Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2002-01-29
2004-06-15
Barlow, John (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S066000, C324S076150
Reexamination Certificate
active
06751566
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus for sampling a fast rate repeated waveform with a slower rate clock to convert it into a low rate waveform for purpose of observation, measurement and analysis (such apparatus will be hereafter referred to as “sampling digitizer”), such a method and a semiconductor integrated circuit testing equipment provided with a sampling digitizer.
BACKGROUND OF THE INVENTION
As is well known in the art, a sampling digitizer, comprises a sampling head
11
, a clock generator
12
, an apparatus (hereafter referred to as “digitizer section”)
13
which observes, measures and/or analyzes a signal waveform, and a trigger circuit
14
, as illustrated in FIG.
1
. The sampling digitizer converts a high rate repeated signal (waveform) HRS input to the sampling head
11
(usually formed by a circuit including a diode bridge) into a low rate repeated signal (waveform) by an equivalent sampling technique to be described later, and performs an observation, measurement and analysis of the input waveform of the high rate repeated signal HRS by observing, measuring and analyzing the waveform of the low rate repeated signal.
The equivalent sampling technique is illustrated in
FIG. 2A
for a high rate repeated signal HRS having a period T and input to the sampling head
11
, as an example. In this instance, the clocking generator
12
generates a clock signal CLK
1
and supplies it to the sampling head
11
at a given sampling rate (period) T
1
equal to (nT+&Dgr;t) such that sample timings t1, t2, t2, . . . for the repeated signal HRS be sequentially offset in their phases within the period T by a minimal time interval &Dgr;t which corresponds to a constant phase (in the example shown, the phase of the sample timings is sequentially lagging by &Dgr;t). The given minimal interval &Dgr;t by which the phase of the sample timing is sequentially offset in the period T is referred to in the art as “equivalent sampling interval”. When the frequency of a clock signal CLK having a period equal to a time interval nT obtained by subtracting the equivalent sampling interval from the period T
1
is denoted by F, n is equal to the quotient of dividing the frequency of the high rate repeated signal HRS by the frequency F of the clock signal CLK. Usually, the frequency F of the clock signal CLK is chosen relative to the frequency of the high rate repeated signal HRS so that the quotient n is an integer.
As a consequence of this, the sampling head
11
delivers a low rate data signal OUT
1
at the sampling rate T
1
. As shown in
FIG. 2C
, the low rate data signal OUT
1
appears as converted into a waveform data train a, b, c, . . . in which the amplitude level changes stepwise in alignment with sample timings t1, t2, t3, . . . Waveform data train a, b, c, . . . is downloaded into the digitizer section
13
, and when it is superimposed every period nT, the waveform data a, b, c, . . . are plotted at a time interval of the equivalent sampling interval &Dgr;t. Accordingly, as shown in
FIG. 2D
, there is obtained a low rate repeated signal LRS
1
having a period T
3
which is equal to the sampling rate T
1
multiplied by the number of samples per period T of the high rate repeated signal HRS. It follows that the waveform of the low rate repeated signal LRS
1
is substantially identical with the waveform of the high rate repeated signal HRS.
It is to be noted that in order to facilitate the understanding of the equivalent sampling technique, the waveform of the high rate repeated signal HRS is shown enlarged and the equivalent sampling interval &Dgr;t is shown lengthened in FIG.
2
. Thus, in
FIG. 2
, n=3 and the sampling rate T
1
=3T+&Dgr;t. However, the high rate repeated signal HRS generally has a frequency which is much greater than the frequency F of the clock signal CLK, and accordingly, n assumes a significantly higher value.
Describing this in terms of specific figures, the high rate repeated signal HRS may have a frequency of 1 GHz (or its period is 1 ns) while the internal clock signal CLK of the clock generator
12
may have a frequency F of 100 kHz. Assuming in this instance that the number of samples per period T (1 ns) of the high rate repeated signal HRS is equal to 100 (thus acquiring 100 data items per period T while sequentially delaying the phase of the sample timing by the equivalent sampling interval &Dgr;t), it follows that adjacent two sample points are spaced apart by 1 ns/100=10 ps, which is the equivalent sampling interval &Dgr;t. Consequently, the clock generator
12
generates and delivers to the sampling head
11
the clock signal CLK
1
at the sampling rate T
1
=1 ns×(1 GHz/100 kHz)+10 ps=10 &mgr;s+10 ps. The sampling head
11
delivers the waveform data train a, b, c, . . . in which the amplitude level changes stepwise at sample timings t1, t2, t3, . . . at the sampling rate T
1
=10 &mgr;s+10 ps. Such waveform data is downloaded into the digitizer section
13
. When downloaded waveform data is synthesized at a time interval between the sample timings or the equivalent sampling interval of 10 ps (or &Dgr;t), there is obtained the low rate repeated signal LRS
1
having a period T
3
corresponding to (10 &mgr;s+10 ps)×100 as shown in FIG.
2
D.
The trigger circuit
14
has the function of establishing a start point of observation, measurement and/or analysis of the waveform of the high rate repeated signal HRS. Specifically, information relating to a start point of observation, measurement and/or analysis of the waveform such as a level, a rising edge, a falling edge or the like (hereafter referred to as “trigger information”) is preset in the trigger circuit
14
. When trigger information contained in the data signal OUT
1
(waveform data train a, b, c, . . .) which is fed from the sampling head
11
to the trigger circuit
14
matches the trigger information which is preset in the trigger circuit
14
, the latter produces a trigger signal TR, which is applied to the digitizer section
13
. The digitizer section
13
initiates downloading the waveform data train from the time the trigger signal is applied thereto. Thus from the time (hereafter referred to as “trigger point”) the trigger circuit
14
produces the trigger signal TR, the observation, measurement, analysis and the like of the waveform of the high rate repeated signal HRS is initiated using the low rate repeated signal LRS
1
. Instead of directly feeding the sampled output of the sampling head
11
to the digitizer section
13
and the trigger circuit
14
, the output may be converted into digital values by an A/D converter, not shown, before being fed to the digitizer section
13
and the trigger circuit
14
. Thus, it should be understood that the output data signal from the sampling head
11
may comprise the original sampled signal or the converted digital signal as the case may be in the description to follow.
As described, with a conventional sampling digitizer, because the start point of the observation, measurement, analysis and the like is defined by the trigger point, the observation, measurement, analysis and the like of the waveform is limited to a portion thereof which occurs after the trigger point as a matter of course. If the trigger point is represented by a point a in the waveform shown in
FIG. 2D
, for example, no observation, measurement, analysis and the like of a waveform portion which precedes point a in time (or located to the left thereof as viewed in
FIG. 2D
) is allowed.
A waveform region of a high rate repeated signal HRS for which an observation, measurement, and/or analysis is desired is generally a fraction of one period T of the high rate repeated signal HRS, which is frequently a rising edge region of the waveform as an example. As described above, because the trigger point defines the start point of the observation, measurement, analysis and the like of the waveform, supposing that point a in the waveform of
FIG. 2A
defines the trigger point, the tr
Advantest Corporation
Barlow John
Gallagher & Lathrop
Lathrop, Esq. David N.
Walling Meagan S.
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