Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
1999-11-22
2002-10-29
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S066000, C324S12100R
Reexamination Certificate
active
06473701
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to triggering mechanisms and associated display modes in a digital storage oscilloscope
BACKGROUND OF THE INVENTION
Prior analog oscilloscopes included a triggering mode known as alternate triggering. In this mode of operation, traces of respective input signals were alternately displayed on the face of a display device, each triggered when it is displayed. The persistence of the phosphors on the screen of the display tube retained the image of each signal long enough for the signals to appear to be displayed stably and simultaneously.
FIG. 1
is a block diagram of a portion of a prior art analog oscilloscope having this triggering mode. In
FIG. 1
, input terminals are illustrated for two input signals, also called channel signals, CH
1
and CH
2
. The input terminals CH
1
and CH
2
may, for example, be oscilloscope probes, which are connected to circuit nodes producing signals which the user wishes to observe. The channel
1
input terminal CH
1
is coupled to an input terminal of a first input amplifier
12
and the channel
2
input terminal CH
2
is coupled to an input terminal of a second input amplifier
14
. An output terminal of the first input amplifier
12
is coupled to respective first data input terminals of a first analog multiplexer
20
and a second analog multiplexer
30
. An output terminal of the second input amplifier
14
is coupled to respective second data input terminals of the first analog multiplexer
20
and the second analog multiplexer
30
. An output terminal of the first analog multiplexer
20
is coupled to an input terminal of a vertical drive amplifier
40
. Differential output terminals of the vertical drive amplifier
40
are coupled to respective vertical deflection plates
52
of a display tube
50
.
An output terminal of the second analog multiplexer
30
is coupled to a first input terminal of a trigger circuit
60
. In
FIG. 1
the trigger circuit
60
is illustrated as a comparator, however one skilled in the art will understand that other triggering circuits were available in analog oscilloscopes as illustrated in
FIG. 1. A
source of a threshold signal, Th, is coupled to a second input terminal of the trigger circuit
60
. An output terminal of the trigger circuit
60
is coupled to an input terminal of a sweep signal generator
70
. Differential output terminals of the sweep signal generator are coupled to respective horizontal deflection plates
54
of the display tube
50
. A status output terminal of the sweep signal generator
70
is coupled to an input terminal of a switch control circuit
80
. Respective control output terminals of the switch control circuit
80
are coupled to control input terminals of the first analog multiplexer
20
and the second analog multiplexer
30
In operation, the first and second analog multiplexers
20
and
30
are simultaneously conditioned to couple to their output terminals a selected channel input signal, that is, either the channel
1
input signal CH
1
or the channel
2
input signal CH
2
, under the control of the switch control circuit
80
. For the following description, it will be assumed that the input signal initially selected is the channel
1
input signal CH
1
. Thus, the first analog multiplexer
20
couples the channel
1
input signal CH
1
to the vertical drive amplifier
40
and the second analog multiplexer
30
couples the channel
1
input signal CH
1
to the trigger circuit
60
.
The trigger circuit
60
compares the channel
1
input signal, CH
1
, to the threshold amplitude Th. When the amplitude of the channel
1
input signal passes through the threshold amplitude Th, the trigger circuit
60
generates a signal at its output terminal which conditions the sweep signal generator
70
to produce a ramp signal. This ramp signal is applied to the horizontal deflection plates
54
. The ramp signal at the horizontal deflection plates
54
produces a single sweep of the electron beam from the left edge to the right edge of the display screen, taking a user controlled period of time.
Simultaneously, the channel
1
input signal CH
1
is amplified by the vertical drive amplifier
40
and applied to the vertical deflection plates
52
. The signal at the vertical deflection plates
52
causes the vertical position of the electron beam sweep to vary as a function of the channel
1
signal amplitude. The combination of the vertical deflection plates
52
and the horizontal deflection plates
54
produce one visible trace on the face of the display tube
50
of the waveform representing the amplitude of the channel signal
1
over the time period specified by the sweep signal generator
70
starting at the time the trigger circuit detected the trigger condition.
When the horizontal sweep is completed, the control signal from the sweep signal generator
70
signals the switch control circuit
80
to condition the first and second analog multiplexers
20
and
30
to select the other channel input signal. That is, the first and second analog multiplexers
20
and
30
now both couple the channel
2
input signal, CH
2
, to their output terminals. The trigger circuit
60
triggers on the amplitude of the channel
2
input signal CH
2
initiating a sweep via the sweep signal generator
70
, and the vertical deflection plates
52
change the vertical position of the sweep according to the amplitude of this channel signal. The display device
50
, thus, displays one trace of the channel
2
input signal CH
2
. When the sweep is complete, the switch control circuit
80
conditions the first and second analog multiplexers
20
and
30
to couple the channel
1
input signal CH
1
to the vertical drive amplifier
40
and trigger circuit
60
once more, and the process begins again. Traces of the channel
1
signal and the channel
2
signal, each triggered by its own amplitude, are alternated on the face of the display tube
50
in this mode of operation, appearing stably and simultaneously due to phosphor persistence.
Digital oscilloscopes operate very differently from analog oscilloscopes.
FIG. 2
is a block diagram of a known digital storage oscilloscope. In
FIG. 2
, elements which are the same as those illustrated in
FIG. 1
are designated by the same reference numbers and are not described in detail below.
In
FIG. 2
, the output terminal of the channel
1
input amplifier
12
is coupled to an input terminal of a first A/D converter
122
and to a first input terminal of a trigger circuit
180
, and more specifically to a first input terminal of a signal selector
182
in the trigger circuit
180
. The output terminal of the channel
2
input amplifier
14
is coupled to an input terminal of a second A/D converter
124
and a second input terminal of the trigger circuit
180
, and more specifically to a second input terminal of the signal selector
182
. An output terminal of the first A/D converter
122
is coupled to an input terminal of a first acquisition memory
132
and an output terminal of the second A/D converter
124
is coupled to an input terminal of a second acquisition memory
134
. An output terminal of the first acquisition memory
132
is coupled to an input terminal of a first unwrap circuit
142
, and an output terminal of the second acquisition memory
134
is coupled to an input terminal of a second unwrap circuit
144
. An output terminal of the first unwrap circuit
142
is coupled to an input terminal of a first waveform memory
152
and an output terminal of the second unwrap circuit
144
is coupled to an input terminal of a second waveform memory
154
. An output terminal of the first waveform memory
152
is coupled to a first input terminal of a rasterizer
160
and an output terminal of the second waveform memory
154
is coupled to a second input terminal of the rasterizer
160
. An output terminal of the rasterizer
160
is coupled to an input terminal of a display device
170
.
An output terminal of the trigger circuit
180
is coupled to a control sequencer
190
. Respective control signal ou
Rockwell Kenneth R.
Tallman James L.
Caracappa David N.
Hoff Marc S.
Kim Paul
Lenihan Thomas F.
Tektronix Inc.
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