Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Cathode ray
Reexamination Certificate
1998-10-06
2002-04-23
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Cathode ray
C324S096000
Reexamination Certificate
active
06377036
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to an electro-optic sampling oscilloscope which measures a signal to be measured by employing optical pulses generated based on a signal from a delay circuit in which a trigger signal is delayed in response to the measured position of the waveform of the signal to be measured. More particularly, the present invention relates to an electro-optic sampling oscilloscope characterized in having a delay circuit in which a trigger signal is delayed.
This application is based on patent application No.Hei 9-273158 filed in Japan, the content of which is incorporated herein by reference.
2. Background Art
It is possible to observe the waveform of a signal to be measured by coupling the electric field generated by the signals to be measured to an electro-optic crystal, causing laser light to enter this electro-optic crystal, and using the polarization state of the laser light. Here, it is possible to use this laser light in pulse form, and to conduct measurement with extremely high time resolution when the sampling of the signal to be measured is conducted. An electro-optic sampling oscilloscope employs an electro-optic probe which takes advantage of this phenomenon.
In comparison with conventional sampling oscilloscopes which employ electrical probes, such an electro-optic sampling oscilloscope herein below termed an “EOS” oscilloscope) has the following characteristic features (Shinagawa, et al: “A High-Impedance Probe Based on Electo-Optic Sampling,” Proceeding of the 15
th
Meeting on Lightwave Sensing Technology, May 1995, pp 123-129):
(1) When signals are measured, a ground wire is not required, so that measurement is simplified.
(2) The metal pin which is at the lead end of the electro-optic probe is isolated from the circuit system, so that it is possible to realize a high input impedance, and as a result, the state at the point at which measurement is conducted is essentially free of fluctuations.
(3) Since optical pulses are employed, measurement is possible in a broad band up to the order of GHz.
The structure of an EOS oscilloscope will now be explained with reference to FIG.
4
.
An EOS oscilloscope is composed of an EOS oscilloscope main body
1
and an electro-optic probe
2
. In EOS oscilloscope main body
1
, a trigger circuit
3
outputs a trigger signal which initiates measurement of the measurement signal. Delay circuit
4
then delays the signal from trigger circuit
3
by the time set by setting unit
9
. Setting unit
9
is composed of switches and the like. The delay time set at setting unit
9
is set in delay circuit
4
via processing circuit
8
. Timing generation circuit
5
generates the timing for generating the optical pulse and the timing for A/D conversion based on the signal from delay circuit
4
. Optical pulse generating circuit
6
generates an optical pulse based on a timing signal from timing generation circuit
5
.
The optical pulse from optical pulse outputting circuit
6
is supplied to electro-optic probe
2
and is subjected to polarization change by an electro-optic element. The optical pulse subjected to polarization change undergoes polarized light detection etc., by a polarized light detecting optical system (not shown) inside electro-optic probe
2
, and that signal is input to EOS oscilloscope main body
1
.
This signal is subjected to signal amplification or A/D conversion by A/D converter
7
, and processing by processing circuit
8
for displaying the signal which is the target of measurement, an so on.
Next,
FIG. 5
will be used to explain the reason for delaying the trigger signal from trigger circuit
3
using delay circuit
4
. As shown in parts (a) and (b) in
FIG. 5
, the trigger signal from trigger circuit
3
is generated roughly in synchronization with the signal to be measured. In
FIG. 5
, the waveform from measurement point A
1
or A
2
is displayed on the display member (not shown) of EOS oscilloscope main body
1
. The user of the EOS oscilloscope may not wish to display the waveform from measurement point A
1
or A
2
, but rather may want to display the waveform from measurement point B
1
or B
2
which is slightly delayed from measurement point A
1
or A
2
. In this way, delay circuit
4
is employed to shift the initial position of the display of the waveform.
For example, when the EOS oscilloscope user wants to display the waveform from measurement point B
1
rather than measurement point A
1
, then setting unit
9
in
FIG. 4
is set to delay the initial position of the display of the signal to be measured. The setting information is analyzed by processing circuit
8
, delay time T′ for measurement point B
1
with respect to measurement point A
1
is determined, and a delay time T′ is set in delay circuit
4
. As a result, as shown in part (c) in
FIG. 5
, delay circuit
4
outputs a trigger signal after delaying it by just delay time T′. Timing for sampling is then generated using the output from delay circuit
4
.
FIG. 6
shows an example of one conventional structure for delay circuit
4
. In
FIG. 6
, delay circuit
4
is composed of a lamp circuit
31
which designates the trigger signal as an input signal; a D/A converter
32
which converts the delay time setting signal from processing circuit
8
from a digital to an analog signal; and a comparing circuit
33
which compares the signal output from ramp circuit
31
and D/A converter
32
.
The operation of the delay circuit shown in
FIG. 6
will now be explained using FIG.
7
.
As shown in part(a) in
FIG. 7
, when a trigger signal is input into ramp circuit
31
, this signal is employed as a trigger for ramp circuit
31
to output a ramp signal as shown in part (c) in FIG.
7
.
As shown in part (b) in
FIG. 7
, D/A converter
32
outputs an output signal in which the delay time setting signal from processing circuit
8
has been converted from a digital to an analog signal. When the value set from delay circuit
7
is delay time T′, then D/A converter
32
outputs a signal which is higher than the reference level by just a component corresponding to the delay time T′ only.
The outputs from ramp circuit
31
and D/A converter
32
are compared at comparing circuit
33
, and a signal is output in which trigger signal has been delayed by just a time T′, as shown in part(c) in FIG.
7
.
Depending on the measured signal, a relatively long delay may be desirable, on the order of milli-seconds or seconds, for example. In the above-described delay circuit
4
for an EOS oscilloscope, a ramp signal from ramp circuit
31
is employed to carry out the setting of the delay time. However, when carrying out a long delay time in this way, the ability to reproduce the signal is not good due to the generation of a shift or fluctuation (jitter) in the ramp signal. In other words, a delay time on the order of milli-seconds or seconds cannot be set with good accuracy.
Depending on the measured signal, a relatively long delay may be desirable, on the order of milli-seconds [ms] or seconds [s], for example. In the above-described delay circuit
4
for an EOS oscilloscope, a lamp signal from lamp circuit
31
is employed to carry out the setting of the delay time. However, when carrying out a long delay time in this way, the ability to reproduce the signal is not good due to the generation of a shift or fluctuation (jitter) in the lamp signal. In other words, a delay time on the order of milli-seconds [ms] or seconds [s] cannot be set with good accuracy.
SUMMARY OF THE INVENTION
The present invention was conceived in consideration of the above-described circumstances, and has as its objective the provision of an electro-optic sampling oscilloscope in which it is possible to set a stable delay time even in the case where a relatively long delay time is being set.
Therefore, the present invention provides an electro-optic sampling oscilloscope having a delay circuit which comprises a delay time detecting circuit, a regu
Endou Yoshio
Kikuchi Jun
Matsuhiro Kazuyoshi
Nagatsuma Tadao
Shinagawa Mitsuru
Ando Electric Co. Ltd.
Darby & Darby
Karlsen Ernest
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