JPH0640109B2 - Oscilloscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention clearly displays the relationship between an oscilloscope, in particular, an input signal to be measured and a trigger level, and is capable of measuring a voltage of an arbitrary part of an input signal waveform to be measured. About the oscilloscope.

[Prior art and its problems] The oscilloscope uses a cathode ray tube (CR
T) It is a general-purpose measuring instrument that displays on a screen and measures the characteristics of the signal, that is, voltage, frequency (cycle), waveform, and the like. The characteristics of the input signal described above are generally determined by the operator by means of vertical and horizontal scales on the CRT screen and the calibrated voltage and time per unit scale.

It has been proposed to sample the input signal voltage at each point using a signal sampling technique and measure it with a digital voltmeter or the like in order to obtain the voltage of any selected portion of the displayed waveform and the voltage difference between the two points. Yes (Japanese Patent Publication Sho 59-11
997 and Japanese Utility Model Publication 57-30619). However, in this case, a selection circuit for selecting a specific point and a high-speed waveform sampling circuit are required in addition to the normal oscilloscope circuit, so that the apparatus becomes expensive, noise for sampling, generation of sampling error, etc. There was a problem.

It has also been proposed to directly connect a digital voltmeter to a vertical input circuit to which an input signal to be measured of an oscilloscope is applied (for example, Japanese Patent Publication Nos. 54-4861 and 59-10506). However, such calibration can only measure the effective value or the average value of the input signal, and the instantaneous value at an arbitrary point cannot be obtained. In addition, the measurement range is limited to low frequencies, and there is a possibility that an undesired load effect will occur on the input of the oscilloscope.

Furthermore, in recent oscilloscopes, a cursor signal generator is provided separately from the display waveform, and one or two controllable cursor lines are superimposed and displayed on the display waveform to display the maximum, minimum and peak values of the input signal. Measuring the peak value or the selection level (see eg US Pat. No. 4,628,254). However, in this case, an expensive cursor generator is required and periodic calibration work is required to completely calibrate the vertical axis that causes drift, etc. Has been done.

Therefore, the present invention makes it possible to display the trigger level and the input signal waveform at the same time with a slight modification to the circuit configuration of the conventional oscilloscope, and to display the trigger waveform and an arbitrary portion of the waveform. An object is to provide an oscilloscope capable of measuring a signal voltage.

SUMMARY OF THE INVENTION In the present invention, first, an input signal to be measured is a buffer amplifier (1
2) receives. The variable voltage generating means (24) generates an analog voltage for the trigger level. This analog voltage may be generated by a potentiometer as is well known. The switch means (14) selectively and alternately supplies the measured input signal or analog voltage that has passed through the buffer amplifier to the vertical amplification circuit. As a result, the measured input signal and the voltage of the trigger level are simultaneously displayed, so that the relationship between the measured input signal and the trigger level becomes clear. The trigger comparison means (26) compares the input signal under measurement and the analog voltage and generates a trigger pulse at the coincidence point. The sweep circuit (28) receives the trigger pulse and supplies a sweep signal to the horizontal amplifier circuit. The voltage measuring means (32) is connected to the output terminal of the variable voltage generating means and measures an analog voltage. Therefore, the voltage at the point where the sweep of the input signal under measurement is started can be measured. The display means receives the outputs of the vertical and horizontal amplification circuits and displays the measured input signal and the analog voltage.

[Embodiment] FIG. 1 shows a block diagram of a preferred embodiment of an oscilloscope according to the present invention. Reference numeral 10 is an input terminal to which an input signal to be measured is applied, and the input signal drives a vertical deflection plate of a CRT 22 via a buffer amplifier 12, a switching circuit 14, an input stage amplifier 16, a delay line 18 and an output stage amplifier 20. To do.

The output of the buffer amplifier 12 is the trigger comparator 26 of the trigger circuit.
An input signal is applied to one of the input terminals and compared with the trigger level from the trigger level variable voltage generator represented by the potentiometer 24. When the input signal matches the trigger level, a pulse generator (not shown) generates a fast trigger pulse to activate the sweep (slope signal) generator 28 to generate a sweep signal of the selected slope. This sweep signal is converted into a differential (push-pull) output by the horizontal output amplifier 30 to drive the horizontal deflection plate of the CRT 22. Reference numeral 32 is a digital voltmeter (DVM) for measuring the voltage of the trigger level potentiometer with high accuracy. The measured value may be displayed on a display device with an LED or the like, but preferably a character is generated in a corner on the screen of the CRT 22. Display on the container. The switch control circuit 34 is, for example, a flip-flop, and switches the switch state of the switching circuit 14 each time the sweep signal of the sweep generator 28 is generated.

The circuit of FIG. 1 is similar to a conventional internally triggered oscilloscope. However, in the conventional oscilloscope, the relationship between the trigger signal to the trigger comparator 26 and the input signal at the input terminal 10 was not an exactly known relationship. In the present invention, the buffer amplifier 12 is, for example, a source follower amplifier or Japanese Patent Publication No.
It should be noted that there is a known relationship in which the gain is 1 and the input signal appears as the amplitude and level as they are, as described in JP-A 1-1926 or JP-A 57-33807.

The operation will be described. First, assuming that the switching circuit 14 is at the position shown in the figure, an input signal is applied to the vertical deflection circuit, and the electron beam of the CRT 22 is driven in the vertical (vertical) direction according to the input signal level. On the other hand, when the input signal exceeds the trigger level from the potentiometer 24, a trigger pulse is generated by the output of the trigger comparator 26 and the sweep generator 28 is activated to generate a sweep signal. By this sweep signal having a predetermined inclination, the electron beam of the CRT 22 is moved (swept) in the horizontal direction (from left to right) at a constant speed. As a result, the input signal waveform is displayed on the screen of the CRT 22 as a function of time. Here, the delay circuit 18 is a well-known means for avoiding that the start of the sweep signal from the sweep generator 28 is delayed by the trigger pulse and a part of the leading edge of the input pulse signal becomes unobservable. After the sweep is completed, the switch control circuit 34 causes the switching circuit 14 to
And the trigger level is input to the vertical deflection circuit.
Therefore, when the sweep circuit 28 is triggered next time, the trigger level is displayed on the screen of the CRT 22. That is, as shown in FIG. 2 (A), the start portion (left end) of the input signal waveform WF and the trigger level TL match. The above operation is repeated.

Since the DVM 32 measures this trigger level, it digitally displays the voltage at the selected trigger point of the input display waveform WF. By selecting the portion of interest of the input waveform as the trigger point, the voltage at that point is immediately digitally determined by the DVM32. It does not require a high speed sampling circuit as in the prior art, nor does it connect another circuit that produces a load effect to the vertical axis circuit. Since the DVM32 measures the direct current level, it can be inexpensive and IC
It may be a commercialized product.

FIG. 3 shows another embodiment of the oscilloscope according to the present invention, in which a broadband multistage attenuator 11 is inserted between the input terminal 10 and the buffer amplifier 12 in order to expand the measurement range. This attenuator 11 may be a well-known L-shaped RC (resistive capacitor) attenuator. Since the input signal to the trigger comparator 26 is attenuated by the insertion of the attenuator 11, the attenuator 25 for correspondingly attenuating the trigger level from the potentiometer 24 is also inserted. Since the attenuator 25 is for attenuating a DC voltage, it may be a simple resistance attenuator, for example, a type in which a series thick film resistor is highly trimmed by laser trimming and switched by a multiplexer. Of course, the attenuator 25 may be omitted, and the DV may be adjusted according to the attenuation of the attenuator 11.
The measured value of M32 may be calculated.

FIG. 4 shows still another embodiment of the oscilloscope according to the present invention. In this embodiment, in addition to switching the trigger level to two controllable values for each sweep, the first potentiometer 2
4 and a second potentiometer 24b, which are alternately switched by a multiplexer (MUX) 27, and the vertical axis switching circuit 14 is also switched between the input signal waveform, the first trigger level and the second trigger level. Also, DVM3
2 allows the first and second trigger levels to be measured individually and the difference between the two trigger levels to be obtained.

In the embodiment shown in FIG. 4, the display waveform as shown in FIG. 2 (B) can be obtained. It can be understood from this that, for example, the minimum value, the maximum value, and the peak / peak value, which are important parameters of the waveform of the input signal, can be easily obtained.

Although the two trigger levels are individually controlled in FIG. 4, it is actually preferable to associate or track the two trigger levels as shown in FIGS. 5 (A) and 5 (B). In the case of FIG. 5 (A), the outputs of both potentiometers 24a-24b are supplied to the voltage follower circuit 4 respectively.
0a-40b through the first and second output terminals 44a, 44
Let be c. Furthermore, the output 44 of the amplifier 42 having a double amplification (R3 = R4) via equal resistors R1-R2.
Output from b. The output voltage of the output terminal 44b is the sum of the outputs of the output terminals 44a and 44c. Therefore, the first trigger level TL1 is obtained from the output terminal 44a, and the second trigger level TL2 is obtained from the output terminal 44b. The voltage of the output terminal 44c is the difference between TL1 and LT2, that is, (TL2-TL1).

In the circuit configuration of FIG. 5 (B), both potentiometers or variable resistors 24a-24b are connected in series and the current of the current source 40 flows. The voltage at each connection point is set to the buffer amplifier 48a-48.
The first and second trigger levels TL1 and TL2 are set via b, and the differential voltage (TL2 to TL1) is obtained from the output terminal 52c via the differential amplifier 50.

[Modifications] Although the oscilloscope of the present invention has been described based on the preferred embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the gist of the present invention. For example, the DVM 32 continuously changes the trigger level from one end to the other end, and holds the trigger level at the time when the trigger comparator 26 detects a match, thereby quickly and semi-automatically determining the minimum value or the maximum value of the input signal. You may make it detect it intentionally. If the input signal is a signal of known level, for example, a theoretical signal such as TTL or ECL, the DVM 32 may be used to set the trigger level to a predetermined level in advance. Further, when the sweep signal is low speed, the switching circuit 14 may be operated not in every sweep but in a constant cycle. Further, instead of alternately switching between the input signal waveform and the trigger level for simultaneous display, a portion corresponding to the trigger level of the input signal waveform is brightness-modulated by a well-known Z-axis circuit to display a bright spot on the display waveform. Good.

[Effects of the Invention] According to the present invention, since a conventional oscilloscope is only slightly modified, it can be implemented easily and inexpensively. On the other hand, the trigger level voltage can be displayed at the same time as the input signal waveform, and the relationship between the measured input signal and the trigger level becomes clear. Further, although the trigger level can be arbitrarily changed, in the present invention, since the analog voltage of the trigger level can be measured by the voltage measuring means, the voltage of an arbitrary portion of the input signal under measurement triggered is sampled. It can be measured without performing.

[Brief description of drawings]

1, 3, and 4 are block diagrams of different embodiments of the present invention, and FIG. 2 is a display example of the oscilloscope of the present invention.
FIG. 5 is a circuit diagram of a trigger level variable voltage generator which is convenient for use in the embodiment of FIG. In the figure, 12 is a buffer amplifier, 14 is switch means, 22 is display means, 24 is variable voltage generating means, 26 is trigger comparing means, 28 is a sweep circuit, and 32 is voltage measuring means.

Claims (1)

[Claims] 1. A buffer amplifier for receiving an input signal to be measured, variable voltage generating means for generating an analog voltage for a trigger level, and the input signal to be measured or the analog voltage passing through the buffer amplifier to a vertical amplifier circuit. Switch means for selectively and alternately supplying, trigger comparing means for generating a trigger pulse by comparing the measured input signal and the analog voltage, and sweep for receiving the trigger pulse and supplying a sweep signal to the horizontal amplification circuit An oscilloscope comprising: a circuit; a voltage measuring unit connected to the output terminal of the variable voltage generating unit to measure the analog voltage; and a display unit receiving the outputs of the vertical and horizontal amplification circuits.