JPH06197019A - Digital oscilloscope - Google Patents

Abstract

PURPOSE:To facilitate broad band processing by dividing a signal into a signal system ADD-converting a DC and low frequency component and a signal system ADD-converting a high frequency component and adding digitally converted data. CONSTITUTION:The input signal is separated into an AC signal system passing through a high pass filter 13 and requiring a broad band and a DC signal system exclusively for a DC and a low frequency signal passing through a low pass filter 14. Thus, AC coupling amplifiers are enough for amplifiers 3, 4, 10. An AC signal sampled by a sample-and-hold circuit 5 is amplified by an amplifier 6 and converted into digital data by an A/D converter 7 and the data are stored in a waveform memory 8 on one hand, and the DC signal is ADD-converted by an A/D converter 16 and the result is fed in a waveform memory 17. The A/D conversion data in the DC system are interpolated via an interpolation device 18 and the result is added digitally and transferred to a display memory and displayed as a waveform. A trigger signal path is formed similarly and the AC signal and the DC signal are added analogically at the input of a trigger comparator 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of an amplifier and an AD conversion system of a digital oscilloscope.

[0002]

2. Description of the Related Art As a prior art, the structure of the main part of a digital oscilloscope is examined. As shown in FIG. 4, an acquisition section composed of an attenuator, an amplifier, a sample holder, an AD converter, a memory, a trigger amplifier and a comparator 4 are provided. , A time control unit composed of a time base,
The display unit displays the data stored in the memory on the display. The signal applied from the input terminal 1 is attenuated by the attenuator 2 at an appropriate ratio and applied to the amplifier 3. One of the signals is added to the amplifier 4 and sampled by the sample holder 5 at the sampling frequency f1. Since the circuit up to this sample holder and the sample holder determine the input band of the digital oscilloscope, the wide band property of the attenuator and amplification up to this point is extremely important. Passing the sample holder 5 makes the amplifier 6 a little easier because it does not require a band higher than the sampling frequency f1. For example, if S / H sampling at 100 MHz is added, the amplifier A3 is realized by a commercially available monolithic type general-purpose Ic. it can. The output of the amplifier 6 is added to the AD converter 7, AD-converted, and temporarily stored in the waveform memory 8. The waveform data sampled at high speed is slowly read at the read clock frequency f3 and sent to the display circuit for display. On the other hand, a part of the input signal is branched to the amplifier 10 and applied to the trigger comparator 11, which is compared with the trigger level V _TH to generate a trigger pulse and give the time base 12 a trigger for starting and stopping sampling.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The signal path from the input terminal 1 to the sample holder 5 and the trigger comparator 11 is required to have a wide band characteristic, and a flatness of gain within a band from DC to 1 GHz is required. However, it is technically difficult to achieve both the DC characteristic and the broadband characteristic. The technical problems such as how to level shift the direct current level without deteriorating the high frequency characteristics and how to reduce the temperature drift of the direct current have been drawbacks. The present invention eliminates this drawback and provides a wide-band digital oscilloscope with a relatively simple technique.

[0004]

In order to achieve the above object, the present invention is divided into a signal system for AD-converting direct current and low frequency components and a signal system for AD-converting high frequency components, and each of them is converted digitally. Data is added, and the trigger system is also divided into a DC amplifier and an AC amplifier and added in front of the comparator.

[0005]

As a result, the amplifier that handles high frequencies can be improved by AC coupling, and the problems such as DC level shift and temperature drift can be eliminated, and the bandwidth can be concentrated. An amplifier capable of handling DC and low frequencies can be easily obtained with a commercially available general-purpose operational amplifier or the like, and if the AD converter also uses an 8-bit AD converter for video, the cost burden will not be so large. .

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. Conventional example The parts added to FIG. 4 are a high-pass filter 13 of a primary system, a low-pass filter 14, a DC amplifier 15, an AD converter 16, a waveform memory 12, and an interpolator 18, which have the same cutoff frequency. . That is, it is separated into a conventional AC signal system that requires a wide band and that passes through the high-pass filter 13, and a new DC signal system that passes through the low-pass filter 14 and that is dedicated to new DC and low-frequency signals. As a result, the amplifier 3,
Reference numerals 4 and 10 may be AC coupling amplifiers, and the frequency characteristics may be, for example, the characteristics indicated by the broken line 22 in FIG. Where fc
Is the cut-off frequency of the filters 13 and 14, and the DC amplification system via the low-pass filter 14 preferably has the frequency characteristics shown by the solid line. By the way, the AC signal sampled by the sample holder 5 is amplified by the amplifier 6,
The AD converter 7 converts the data into digital data, and the waveform memory 8
The DC signal is also taken into the AD converter 16
AD conversion is performed and the waveform memory 17 is once loaded. At this time, the sampling frequencies of the AC signal system and the DC signal system are not necessarily the same as long as they are synchronized. If the AC signal system sampling frequency f1 is 100 MHz, for example, the sampling frequency f2 of the DC AD converter may be a low frequency of about 1 MHz, for example. The direct current AD conversion data is interpolated through the interpolator 18 to match the number of alternating current sampling data at the time of reading, digitally added, transferred to the display memory and displayed as a waveform. Similarly, the signal path of the trigger adds the AC signal and the DC signal in an analog manner at the input of the comparator 19. The operation of each unit will be described with reference to the step response of FIG. 3. The input signal 23 becomes a differential waveform as a result waveform 24 after passing through the high-pass filter 13, and the waveform passing through the low-pass filter 14 becomes the waveform 2
It becomes like 5. These waveforms are AD-converted to form data strings 28 and 29, respectively. Here, the data sequence in the dotted line frame 27 is the rising portion 2 of the waveforms 24 and 25.
6 is an enlarged view of 6. The sampling frequency f1 of the AC system is assumed to be four times the sampling frequency f2 of the DC system here for simplicity, but 100 MHz
It doesn't matter if there is a gap of 1MHz. The lower limit of the sampling frequency f2 of the DC system may be selected to be about 1000 times the cutoff frequency of the filter of FIG. 1
If a frequency difference of 000 times is given, the distortion given after addition is attenuated to 1/1000, so that no great influence occurs. However, as it is, since there is a difference in the number of data between the digital data 28 for AC and the digital data 29 for DC, it cannot be added as it is. Therefore, the interpolator 18 linearly interpolates the number of data for DC to the number of data for DC. , Waveform 30, and waveform 28 and waveform 30
Are added to obtain a digital data string like the waveform 31.
These processes may be slowly processed when reading from the waveform memories 8 and 17, and finally sent to the display unit 9 for display.

[0007]

According to the present invention, an amplifier which is required to have a wide band characteristic can be composed of an AC coupling amplifier, which facilitates wide band. In addition, since the sampling frequency of the direct current and low frequency AD conversion system can be set low, it is possible to use an AD converter with a low conversion degree and high resolution. If this system is operated separately, a low speed AD conversion system with high power division can be used. It is possible to configure a high-performance digital oscilloscope that has both a high-speed and low-resolution AD conversion system and can select them according to the application.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention.

FIG. 2 is a frequency characteristic diagram of a signal system divided into two in the present invention.

FIG. 3 is a step response diagram of each part in the embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional example.

[Explanation of symbols]

 2 Attenuator 3, 4, 6, 10, 15 Amplifier 5 Sample holder 13 High-pass filter 14 Low-pass filter 7, 16 AD converter 8, 17 Waveform memory 18 Interpolator 11 Trigger comparator

Claims (2)

[Claims] 1. A high-pass filter and a low-pass filter that divide an input signal into a high-pass component and a low-pass component at the same cutoff frequency, and an amplifier, an AD converter, and a memory are provided in the subsequent stages of the respective filters. And a digital oscilloscope characterized by adding both digitally after AD conversion. 2. The number of data up to the sampling frequency of the AD converter connected to the high-pass filter after conversion is set so that the sampling frequency of the AD converter connected to the low-pass filter is lower than that of the other AD converter. A digital oscilloscope having an interpolator for interpolating.