Capture and analysis of abnormal signals

　　Abstract: Abnormal signals are highly concealed and difficult to analyze, which has caused countless engineers to fail under their spell. However, due to their great influence on the analysis and debugging of signals, engineers have to fight again and again and go forward with many difficulties. This article will analyze with examples and share a novel and practical abnormal signal capture method, which may give you a refreshing experience.

　　

　　1. Find abnormal signals

　　Step 1: Observe the abnormality

　　How do you know if there is an abnormal signal?

　　Seeing is believing. ZDS2000 series oscilloscopes provide a simple and effective way - infinite afterglow, which allows the captured signal to stay on the display. Combined with the ZDS2000 series oscilloscope's unique 330K "waveform refresh rate", under the condition of high waveform refresh rate, all abnormal signals have nowhere to escape.

　　

　　Figure 1 The shadow of an abnormal signal

　　Generally speaking, the probability of abnormal signals is low and they are different from normal signals. Therefore, the light gray waveform (low probability) in Figure 1 is very likely the abnormal signal we are looking for. Unfortunately, although we have seen the abnormality, we cannot view its details or do further analysis because we have not yet saved the abnormal data.

　　Step 2: Conditional capture

　　Through Step 1, you can roughly understand the characteristics of abnormal signals, regard their unique conditions as trigger conditions, and use triggers to quickly capture abnormal signals. The ZDS2000 series oscilloscopes come with a variety of "trigger types" for free, including 11 basic triggers and 21 protocol triggers. In addition, users can also use "template triggers" based on the shape characteristics of the waveform to make the trigger more arbitrary.

　　

　　Figure 2 Using pulse width feature trigger to capture anomalies

　　

　　Figure 3 Using template touch to capture exceptions

　　Step 3: Manual capture

　　Many times, there is no pattern to anomalies. Even the most powerful triggers will feel powerless in the face of them. "Manual capture" can capture a large amount of data, save the data, and collect the abnormal signals. Specific steps:

　　Save all waveforms within a period of time. If any abnormality occurs, it will be in the saved data. The ZDS2000 series oscilloscope comes standard with a maximum storage depth of 250Mpt, which can save 250 seconds of data at a sampling rate of 1MHz.

　　2. Accurately locate the anomaly

　　Is it enough to capture the abnormal signal? No, that is only the basis for analyzing it. Next, we need to further understand the details and characteristics of the abnormal signal, and finally analyze the cause of the abnormal signal from the essence. This is what we really need to do.

　　1. Measurement

　　It is far from enough to analyze abnormal signals only through the intuitive performance of the waveform. Only by accurately quantifying the various indicators of the waveform can we see through the essence of the waveform abnormality. The 51 "real" parameter measurements that come standard with the ZDS2000 series oscilloscope will perform statistical analysis on all waveforms captured on the screen to obtain the current value, maximum value, minimum value, average value, standard deviation, and statistical times of each item. Users can quickly understand possible abnormalities in the waveform by observing the maximum and minimum values, and quickly evaluate signal characteristics by observing the average value and standard deviation.

　　

　　Figure 4 Parameter measurement to find abnormal signals

　　2. Search

　　When debugging abnormal signals, we usually need to clarify how often the abnormality occurs and whether it occurs periodically. In order to figure out these problems, it is generally necessary to record the waveform for a long time, and then locate and analyze the abnormality based on such a huge database. The "search function" standard on the ZDS2000 series oscilloscope can quickly locate the signal of interest in the massive data and automatically mark it. Users can quickly understand the location, frequency, period and other characteristics of the abnormality by observing the mark.

　　

　　Figure 5 Searching for abnormally large pulses

　　

　　Figure 6 Searching for abnormal small pulses

　　3、FFT

　　Abnormalities are usually accompanied by interference signals. Through the 4M-point "FFT operation" standard on the ZDS2000 series oscilloscope, the time domain is converted to the frequency domain for analysis. At a sampling rate of 1GHz, the resolution of FFT can be accurate to 250Hz. Users can quickly and accurately analyze abnormal signals and their sources by analyzing the power, effective value, phase and other characteristics of each frequency.

　　The ZDS2000 oscilloscope provides a variety of powerful functions such as triggering, measurement, searching, FFT, etc. However, the uncertainty of abnormal signals is very large. In practical applications, it is necessary to flexibly combine and use them according to the specific situation to maximize work efficiency.