U.S. patent application number 12/774648 was filed with the patent office on 2011-11-10 for logical triggering in the frequency domain.
This patent application is currently assigned to TEKTRONIX, INC. Invention is credited to JOHN A. DEMENT.
Application Number | 20110274150 12/774648 |
Document ID | / |
Family ID | 44901900 |
Filed Date | 2011-11-10 |
United States Patent
Application |
20110274150 |
Kind Code |
A1 |
DEMENT; JOHN A. |
November 10, 2011 |
LOGICAL TRIGGERING IN THE FREQUENCY DOMAIN
Abstract
A frequency mask trigger capable of triggering based on a
logical combination of two or more areas of a frequency mask
transforms a frame of digital data representing an input signal
into a frequency spectrum having a plurality of frequency bins,
with each frequency bin having a power amplitude value. A frequency
mask is defined having a plurality of reference power levels, one
reference power level being associated with each frequency bin. Two
or more areas of the frequency mask are defined, with each mask
area corresponding to one or more of the frequency bins. A
violation status is determined for each mask area by comparing all
of the power amplitude values within each mask area to the
associated reference power level. If any of the power amplitude
values within the mask area violates the associated reference power
level, then the entire mask area is deemed to be violated. A
trigger signal is generated when a logical combination of the
violation statuses of the mask areas is satisfied.
Inventors: |
DEMENT; JOHN A.; (WALDORF,
MD) |
Assignee: |
TEKTRONIX, INC
BEAVERTON
OR
|
Family ID: |
44901900 |
Appl. No.: |
12/774648 |
Filed: |
May 5, 2010 |
Current U.S.
Class: |
375/224 |
Current CPC
Class: |
G01R 23/167 20130101;
H04B 17/0085 20130101; G01R 23/16 20130101; G01R 23/163 20130101;
G01R 13/345 20130101; H04B 17/327 20150115; G01R 13/0245 20130101;
G01R 23/165 20130101 |
Class at
Publication: |
375/224 |
International
Class: |
H04B 17/00 20060101
H04B017/00 |
Claims
1. A test and measurement instrument comprising: an input processor
for receiving an input signal and producing a digital signal; a
trigger signal generator for generating a trigger signal based on a
logical combination of the violation statuses of two or more areas
of a frequency mask; and an acquisition memory for storing a
seamless block of digital data from the digital signal in response
to the trigger signal.
2. The test and measurement instrument as recited in claim 1
wherein the trigger signal generator comprises: a time-to-frequency
converter for converting a frame of digital data from the digital
signal into a frequency spectrum having a plurality of frequency
bins, with each frequency bin having a power amplitude value; a
comparator for comparing the plurality of power amplitude values to
an associated plurality of reference power levels that define the
frequency mask, and for generating a plurality of output signals,
with each output signal indicating whether a particular power
amplitude value violates the associated reference power level; and
a logic qualifier for determining the violation status of the two
or more mask areas of the frequency mask by examining the output
signals of the comparator that correspond to each mask area, and
for generating the trigger signal based on a logical combination of
the violation statuses of the two or more mask areas.
3. The test and measurement instrument as recited in claim 1
wherein the trigger signal generator comprises: a time-to-frequency
converter for converting a frame of digital data from the digital
signal into a frequency spectrum having a plurality of frequency
bins, with each frequency bin having a power amplitude value; a
comparator for determining the violation status of the two or more
mask areas by comparing those power amplitude values that
correspond to the two or more areas of the frequency mask to
associated reference power levels, and for generating a plurality
of output signals, with each output signal indicating the violation
status of one of the two or more mask areas; and a logic qualifier
for generating the trigger signal based on a logical combination of
the output signals of the comparator.
4. The test and measurement instrument as recited in claim 2
wherein the trigger signal generator further comprises a windowing
function for windowing the frame of digital data.
5. The test and measurement instrument as recited in claim 3
wherein the trigger signal generator further comprises a windowing
function for windowing the frame of digital data.
6. The test and measurement instrument as recited in claim 1
wherein the input processor comprises: a mixer for mixing the input
signal with a local oscillator signal to produce an intermediate
frequency signal; a bandpass filter for filtering the intermediate
frequency signal to produce a filtered intermediate frequency
signal; and an analog-to-digital converter for digitizing the
filtered intermediate frequency signal to produce the digital
signal.
7. The instrument as recited in claim 6 wherein the input processor
further comprises an image reject filter for filtering the input
signal.
8. The test and measurement instrument as recited in claim 1
wherein the time-to-frequency converter comprises a
time-to-frequency transform selected from the group consisting of a
discrete Fourier transform, a discrete Hartley transform, and a
chirp-Z transform.
9. The test and measurement instrument as recited in claim 1
wherein the time-to-frequency converter comprises a bank of
parallel filters selected from the group consisting of finite
impulse response filters and continuous time analog filters.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to test and measurement
instruments, and more particularly to frequency domain
triggers.
BACKGROUND OF THE INVENTION
[0002] Real-time spectrum analyzers such as the RSA6100 and RSA3400
families available from Tektronix, Inc. of Beaverton, Oreg. trigger
on, capture, and analyze RF signals in real-time. These instruments
seamlessly capture RF signals so that, unlike conventional swept
spectrum analyzers and vector signal analyzers, no data is missed
within a specified bandwidth.
[0003] These instruments have the capability to trigger on events
which occur in the frequency domain. This capability, known as a
"frequency mask trigger," is described in U.S. Pat. No. 5,103,402.
The frequency mask trigger calculates the frequency spectrum of
real-time data provided by the instrument's receiver system and
then compares the frequency spectrum to a user-defined frequency
mask. When the frequency spectrum violates the frequency mask, a
trigger signal is generated which causes a seamless block of data
representing the received RF signal to be stored containing the
triggering event as well what happened immediately before and
immediately after the triggering event. In this manner the
frequency mask trigger waits for a single specific spectral event
to occur.
SUMMARY OF THE INVENTION
[0004] In some instances, a user may want to trigger based on a
logical combination of two or more areas of a frequency mask. For
example, consider a system in which two signals are used, with each
signal being at a different frequency. Either signal may be present
at any given time, but it is only an error condition if both
signals are present at the same time. A conventional frequency mask
trigger cannot detect this error condition, that is, it cannot
generate a trigger signal only when both signals are present at the
same time, because a conventional frequency mask trigger generates
a trigger signal as soon as any point of the frequency mask is
violated. A conventional frequency mask trigger does not have the
capability to trigger only when the frequency mask is violated at
two different locations.
[0005] What is desired is a frequency mask trigger capable of
triggering based on a logical combination of two or more areas of a
frequency mask.
[0006] Accordingly, embodiments of the present invention provide a
frequency mask trigger capable of triggering based on a logical
combination of two or more areas of a frequency mask. A frame of
digital data representing an input signal is transformed into a
frequency spectrum having a plurality of frequency bins, with each
frequency bin having a power amplitude value. A frequency mask is
defined having a plurality of reference power levels, one reference
power level being associated with each frequency bin. Two or more
areas of the frequency mask are defined, with each mask area
corresponding to one or more of the frequency bins. A violation
status is determined for each mask area by comparing all of the
power amplitude values within each mask area to the associated
reference power level. If any of the power amplitude values within
the mask area violates the associated reference power level, then
the entire mask area is deemed to be violated. A trigger signal is
generated when a logical combination of the violation statuses of
the mask areas is satisfied.
[0007] The objects, advantages, and other novel features of the
present invention are apparent from the following detailed
description when read in conjunction with the appended claims and
attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 depicts a simplified, high-level block diagram of a
real-time spectrum analyzer.
[0009] FIG. 2 depicts a simplified, high-level block diagram of a
trigger generator according to an embodiment of the present
invention.
[0010] FIG. 3 depicts a frequency mask having two mask areas.
[0011] FIG. 4 depicts a frequency mask having four mask areas.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Referring now to FIG. 1, a real-time spectrum analyzer 10 is
shown having an input processor 20 for receiving a radio frequency
(RF) input signal. The input processor 20 includes an optional
image reject filter 22 followed by a mixer 24 that converts the
filtered input signal to an intermediate frequency (IF) signal
using a local oscillator (LO) 26. The image reject filter 22 may be
implemented using a lowpass filter, a bandpass filter, or a
highpass filter. The IF signal is passed through a bandpass filter
28 and then input to an analog-to-digital (A/D) converter 30 to
provide a digital signal for further processing. The digital signal
is input to a digital signal processor (DSP) 32 for real-time
processing for display on a display device 34, such as in the form
of a spectrogram as described in U.S. Pat. No. 4,870,348. The
digital signal also is input to an acquisition memory 36 and to a
trigger generator 40. In some embodiments, the acquisition memory
36 may be implemented using a circulating memory. When the trigger
generator 40 detects a trigger event, a trigger signal is generated
that causes the acquisition memory 36 to store a seamless block of
digital data from the digital signal for subsequent processing by
the DSP 32 or for offloading to another processor (not shown) for
non-real-time post-processing.
[0013] Referring now to FIG. 2, a trigger generator 40 according to
an embodiment of the present invention is shown having a
circulating buffer 42 for storing digital data representing the
digital signal. In one embodiment, circulating buffer 42 may be
implemented as a part of acquisition memory 36. In another
embodiment, circulating buffer 42 may be implemented as a separate
memory. A frame of digital data is read from circulating buffer 42
and windowed by a windowing function (W) 44 such as a
Blackman-Harris window. The windowed frame is converted to the
frequency domain using a Discrete Fourier transform (DFT) 46 to
produce a frequency spectrum having a plurality of frequency bins,
with each frequency bin having a power amplitude value. A frequency
mask is defined by the user having a plurality of reference power
levels, one reference power level being associated with each
frequency bin. Two or more areas of the frequency mask are also
defined by the user, with each mask area corresponding to one or
more of the frequency bins.
[0014] A comparator 50 compares each of the power amplitude values
within each frequency spectrum to the associated reference power
levels and produces a plurality of output signals, with each output
signal indicating whether a particular power amplitude value
violates an associated reference power level. "Violate" means that
the power amplitude value is either greater than or less than the
associated reference power level depending on whether the user
defines a trigger slope as "positive" or "negative." The plurality
of output signals from the comparator 50 are input to a logic
qualifier 52. The logic qualifier 52 determines a violation status
for each mask area by examining the output signals of the
comparator 50 that correspond to each mask area. If any of the
output signals that correspond to a particular mask area indicate
that a particular frequency bin is violated, then the entire mask
area is deemed to be violated. The logic qualifier 52 generates a
trigger signal when a user-specified logical combination of the
violation statuses of the mask areas is satisfied. The logical
combination may comprise any combination of logical functions such
as AND, OR, XOR, NOT, NAND, NOR, XNOR, and so on.
[0015] It will be appreciated that various modifications may be
made to the trigger generator 40 without departing from the spirit
and scope of the invention. For example, in an alternative
embodiment, the comparator 50 does not compare all of the power
amplitude values within each frequency spectrum, but instead
compares only those power amplitude values that correspond to mask
areas. In that case, the comparator 50 generates a plurality of
output signals that indicate the violation status of the mask
areas, and the logic qualifier 52 generates the trigger signal
based on a logical combination of those output signals.
[0016] In operation, a user may specify the logical combination of
the violation statuses of the mask areas that must be satisfied in
order to generate a trigger signal. For example, given the
frequency mask shown in FIG. 3 having two user-defined mask areas A
and B, a user may specify that the trigger signal is to be
generated when the input signal violates mask areas A AND B, A OR
B, A XOR B, A NOT B, and so on.
[0017] More complex logical combinations may be used if more mask
areas are added. For example, given the frequency mask shown in
FIG. 4 having four user-defined mask areas A, B, C, and D, a user
may specify that the trigger signal is to be generated when the
input signal violates mask areas (A AND B) OR (C AND D). It will be
appreciated that numerous other logical combinations are also
possible. For example, the user may specify that the trigger signal
is to be generated when the input signal violates mask areas (A OR
(B AND C AND D)), ((A AND B AND NOT C) OR D), (A XOR (B XOR (C XOR
D))), and so on.
[0018] The embodiments described above use a discrete Fourier
transform to convert a time domain signal into a frequency
spectrum. Alternatively, other transforms may be used such as a
Hartley transform or a chirp-Z transform. Additionally,
non-transform-based techniques may be used such as a bank of
parallel filters, including finite impulse response filters and
continuous-time analog filters.
[0019] In various embodiments, the trigger generator 40 may be
implemented in hardware, software, or a combination of the two, and
may comprise a general purpose microprocessor, a digital signal
processor (DSP), an application specific integrated circuit (ASIC),
a field-programmable gate array (FPGA), or the like.
[0020] Although many of the parameters described above are
described as being "user-specified" or "user-defined," it will be
appreciated that in other embodiments, those parameters may
alternatively be determined by a standard or automatically
determined by a test and measurement instrument.
[0021] Although embodiments of the present invention have
application to real-time spectrum analyzers in particular, it will
be appreciated that any test and measurement instrument that
acquires data in response to a trigger signal may advantageously
use a frequency mask trigger capable of triggering based on a
logical combination of two or more areas of a frequency mask.
[0022] It will be appreciated from the foregoing that the present
invention represents a significant advance in the field of
frequency domain triggering. Although a specific embodiment of the
invention has been illustrated and described for purposes of
illustration, it will be understood that various modifications may
be made without departing from the spirit and scope of the
invention. Accordingly, the invention should not be limited except
as by the appended claims.
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