined by voltages VIH and VIL and the specifications of the IC under test 10. Reference numeral 20 denotes the optical driver according to the present invention. The optical driver 20 can be made up of: a dielectric substrate 21 as of lithium niobate (LiNbO3) in which internal optical waveguides 22A, 22B and 22C can be formed ; the internal optical waveguides 22A, 22B and 22c formed in the dielectric substrate 21; photoconductive elements 23A, 23B and 23C optically coupled to the internal optical waveguides 22A, 22B and 22c at one end thereof, respectively; and input electrodes 25A, 25B and 25C electrically connected to an output electrode 24 by the photoconductive elements 23A, 23B and 23C, respectively.

Incidentally, the dielectric substrate 21 is shown to be provided with an electrode 26 for external connection use other than the output electrode 24 and the input electrodes 25A, 25B and 25C and a terminating resistor TMR formed between the external connection electrode 26 and the output electrode 24.

To the internal optical waveguides 22A, 22B and 22C formed in the dielectric substrate 21 there are optically coupled external

optical waveguides 32A, 32B and 3 2C formed, for example, by optical fibers; and the other ends of the external optical waveguides 32A, 32B and 32C at the side of the mainframe MIN are connected to an optical signal converter 33 by which the test pattern signal PGSIG from the waveform generator FOM is converted to an optical signal.

The optical signal converter 33 comprises three light sources 33A, 33B and 33C provided for each input terminal of the IC under test 10, and lights the light sources 33A, 33B and 33C in response to the test pattern signals, thereby selectively activating the photoconductive elements 23A, 23B and 23C by light that the light sources 33A, 33B and 33C emit. By the selective conduction of the photoconductive elements 23A, 23B and 23C, any one of the voltages VIH, VIL and VT, which are provided to the input electrodes 25A, 25B and 25C, can be fed to the external connection electrode 26; thus, the three-valued drive signal DRV can be output.

With the configuration of the optical driver 20 according to the present invention, the optical driver 20 and voltage sources 31A, 31B and 31C are mounted in the test head THD, the light sources 33A, 33B and 33C are mounted in the mainframe MIN, and by transmitting the test pattern signals as optical signals from the mainframe MIN to the test head THD over the external optical waveguides 32A, 32B and 33C, the three-valued drive signal DRV can be provided to the external-connection electrode 26. By applying the three-valued drive signal DRV to the IC under test 10, in the Fig. 1 example, via an input-only terminal TIN, the test pattern signals can be input into the IC under test 10.

In the above, the photoconductive elements 23A, 23B and 23C

may each be formed by an element of Si, GaAs, InAs, or similar semiconductor material which, when irradiated with light, exhibits photoconductivity by carriers that are generated by the optical input thereto. While in the above the internal optical waveguides 22A, 22B and 22C have been described to be formed on the dielectric substrate 21, they may also be formed by optical fibers like the

i tiii external optical waveguides 32A, 32B and 32C. In this case, the optical fibers forming the internal optical waveguides 22A, 22B, 22C and the optical fibers forming the external optical waveguides 32A, 32B, 32C need to be adapted so that they are connected to and disconnected from each other by means of optical connectors.

Fig. 2 illustrates an embodiment of the IC testing apparatus that employs the optical output type voltage sensor according to the present invention. In this embodiment of Fig. 2, a voltage signal Vout provided from an output-only terminal Tout is converted to an optical signal and is transmitted to the mainframe MIN. In Fig. 2, reference numeral 50 denotes the optical output type voltage sensor according to the present invention. The optical output type voltage sensor according to the present invention can be made up of : a terminating resistor TMR which receives the voltage signal Vout from the IC under test 10 with an appropriate impedance; an optical modulator 52 that converts the voltage Vo of the voltage signal Vout received by the terminating resistor TMR into the quantity of light modulated and outputs interference light based on the quantity of light modulated; and a substrate 51 which supports them.

The optical modulator 52 comprises, as depicted in Fig. 3, an optical branching part 52-1 for branching the optical waveguide

formed in the dielectric substrate 52-7, an optical coupling part 52 1, two optical waveguides 52-3A and 52-3B formed between the optical branching part 52-1 and the optical coupling part 52-2, and electric field application electrodes 52-4, 52-5 and 52-6 formed along both sides of the two optical waveguides 52-3A and 52-3B.

The optical branching part 52-1, the optical coupling part 52-2 and the optical waveguides 52-3A and 52-3B can be formed, for example, by diffusing titanium or the like into the dielectric substrate 52-7 made as of lithium niobate (UNbO3)'Optical fibers or similar optical waveguides 54 and 55 are optically coupled to a light receiving end 52-8A and a light emitting end 52-8B exposed on opposite end faces of the dielectric substrate 52-7 ; a laser diode or similar light source 61 is coupled to the other end of the input optical waveguide coupled to the light receiving end 52-8A, and a photodetector 63, such as a photodiode, is coupled to the other end of the output optical waveguide 55 coupled to the light emitting end 52-8B 63.

The light source 61 is lit be being driven by a light source driving circuit 62. In this example, the light source is shown to be driven by a DC power supply. Accordingly, the light source 61 launches a fixed quantity of laser light into the input optical waveguide 54. The photodetector 63 is connected to a detecting circuit 64, from which the intensity of light emitted from the output

optical waveguide 55 is derived as a voltage signal V. i. A voltage 0 Vo that is developed across the terminating resistor TRM is applied across one of the pairs of electric field application electrodes 52-4, 52-5 and 52-6. The example of Fig. 3 shows the case where the voltage Vo developed across the terminating resistor TMR is applied across the electric field application electrodes 5 2-4 and 5 2-4 but no electric field is applied across the electric field application electrodes 5 2-4 and 52-6 of the other pair which are connected together. By applying an electric field to the one optical waveguide 52-3A but no electric field to the other optical waveguide 52-3B, light is phase modulated in the optical waveguide 5 2-3 A applied the electric field but no optical modulation takes place in the optical waveguide 52- 3B applied no electric field. Owing to the phase modulation of light in the optical waveguide 52-3A, interference of light occurs in the optical coupling part 52-2, causing variations in the intensity of light that is emitted to the output optical waveguide 55.

This will be described below with reference to Figs. 3 and 4. Let he intensity of light incident on the input optical waveguide 54, the intensity of light for emission to the output optical waveguide 55 and the voltage to be applied to the electric field application electrodes 5 2-4 and 52-5 be represented by Pin, Pout and Vo, respectively. With a change in the appliedvoltage Vo, the intensity Pout of light which is emitted to the optical waveguide 55 varies along a Cos curve as depicted in Fig. 4A. That is, when the applied voltage Vo is zero, Pout=Pin ! when the applied voltage Vo is gradually varies in the + direction or-direction, the quantity of light emitted gradually decreases along the Cos curve, and at a certain applied voltage the quantity of light emitted goes down to zero. With a further increase in the applied voltage Vo, the emitted light intensity Pout gradually increases along the Cos curve, and when a certain

voltage is reached, the emitted light intensity Pout goes to a 1, that is, Pout-Pin. With the subsequent change in the applied voltage Vo, the emitted light intensity Pout presents an optical modulation ZD characteristic that it goes up and down between 1 and 0.

The optical modulation characteristic shown in Fig. 4A is in the case where the optical waveguide 52-3A and 52-3B have the same optical path length; when the optical path lengths differ by one quarter wavelength of the light which propagates over the both waveguides or when a bias voltage V BAS is applied to the electric field application electrodes connected as depicted in Figs. 3 and 5, the optical modulation characteristic becomes such as shown in Fig.

4B wherein the emitted light intensity varies along the Sin curve with the change in the applied voltage V0. That is, the emitted light intensity sharply varies about the applied voltage VO=O. The following description on Fig. 6 et seq. will be given on the assumption that the optical modulator is initialized to such a state as depicted in Fig. 4B, by making the optical path lengths of the optical waveguides 5 2-3 A and 52-3B differ by one quarter wavelength.

As is evident from the modulation characteristic of the optical modulator 52 described above, the optical modulator 52 modulates the incident light to an optical signal such that the emitted light intensity Pout assumes a value between Pout=Pin and Pout=0, that is, between Pou/Pin=l and Pouin=O in accordance with the applied electric field within a certain range (which keeps the phase

modulation of light within a 3600-range). Hence, the detecting Z > circuit 64 shown in Fig. 2 outputs the voltage signal Vout-l (see Fig. 2) equivalent in waveform to the voltage signal Vout output from the IC under test 10.

The process after the voltage signal Vout-l is obtained is the same as in the case of the conventional IC testing apparatus ; that is, the voltage signal Vout-l is compared by a voltage comparator 13 with the H-logic level Von and the L-logic level VOL to decide whether the voltage signal has a predetermined logic level; and if the decision result is good, the voltage comparison result and an expectation are subjected to a logical comparison to decide whether the operation of the IC under test 10 is normal or not. In Fig. 2 there is depicted the structure including the voltage comparator 13, there are not shown the logical comparator for comparing the

voltage signal Vout-l and the expectation to see if they match, and 0 the pattern generator for generating the expectation, and so forth.

ZD Incidentally, the sensitivity of the optical modulator 52 depicted in Fig. 3 for detecting the voltage signal Vout is proportional to the

electrode length L (see Fig. 3) and is inversely proportional to the 11 electrode spacing. Accordingly, the detecting sensitivity for the voltage signal Vout can be enhanced by increasing the electrode length L and decreasing the electrode spacing.

The sensitivity of the optical modulator 52 can be doubled by differentially applying the voltage signal Vout from the IC under test

10 to the both pairs of electric field application electrodes 52-4, 52 5 and 52-4, 52-6 as depicted in Fig. 5. Another possible method for improving the sensitivity is to increase the intensity of light that is emitted from the light source 61.

At any rate, by converting the response signal Vout output from the IC under test 10 to an optical signal and sending the voltage signal Vout of the IC under test 10 as the optical signal from the test head THD to the mainframe MIN, the quality of the optical signal will not deteriorate even if the distance of transmission is somewhat long, for example, approximately tens of to one hundred meters. In addition, no electrically induced noise gets mixed into the optical signal from the outside nor is it affected by a parasitic capacitance, a parasitic inductor and so on unlike in the case of the electrical transmission line--this also ensures high-quality optical signal transmission. Furthermore, since the number of parts handling electric signals in the test head THD is small, the heat generation in the test head THD can be reduced. This suppresses the total amount of heat generated in the test head THD and hence prevents a temperature rise in the test head THD, bringing an advantage that such an expensive device as a cooling system can be dispensed with.

Fig. 6 illustrates a modified form of the optical output type voltage sensor 50. In this embodiment, the'electric field application electrode 52-6 forming the optical modulator 52 has a signal transmission line structure formed by a microstrip line matched to a predetermined characteristic impedance, and the electric field application electrode 52-6 of the signal transmission line structure is caused to propagate therethrough the voltage signal Vout that is output from the IC under test 10. The terminating resistor TMR and the voltage source 14 which outputs the terminating voltage VT are connected in series to the terminating end of the electric field application electrode 52-6 and are connected to a common potential point.

The optical waveguide 52-3B forming the optical modulator 52 transmits light in the same direction as that of propagation of the

voltage signal Vout, and the light passing through the optical 0 waveguide 5 2-3B is applied the voltage Vo of the voltage signal V out between the electric field application electrodes 52-6 and 52-4. The electrodes 5 2-4 and 5 2-5 of the other electrode pair are kept equipotential and no electric field is applied to the optical waveguide 52-3B. The light source 61 in this example is shown to be lit DCwise by a DC light source driving circuit.

By making the voltage signal Vout and the light travel at the same velocity by making them travel in the same direction as in this embodiment, the optical modulator operates as a traveling-wave type optical modulator. As a result, the modulation characteristic of the optical modulator 52 is made wide-band, an the pulse signal Vout-I, which is reproduced by the interference light in the

mainframe MIN faithfully reproduces the waveform of the voltage / signal Vom at the sending side. Moreover, since the voltage signal Vout and the light travel at the same velocity, the voltage detecting sensitivity also provides a high gain.

Fig. 7 depicts a modification of the Fig. 6 embodiment. This embodiment shows a structure in which the electric field application field electrodes 5 2-2 and 5 2-3 are connected together and each have the signal transmission line structure with a view to differential application of an electric field to the optical waveguides 52-3A and 52-3B. In this instance, the impedances of the signal transmission

lines formed by the electric field application electrodes 52-5 and 526 are set at about twice higher than in the case of Fig. 6, and the resistance value of the terminating resistor TMR is also twice higher than in the case of Fig. 6. With the structure of Fig. 7 it is possible to obtain an advantage that the voltage detecting sensitivity can be around twice higher than in the Fig. 6 embodiment.

Fig. 8 illustrates a modified form of the embodiment shown in Fig. 2. In the embodiment of Fig. 8 an optical switch 65 is connected to the light source 61 side; the light emitted from the light source 61 is converted by the optical switch 65 to a narrow-width optical pulse PPS (see Fig. 9B), and the optical pulse PPS is provided via the input optical waveguide 54 to the optical modulator 52. The timing of for applying a switch control signal SWP to the optical switch 65 is chosen so that the optical pulse PPS is generated at the timing which

the voltage signal Vout from the IC under test 10 reaches a stable the voltage signal V,,,, value. By the application of the optical pulse PPS at the predetermined timing of the voltage signal Vout, the pulse-shaped .,/ interference light that is provided from the optical modulator 52 has light interference levels that correspond to the H-and L-logic values of the voltage signal Vout. Accordingly, the detecting circuit 64 provides such a voltage signal Vout-l as depicted in Fig. 9C. At the output side of the detecting circuit 64 there is placed an integration circuit 66, which integrates the output voltage signal Vout-l from the detecting circuit 64.

The integration time constant of the integration circuit 66 is ty chosen to be large enough for the integrated voltage INTV to reach a

target value within the duration of the optical pulse PPS. With such a chosen time constant of the integration circuit 66, it is possible to sufficiently detect the peak value of the voltage signal V that is output from the detecting circuit 64. The voltage integration by the integration circuit 66 to the target value allows sufficient time to execute the subsequent processing. Therefore, it is possible to obtain an advantage that no fast-acting circuits are needed at the stages following the integration circuit 66.

That is, once the integration circuit 66 integrates the peak value Vout-i' maintains the integrated voltage thereafter, so that the voltage comparators 13A and 13B need only to make the comparison of the integrated voltage INTV of the integration circuit 66 by strobe pulse STB (see Fig. 9E) at timing delayed by a time interval-c until the integrated voltage INTV becomes settled.

The comparison results CP1 and CP2 by the comparators 13A and 13B are shown in Figs. 9G and H. After the voltage comparison the integrated voltage INTV of the integration circuit 66 is reset by a reset pulse RSP depicted in Fig. 9F.

By sampling the voltage signal Vout from the IC under test 10 with the optical pulse PPS as in the embodiment of Fig. 8, the voltage signal Vout can be sampled with fine resolution in the time-base direction. That is, the value of the voltage signal Vout within the range of the pulse width of the optical pulse PPS can be measured with accuracy; for example, even if the waveform of the voltage

signal Vout is dull at the leading and trailing edges as shown in Fig. t. 7 10, final logical voltage values VH and VL of the voltage signal Vout-l 0

can be sampled by applying the optical pulse PPS at the timing when the voltage signal Vout reaches the final logical voltage values VH and VL. When the voltage signal Vout has a fixed repeating cycle, its n waveform itself can be observed by sampling the voltage signal Vout while shifting the timing for the application of the optical pulse little by little. Incidentally, while the voltage measuring method using the optical switch 65 in the embodiment of Fig. 8 has been described to be applied to the embodiment of Fig. 2, it will readily understood that it is applicable to the embodiments of Figs. 6 and 7 as well.

Fig. 11 illustrates the case of applying the present invention to an input/output terminal TIO which serves both as an input terminal and as an output terminal of the IC under test 10. In this case, the test pattern signal is input into the IC under test 10 through utilization of both of the optical driver 20 and the optical output type voltage sensor 50 described previously with reference to Figs. 1 and 6, respectively, and the voltage signal Vout from the IC under test 10 is converted by the optical output type voltage sensor 50 to an optical signal, which is sent to the mainframe MIN through the output optical waveguide 55.

The electric field application electrode 52-6 forming the optical output type voltage sensor 50 has a signal transmission line structure such as a microstrip line, and the electric field application electrode 5 2-6 is electrically connected at one end to the input /output terminal TIO of the IC under test 10 and at the other end to the externally-connected electrode 26 of the optical driver 20.

In the case of applying the test pattern signal to the IC under

test 10, the waveform generator FOM controls the light sources 33A, 33B and 3C of the optical signal converter 33 to light in accordance with test pattern data, and the light is fed via the optical waveguides 32A, 32B and 32C to the photoconductive elements 23A, 23B and 23C placed in the test head THD, thereby driving the optical driver

20.

While the test pattern signal is applied to the 1C under test 10, the light sources 33A and 33B are controlled to blink. On the other hand, in the case of outputting the voltage signal Vout from the IC under test 10, the light source 33C is lit to bring the photoconductive element 23C into conduction, and one end of the terminating resistor TMR is connected to the common potential point via the DC power supply 31C that outputs the terminating voltage VT, thereby terminating the input/output terminal TIO of the IC under test 10 in a state in which it is matched to a predetermined impedance.

When the IC under test 10 outputs the voltage signal Vout in the terminated state, the phase of light passing through the optical modulator 52 is modulated by the voltage signal Vout, then interference light is generated in the coupling part due to the phase modulation of light, and the interference light is sent via the output optical waveguide 55 to the mainframe MIN, wherein it is converted by the photodetector 63 to an electric signal, and the detecting circuit 64 outputs the voltage signal Vout i. The voltage signal Vout-l is checked by the comparators 13A and 13B to decide whether it has

the voltages of the H-and L-logic levels, and the compared outputs 0 PC1 and PC2 are fed into the logic comparator LOG (see Fig. 16) to

determine whether the IC under test 10 is nondefective or defective.

While in the embodiment of Fig. 11 the light source 61 is shown to be lit DC-wise, it is also possible to employ such a configuration as depicted in Fig. 8 wherein the optical switch 65 is inserted in the optical waveguide 54, the light to be provided to the optical modulator is made pulse-shaped by the optical switch 65 and the voltage signal Vout from the IC under test 10 is sampled by the optical pulse in the optical modulator 52.

Also the embodiment of Fig. 11 may adopt such a voltage sensor configuration as depicted in Fig. 12, wherein the electric field application electrodes 52-5 and 52-6 both have the microstrip line structure and the voltage signal Vout is applied to each of them to differentially apply the electric field to the optical waveguides 52- 3A and 52-3B, thereby providing doubled sensitivity for voltage detection.

Fig. 13 illustrates a modified form of the IC testing apparatus of the present invention depicted in Fig. 12. In the embodiment of Fig.

13, a correcting optical waveguide 52-9 is formed in the dielectric substrate 52-7 ; the correcting optical waveguide 52-9 transmits a portion of light to be provided to the optical modulator 52, and the transmitted light is fed via the optical waveguide 56 into the mainframe MIN, generating a reference signal REF by a photodetector 63B and a detecting circuit 64B placed in the mainframe MIN. The reference signal REF is subtracted from the

voltage signal Vout-l provided from the detecting circuit 64A, and at b the same time the reference signal REF is applied to the light source t, t driving circuit 62 to control the light source 61 to stabilize the

intensity of light it emits.

According to the embodiment of Fig. 13, the intensity of light from the light source 61 is controlled to stabilize, and consequently, the intensity of light incident on the optical modulator 52 also stabilizes, providing increased reliability of the optical modulator 52.

Furthermore, in this embodiment the correcting optical waveguide 52-9 is formed adjacent the optical modulator 52 and the light passing through the correcting optical waveguide 52-9 is used to generate the reference signal REF; therefore, even if the quantities of light transmitted through the optical waveguides 52-3A and 52-3B forming the optical modulator 52 vary, for example, due to a temperature change, the variation can be detected by a change in

the reference signal, so that a variation in the voltage signal Vout-I I z can be corrected by detecting the change in the reference signal REF.

Moreover, an offset component can be removed from the voltage signal Vout-I by subtracting the reference signal REF from the voltage signal Vout-i.

Fig. 14 illustrates still another embodiment. The embodiment of Fig. 14 shows the application of the optical driver 20 and the optical output type voltage sensor 50 of the present invention to the case where probes 73 are held in direct contact with IC chips 71 formed all over the surface of a semiconductor wafer 71 to test the ICs on the IC chips 71 for normal operation. A probe card 72 is usually formed in the form of a ring, and the probes 73 project at one end inwardly from the marginal edge of its center hole and are supported at the other end on the probe card 72. The tips of the probes 73 are each held in contact with an electrode portion formed

on the IC chip 71, and the integrated circuit formed on the IC chip 71 is operated for testing.

In such an IC testing apparatus, a substrate 80 is prepared on which the optical driver 20 and the optical output type voltage sensor 50 are mounted together. The optical driver 20 and the optical output type voltage sensor 50 can be mounted together on a substrate of about 10 to 15 mm square. The substrate 80 is placed on each probe 73. The test pattern signal is applied via the probe 73 to the IC chip 71 from the optical driver 20, and at the same time the output signal Vout from the IC chip 71 is taken out via the probe 73. The voltage signal Vout is converted by the optical output type voltage sensor 50 to interference light for application to the mainframe through the output optical waveguide 55.

INDUSTRIAL APPLICABILITY As described above, it is possible, with the use of the optical driver and the optical output type voltage sensor according to the present invention, to transmit the drive signal as an optical signal and the measured signal as an optical signal, too. The optical waveguides over which to transmit the optical signals are completely free from the possibility of electro-magnetically induced noise or similar electrical noise getting mixed thereinto as in the case of an electric signal transmission line and have no components such as a parasitic capacitance and a parasitic inductor; hence, no trouble occurs even if the signal transmission lines are made long.

Accordingly, by the application of the optical driver and the optical output type voltage sensor of the present invention to the IC

testing apparatus, the test pattern signal can be applied to the IC under test 1 without being subjected to an electrical disturbance even if the distance between the test head THD and the mainframe MIN is long, because signals are transmitted therebetween as optical signals. Furthermore, the voltage signal Vout from the IC under test 10 can be sent into the mainframe MIN without deteriorating its waveform.

In addition, since there is not present in the signal transmission line such components as a parasitic capacitance or parasitic inductor, the frequency of the optical signal which propagates through the optical waveguide can also be set high. As the result of this, the frequency of the test pattern signal to be applied to the IC under test 10 can also be set at a frequency sufficiently higher than in the

case of an electric signal. This speeds up the testing of the IC under test 10, providing the advantage of dramatically increasing the test speed of the IC testing apparatus.

Moreover, since the optical driver 20 and the optical output type voltage sensor 50 do not use any electronic active elements that consumes power in quantities, the heat generation is close to zero. Accordingly, even if large numbers of optical drivers 20 and the optical output type voltage sensors 50 are mounted in the test head THD, the calorific value is so slight that there is no particular need for using a cooling device. Hence, reduction of the manufacturing costs of the IC testing apparatus can be expected.

Claims

Claims: 1. A voltage sensor for converting an electric input signal into an optical output signal, the voltage sensor comprising: an interferometric optical modulator, including: - a dielectric substrate,

- an optical branching portion formed in the substrate for dividing Z-) ZD input light supplied thereto into two parts, - an optical coupling portion formed in the substrate, - first and second optical waveguides formed in the substrate so as to be provided between the optical branching portion and the optical coupling portion, and - a first electrode, a second electrode and a common electrode formed in the substrate so that the first electrode and the common electrode are arranged as a first electrode pair along opposite sides of the first optical

waveguide, and the second electrode and the common electrode are arranged wavegul tn as a second electrode pair along opposite sides of the second optical waveguide, the common electrode being operable for receiving a bias voltage, the first and second electrodes being connected together to form parallel-connected electrodes so as to be operable for receiving the electric input signal applied between the parallel-connected electrodes and the common electrode, and wherein the sensor is operable for generating interference light as the optical output signal outputted by the coupling portion in accordance with the

difference between the electric input signal and the bias voltage. c 2. The voltage sensor according to claim 1, modified in that the second electrode is connected together with the common electrode so as to be operable for receiving bias voltage, and the first electrode and the common electrode are operable for receiving the electric input signal applied therebetween.

3. A voltage sensor according to claim 1 or claim 2 characterized in that the input light is pulse-like light.

4. An IC testing apparatus comprising: a mainframe which includes means for generating test pattern signals

applicable to an IC under test and a logic comparator for effecting a logic z : t : l comparison between an electric response signal outputted from the IC under test and an expected pattern signal for establishing whether the IC under test is z : l fault-free or defective, and a test head which is disposed apart from the mainframe and to which the IC under test is contacted, characterized in that: the test head includes a voltage sensor according to any preceding claim, wherein the voltage sensor is operable for receiving the electric response signal outputted from the IC under test as the electric input signal; and the mainframe further includes a light source for producing the input light for transmission to the voltage sensor and a photoelectric detector for receiving the optical output signal from the voltage sensor and for converting it back into the electric response signal for comparison by the logic comparator.

5. An IC testing apparatus according to claim 4, wherein in the proximity of one of the optical waveguide of the optical modulator in the substrate the voltage sensor further has a correcting optical waveguide for transmission of a part of the input light, in order then to be returned to the mainframe for conversion-into a reference signal and for combination with the electric output signal which has been converted back to form a corrected output signal as the electric response signal for the logic comparison.

6. The IC testing apparatus according to claim 5, wherein the mainframe further comprises feedback means for feeding back the reference signal is fed back to a driver circuit for the light source in order to regulate the output intensity of the light source.

7. The IC testing apparatus according to claim 4, characterized in that: a probe card having a multiplicity of probes for contacting the pins of an IC under test is arranged in the test head; and a multiplicity of the voltage sensors are mounted on the multiplicity of the probes in a manner such that each probe is associated with one of the voltage sensors.

8. The IC testing apparatus according to claim 4, wherein the mainframe also includes means for generating test pattern signals applicable to an IC under test and an optical signal converter for converting the test pattern signal to optical driver signals, and the test head also includes an optical driver for receiving the optical driver signals from the mainframe and for generating an

electric test pattern signal in accordance with the optical driver signal. l 9. A voltage sensor substantially as hereinbefore described with reference to the accompanying drawings of Figures 2 to 14.

10. An IC testing apparatus substantially as hereinbefore described with reference to the accompanying drawings of Figures 2 and 6 to 14.

Z : > tn I I. An optical driver, characterized by: a plurality of optical waveguides; a plurality of photoconductive elements optically coupled to the plurality of optical waveguides at one end thereof ; a plurality of DC voltage sources connected to the photoconductive elements at one end thereof; an output terminal connected in common to the other ends of said photoconductive elements; and a terminating resistor formed between the output terminal and an externally-connected electrode.

12. The optical driver as claimed in claim H, characterized in that said plurality of DC voltage sources are each provided with : two DC voltage sources for generating two voltages which define H-and Llogic voltages of a test pattern signal to be applied to an IC under test; and a voltage source for generating a terminating voltage which is determined by the specifications of the IC under test. j 3. An optical output type voltage sensor, characterized by a configuration which comprises an optical branching part, an optical coupling part, two optical waveguides formed between the optical branching part and the optical coupling part, and an interferometric optical modulator provided with two pairs of electric field application electrodes disposed along opposite sides of the two optical waveguides, and wherein a measured voltage signal is applied to the electric field application electrodes of one of the two pairs of the interferometric optical modulator, the electrical field application electrodes of the other pair are connected together, light output from said coupling part is made interference light and is sent over the optical waveguide concerned, and said measured voltage signal is reproduced.

14. An optical output type voltage sensor, characterized by a configuration which comprises an optical branching part, an optical coupling part, two optical waveguides formed between the optical branching part and the optical coupling part, and an interferometric optical modulator provided with two pairs of electric field

-iDl) oSj4, application electrodes disposed along opposite sides of the two optical waveguides, and wherein a measured voltage signal is applied to the electric field application electrodes of one of the two pairs of the interferometric optical modulator, the electrical field application electrodes of the other pair are connected together, light to be applied to said optical branching part is made pulse-shaped, the pulse-shaped light is used as interference light corresponding to the voltage value of said measured voltage signal and is sent over the optical waveguide concerned, and said measured voltage signal is reproduced.

IS. The optical output type voltage sensor as claimed in claim characterized by a configuration wherein one of the electric field application electrodes of one of said two pairs of electric field application electrodes and one of the electric field application electrodes of the other electrode pair are connected together, the measured voltage is applied across the electric field application electrodes connected together and the other electric field application electrodes to differentially apply electric fields to said two optical waveguides.

16 The optical output type voltage sensor as claimed in claim ; characterized by a configuration wherein one of the electric field application electrodes of one of said two pairs of electric field application electrodes and one of the electric field application electrodes of the other electrode pair are connected together, the measured voltage is applied across the electric field application electrodes connected together and the other electric field application electrodes to differentially apply electric fields to said two optical waveguides.

17. The optical output type voltage sensor as claimed in claim 1 S, characterized by a configuration wherein said electric field application electrodes connected together each have a signal transmission line structure of a predetermined impedance and a voltage signal applied to this electric field application electrode and light passing through said optical waveguide propagate in the same direction.

18. The optical output type voltage sensor as claimed in claim 16, characterized by a configuration wherein said electric field application electrodes connected together each have a signal transmission line structure of a predetermined impedance and a voltage signal applied to this electric field application electrode and light passing through said optical waveguide propagate in the same direction.

I q. An IC testing apparatus which applies a test pattern signal to

an IC under test and makes logical comparison between a response signal from the IC under test and an expected pattern to determine whether said IC under test is nondefective or defective, characterized by a configuration wherein: the optical driver of claim 11 orbis placed near said IC under test; an optical test pattern signal, converted from a test pattern signal output from a waveform generator, is applied to the optical driver; and an electrical test pattern signal generated by the actuation of the optical driver is applied to the IC under test.

20. An IC testing apparatus which applies a test pattern signal to an IC under test and makes logical comparison between a response signal from the 1C under test and an expected pattern to determine whether said IC under test is nondefective or defective, characterized by a configuration wherein: the optical output type voltage sensor of any one of claims 13 to 18 is placed near said IC under test; an optical test pattern signal is converted by said optical output type voltage sensor to interference light; the interference light is transmitted over an optical waveguide and is converted by the target photodetector to an electric signal; and the electric signal is subjected to a logical comparison with said expected pattern.

2 . An IC testing apparatus which applies a test pattern signal to an IC under test and makes logical comparison between a response signal from the IC under test and an expected pattern to determine whether said IC under test is nondefective or defective, characterized by a configuration wherein: the optical driver of claim, I or Ilis placed near said IC under test; said optical driver is driven by a test pattern signal sent as an optical signal to generate an electric test pattern signal near the IC under test; the electric test pattern signal is applied to the IC under test; the optical output type voltage sensor of any one of claims 3 to 8 is placed near said IC under test; interference light corresponding to the response signal from said IC under test, which is output from the optical output type voltage sensor, is sent over an optical waveguide and is converted by the target photodetector to an electric signal; and the converted electric signal is subjected to a logical comparison with said expected pattern to determine whether the IC under test is nondefective or defective.

2 t. An IC testing apparatus which comprises: a mainframe having housed therein a pattern generator, a waveform generator for generating a test pattern signal to be applied to an IC under test based on test pattern data output from the pattern generator, and a logic comparator for making a logical comparison of a response

signal from the IC under test with an expected pattern available from said pattern generator to determine whether the IC under test is nondefective or defective; and a test head placed apart from the mainframe and provided with an IC socket for contact with the IC under test, characterized by a configuration wherein: the optical driver of claim I or 12 is placed in said test head; an optical signal converter for converting the test pattern signal from said waveform generator to an optical signal is placed in said mainframe; an optical test pattern signal converted by the optical signal converter is sent to the test head through an optical waveguide formed between said mainframe and the test head; said optical driver is driven by the optical test pattern signal; and an electric test pattern signal available from the optical driver is applied to the IC under test.

23. An IC testing apparatus which comprises: a mainframe having housed therein a pattern generator, a waveform generator for generating a test pattern signal to be applied to an IC under test based on test pattern data output from the pattern generator, and a logic comparator for making a logical comparison of a response signal from the IC under test with an expected pattern available from said pattern generator to determine whether the IC under test is nondefective or defective; and a test head placed apart from the mainframe and provided with an 1C socket for contact with the IC under test, characterized by a configuration wherein: the optically output type voltage sensor of any one of claims to IV is placed in said test head; the response signal from said IC under test is converted by said optical output type voltage sensor to an optical signal; the optical signal is sent to said mainframe through an optical waveguide formed between said test head and the' mainframe and is converted to an electric signal by a photodetector placed in the mainframe; and the electric signal is subjected to a logical comparison with an expected pattern in said logic comparator to determine whether the 1C under test is nondefective or defective.

24. An IC testing apparatus which comprises: a mainframe having housed therein a pattern generator, a waveform generator for generating a test pattern signal to be applied to an IC under test based on test pattern data output from the pattern generator, and a logic comparator for making a logical comparison of a response signal from the IC under test with an expected pattern available from said pattern generator to determine whether the IC under test is nondefective or defective; and a test head placed apart from the mainframe and provided with an IC socket for contact with the IC

under test, characterized by a configuration wherein : 0 the optical driver of claim t or or'lis placed in said test head; an optical signal converter for converting the test pattern signal from said waveform generator to an optical signal is placed in said mainframe; an optical test pattern signal converted by the optical signal converter is sent to the test head through an optical waveguide formed between said mainframe and the test head; said optical driver is driven by the optical test pattern signal; an electric test pattern signal available from the optical driver is applied to the IC under test; the optical output type voltage sensor of any one of claims 3 to 8 is placed in said test head; the response signal from said IC under test is converted by said optical output type voltage sensor to an optical signal; the optical signal is sent to said mainframe through an optical waveguide formed between said test head and the mainframe and is converted to an electric signal by a photodetector mounted in the mainframe ; and the electric signal is compared by said logic comparator with an expected pattern to determine whether the IC under test is nondefective or defective.

2. The IC testing apparatus as claimed in claim 2 4, characterized by a configuration wherein: a correcting optical waveguide is formed adjacent an optical modulator forming said optical output type voltage sensor; the correcting optical waveguide transmits a portion of light to be applied to said optical modulator; the light transmitted through the correcting optical waveguide is sent to said main frame and is converted there to a reference signal; the reference signal is computed with an electric signal generated by the optical signal from said optical output type voltage sensor and is taken out as the response signal from the IC under test.

Z 6 The IC testing apparatus as claimed in claim 2 It, characterized by a configuration wherein: a correcting optical waveguide is formed adjacent an optical modulator forming said optical output type voltage sensor; the correcting optical waveguide transmits a portion of light to be applied to said optical modulator; the light transmitted through the correcting optical waveguide is sent to said main frame and is converted there to a reference signal; the reference signal is fed back to a driving circuit for a light source for emission of light to said optical output type voltage sensor to stabilize the output intensity of the light source; and the response signal from the 1C under test is taken out.

27. The IC testing apparatus as claimed in claim 2 It, characterized by a configuration wherein: a probe card is mounted in said test head: said optical driver and said optical output type voltage sensor are mounted on each probe projecting out from the probe card but supported at one end thereto; and said probes are each held in contact with a terminal portion of an IC chip formed on a semiconductor wafer to test the IC chip,