Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Reexamination Certificate
2001-08-08
2002-11-19
Oda, Christine K. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
C324S076410, C324S076420
Reexamination Certificate
active
06483287
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-242865, filed Aug. 10, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a waveform measuring apparatus. More particularly, the present invention relates to a waveform measuring apparatus for measuring a signal waveform of a signal under test having an input arbitrary repetition cycle.
2. Description of Related Art
Conventionally, there have been proposed a variety of measuring techniques for measuring a signal waveform of a signal under test such as an electrical signal or an optical signal and the like having an input arbitrary repetition cycle.
However, in the case of a high frequency synthesized signal of which a repetition cycle of a signal under test, i.e., a repetition frequency exceeds 10 GHz, the signal waveform of the signal under test cannot be directly observed on a display screen of an oscilloscope or the like. Thus, the selection range of such waveform measuring technique is limited itself.
A conventional typical technique for measuring a signal waveform of a signal under test of which the repetition frequency exceeds 10 GHz will be described with reference to
FIGS. 7A
,
7
B, and
7
C.
As shown in
FIGS. 7A and 7B
, a signal under test “a” having a repetition cycle Ta (for example, repetition frequency fa=10 GHz) is sampled by means of a sampling signal “b” having a cycle Tb (for example, repetition frequency “fb”=999.9 MHz) longer than the repetition cycle Ta of this signal under test “a”.
In this case, a mutual relationship between the repetition cycle Ta of the signal under test “a” and the cycle Tb that is longer than the repetition cycle Ta of the signal under test “a” is adjusted. As shown in
FIGS. 7A and 7B
, with an elapse of time, a sampling position of the sampling signal “b” in the signal waveform in the repetition cycle Ta of the signal under test “a” is shifted by a very small amount of time &Dgr;T, so that the time is delayed by 2&Dgr;T, 3&Dgr;T, 4&Dgr;T, 5&Dgr;T, 6&Dgr;T, . . . n&Dgr;T.
Therefore, a signal under test “c” after sampled by this sampling signal “b” is obtained as a discrete waveform of which a pulse shaped waveform is generated at a position synchronized with the sampling signal “b”, as shown in FIG.
7
C.
Then, the enveloped waveform of such each pulse waveform is obtained as a signal waveform “d” extended in a time axis direction of the signal under test “a”.
Based on the sampling technique shown in
FIGS. 7A
,
7
B, and
7
C, a waveform measuring apparatus for measuring a signal waveform “d” of the signal under test “a” is configured as shown in FIG.
8
.
The signal under test “a” having the repetition cycle Ta (repetition frequency “fa”) is input to a sampling circuit
1
and a timer circuit
2
.
The timer circuit
2
outputs a timing of generating each pulse of the sampling signal “b” to a sampling signal circuit
3
.
In this case, the timing of generating each pulse of the sampling signal “b” is required to be shifted by &Dgr;T from a start time of the repetition cycle Ta of the signal under test “a”, and thus, is synchronized with the signal under test “a” having an input reference time signal.
The sampling signal generator circuit
3
applies to the sampling circuit
1
a sampling signal “b” having a pulse form every time a pulse generation timing is input from the timer circuit
2
.
The sampling circuit
1
samples the input signal under test “a” by means of the sampling signal “b” input from the sampling signal generator circuit
3
, and delivers the sampled signal under test “c” to a signal processing/waveform display section
4
.
The signal processing/waveform display section
4
calculates an enveloped waveform of the sampled signal under test “c”, converts a scale of the time axis of this enveloped waveform to a scale of the original signal under test “a”, and displays and outputs a signal waveform “d” of the signal under test “a”.
FIG. 9
is a block diagram depicting a schematic configuration of another conventional waveform measuring apparatus for measuring a signal waveform “d” of a signal under test “a” by using a principle of the sampling technique shown in
FIGS. 7A
,
7
B, and
7
C.
The signal under test “a” having the repetition frequency “fa” (repetition cycle Ta) is input to the sampling circuit
1
and a frequency divider
5
.
The frequency divider
5
divides the repetition frequency “fa” of the signal under test “a” by 1
, and delivers it to a phase comparator
6
.
A voltage control oscillator (VCO)
7
generates a signal having a frequency (fa
) that is 1
(n: positive integer) of the repetition frequency “fa”, and feeds it back to the phase comparator
6
.
The phase comparator
6
detects a phase difference between a phase of an output signal of the voltage control oscillator and a phase of an output signal of the frequency divider
5
, and delivers the phase difference signal to the voltage control oscillator (VCO).
By means of such a phase synchronization loop (PLL), the phase of the output signal from the voltage control oscillator (VCO)
7
is controlled so as to be synchronized with the phase of the signal under test “a”.
An output signal having a frequency (fa
) output from the voltage control oscillator (VCO)
7
is converted into a frequency of (fa
)−&Dgr;f by means of a next frequency divider
8
a
having a fixed rate of frequency dividing and a multiplier
8
b
having a fixed rate of frequency multiplying, and the converted signal is input to a sampling signal generator circuit
3
a.
The sampling signal generator circuit
3
a
applies to the sampling circuit
1
the sampling signal “b” having a repetition frequency synchronized with an
input signal
fb=fa
)−&Dgr;
f
(1)
and a repetition
cycle of
Tb=
(
nTa
)+&Dgr;T (2).
However, a relationship between &Dgr;f and &Dgr;T is approximately shown by the formula below.
&Dgr;f/&Dgr;T=fa
2
2
(3)
The sampling circuit
1
samples the input signal under test “a” by means of the sampling signal “b” input from the sampling signal generator circuit
3
a
, and delivers the sampled signal under test “c” to the signal processing/waveform display section
4
.
The signal processing/waveform display section
4
calculates an enveloped waveform of the input, sampled signal under test “c”, converts a scale of a time axis of this enveloped waveform into a scale of the original signal under test “a”, and displays and outputs a signal waveform “d” of the signal under test “a”.
In this case, a magnification rate of the signal under test “a” of the measured, enveloped waveform to the signal waveform “d” is defined as (fa
&Dgr;f)
In the case where the signal under test “a” is obtained as an optical signal instead of an electrical signal, this optical signal is converted into an electrical signal, and the converted signal is applied to the timer circuit
2
or frequency divider
5
.
In addition, in the case of the optical signal, an electro-absorption modulator is employed instead of the sampling circuit
1
.
This electro-absorption modulator applies a pulse shaped electric field caused by a sampling signal to a forwarding direction of an incident optical signal, thereby making it possible to sample a pulse shaped signal under test “a” that consists of an input optical signal.
Then, the signal under test “c” such as the sampled optical signal is converted into an electrical signal, and the converted signal is delivered to the signal processing/waveform display section
4
.
However, in a conventional measuring apparatus employing a sampling technique shown in
FIGS. 8 and 9
as well, there has been the following problems to be solved.
That is, in the waveform measuring apparatus shown in
FIG. 8
, an output timing of a timing signal output by the timer circuit
2
is set by employing a reference time signal outpu
Otani Akihito
Otsubo Toshinobu
Watanabe Hiroto
Anritsu Corporation
Frishauf Holtz Goodman & Chick P.C.
LeRoux Etienne
Oda Christine K.
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