U.S. patent application number 11/285706 was filed with the patent office on 2007-05-24 for system and method for generating triggers based on predetermined trigger waveform and a measurement signal.
Invention is credited to Paul L. Corredoura.
Application Number | 20070118317 11/285706 |
Document ID | / |
Family ID | 38054582 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070118317 |
Kind Code |
A1 |
Corredoura; Paul L. |
May 24, 2007 |
SYSTEM AND METHOD FOR GENERATING TRIGGERS BASED ON PREDETERMINED
TRIGGER WAVEFORM AND A MEASUREMENT SIGNAL
Abstract
A test measurement system and method which uses parallel digital
samples of an input measurement signal to determine a trigger point
for a predetermined trigger waveform. The system correlates the
predetermined trigger waveform with digital samples of the input
measurement signal. The result of this correlation is then used to
identify a trigger point. Generally the point in time where the
trigger waveform has the strongest correlation with the digital
samples identifies the desired trigger point. This trigger point is
then used to identify the selected measurement data, where the
selected measurement data corresponds to the digital samples
obtained at the trigger point time.
Inventors: |
Corredoura; Paul L.;
(Redwood City, CA) |
Correspondence
Address: |
AGILENT TECHNOLOGIES INC.
INTELLECTUAL PROPERTY ADMINISTRATION,LEGAL DEPT.
MS BLDG. E P.O. BOX 7599
LOVELAND
CO
80537
US
|
Family ID: |
38054582 |
Appl. No.: |
11/285706 |
Filed: |
November 21, 2005 |
Current U.S.
Class: |
702/79 |
Current CPC
Class: |
G01R 13/0254
20130101 |
Class at
Publication: |
702/079 |
International
Class: |
G01R 25/00 20060101
G01R025/00; G06F 19/00 20060101 G06F019/00 |
Claims
1. In a measurement system a method for capturing a waveform
contained in an input signal, the method comprising: generating a
plurality of digital samples from the input signal; providing a
predetermined trigger waveform having a frequency spectrum that
substantially matches that of the waveform contained in the input
signal; and correlating the predetermined trigger waveform with the
plurality of digital samples to identify a trigger point time when
the input signal contains the waveform.
2. The method of claim 1 further comprising: providing a plurality
of parallel analog to digital converters which receive the input
signal and generate the plurality of digital samples.
3. The method of claim 1 further comprising: performing a fast
Fourier transform on the plurality of digital samples; performing a
fast Fourier transform on the predetermined trigger waveform; and
wherein the correlating of the predetermined trigger waveform with
the digital samples includes correlating the Fourier transform of
the plurality of digital samples with the Fourier transform of the
predetermined trigger waveform.
4. The method of claim 1 wherein generating the plurality of
digital signals includes generating an absolute value signal which
corresponds to the waveform contained in the input signal.
5. The method of claim 1 further including: using the trigger point
time to generate a plurality of trigger point times; and using the
plurality of trigger point times to capture a periodic waveform
contained in the input signal.
6. The method of claim 1 further wherein the input signal is a
serial data stream, and wherein generating the plurality of digital
samples includes preprocessing the plurality of digital samples to
isolate a runt pulse.
7. The method of claim 6, wherein correlating the predetermined
trigger waveform with the plurality of digital samples operates to
provide a trigger point time when the runt pulse occurs in the
input signal.
8. A measurement system which uses digital samples of an input
signal to generate a trigger point, the system comprising: an
analog to digital converter which operates to generate a plurality
of digital samples from the input signal, wherein the digital
samples include a waveform of interest; a predetermined trigger
waveform generator, which generates a predetermined trigger
waveform that has a correlation to the waveform of interest; a
correlator which correlates the predetermined trigger waveform with
the plurality of digital samples; and an analyzer which operates to
analyze an output of the correlator to identify a trigger point
which is used for identifying the waveform of interest in the
plurality of digital samples.
9. The system of claim 8 wherein the analog to digital converter
comprises a plurality of analog to digital converters which are
configured in parallel, to generate the plurality of digital
samples.
10. The system of claim 8 further including: a fast Fourier
transformer module which operates to transform the plurality of
digital signals to the frequency domain; wherein the correlator
operates to correlate the predetermined trigger waveform with the
digital signals in the frequency domain.
11. The system of claim 8 further including: an internal clock
which operates to synchronize multiple trigger points with a
periodic waveform contained in the input signal.
12. The system of claim 8 further including: a first fast Fourier
transformer module which operates to transform the plurality of
digital signals to the frequency domain; a second fast Fourier
transformer module which operates to transform the predetermined
trigger waveform to the frequency domain; and wherein the
correlator operates to correlate the predetermine trigger waveform
with the digital signals in the frequency domain.
13. The system of claim 8 wherein the analog to digital converter
comprises a plurality of analog to digital converters configured in
parallel, and wherein the plurality of analog to digital converters
operate to output the plurality of digital samples in parallel, and
wherein the system further includes: an interim memory which
operates to store the plurality of digital samples while the
correlator is operating to correlate the predetermined trigger
waveform with the plurality of digital samples; and wherein the
analyzer operates to use the identified trigger point to identify a
first set of the digital samples in the interim memory which
corresponds to the waveform of interest.
14. The system of claim 8 further including: a preprocessing module
which operates to process the plurality of digital samples prior to
inputting the digital samples into the correlator, and wherein the
preprocessing module operates to generate absolute values
corresponding to the waveform of interest.
15. The system of claim 8 further including: a preprocessing module
which operates to process the plurality of digital samples prior to
inputting the digital samples into the correlator, and wherein the
preprocessing module operates to isolate the waveform of
interest.
16. The system of claim 8 wherein the waveform of interest
corresponds to a runt pulse contained in the input signal and the
predetermined trigger waveform has a correlation to the runt
pulse.
17. The system of claim 8 wherein the waveform of interest
corresponds to an impulse signal contained in the input signal and
the predetermined trigger waveform has a correlation to the impulse
signal.
18. A method of generating a trigger to capture a signal waveform
contained in an input signal, the method comprising: sequentially
sampling the input signal to generate a plurality of waveform
samples staggered in time with respect to each other; providing a
trigger waveform having a waveshape approximating that of the
signal waveform contained in the input signal; correlating the
trigger waveform with each of the plurality of waveform samples to
identify a specific waveform sample that provides the highest
degree of correlation; generating a trigger upon identifying the
specific waveform sample; operating the trigger to capture the
specific waveform sample; and using the specific waveform sample to
obtain information of the signal waveform.
19. The method of claim 18 wherein correlating the trigger waveform
with each of the plurality of waveform samples is carried out in
the frequency domain.
20. The method of claim 18 wherein correlating the trigger waveform
with each of the plurality of waveform samples is carried out in
the time domain.
21. The method of claim 18 wherein using the trigger to capture the
specific waveform sample comprises storing the specific waveform
sample in a memory.
22. The method of claim 18 wherein the signal waveform is one of a)
a runt pulse, b) a truncated pulse, and c) an impulse.
Description
BACKGROUND
[0001] One widely used available test system is an oscilloscope.
Generally an oscilloscope is an instrument which captures a
waveform for a period of time and can then generate an image
corresponding to the time domain waveform samples on a display of
the oscilloscope. Additionally, the information captured by the
oscilloscope can be stored on a storage device, and further
processed to provide a wide range of measurement information. One
of the challenges in using an oscilloscope is determining when to
start, or trigger, the capturing or displaying of data. Frequently,
the signal which is being measured using an oscilloscope is a
periodic, or sporadic, type of signal where the voltage of interest
occurs at different points in time, and for relatively short
periods of time. Thus, one of the challenges in using an
oscilloscope is determining when to trigger the capture or display
of measurement data, because for relatively long stretches of time
there can frequently be no information of interest.
[0002] In the past, some oscilloscopes were triggered based on the
magnitude and the slope of an incoming measurement signal waveform.
With the advent of higher speed oscilloscopes based on an array of
moderate speed analog to digital converters (ADC) running in
parallel, some of the previously used trigger techniques have been
found to have significant limitations.
[0003] Some prior high speed oscilloscopes have used dedicated
analog circuitry to generate trigger signals. The analog signal may
come from the input signal directly, or in some cases the analog
trigger can actually be reconstructed from a digital data stream
(or a subset of the data stream) coming from the ADC. Generally,
many of the prior implementations have been found to have
significant limitations, particularly at high sampling rates and
for higher frequency measurement signals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a block diagram showing an embodiment of a system
of the invention.
[0005] FIG. 2 shows a series of plots with a number of signals
which illustrate a correlation operation of an embodiment of the
invention.
[0006] FIG. 3 is a block diagram showing an embodiment of a
correlator module of system according to an embodiment of the
present invention.
[0007] FIGS. 4A-4C show a series of plots with signals
corresponding to a predetermined trigger waveform, an input
measurement signal, and a correlation between the predetermined
trigger waveform, and the input measurement signal, according to an
embodiment of a method of the invention.
[0008] FIG. 5 shows a series of plots with numerous different
signals corresponding to different processing stages according to
an embodiment of a method of the invention.
[0009] FIG. 6 shows a flow diagram illustrating a method to an
embodiment of the invention herein.
[0010] FIG. 7 shows a flow diagram illustrating a method an
alternative embodiment of the invention herein.
DETAILED DESCRIPTION
[0011] An embodiment of the invention herein provides for using the
digital output of an ADC, or a parallel array of ADCs, to determine
a trigger point. For example, in one embodiment of the invention
the trigger generation is done digitally using parallel digital
signal processing on a parallel data stream of digital samples
coming from a bank of moderate speed ADCs, which together form a
high speed ADC. This operation can allow the trigger circuitry to
have the same fidelity and signal bandwidth as the high speed
ADC.
[0012] FIG. 1 shows an embodiment of a system 100 of the invention.
The system 100 provides for an input of a measurement signal 102,
which will typically be an analog signal. The input measurement
signal 102 will be routed to an array of N parallel analog to
digital converters (ADCs) 104, 106, 108, . . . N.
[0013] Each ADC is clocked with a slight time delay relative to the
proceeding ADC so the incoming waveform is sampled in a parallel
manner, such that each sample is slightly delayed in time relative
to the sample from the upstream ADC. At each ADC clock cycle there
are N consecutive waveform samples 112-118. A memory 120 is
provided which receives the waveform samples 112-118. Additional
registers (not shown) or memory could be provided to buffer
additional samples to increase the number of consecutive samples
used in each block of trigger calculations. In one embodiment, the
memory 120 can serve as an interim memory while the correlator is
processing the digital samples.
[0014] The system also provides a trigger waveform module 122. The
trigger module provides the correlator 126 with the frequency
domain representation of the desired trigger waveform. The trigger
module can generate a wide range of different trigger waveforms
123. A user interface 124 can be provided with the system. The UI
124 and include a mouse controller and a keyboard through which a
user can input different waveform parameters. The trigger waveform
module 122 can also be preloaded with a number of different
waveforms which a user can select from. Additionally, a range of
different modes of operation can be provided where the system
operates to automatically detect a suitable trigger waveform.
[0015] A trigger waveform output 123 and the N digital samples from
the array of N parallel ADCs are input to a correlator module 126.
Optionally the data from the parallel ADCs 104- . . . N can be
buffered to provide the correlator 126 with a longer (more than N)
waveform record. The correlator module operates to correlate the
trigger waveform 123 with waveform samples. The correlation between
the trigger waveform and the waveform samples then provides results
which can be analyzed. The correlation can be performed in the
time-domain but the frequency domain option takes advantage of the
efficiency of the Fast Fourier Transform (FFT) and simplifies the
complexity of the required operation. The correlator 126 can
include an analyzer module which then determines a trigger point
time for initiating the trigger, which corresponds to the capture
of information from the samples 112-N. Thus, the trigger point time
operates to identify selected samples of the N digital samples,
where the selected samples include selected measurement data from
the measurement signal.
[0016] FIG. 2 shows a number of plots 200 with different signals
202-208. Signal 202 illustrates a trigger pulse in a test system
such as an oscilloscope. The trigger point in time for the trigger
pulse is centered at a time T1. The signal 204 illustrates a
measurement signal input to the test system. This signal 204 would
correspond to N number of samples with each sample slightly offset
in time from an adjacent sample. Signals 206-208 illustrate the
input signal as time advances. At a time where the input signal 204
is centered at time T2 there is no correlation between the trigger
pulse 202 and the measurement signal 204. At a time where the input
signal 206 is centered at a time T3 there is some correlation
between the trigger pulse 202 and the measurement signal 206. At a
time where the input signal 208 is centered at T1 there is a very
high correlation between the trigger pulse 202 and the measurement
signal 208. In one embodiment the correlator would operate to
determine the trigger time point which provides the highest degree
of correlation between the measurement signal and the trigger
waveform. Once the trigger time point is determined the correlator
module will generate a trigger signal 128 to the memory module 120
which provides a signal indicating a trigger point time that
identifies which digital samples should then be selected for
transmission to other elements of the system, where the information
in the selected digital samples can be captured.
[0017] For example, in the system 100 the selected samples 130
would be transmitted from the memory 120 to a data bus 132. The
data bus can then make the data available to a processor 134. The
processor 134 can then provide for generating an image on a display
136, where the image corresponds to the measurement data from the
data samples which were generated based on the measurement signal
received at a time corresponding to the trigger point time. The
processor 134 can further provide for printing out the measurement
data, and/or for storing the measurement data in a data storage
system 138. Further, the processor can receive user input
information from a user input device 124 to change the display, or
storage of the information. This user input information could also
include information identifying or selecting a particular
predetermined waveform, as discussed above.
[0018] In general the operation of determining the correlation
between the trigger waveform and the input measurement signal can
be achieved by processing the trigger waveform and the input signal
in either the time domain on in the frequency domain. For
discussion purposes one can assume that the input measurement
signal is given as a finite length of input samples Q(nT)=data
(nT+offset), n=0-L; and that the predetermined trigger waveform is
a finite length sampled trigger pattern given as P(nT), n=0-M. A
convolution search for the trigger waveform in the collection of
digital samples of the input measurement signal can be performed,
where the correlation of the trigger waveform to the input signals
can be described by the equation: correlation .times. .times. ( nT
) = P .function. ( nT ) * Q .function. ( nT ) = m = - .infin. m = +
.infin. .times. P .function. ( nT ) .times. Q .function. ( nT + m )
##EQU1## The above described correlation operation can performed in
either the time domain or in the frequency domain. Generally
speaking it will be more efficient to perform the above
calculations in the frequency domain. Processing using frequency
domain information, where a fast Fourier transformation (FFT) from
the time domain to the frequency domain is used, becomes
increasingly beneficial from a processing stand point as the length
of input measurement signal increases.
[0019] In the system 100 the correlator 126 can be a parallel
correlator which calculates the correlation of the input waveform
to the predetermined trigger waveform in parallel for each of the N
different samples. The result of the this correlation then
identifies a trigger point time 128 which operates to time stamp
the digital signals in the memory 120 so that these digital signals
corresponding to the trigger point time stamp can be captured from
the memory 120, as the memory 120 will generally operate as a
temporary storage buffer for a limited amount of data.
[0020] Additionally, where multiple trigger points have been
identified, and there is an identifiable periodic function with the
occurrence of these trigger points the trigger point signal 128 can
be used to synchronize a clock 140, which can then be used to
provide a plurality of trigger points in time corresponding to the
identified period. In one such embodiment past correlation based
triggers are used to train an estimator which will allow the
prediction of future periodic triggers.
[0021] FIG. 3 shows elements of an embodiment of a correlator 300
of an embodiment of the invention herein, and which can be utilized
to provide the correlation function of the correlator module 126
shown in FIG. 1. The trigger waveform module 122 can provide the
trigger waveform signal 123. This trigger waveform signal can then
be input to a FFT module 302 which operates to provide a FFT of the
trigger waveform, whereby the frequency components of the trigger
waveform are provided. The N digital samples output by the ADCs 104
. . . N are input to a measurement signal FFT module 304. A
parallel array of input signal frequency domain components 306 . .
. N are then output by the FFT module 304. The frequency components
306 . . . N are then correlated with the FFT signal 304 from the
FFT module 302. An array of correlated signals 314 . . . N are then
input to an inverse fast Fourier transform (IFFT) module 322. The
operation of the IFFT module 322 then operates to convert the
frequency domain signals to time domain signals 324-330. These
signals are then input to an analyzer module 332 which operates to
determine when a trigger point time which has the sufficiently
strong correlation with the input measurement signal, and this
trigger signal is output as a trigger point time signal 128 as
described above in connection with FIG. 1.
[0022] Embodiments of the invention herein provide a number of
significant benefits. One aspect of the invention is that it can be
implemented in a topology which takes advantage of the parallel ADC
structure which is utilized in many modern high speed
oscilloscopes. The topology of the system described above allows
for the correlation to be calculated at the sampling rate of the
individual ADCs as opposed to the combined sampling rate where
performing these calculations at the combined sampling rate could
be very difficult.
[0023] It should be recognized that the correlator module could be
implemented in a number of different ways. One option would be to
perform the correlation operation on the time domain. N parallel
banks of correlators could be provided to cover all the possible
phases of the input versus the predetermined trigger waveform.
Another possibility is the FFT based approach, as discussed above,
where the N input data samples are converted to the frequency
domain, where the result is multiplied with the FFT of the trigger
waveform and finally converted back to the time domain with an
inverse fast Fourier transformation (IFFT). This later approach
will be significantly more efficient for large values of N.
[0024] Another benefit of an embodiment herein, is that the trigger
point time is generated based on an analysis of N different
samples, this use of multiple different samples provides for a
processing gain which may allow for better performance than
conventional analog trigger circuitry, especially in the present of
significant measurement noise.
[0025] In some applications the operations of the oscilloscope will
require a correlation using a trigger waveform and an inverse
polarity of the trigger waveform. This type of application could be
handled by performing a correlation between the absolute value of
the input measurement signal and the trigger waveform. One example
of this type of application is measuring a signal from an impulse
radio where a digital "1" may be represented by a positive impulse
while a digital "0" may be represented by an impulse of the
opposite polarity. Another application would be detecting signals
from an impulse radar system. Both the impulse radios and impulse
radars have signals with very short (often less than a nanosecond)
durations. To detect these signals one needs to use a very high
sample rate but the duty factor is typically very low. If one were
to process and store the full data stream in memory to find the
desired impulses, the amount of data gathered which would be stored
could be massive, and most of the information would not be of
interest. An embodiment of the system and method herein provide for
realtime correlation of the digital samples with the trigger
waveform which allows for identification of the signal in
measurement data contained in the digital samples derived from the
measurement signal. In essence, in parallel with the information
being stored in an interim memory 120, the correlator would operate
to identify trigger points, and these trigger points can be used to
capture selected measurement data from the memory 120.
[0026] In one embodiment of a system and method of the invention
when the correlation operation provides a trigger point time, the
measured data corresponding to that point in time is captured, and
an accurate time stamp can be added to the data so the exact time
of reception can be determined when the data is processed. In some
embodiments this operation can allow for calculating error vector
magnitude (EVM) values for received signals even though no external
trigger was supplied to the receiver.
[0027] For systems where the incoming measurement signal includes a
periodic signal of interest, an internal clock can in some
implementations use the result of the correlator to synchronize the
internal clock. Once the clock is successfully synchronized, the
correlator could be disabled. Captured data could then be used to
keep the timer synchronized. Where the memory 120 is large enough,
it can be used to provide for pipelining such that it stores large
numbers of digital samples surrounding the trigger point time, and
it could also be used to compensate for delays related to the
calculation of the correlation.
[0028] Another embodiment of a system and method of the present
invention provides for the detection of a specific sequence of
input samples as opposed to just detecting a rising edge of a pulse
which exceeds a particular threshold. The longer the specific
sequence the better the correlator can perform in terms of
detecting the desired sequence from noise or disturbance signals.
Once the correlator has detected the known sequence, the entire
transmission could be stored for detailed evaluation. By using a
circular buffer, signals before and after the correlation trigger
can be recorded.
[0029] The embodiment of the system 100 shown in FIG. 1 shows a
single trigger waveform module 122, and a single correlator module.
However, an embodiment of the system herein could provide for using
multiple trigger waveform modules and multiple correlator modules
in parallel, to correlate the same input data samples using
different trigger waveforms. If a FFT based correlator is used,
each parallel correlator could share the FFT of the input data
stream. Each correlator could then apply the additional
multiplication and inverse FFT operations for each additional
trigger pattern (which could be computed ahead of time).
[0030] FIGS. 4A-4C show a series of plots which illustrate a
simulation of detecting an impulse in a noise measurement data
stream. FIG. 4A shows a predetermined trigger waveform 402, which
in this case is a truncated sync pulse. FIG. 4B shows an input
measurement signal 404, where the trigger is embedded in random
noise with 0.6 RMS level. FIG. 4C shows a detected correlation
signal 406 as output by a correlator module, where the correlation
module determines a correlation between the trigger pattern
waveform and the noisy input measurement signal.
[0031] The method of operation illustrated in FIGS. 4A-4C shows a
characteristic of an embodiment of the invention which provides an
advantage over a simple level detection triggering approach. If a
simple threshold level detection method is used there could be many
false triggers since the peak noise level in the signal 404 could
often exceed the peak value of the desired impulse. The result of
the correlation shown as signal 406 clearly distinguishes the
pattern of the trigger from that of the noise. This simulation uses
a 21 sample truncated sync pulse as a trigger pattern. Longer
trigger patterns will generally result in higher processing gain
and improve the ability to detect signals buried in noise.
[0032] FIG. 5 shows a series of graphs which illustrate a method of
the invention herein for the detection of runt pulses in a digital
data stream, where a runt pulse is shown in the data bit stream
signal 502 as pulse 504. The detection of runt pulses in data
streams is an example of an application for which high speed
oscilloscopes are often used, and this is particularly the case due
to the prevalence of increasingly fast serial data links. One goal
in such applications is to detect pulses that are above the value
allowed for a logical 0 and below that level required for a logical
1.
[0033] The data bit stream signal 502 of the example shown in FIG.
5 illustrates a random set of data bits clocking at 6.67 GHz. The
sample pulse 504 which starts just prior to 2 ns is an invalid bit
having undefined amplitude. The signal 506 shown in the second plot
is a filtered and upsampled version of the original bit stream
intended to represent what a 20 Gs/s oscilloscope would actually
record. The signal 508 shown in third plot shows the processed data
stream where the mean is removed from the signal 506, and the
absolute value is taken, and then the original mean is removed
again. Ideally this plot would be a constant zero value. The final
plot shows a signal 510 which is the result of the correlation
between the processed data stream, which is the signal 508, and the
signal of a 1/2 scale runt pulse, where the 1/2 scale runt pulse is
used as a predetermined trigger waveform in the correlator
module.
[0034] The preprocessing which generates the signal 508 can be
performed in a parallel manner by a preprocessing module (not
shown) before a FFT module which operates to transform the digital
data samples generated by the ADCs, the processed signal is then
transformed by the FFT module and the correlation is then
performed. The system 100 shown in FIG. 1, for example, could
include a preprocessing module (not shown) which would preprocess
the digital samples prior to inputting them into correlator module
126. By providing for some amount of preprocessing the correlation
operation can be used to provide for searching for specific types
of signals in the input measurement signal.
[0035] The above discussed examples show cases where parallel
signal processing is used to generate triggers for high-speed
oscilloscopes that rely on a bank of parallel moderate speed analog
to digital converters to achieve the high sample rates. The
examples illustrate how a FFT based correlator can be used, but the
concept should not be limited to using FFT based processing.
Indeed, one aspect of the invention herein is to advantageously
utilize the multiple signal samples available from the ADCs and
process these signals in parallel at the sample rate of the
individual (moderate speed) ADC clock. If longer vectors are
desired, the parallel ADC outputs can be registered, or stored, to
hold as many data samples as required for the triggering task
[0036] FIG. 6 is a flow chart illustrating aspects of an embodiment
of a method 600 of the present invention. One aspect of the method
600 is receiving 602 an input measurement signal. The method
further includes providing a parallel array of ADC, which generates
604 digital samples of the measurement signal in parallel. A search
signal which is to be searched for in the input measurement signal
is then identified 606. A signal processing operation is applied
608 to modify the digital samples to provide preprocessed samples,
such that when the search signal is in the measurement signal it
will be somewhat isolated in the digital samples. A trigger
waveform which corresponds to the search signal is generated 610.
The predetermined trigger waveform is then correlated 612 with the
preprocessed digital samples of the input measurement signal. As
discussed above the correlation operation could be done in either
the time domain or the frequency domain. This correlation of the
digital samples with the predetermined trigger waveform then
operates to provide a correlation output. A threshold level is
determined 614. An analysis is then performed 616 to identify
trigger points in time where the correlation reaches the threshold
level, and the identification of trigger points provides an
indication that predetermined trigger waveform has been located in
the measurement signal. The digital samples of the measurement
signal which correspond to the trigger points are then captured
618. This capturing can include for example, storing the digital
samples which correspond to the trigger points in a storage device
and/or generating an image on a display of the digital samples
which correspond to the trigger points. The method 600 can be
implemented as a continuous and on-going process where an input
measurement signal is continuously being input the system, and the
method 600 is continuously being applied to the input signal so
that information of interest in the signal is continuously being
captured.
[0037] FIG. 7 provides a flow chart 700 illustrating an alternative
method of the invention herein. The method includes generating 702
a plurality of digital samples from a measurement signal. This
generation of the plurality of digital samples can be achieved by
providing a parallel array of ADCs. The digital samples can be
generated as a parallel stream of digital samples. Additionally a
predetermined trigger waveform is provided 704. This predetermined
trigger waveform can be identified and stored prior to generating
the digital samples. The digital samples are transformed 706 from
the time domain to the frequency domain using a FFT. Also, though
not shown the digital samples can be preprocessed as described
above prior to the FFT operation. This FFT process can be provided
to make the method of correlation more efficient, however, as noted
above the correlation could also be done without this
transformation.
[0038] The predetermined trigger waveform can also be transformed
708 using a FFT process. This processing of the predetermined
trigger waveform could be done realtime, or it could also be done
in advance of the generation and digital samples, and the
predetermined trigger waveform information can be stored in a
memory of the system, and this information could then be used
during the processing of the method herein.
[0039] The FFT of predetermined trigger waveform is then correlated
710 with the FFT of the digital samples. The output of this
correlation is then transformed 712 using an IFFT back to the time
domain. The output of the IFFT is then analyzed 714 to identify
trigger points in time where there is a strong correlation between
the digital samples and the predetermined trigger waveform. The
identification of a strong correlation could include identifying a
point in time which has the highest correlation value for a given
set of digital samples obtained during a given time period, or it
could include identifying points in time where the correlation
result exceed some given threshold value. The identified trigger
points correspond to points in time where the digital samples
corresponding to that point in time are identified as selected
digital samples, which include selected measurement data. This
identification could be done by providing a time stamp to identify
a time when the selected digital samples were received. This
selected data is then transmitted 716 from an interim memory of the
oscilloscope to other elements of the measurement system which
capture 718 the selected data. This capture of the selected data
can include providing the selected data to a processor of the
system which generates an image which can be shown on a display of
the system; and the selected data could also be stored in a storage
element such as a solid state memory, or a hard disk drive of the
system, and used for further analysis; the selected data could also
be printed out for future reference.
[0040] Where multiple trigger points are identified the method can
further provide for determining 720 if the measurement signal
includes a periodic signal. Where it has been determined that there
is a periodic signal in the measurement signal, then an internal
clock in the oscilloscope could be set to provide for a periodic
trigger point based on the period of the detected periodic signal,
and the measurement signal could be used to maintain the
synchronization, thereafter.
[0041] The method 700 can be implemented as a continuous and
on-going process where the input measurement signal is continuously
being input the system, and the method 700 is continuously being
applied to the input signal so that information of interest in the
signal is continuously being captured.
[0042] As discussed above, the invention herein can be implemented
in a range of different systems and methods. One aspect an
embodiment of the invention provides for correlation between the
outputs of a high-speed ADC, which is realized using many parallel
lower speed ADCs, and a user supplied trigger waveform to generate
a trigger point for storing a finite time record of data
surrounding the interval where the correlation exceeded a
predetermined threshold. Adding an accurate time stamp to the data
when stored following the detection of a trigger point can allow
for a demodulation of signal where time shifts are applied to
encode a carrier with data, for example in an impulse radio. There
are of course a wide range of alternative embodiments and
applications for the invention herein.
[0043] Thus, although only specific embodiments of the present
invention are shown and described herein, the invention is not to
be limited by these embodiments. Rather, the scope of the invention
is to be defined by these descriptions taken together with the
attached claims and their equivalents.
* * * * *