U.S. patent application number 09/106386 was filed with the patent office on 2001-08-09 for method and apparatus for providing single button access to oscilloscope delay and trigger centric horizontal display modes.
Invention is credited to DOBYNS, KENNETH P., MAGUIRE, DAVID.
Application Number | 20010012009 09/106386 |
Document ID | / |
Family ID | 22311133 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012009 |
Kind Code |
A1 |
MAGUIRE, DAVID ; et
al. |
August 9, 2001 |
METHOD AND APPARATUS FOR PROVIDING SINGLE BUTTON ACCESS TO
OSCILLOSCOPE DELAY AND TRIGGER CENTRIC HORIZONTAL DISPLAY MODES
Abstract
A system for displaying waveforms representing an input signal
includes a display subsystem, coupled to a source of the input
signal, for displaying a waveform representing the input signal in
response to a display control signal. A trigger circuit is coupled
to the input signal source and detects a trigger event. A time
displacement circuit is coupled to the trigger circuit and
generates a time displaced trigger signal a controllable amount of
time after detection of a trigger event. A switch is coupled
between the trigger circuit, the time displacement circuit, and the
display subsystem. The switch selectively generates a display
control signal in response to either a detected trigger event or a
time displaced trigger signal.
Inventors: |
MAGUIRE, DAVID; (BEAVERTON,
OR) ; DOBYNS, KENNETH P.; (BEAVERTON, OR) |
Correspondence
Address: |
THOMAS F LENIHAN
TEKTRONIX INC
P O BOX 500
DELIVERY STATION 50 LAW
BEAVERTON
OR
97077
|
Family ID: |
22311133 |
Appl. No.: |
09/106386 |
Filed: |
June 25, 1998 |
Current U.S.
Class: |
345/418 |
Current CPC
Class: |
G09G 1/162 20130101;
G01R 13/345 20130101 |
Class at
Publication: |
345/418 |
International
Class: |
G09G 005/36 |
Claims
What is claimed is:
1. A system for displaying waveforms representing an input signal,
comprising: a display subsystem, coupled to a source of the input
signal, for displaying a waveform representing the input signal in
response to a display control signal; a trigger circuit, coupled to
the input signal source, for generating a trigger signal upon
detecting a trigger event; a time displacement circuit, coupled to
the trigger circuit, for generating a time displaced trigger signal
displaced an amount of time from the trigger signal; and a switch,
coupled between the trigger circuit, the time displacement circuit,
and the display subsystem, for selectively generating a display
control signal in response to one of the trigger signal and the
time displaced trigger signal.
2. The system of claim 1, wherein the switch operates in response
to a user input.
3. The system of claim 2 wherein the switch is a physical switch
having a first position for coupling the trigger signal to the
display system as the display control signal, and a second position
for coupling the time displaced trigger signal to the display
subsystem as the display control signal.
4. The system of claim 2 further comprising: a control circuit,
responsive to user input, and generating a switch control signal;
wherein: the switch is an electronically controllable switch,
having a first position for coupling the trigger signal to the
display subsystem as the display control signal, and a second
position for coupling the time displaced trigger signal to the
display subsystem as the display control signal, responsive to the
switch control signal.
5. The system of claim 4 further comprising a physical switch,
responsive to user input, and coupled to the control circuit.
6. The system of claim 1, wherein the display subsystem comprises:
an acquisition circuit, coupled to the source of the input signal,
for generating a sequence of samples representing the input signal;
an acquisition memory, coupled to the acquisition circuit, for
storing the sample sequence; and a rasterizer, coupled to the
acquisition memory, for retrieving the sample sequence from the
acquisition memory and generating a signal representing a raster
representing an image of the acquired input signal.
7. A method for operating a waveform displaying system, comprising
the steps of: generating a trigger signal when a trigger event is
detected in an input signal; generating a time displaced trigger
signal displaced an amount of time from the trigger signal;
selectively operating in one of a first mode of operation to
display a waveform representing the input signal in response to the
trigger signal and a second mode of operation to display a waveform
representing the input signal in response to the time displaced
trigger signal.
8. The method of claim 7 further comprising, before the selective
operating step, the steps of: setting a switch into one of a first
position and a second position; when the switch is in the first
position, operating in the first mode of operation; and when the
switch is in the second position, operating in the second mode of
operation.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to user controls for an
oscilloscope, and in particular to control of horizontal display
modes in an oscilloscope.
BACKGROUND OF THE INVENTION
[0002] Earlier analog oscilloscopes included a trigger circuit
which analyzed an acquired input signal for a user selected event,
e.g. a negative-going or positive-going transition at a user
selected voltage level, and in a specified channel if the
oscilloscope was a multichannel oscilloscope. When the trigger
event occurred, a waveform representing the acquired input signal
occurring from that point forward in time was displayed on the
display screen of the oscilloscope. The trigger point was displayed
as the leftmost point in the displayed waveform. The timing of the
displayed waveform was controlled by the user, and could be
changed. As the timing changed, the time (horizontal) magnification
of the waveform also changed. The change was made relative to the
trigger point, which remained fixed at the leftmost point of the
displayed waveform.
[0003] FIG. 1 is a combined waveform and oscilloscope display
diagram illustrating the trigger and horizontal magnification
characteristics of an analog oscilloscope. In FIG. 1, a waveform 10
represents e.g. the voltage of an acquired input signal supplied to
the oscilloscope via an oscilloscope probe. A user has set the
trigger to the illustrated trigger point 12 in a known manner. A
first display 11 is a waveform display on the display screen of the
oscilloscope in which the time base is set to display the waveform
10 from the trigger paint 12 to the point 14. A second display 13
is a waveform display on the display screen of the oscilloscope in
which the trigger point is the same as that in the first display
11, but the time base has been adjusted to display the waveform 10
from the trigger point 12 to the point 16.
[0004] It is apparent from FIG. 1 that the trigger point 12 is
displayed in the waveform display, regardless of the setting of the
time base, and that the trigger point 12 is always displayed as the
leftmost point of the waveform display. Furthermore, it is apparent
that the displayed waveform is magnified from the trigger point 12
on. That is, the trigger point is co-located with the magnification
point. Consequently, the waveform display may be magnified
horizontally to any desired degree without losing the display of
the trigger point 12.
[0005] As digital oscilloscopes were developed, it became possible
to display portions of the waveform occurring before the trigger
point, as well as after. The trigger could be set by a user in the
same manner as in analog oscilloscopes. However, instead of
displaying the trigger point as the leftmost point in the displayed
waveform. The trigger point could be displayed at any point in the
displayed waveform. Also as with analog oscilloscopes, the timing
of the displayed waveform was controlled by the user, and could be
changed, thus changing the time (horizontal) magnification of the
waveform. Again, as with analog oscilloscopes, the change was made
relative to the trigger point, but in digital oscilloscopes, the
trigger point was not constrained to be the leftmost point in the
displayed waveform.
[0006] FIG. 2 is a combined waveform and oscilloscope display
diagram illustrating the trigger and horizontal magnification
characteristics of a digital oscilloscope. In FIG. 2, again a
waveform 10 represents e.g. the voltage of an input signal supplied
to an oscilloscope via an oscilloscope probe. A user has set the
trigger to the illustrated trigger point 12' in a known manner.
This trigger point 12' is different than that set in FIG. 1,
however. A first display 21 is a waveform display on the display
screen of the oscilloscope in which the time base is set to display
the waveform 10 from the point 22 to the point 24, and includes the
trigger point 12' within the displayed waveform. A second display
23 is a waveform display on the display screen of the oscilloscope
in which the trigger point 12' is displayed in the same position as
that in the first display 21, but the time base has been adjusted
to display the waveform 10 from the point 26 to the point 28.
[0007] It is apparent from FIG. 2 that, as in FIG. 1, the trigger
point 12' is displayed in the waveform display, regardless of the
setting of the time base. However, in FIG. 2, the trigger point 12'
is displayed within the waveform display, not at the leftmost edge,
as in FIG. 1. It is also apparent that, as in FIG. 1, the magnified
signal in display 23 is magnified about the location of the trigger
point 12'. Thus, the trigger point is co-located with the
magnification point. That is, the trigger point remains in the same
place in the waveform display, while the displayed waveform expands
or contracts around that point as the time base is changed by the
user. Consequently, the waveform display may still be magnified
horizontally to any desired degree without losing the display of
the trigger point.
[0008] Other digital oscilloscopes used a different technique for
triggering the waveform display, termed a viewport technique. In
such a digital oscilloscope, the displayed waveform is displaced by
some user controlled amount of time from the trigger point. This
display is termed a viewport. The displayed waveform in the
viewport does not, necessarily, contain the trigger point. The
magnification of the displayed waveform takes place within the
viewport and the displayed waveform expands and contracts around a
magnification point, which may be any point on the display screen,
such as the leftmost point of the viewport. In a preferred
embodiment, however, the magnification point is the center point of
the display screen.
[0009] FIG. 3 is a combined waveform and oscilloscope display
diagram illustrating the trigger and horizontal magnification
characteristics of a digital oscilloscope. In FIG. 3, again a
waveform 10 represents e.g. the voltage of an input signal supplied
to an oscilloscope via an oscilloscope probe. A user has set the
trigger to the illustrated trigger point 12 in a known manner. This
trigger point 12 is the same that set in FIG. 1. In FIG. 3, a user
has set a time displacement to point 32 of the input signal. This
is a point after the trigger point, and is referred to as a
positive time displacement. It is also possible for a user to
specify a negative time displacement to a point before the trigger
point. A first display 31 is a waveform display on the display
screen of the oscilloscope in which the time base is set to display
the waveform 10 starting from the time displacement point 32 to the
point 34. The center point of the display screen corresponds to
point 35 of the waveform 10. A second display 33 is a waveform
display on the display screen of the oscilloscope in which the time
base has been adjusted to display the waveform 10 from the point 36
to the point 38. The center point of the display screen continues
to correspond to point 35 of the waveform 10. The point 35, thus,
is the magnification point.
[0010] It is apparent from FIG. 3 that the trigger point 12 is not
necessarily displayed in the waveform display, depending upon the
settings of the time displacement and the time base. Also, in FIG.
3, the magnified signal in display 33 is magnified about the center
point of the waveform display. Thus, in FIG. 3, the trigger point
12 is not co-located with the magnification point 35. Instead, the
displayed waveform expands or contracts around the magnification
point 35, which corresponds to the display screen center point, as
the time base is changed by the user.
[0011] One skilled in the art will understand that more
sophisticated triggering techniques exist. For example, there may
be what it termed a main trigger, which analyzes an acquired input
signal for a user specified main trigger event, and a secondary, or
delayed trigger. These operate in the following manner: after the
main trigger detects the main trigger event, the secondary trigger
analyzes the acquired input signal for a user specified secondary
or delayed trigger event. This secondary trigger event, then
initiates the waveform display. The oscilloscope may be controlled
to display the waveform after, or surrounding the main trigger
event; or after, or surrounding, the secondary or delayed trigger
event.
[0012] Alternatively, the oscilloscope may include what is termed
an A and a B trigger. The A trigger may be set by the user in the
known manner, e.g. a positive going or negative going signal
through a user set voltage level on a selected channel. The B
trigger may be similarly set. The combination of the A trigger and
the B trigger initiates the waveform display. Either or both of the
A and B triggers may also have a time displacement associated with
them. Additional such triggers are also possible, e.g. C trigger, D
trigger, etc. in any case, using the waveform display techniques
illustrated in FIG. 1 or 2, the displayed waveform contains the
trigger event, and the magnification occurs around the display
point representing the time of that event. Using the waveform
display technique illustrated in FIG. 3, the trigger point is not
necessarily contained in the displayed waveform, and the displayed
waveform is time magnified about the magnification point, which is
the center point of the display screen in a preferred
embodiment.
[0013] The trigger-centric techniques of FIGS. 1 and 2 are useful
for a user to observe phenomena surrounding the trigger point
because, regardless of the time magnification, the trigger point is
never removed from the waveform display. For example, in
manufacturing or production environments, in which signals
containing trigger events can be reliably and accurately supplied
to and detected by the oscilloscope, the trigger centric technique
allows observation of a signal near such trigger points. On the
other hand, the viewport technique of FIG. 3 is useful to observe
phenomena located at some time distance from the trigger point. For
example, a location in the middle of a pulse train, can be easily
observed by adjusting the trigger to detect the start of the pulse
train, and adjusting the time displacement to the location of
interest in the middle of the pulse train.
[0014] In existing oscilloscopes, to switch from a trigger centric
waveform display to a viewport waveform display requires resetting
of trigger controls on the oscilloscope, which can involve properly
setting several switches and making appropriate adjustments to user
controls for trigger voltage levels and time displacements for each
trigger. It is desirable to provide a simple and fast way for a
user to switch between the trigger centric and the viewport modes
of operation so that the user can observe the acquired input
waveform both in the location of the trigger to ensure it is
operating reliably and accurately, and easily switch to observe the
acquired input waveform in the time location of the delayed
phenomenon.
SUMMARY OF THE INVENTION
[0015] In accordance with principles of the present invention, a
system for displaying waveforms representing an input signal
includes a display subsystem, coupled to a source of the input
signal, for displaying a waveform representing the input signal in
response to a display control signal. A trigger circuit is coupled
to the input signal source and detects a trigger event. A time
displacement circuit is coupled to the trigger circuit and
generates a time displaced trigger signal a controllable amount of
time after detection of a trigger event. A switch is coupled
between the trigger circuit, the time displacement circuit, and the
display subsystem. The switch selectively generates a display
control signal in response to either a detected trigger event or a
time displaced trigger signal.
BRIEF DESCRIPTION OF THE DRAWING
[0016] In the drawing:
[0017] FIG. 1 is a combined waveform and oscilloscope display
diagram illustrating the trigger and horizontal magnification
characteristics of an analog oscilloscope;
[0018] FIGS. 2 and 3 are combined waveform and oscilloscope display
diagrams illustrating the trigger and horizontal magnification
characteristics of a digital oscilloscope;
[0019] FIG. 4 is a block diagram of a portion of a digital
oscilloscope in accordance with the present invention.
DETAILED DESCRIPTION
[0020] FIG. 4 is a block diagram of a portion of a digital
oscilloscope in accordance with the present invention. FIG. 4
illustrates only those elements necessary to understand the design
and operation of the present invention. One skilled in the art will
understand that other elements are necessary in a digital
oscilloscope, and will understand what those elements are, and how
they are interconnected with the elements illustrated in FIG.
4.
[0021] In FIG. 4, an input terminal 5 is coupled to a source (not
shown) of an input signal. For example, input terminal 5 may be an
oscilloscope probe. Input terminal 5 is coupled to respective input
terminals of an acquisition circuit 102 and a trigger circuit 108.
An output terminal of the acquisition circuit 102 is coupled to an
input terminal of an acquisition memory 104. An output terminal of
the acquisition memory 104 is coupled to an input terminal of a
rasterizer 106. An output terminal of the rasterizer 106 is coupled
to an output terminal 15. Output terminal 15 produces a signal
representing a raster displaying the acquired input signal, and is
coupled to utilization circuitry (not shown). The utilization
circuitry receives the raster representative signal from output
terminal 15, and generates a image on a display device, such as the
oscilloscope display screen, of the waveform display, as
represented by the raster, all in a known manner.
[0022] A first output terminal of the trigger circuit 108 is
coupled to a first input terminal of a switch circuit 112, and a
second output terminal of the trigger circuit 108 is coupled to an
input terminal of a time displacement circuit 110. An output
terminal of the time displacement circuit 110 is coupled to a
second input terminal of the switch circuit 112. Respective output
terminals of the switch circuit 112 are coupled to corresponding
control input terminals of the acquisition circuit 102, the
acquisition memory 104 and the rasterizer 106.
[0023] A user input terminal 25 is coupled to a source (not shown)
of user oscilloscope control inputs. For example, the user input
terminal 25 may be coupled to receive signals indicating the
positions of various switches, and settings for variable controls,
such as dials, which are placed on the control panel of the
oscilloscope. The user input terminal 25 is coupled to an input
terminal of a control circuit 114. Respective output terminals of
the control circuit 114 are coupled to corresponding control input
terminals of the time displacement circuit 110, the trigger circuit
108 and the switch circuit 112.
[0024] One skilled in the art will understand that the various user
controls described above could be incorporated directly into the
circuit being controlled, e.g. trigger circuit 108, time
displacement circuit 110 and/or switch circuit 112, instead of
passing through the control circuit 114. Specifically, the switch
circuit 112 could be implemented as a user controllable, physical,
single pole double throw (SPDT) switch 116 having a pole (movable
contact) coupled to the respective control input terminals of the
acquisition circuit 102, the acquisition memory 104 and the
rasterizer 106. A first throw (non movable contact) of the SPDT
switch 116 is coupled to the output terminal of the trigger circuit
108 and a second throw of the SPDT switch 116 is coupled to the
output terminal of the time displacement circuit 110, all as
illustrated in phantom in FIG. 4. In a preferred embodiment,
however, this switch is an electronic switch controlled by a signal
from the control circuit 114, also as illustrated in phantom in
FIG. 4.
[0025] In operation, the acquisition circuit 102 operates to
reproduce an exact replica of the input signal at the input
terminal 5, and then convert this signal to a series of multi-bit
digital samples representing the input signal. This series of
samples is stored in the acquisition memory 104. The rasterizer 106
retrieves these samples from the acquisition memory 104 and
generates a raster representative signal at output terminal 15.
This raster, when displayed by the utilization circuitry (not
shown), produces an image of the waveform of the acquired input
signal on the oscilloscope display screen, all in a known
manner.
[0026] The control circuit 114 receives user control inputs through
the user input terminal 25. Among other things, these user control
inputs select the trigger event criteria and (if necessary) the
location of the trigger point within the displayed waveform, or the
time displacement of the waveform display from the trigger point.
Control signals representing these user control inputs are supplied
to the trigger circuit 108 and the time displacement circuit 110.
These control signals condition the trigger circuit 108 and time
displacement circuit 110 to operate in the manner specified by the
user to set the trigger event criteria, trigger point location and
time displacement, all in a known manner.
[0027] The display of the waveform by the acquisition circuit 102,
the acquisition memory 104 and the rasterizer 106 is controlled by
display control signals from the switch circuit 112. These display
control signals control, among other things, which part of the
input signal is acquired, rasterized and displayed. These control
signals, in turn, are derived from either the trigger circuit 108
for trigger centric waveform displays, or from the time
displacement circuit 110 for viewport waveform displays.
[0028] In a first mode of operation, the trigger centric mode, the
switch 116 in the switch circuit 112 is in a first position as
illustrated in FIG. 4. In addition, a user controllable dial on the
oscilloscope control panel is set by the user to specify the
location within the displayed waveform at which the trigger point
is to be displayed. In a preferred embodiment, this dial is
calibrated from 0 to 100, in which 0 represents the left hand edge
of the displayed waveform and 100 represents the right hand edge of
the displayed waveform. In this case, the trigger circuit 108
analyzes the input signal from input terminal 5 and detects the
trigger event according to the criteria specified by the user as
described above. When the trigger event is detected, a trigger
signal is generated by the trigger circuit 108. The trigger signal
from the trigger circuit 108 is used to generate a display control
signal, which is coupled to the control input terminals of the
acquisition circuit 102, the acquisition memory 104 and he
rasterizer 106 through the switch circuit 112.
[0029] In a second mode of operation, the viewport mode, the switch
116 in the switch circuit 112 is in a second position, in which the
time displacement circuit 110 is coupled to the respective output
terminals of the switch circuit 112, opposite to that illustrated
in FIG. 4. The same user controllable dial on the oscilloscope
control panel used in the first, trigger centric, mode of operation
to set the trigger point location in the displayed waveform, is set
by the user to specify the positive or negative time displacement
from the trigger point to the displacement point. In this case, the
trigger circuit 108 analyzes the input signal from the input
terminal 5 and detects the trigger event according to the criteria
specified by the user, as described above. This trigger signal from
the trigger circuit 108 is supplied to the time displacement
circuit 110. The time displacement circuit 110 provides a time
displaced trigger signal, displaced by a positive (delay) or
negative (advanced) time period as specified by the user. The time
displaced trigger signal from the time displacement circuit 110 is
used to generate a display control signal, which is coupled to the
acquisition circuit 102, the acquisition memory 104 and the
rasterizer 106. Thus, a single switch, used in conjunction with a
single user controlled dial, can allow a user to easily switch
between the trigger centric mode and the viewport mode.
[0030] One skilled in the art will understand that several display
control signals may simultaneously need to be switched between the
trigger circuit 108 and the time displacement circuit 110. Several
electronically controlled switches, such as switch 116 illustrated
in FIG. 4, one for each such signal, may be included in the switch
circuit 112, all controlled by the same control signal from the
control circuit 114. In this case, a single switch on the
oscilloscope control panel is coupled to the control circuit 114
through user input terminal 25. The control circuit 114 generates a
trigger centric/viewport (T/V) control signal. The T/V control
signal simultaneously controls all of the electronically controlled
switches in the switch circuit 112.
[0031] An oscilloscope as illustrated in FIG. 4 can provide simple
switching between the trigger centric waveform viewing mode, in
which the waveform in the vicinity of the trigger point can be
observed, and the viewport waveform viewing mode, in which the
waveform at some time displacement from the trigger point can be
observed. This switching between these operating modes can be
provided through the operation of a single switch on the
oscilloscope control panel. In addition, a single user controlled
dial on the oscilloscope control panel can control both the
location of the trigger point within the displayed waveform when
the switch is in the `trigger centric` position, and the time
displacement of the displayed waveform when the switch is in the
`viewport` position.
* * * * *