JPH0540133A - Signal-waveform measuring apparatus - Google Patents

Abstract

(57) [Abstract] [Object] The present invention relates to a signal waveform measuring apparatus capable of observing a high-speed electrical signal waveform by utilizing an electro-optical effect, and particularly, to a signal waveform measurement with improved measurement accuracy and operability. It is an object of the present invention to provide a highly efficient signal waveform measuring device by performing differential amplification in an optimum state. [Structure] A change in electric field intensity induced inside an electro-optic crystal 4 which is provided with a laser light source 1, light receivers 6 and 7, and a differential amplifier circuit 10 and is arranged close to or in contact with an object to be measured 20. Is detected as a change in the polarization state of light that repeatedly reciprocates in the crystal 4, and a difference amount of a pair of signal light intensities obtained by polarization-splitting reflected light is detected to measure the voltage waveform applied to the measurement target 20. A lower limit limiting circuit 8 and 9 that does not sense a value equal to or lower than a predetermined limit value and passes a signal equal to or higher than the limit value, and a control circuit that sets the limit value of the lower limit limit circuits 8 and 9. And 13 are configured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal waveform measuring apparatus capable of observing a high-speed electric signal waveform by utilizing electro-optic effect, and more particularly to a signal waveform measuring apparatus having improved measurement accuracy and operability. ..

In manufacturing and utilizing a semiconductor device such as an LSI, it is indispensable to accurately measure signal waveforms inside and outside the device. However, as the speed of elements has increased in recent years, it has become difficult to perform accurate measurement by an electric measurement method using a conventional LSI tester or the like. Therefore, an optical signal waveform measuring method using the electro-optic effect of the semiconductor element substrate crystal has been devised, and it has been confirmed that high-speed signals can be measured (for example, JAValdmanis an
d G. Mourou, "Subpicosecond electronics sampling: p
rinciples and application ", IEEE JOURNAL OF QUANTU
M ELECTRONICS, VOL.QE-22, pp.69-78., Etc.).

Further, a detection method has been filed (Japanese Patent Laid-Open No. 01-28566) in which a test LSI is mounted on a detection crystal and the waveform of an electric signal is measured, but improvement in measurement accuracy is demanded. ..

[0004]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional signal waveform measuring apparatus. In this conventional example, the system to be measured 20, the electro-optic crystal 4 having a birefringence property by a voltage, and the electro-optic crystal 4
A laser light source 1 for generating a laser beam to be incident on the optical axis, a polarization control element 2 as an optical system for converting the optical axis of the laser beam, a beam splitter 3, and a polarization separating element 5, and the laser beam subjected to the optical axis conversion to be measured. Light receivers 6 and 7 for converting the light quantity proportional to the measured voltage of the system 20 into an electric signal, and the light receiver 6
Current-voltage conversion circuits 51 and 52 for converting the current change of the signals from the signals 7 and 7 into a voltage change, the differential amplifier circuit 10 for amplifying the difference between the two converted voltages, and the A / D conversion for converting the signals into digital signals. The circuit 11 includes a signal processing unit 12 that performs signal processing, and a control circuit 53 that controls these operations.

In the outline of the operation of the conventional example, first, in order to detect a change in the polarization state of the signal light, the signal light is polarized and separated, and then each polarization component is individually received by the photodetectors 6 and 7. Since the received signal is extracted as a current signal,
After being converted into a voltage by the current-voltage conversion circuits 51 and 52, it is input to the two input terminals of the differential amplifier circuit 10. The output of the differential amplifier circuit 10 is A / D converted by the A / D conversion circuit 11.
The signal is converted and the signal processing unit 12 performs signal processing.

FIG. 5 shows the input / output voltage waveform of the differential amplifier circuit of this conventional example. Originally, as shown in (a) of the figure, the present apparatus reduces the output waveforms of the photodetectors 6 and 7 by application of a voltage, respectively, and increases them, and inputs them to the differential amplifier circuit 10 to perform differential amplification Then, the signal I and the signal II of FIG.
The signal processing is performed by obtaining the output waveform as in the case where the characteristics of (1) match.

However, the characteristics of the two signal transmission lines,
Particularly, when the characteristics of the current-voltage conversion circuits 51 and 52 do not completely match, a signal amplitude other than the signal due to the crystal applied voltage may appear in the output of the differential amplifier circuit 10 (FIG. 5B). Refer to the case where the characteristics of the signal I and the signal II are deviated). When these unexpected signal amplitudes are equal to or larger than the signal voltage amplitude, if the gain of the differential amplifier circuit 10 in the subsequent stage is set according to the signal amplitude, the unexpected signal saturates the differential amplifier circuit 10. Then, the response characteristic of the differential amplifier circuit 10 is deteriorated.

[0008]

Therefore, in the conventional signal waveform measuring apparatus, the crystal applied voltage is caused in the output of the differential amplifier circuit due to the variation of the characteristic of the signal transmission line, especially the characteristic of the current-voltage conversion circuit. Since the signal amplitude appears and the response characteristic of the differential amplifier circuit is deteriorated, there is a problem that the gain of the amplifier circuit sufficient for signal detection cannot be set.

The present invention solves such a problem, and an object of the present invention is to provide a highly efficient signal waveform measuring apparatus which performs differential amplification in an optimum state.

[0010]

In order to solve the above problems, the present invention provides a laser light source 1 as shown in FIGS. 1 and 2.
, The photodetectors 6 and 7, and the differential amplifier circuit 10, and a change in the electric field intensity induced inside the electro-optic crystal 4 arranged close to or in contact with the object to be measured 20 is measured in the crystal 4. A signal waveform measuring device that detects a difference amount of a pair of signal light intensities obtained by polarization-separating reflected light as a change in the polarization state of light that repeatedly reciprocates, and measures the voltage waveform applied to the measurement target 20. The lower limit limit circuits 8 and 9 which do not sense a value equal to or lower than a predetermined limit value and pass a signal equal to or higher than the limit value, and a control circuit 13 which sets the limit value of the lower limit limit circuits 8 and 9 are provided. Constitute.

The lower limit circuits 8 and 9 convert the current signals output from the photodetectors 6 and 7 into voltage signals, and the current-voltage conversion circuit 21.
A sample hold circuit 22 for holding the base amount of the output in synchronization with the laser irradiation pulse of the laser light source 1, and an adder amplifier 24 for adding the output of the sample hold circuit 22 and a predetermined offset value. ..

[0012]

In the present invention, as shown in FIG. 1, signals obtained by receiving a pair of polarization-separated signal lights by the photodetectors 6 and 7 are treated as signals limited by the lower limit limiting circuits 8 and 9, respectively.
The signal is input to the differential amplifier circuit 10 for signal processing.

That is, by sending to the differential amplifier circuit 10 without sensing below the set limit value of the light detection signal amount,
It is possible to avoid generation of an unexpected signal amplitude, and it is possible to perform differential amplification in an optimum state without degrading the response characteristics of the differential amplification circuit.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a block diagram of a signal waveform measuring apparatus according to an embodiment of the present invention. In FIG. 1, the same parts as those in FIG. 4 (conventional example) are designated by the same reference numerals.

In this embodiment, the system to be measured 20, an electro-optical crystal 4 having a birefringence according to a voltage, for example, BSO: Bi ₁₂ SiO _{20 and the} like, and a laser for generating a laser beam incident on the electro-optical crystal 4. The light source 1, the polarization control element 2 as an optical system for converting the optical axis of the laser light, the beam splitter 3, the polarization separating element 5, and the optical axis-converted laser light are proportional to the measured voltage of the measured system 20. Light receivers (photodiodes, etc.) 6 and 7 for converting the amount of light into electric signals,
The photodetector 12 which does not detect below a predetermined limit value and is above the limit value
Lower limit limiting circuits 8 and 9 for passing the signal from, a differential amplifying circuit 15 for amplifying the difference between the voltage signals of the outputs of the lower limit limiting circuits 8 and 9, and an A / D conversion circuit 16 for converting into a digital signal, It is composed of a signal processing unit 17 that performs signal processing, and a control circuit 18 that controls these operations.

Further, the lower limit limiting circuits 8 and 9 are, as shown in FIG. 2, a current-voltage converting circuit 21 for converting the current signals output from the photodetectors 6 and 7 into voltage signals, and a current-voltage converting circuit, respectively. 21. A sample-hold circuit 22 that holds the base amount of the output in synchronization with the laser irradiation pulse of the laser light source 1, a D / A conversion circuit 23 that inputs predetermined offset data and outputs an offset voltage, and a sample-hold circuit 22. It is composed of a summing amplifier 24 for adding the output and the offset voltage, and a diode 25 capable of high-speed operation.

Next, the operation of this embodiment will be described with reference to FIG. The laser light repeatedly reciprocating in the electro-optic crystal 4 is
The polarization state changes according to the voltage applied to the crystal 4.
The reflected light is polarized and separated by a polarization separation element such as a polarization beam splitter 3, and the separated signal lights are respectively received by a light receiver 6
And 7 to receive light, and lower limit limiting circuits 8 and 9 are used as current signals.
Is output to.

In the lower limit limiting circuits 8 and 9, since the signals detected by the photodetectors 6 and 7 are current outputs, the current-voltage converting circuit 21 first converts them into voltage signals. Next, the voltage-converted signal is branched, and one of them is sample-hold circuit 22.
And hold it at the timing synchronized with the laser irradiation pulse. The holding timing is the timing at which the light detection signal takes the base value. Here, the base value is the output value of the photodetector when no optical signal is received (FIG. 3).
(Hold value in (a)). A voltage value (offset voltage) set by the control circuit 13 is added to the held base value by an adding amplifier 24, and a diode 25
The signal combined with the output of the current-voltage conversion circuit 21 is input to the differential amplifier circuit 10 via. Note that offset data is given from the control circuit 13, and the offset voltage is determined by the D / A conversion circuit 23. At the input of the differential amplifier circuit 10, the larger signal of the signal amount voltage-converted by the action of the diode 25 and the base value + the set offset voltage value appears (see FIG. 3A).

Next, the differential amplifier circuit 15 amplifies the difference between these two polarization-separated light detection signals and outputs a difference signal (see FIG. 3B). Further, this signal is converted into an A / D conversion circuit 16
The voltage applied to the crystal 4 can be obtained by converting the data into digital data and processing the signal in the signal processing section 17.

[0020]

As described above, according to the present invention,
By receiving a pair of polarization-separated signal lights by the photodetector and inputting them to the differential amplifier circuit as signals limited by the lower limit limiting circuits 8 and 9, respectively, and performing signal processing, The effect of the difference between the two sets of transmission path characteristics can be eliminated by ignoring the signal, and the effect of vertical fluctuations of the entire signal can be obtained by adding to the base value beforehand the base value information that should be lost by limiting. Can also be removed.

Therefore, it is possible to avoid generation of an unexpected signal amplitude, and it is possible to perform differential amplification in an optimum state without degrading the response characteristics of the differential amplification circuit.
As a result, it is possible to provide a signal waveform measuring device capable of highly accurate voltage measurement.

[Brief description of drawings]

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

FIG. 2 is a detailed configuration diagram of a lower limit limiting circuit of the signal waveform measuring apparatus according to the embodiment of the present invention.

FIG. 3 is an operating voltage waveform diagram of the signal waveform measuring apparatus according to the embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional signal waveform measuring device.

FIG. 5 is an operating voltage waveform diagram of a conventional signal waveform measuring device.

[Explanation of Codes] 1 ... Laser light source 2 ... Polarization control element 3 ... Beam splitter 4 ... Electro-optic crystal 5 ... Polarization separation element 6, 7 ... Photoreceiver 8, 9 ... Lower limit limiting circuit 10 ... Polarization coupling element 15 ... Differential Amplification circuit 16 ... A / D conversion circuit 17 ... Signal processing unit 18, 53 ... Control circuit 20 ... Object to be measured 21, 51, 52 ... Current-voltage conversion circuit 22 ... Sampling hold circuit 23 ... D / A conversion circuit 24 ... Addition Amplifier 25 ... Diode

Claims (3)

[Claims] 1. An electro-optic crystal (1) provided with a laser light source (1), a light receiver (6 and 7), and a differential amplifier circuit (10), which is arranged close to or in contact with an object to be measured (20). The change in the electric field intensity induced in 4) is defined as the change in the polarization state of the light repeatedly reciprocating in the crystal (4).
A signal waveform measuring device for measuring a voltage waveform applied to an object to be measured (20) by detecting a difference amount of a pair of signal light intensities obtained by polarization-splitting reflected light, and detecting a voltage waveform below a predetermined limit value. Without a lower limit limiting circuit (8 and 9) that allows a signal equal to or more than the limit value to pass, and the signals obtained by receiving the pair of polarization separated signal lights by the photodetectors (6 and 7) are respectively set to the lower limit. A signal waveform measuring device, characterized in that the signal limited by the limiting circuits (8 and 9) is input to the differential amplifier circuit (10) for signal processing. 2. A control circuit (13) for setting the limit value of the lower limit limit circuit (8 and 9) in the signal waveform measuring apparatus.
The signal waveform measuring apparatus according to claim 1, further comprising: 3. The lower limit circuit (8 and 9) includes a current-voltage conversion circuit (21) for converting a current signal output from the photodetector (6 and 7) into a voltage signal, and the current-voltage conversion circuit. (21) A sample and hold circuit (22) that holds the base amount of the output in synchronization with the laser irradiation pulse of the laser light source (1), and an addition that adds the output of the sample and hold circuit (22) and a predetermined offset value. The signal waveform measuring device according to claim 1 or 2, further comprising an amplifier (24).