Characteristics and application of oscilloscope waveform capture mode
“Everyday we use the capture mode of the oscilloscope, generally only the default standard capture mode is used. But what are the capture modes? How much do you know about how each sampling point is processed? Which waveform is each mode suitable for? This article will compare and analyze the characteristics of these modes, which will give you different findings.
Everyday we use the capture mode of the oscilloscope, generally only the default standard capture mode is used. But what are the capture modes? How much do you know about how each sampling point is processed? Which waveform is each mode suitable for? This article will compare and analyze the characteristics of these modes, which will give you different findings.
In fact, when measuring waveforms, it is necessary to select a suitable capture mode for the measurement of some signals with certain characteristics. Here we take the ZDS4054 Plus oscilloscope as an example to share the principles and characteristics of several oscilloscope capture modes and their suitable applications. Press the[Acquire]key on the front Panel of the oscilloscope, and you can see that there are 4 capture modes in the capture mode menu: standard, peak, average and high resolution.
Simply put, an oscilloscope’s capture mode is used to control how waveform points are obtained from sample points. The digital oscilloscope we use now captures a series of samples of the waveform, and stores the samples. The storage limit is to judge whether the accumulated samples can draw the waveform, and then the digital oscilloscope reconstructs the waveform. Due to the different processing methods, the reconstructed signal waveforms will also have certain differences. The similarities and differences of the reconstructed waveforms of these four capture modes are described below.
1. Standard capture mode
For most waveforms, using the standard mode produces the best Display. In general, if you have no special requirements for how the oscilloscope captures waveforms, the capture mode can be selected as the default capture mode of the ZDS 4054 Plus oscilloscope: standard capture mode.
l Principle: The signal is sampled at equal time intervals to reconstruct the waveform. The specific principle diagram is shown in Figure 1.
l Applicable scenarios: Use when there is no special requirement for waveform capture mode.
Figure 1 Schematic diagram of standard capture mode
2. Peak capture mode
In this mode, the oscilloscope can Display all pulses at least as wide as the sample period.
l Principle: The maximum and minimum values of the sampling interval signal are collected. The specific principle diagram is shown in Figure 2.
l Applicable scenarios: Capture narrow pulses and high-frequency glitches that may be lost.
l Note: Although this mode can avoid signal confusion, the displayed noise is larger.
Figure 2 Schematic diagram of peak capture mode
3. Average capture mode
In this mode, an average number N can be set first. The specific setting method is: press the[Acquire]key on the front panel of the oscilloscope, press the menu soft key[Average Number]and set the average number of times by adjusting the A/B knob. numerical value.
l Principle: The oscilloscope will align the collected N-segment waveforms according to the trigger position, and average the N-segment waveforms to obtain an averaged waveform. The specific schematic diagram is shown in Figure 3. In the ZDS4054 Plus oscilloscope, the average number can be set in the range of 2~65536, and the system defaults to 64 times.
l Applicable scenarios: Use when you want to reduce random noise in waveforms and improve vertical resolution.
l Notes: (1) Average capture mode is not supported in scroll view mode.
(2) The higher the average times, the smaller the noise, but the slower the waveform display responds to the waveform changes.
Figure 3 Schematic diagram of average capture mode
4. High-resolution capture mode
In this mode, this mode employs an oversampling technique that averages adjacent points of the sampled waveform, reducing random noise on the input signal and producing a smoother waveform on the screen.
l Principle: Average every N points in a waveform, and replace the original N sampling points with an average point to display. The specific principle diagram is shown in the figure.
l Applicable scenarios: It is usually used in the situation where the sampling rate of the digital converter is higher than the storage rate of the acquisition memory, which can provide waveforms with higher resolution and lower bandwidth.
l Note: “Average” and “High Resolution” mode use different averaging methods. The former is “Waveform Average” and the latter is “Point Average”.
Figure 4 Schematic diagram of high-resolution capture mode
After understanding the capture mechanism and application characteristics of these four capture modes, let’s take a look at their display of the same input signal. Set the capture mode to standard, peak, average and high resolution modes in turn. It is obvious that in contrast, in the standard capture mode (as shown in Figure 5), the signal noise is moderate, and in the peak capture mode (as shown in Figure 6) ), the noise of the signal is obvious, while the waveform displayed in the average (as shown in Figure 7) and high-resolution (as shown in Figure 8) capture modes has almost no random noise.
After understanding the different display effects of the same input signal in different capture modes, let’s summarize the similarities and differences of the four capture modes: When there is no special requirement for the waveform capture mode, the default standard capture mode of the oscilloscope is generally used. To capture narrow pulses or high frequency glitches, select the peak capture mode. To reduce noise and increase resolution, use average capture mode. Select the high-resolution capture mode when you want to provide higher-resolution, lower-bandwidth waveforms.
Figure 5 Waveform in standard capture mode
Figure 6 Waveform in Peak Capture Mode
Figure 7 Waveform in Average Capture Mode
Figure 8 Waveform in high resolution capture mode
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