JPH0340345B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a waveform display device, and particularly to an oscilloscope that displays the waveform of an input signal after a trigger point in real time, and digitally stores and displays the waveform portions before and after the trigger point.

[Prior art and its problems]

A general oscilloscope generates a sweeping sawtooth wave using a trigger signal extracted from the input signal itself and observes the waveform, so only the waveform after the trigger point of the input signal can be observed. In order to enable long-term storage and observation of this input signal, a so-called digital storage was assigned to the applicant of the present invention.
It is disclosed in Publication No. 49-104531 and the like. According to the invention described in this publication, it is possible to digitize while observing the input signal waveform up to high frequencies as long as the input signal is a repetitive input signal. However, it is not possible to digitize and display the input signal, especially the waveform before the trigger point of a single event. Also, JP-A-54-37787
The publication describes a waveform comparison method that can display input signals in real time and display digitally stored waveforms. This publication also mentions that in order to digitize signals that occur during the sweep retrace period during real-time display, digitizing is performed for a certain period of time from the rise of the sweep signal, and that the waveform before the trigger point is digitized and stored. are doing. However, the specific means is only described as controlling using a counter, but the details are not described.

For oscilloscopes, the sweep speed is switched over a wide range from the order of seconds to the order of nanoseconds (ns), so determining the amount of digitization before the trigger point (pre-trigger amount) using conventional digital techniques requires complex calculations. Not only is it difficult to quickly set the selection, but it is also impossible to check on the cathode ray tube screen whether the calculation is correct or not, in other words, what the pre-trigger amount is.

[Purpose of the invention]

The present invention was developed in view of the above-mentioned drawbacks of conventional digital storage oscilloscopes, and it displays and observes the input signal waveform after the trigger point in real time, and digitizes a selectable range of the waveform before and after the trigger point. To enable display observation when necessary, and also to enable a pre-trigger amount to be selected easily and quickly in an analog manner, and to be able to be identified and displayed by a luminance difference in a real-time display waveform.

In order to achieve this object, the present invention provides the following waveform display device as a preferred embodiment. That is, the vertical and horizontal deflection means of the cathode ray tube are respectively driven by the input signal and the sweeping sawtooth signal generated by the input signal, and the signal waveform of the input signal after the trigger point is applied to the screen of the cathode ray tube. and selectively display the waveform portions of the input signal before and after the trigger point on the cathode ray tube screen based on the input signal digitized and stored data. A clock that generates a clock pulse whose period is selected according to the sweep period so that a substantially constant number of samples are always taken during one sweep period of the above-mentioned sawtooth signal, and continues digitizing the above-mentioned input signal until a stop command pulse is received. a generator, a variable reference signal generator that generates a variable reference signal that changes between peak-to-peak levels of the sawtooth wave signal, compares the sawtooth wave signal and the variable reference signal, and issues the stop command pulse at the point where they match; and a brightness control means for controlling the display brightness of the cathode ray tube by combining the comparison output of the comparator with a sweep gate pulse, A waveform display for displaying a real-time waveform and a digitally stored waveform, characterized in that the signal portion to be digitized can be arbitrarily selected, and the signal portion to be digitized can be identified by different brightness on the input signal waveform displayed in real time. It is a device.

[Summary of the invention]

The waveform display device of the present invention determines a clock pulse of an appropriate period according to the selected sweep speed.
A substantially constant number of samples are obtained during the sweep period, and the signal continues to be uniformly digitized from a period corresponding to the entire real-time display waveform. Then, the sweep signal is compared with a variable reference signal that can be varied over its entire amplitude range, and the digitizing operation is stopped at a matching point, and the comparison output is combined with the sweep gate pulse to control the display brightness of the cathode ray tube. ,
The pre-trigger amount can be easily identified by the brightness difference in the real-time display waveform.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram of a waveform display device according to the present invention. An input signal applied to an input terminal 10 is transmitted through an input circuit 11 including a switchable attenuator, a preamplifier 12, and a delay line 1.
3. Via the switch circuit 14 and main amplifier 15,
Display device 16 (CRT or X-Y recorder, etc.)
is applied to A portion of the signal is extracted from the preamplifier 12 and applied to a trigger circuit 17 .
As will be explained later, the trigger circuit 17 generates a trigger pulse when the level of the applied signal exceeds a predetermined value, and applies this trigger pulse to the sawtooth wave generator 18. The sawtooth generator 18 begins to generate a sawtooth signal by the trigger pulse. 19 is a sawtooth wave slope control circuit for controlling the slope of the sawtooth wave signal. The sawtooth signal is
The signal is applied to an X-axis (time axis) circuit (not shown) of the display device 16 via a preamplifier 20, a switch circuit 22, and a main amplifier 23. In addition, preamplifier 2
The gain of 0 can be switched by the operator operating the amplification switching circuit 21. The outputs of preamplifiers 12 and 20 are applied to sampling circuits 26 and 27 via amplifiers 24 and 25, respectively, under the control of clock pulse generator 29. The sampling outputs from the sampling circuits 26 and 27 are applied to an analog-to-digital converter (ADC) 31 via a multiplexer 30,
converted into a digital signal. In normal operation, multiplexer 30 alternately selects the output of sampling circuit 26 or 27. The output from ADC 31 when sampling circuit 26 is selected is:
This is the waveform data of the input signal. Further, when the multiplexer 30 selects the sampling circuit 27, the output from the ADC 31 is the value at the time of sampling the sawtooth wave synchronized with the input signal, and is used as an address signal when storing the corresponding waveform data. This configuration is, for example,
This is a well-known technique described in detail in Japanese Patent No. 104531, and the well-known peripheral circuits are not shown in FIG. That is, the input signal and the sawtooth wave synchronized therewith are simultaneously sampled, and the waveform data corresponding to that point is stored in the storage means 3 by the address signal corresponding to the value at the time of sampling the sawtooth wave.
Store in 2. In this case, the input signal is assumed to be a repetitive signal, and since the clock signal of the clock generator 29 and the input signal are not synchronized, the points of the waveform data sampled over a large number of repetitive cycles are Randomly distributed on the repeating waveform. In order to accurately reproduce the input signal from these randomly sampled waveform data, a sawtooth wave synchronized with the input signal is simultaneously sampled, and the corresponding waveform data is stored in the storage means 32 using an address signal generated from the data. . As a result, the waveform data randomly sampled over a plurality of cycles becomes waveform data that accurately represents the input signal when stored in the storage means 32. This is one of the so-called random sampling techniques among the equivalent time sampling techniques, and allows a high frequency repetitive signal to be captured by a relatively low frequency sampling clock. When sufficient waveform data is stored in the storage means 32 by repeating the above sampling process, this waveform data is read out in the order of the addresses, converted into an analog waveform signal by the digital-to-analog converter (DAC) 33, and then sent via the switch 14. and sends it to the vertical amplifier 15. On the other hand, the output of a counter (not shown) for counting clock pulses is converted into analog by the DAC 33 to generate a sawtooth wave, and this sawtooth wave is sent to the horizontal amplifier 23 via the switch 22. As a result, a waveform that accurately represents the input signal is reproduced and displayed on the screen of the display device 16 based on waveform data randomly sampled over a plurality of cycles.

Further, as shown in the embodiment of FIG. 1, real-time sampling is performed by selecting only the output of the sampling circuit 26 by the multiplexer 30 and selecting the clock frequency of the clock generator 29 to a high frequency. You can also do it. The real-time sampling technique is a method that sequentially obtains the number of waveform data required for waveform display during one sweep period, and although it cannot sample high-frequency repetitive signals like the equivalent time sampling technique, Suitable for sampling single-shot signals. To implement the pre-trigger display function of the present invention, multiplexer 30 selects sampling circuit 26 to sequentially sample the input signal in real time using high frequency clock pulses determined by the horizontal sweep rate. do. The comparator 34 compares the sawtooth signal voltage generated from the sawtooth wave generator 18 with the control DC voltage (variable reference signal) from the pre-trigger control potentiometer 35. The output of comparator 34 is applied to Z-axis amplifier 36. When the sawtooth signal voltage exceeds the control DC voltage from the potentiometer 35, the output of the comparator 34 is applied to the Z-axis amplifier 3.
6, the clock pulse generation of the clock pulse generator 29 is stopped. The output of Z-axis amplifier 36 is applied to display device 16 as a brightness control signal.

Further, the operation of the waveform display device shown in FIG.
This will be explained with reference to the waveform diagrams shown in FIGS. 3A to 3H. It is assumed that an input signal having a waveform as shown in FIG. 3A is applied to the input terminal 10. The trigger circuit 17 generates a trigger pulse (FIG. 3B) when the level of the input signal exceeds a controllable trigger level Tl at time _t1 . Sawtooth wave generator 18
is triggered by this trigger pulse and generates a sawtooth signal (FIG. 3C) with a slope selected by the sawtooth slope control circuit 19, and at the same time generates a sweep gate pulse (FIG. 3D) during the generation period of the sawtooth signal. ) occurs. The comparator 34 is connected to the pre-trigger control potentiometer 3 when the level of the sawtooth signal is
When the reference voltage Vref set by 5 is exceeded (time t ₂ ), the pulse shown in FIG. 3E is output. Reset circuit within sawtooth generator 18 (not shown)
resets the sawtooth generator 18 when the sawtooth signal level reaches a predetermined maximum value at time _t3 . Therefore, the sweep gate pulse and comparator 3
The output pulse 4 also returns to its initial state at time _t3 . The sampling circuits 26, 27 are controlled by clock pulses (FIG. 3H) to sample the input signal and the sawtooth signal, and the stop pulse (or pre-trigger control pulse) shown in FIG. 3G occurs at time _t2.
Sampling continues until the clock pulse generator stops generating clock pulses. It should be noted here that since real-time sampling techniques are used to implement the pre-trigger display function according to the present invention, multiplexer 30 only sends the output of sampling circuit 26 to ADC 31. Third
The stop pulse in Figure G is applied at time _t2 , for example in Figure 3E.
is obtained by differentiating the leading edge of the output pulse of the comparator 34. The storage means 32 stores the waveform data sampled by the sampling circuit 26 during the period t ₀ to _{t 2} . Incidentally, the period t ₀ to _{t 2} is determined by taking into account the period of the clock pulse and the storage capacity of the storage means 32. It is preferred that the clock pulse generator 29 be provided with a plurality of frequency division circuits in order to automatically select the optimum clock pulse period in consideration of the selected sweep speed and storage capacity.

For real-time waveform display, switch 14
selects the input signal from delay line 13 (FIG. 3A), switch 22 selects the sawtooth waveform from preamplifier 20 (FIG. 3C), and displays on display 16 the period t ₁ -t _{3 .} The input signal waveform of is displayed. Period t ₁ ~
In order to indicate the portion of the input signal waveform at _t3 that is stored in the storage means 32, the output pulse of the comparator 34 (Fig. 3E) is subtracted from the sweep gate pulse (Fig. 3D) to calculate the luminance. A control pulse (FIG. 3F) is obtained. This brightness control pulse is applied to the display device 16, for example, to control the grid voltage of the CRT. Therefore, since the brightness of the waveform part in the period t ₁ to t ₂ is greater than the brightness of the waveform part in the period t ₂ to _{t 3} ,
The operator can easily identify the waveform portions stored in the storage means 32. Note that the time t ₂ , that is, the period
The pre-trigger period from t ₀ to _{t 1} can be controlled very easily by the pre-trigger control potentiometer 35 .

In the case of stored waveform display, the switch 14
The switch 22 selects the stored waveform signal of the period t ₀ to t ₂ supplied from the DAC 33 and selects the sawtooth wave signal of the period t ₀ to t ₂ supplied from the DAC 33 . Although the sawtooth wave during this period t ₀ to _{t 2} is not shown, it can be easily generated by the well-known means of digital-to-analog conversion of the output of a counter (not shown) that counts clock pulses that drive the storage means 32. Needless to say. As a result, the display device 16 displays a pre-trigger portion (period t ₀ ~
t ₁ ) and, in the case of real-time waveform display, a stored waveform including a brightness-modulated portion (period t ₁ -t ₂ ). Furthermore, by switching between the real-time waveform display and the stored waveform display described above in a time-sharing manner, it is possible to display both the signal waveforms before and after the trigger pulse (time t ₁ ) at the same time. The measuring device is ideal for detailed observation of single phenomena.
Incidentally, if a storage tube (in particular, a so-called split screen type storage tube (disclosed in Japanese Patent Publication No. 41-1813) for which the present applicant has patent rights) is used in the device shown in FIG.
It's even more convenient. That is, the input signal waveform after the trigger point can be accumulated and stored on the CRT screen, and the input signal waveform before the trigger point can be stored in the storage means 32 and displayed on the non-accumulated screen portion of the CRT. .

FIG. 2 is a circuit diagram showing one embodiment of the input stage of the comparator 34 and the Z-axis circuit 36. The comparator 34 is
Emitter-coupled transistor (TR) pair 43,4
4, the collector of TR 43 is connected to the base of control TR 46, and the collector of TR 44 is connected to the collectors of the former of Schmitt TRs 47, 48. A positive slope sawtooth signal is applied to the input terminal 40 connected to the base of the TR 43, while a pre-trigger control DC voltage from the potentiometer 35 is applied to the voltage follower (or buffer amplifier).
41 to the base of TR 44.
The collector of the TR 48 is connected to the connection point of the series-connected resistors 51 and 52 in the input stage of the Z-axis circuit 36, and the series-connected resistors 51 and 52 are connected to the emitter-connected TR.
It is connected between the emitters 49 and 50 and a negative voltage source. The base of TR 49 is grounded, and the gate pulse (FIG. 3D) from sawtooth signal generator 18 is applied to the base of TR 50 via terminal 54.

The operation of the circuit shown in FIG. 2 will be explained. The sawtooth signal level is the reference level Vref set by the pre-trigger control potentiometer 35.
If below, TR43 and TR44 are on and off, respectively, and the collector current of constant power supply TR45 is:
It flows through TR43 to the base of TR46. In this state, TR46 and TR47 are both on, and TR4
8 is off. On the other hand, when the level of the sawtooth signal exceeds Vref, TRs 44 and 48 are turned on at high speed. When a trigger gate pulse with a rising leading edge is applied to terminal 54, output terminal 5
A positive pulse occurs in 3, but Schmitt TR4
When a collector current of 8 flows to the connection point between the resistors 51 and 52, the level of the positive pulse described above decreases.
In this way, the brightness control pulse shown in FIG. 3F is obtained. Therefore, in the waveform displayed on the display device 16, a portion corresponding to the period _t1 to _t2 is displayed with higher brightness than other portions, and the pre-trigger amount of the stored waveform can be clearly displayed.

A preferred embodiment of the present invention has been described above, but
Those skilled in the art can make modifications to the above-described embodiments depending on the application. For example, the display device 16
An X-Y recorder or plotter may be used instead of a CRT, or a stop pulse (pre-trigger control pulse) may be indicated with a line of a different color or width than other parts.

〔Effect of the invention〕

As is clear from the above description, the waveform display device of the present invention has the following various remarkable effects.

(1) Since the real-time signal waveform after the trigger point and the digital storage waveform including the trigger point and having approximately the same time width as the real-time waveform before and after the trigger point can be displayed and observed, it is particularly suitable for fault diagnosis.

(2) The pre-trigger amount can be selected extremely quickly and continuously in an analog manner, and the setting appears as a display brightness difference on the real-time waveform and can be checked in advance, so it is not only easy to set the optimal pre-trigger amount. Measurement errors can be avoided.

(3) The trigger point position in the digital storage waveform can be set to any position between the left end and right end of the real-time waveform, and this is independent of the sweep speed setting.

(4) Since the variable reference signal for pre-trigger amount selection is within the peak-to-peak value of the sawtooth wave signal for sweep, it can also be used as the delay time control potentiometer of a conventional slow sweep oscilloscope.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a waveform display device according to the present invention, and FIG. 2 is an example of a main circuit diagram constituting the present invention.
FIG. 3 is a waveform diagram for explaining the operation of the present invention. 18...Sawtooth wave generator, 26, 27...Sampling circuit, 29...Clock pulse generator, 31...Analog-to-digital converter, 32...
...Storage means, 34...Comparator, 35...Pre-trigger control potentiometer.

Claims (1)

[Claims] 1. Drive the vertical and horizontal deflection means of the cathode ray tube with an input signal and a sweeping sawtooth signal generated by the input signal to determine the signal waveform of the input signal after the trigger point. Displaying the input signal on the screen of the cathode ray tube and selectively displaying the waveform portion before and after the trigger point of the input signal on the screen of the cathode ray tube based on the data stored by digitizing the input signal, One of the above sawtooth wave signals that can be selected and set arbitrarily
a clock generator that generates a clock pulse whose period is selected according to the sweep period so as to always take a substantially constant number of samples during the sweep period, and continues to digitize the input signal until a stop command pulse is received; a variable reference signal generator that generates a variable reference signal that changes between peak-to-peak levels of the wave signal; a comparator that compares the sawtooth wave signal and the variable reference signal and generates the stop command pulse at a point of agreement; brightness control means for controlling the display brightness of the cathode ray tube by combining the comparison output of the comparator with a sweep gate pulse; A waveform display device for displaying a real-time waveform and a digitally stored waveform, characterized in that the signal portion to be digitized can be identified by different brightness on the input signal waveform displayed in real time.