Oscilloscope triggering and signal storage according to the different types of oscilloscopes have a variety of ways to fully understand the trigger coupling, trigger isolation, record length and waveform storage methods, as well as digital oscilloscopes such as pulse width triggering and short pulse triggering.

Oscilloscope triggering:

The role of the trigger circuit is to ensure that each time the time base scanned on the screen, are from the input signal and the definition of the trigger point of the same point to start, so that each scanning waveform will be synchronized to show a stable waveform, see Figure b/c; without the trigger circuit on the screen will see a lot of waveforms with a random starting point of the chaotic overlap of the image, see Figure a .

Triggering is one of the most troublesome aspects of using oscilloscopes, which offer a number of triggering methods that can be applied according to the measurement problem.

As a digital oscilloscope, triggering is actually involved in determining the starting point for storing the waveform.

Normal and abnormal triggering of oscilloscopes

Normal and abnormal triggering of oscilloscopes

triggered coupling

Trigger coupling is defined as the way the trigger signal is coupled to the trigger circuit.

  • DC-coupled by default, with the trigger source connected directly to the trigger circuit
  • AC coupling: The trigger source is connected to the trigger circuit via a series capacitor.
  • HF Suppression: Passes the trigger source signal through a low-pass filter to suppress the high-frequency component, which means that even if a low-frequency signal contains a lot of high-frequency noise, it can still be triggered as a low-frequency signal.
  • LF Suppression: causes the trigger source signal to pass through a high pass filter to suppress its low frequency components, which is useful when displaying signals that contain a lot of power AC sound.
  • TV Trigger: The trigger level control does not work in TV mode. In this case, the oscilloscope uses the synchronized pulse in the video signal as the trigger signal.TV trigger has two modes, TVF field and TVL line.
  • Advanced triggering functions for digital oscilloscopes: single, burr, width, under-amplitude pulse, slope, build/hold logic (timing relationships and state analysis) TV (optional field/row and line counting)

Trigger isolation (HOLD OFF)

Some signals have more than one possible trigger point, such as the digital signal at right.

While the signal is repetitive over longer time periods, this is not the case over short periods of time, so that the waveforms scanned by normal triggering appear to be intermixed.

To solve this problem, a trigger isolation function is used, i.e., a delay time base is added between scans so that each trigger of a scan always starts from the same signal edge. Thus a stable waveform display is obtained.

On the other hand, the use of trigger isolation clearly suffers in terms of waveform capture.

Too short trigger time and normal trigger time

Too short trigger time and normal trigger time

Record length

Definition of Oscilloscope Record Length: A waveform record is the number of waveform points that can be captured by the oscilloscope at one time.

The maximum record length is determined by the storage capacity of the oscilloscope, and it is necessary to increase the storage capacity to increase the record length.

Record length is related to viewing waveform details:

Calculation of record length

Recording time = Recording length / Sampling rate

Example: TDS3012B, recording length 10K is about 10000 points

Time base versus sample rate

Storage of waveforms

Oscilloscope storage is accomplished in two ways:

  • The trigger signal and delay settings determine the starting point of the oscilloscope storage;
  • The storage depth of the oscilloscope determines the end point of data storage.

Recording time = Recording length / Sampling rate

Relationship between storage depth and triggering

Relationship between storage depth and triggering

Pre-trigger/post-trigger

One of the most significant features of a digital oscilloscope is that it allows the user to view events before they are triggered. This is because the data is stored continuously in memory, while the triggering event stops being captured after a sufficient amount of data is available.

  • Digitization of sampling points
  • time interval
  • Optional pre/post trigger
Pre-trigger and post-trigger

Pre-trigger and post-trigger

Pre-trigger:

Pre-triggering can capture signal burrs, among other applications: switching characterization of input and output transients, triggering with output signals to watch and study small input signals.

Pre-trigger to capture burrs

Pre-trigger to capture burrs

Advanced Trigger Functions for Digital Oscilloscopes

Mode for advanced trigger functions, mainly for digital signals:

  • First, predictions are made for signaling phenomena that are occasionally problematic;
  • Determine the restricted state conditions of the pulse, as well as arranging to trigger with a pulse, or a pulse that matches those conditions.

Specific forms are:

  • Pulse width trigger;
  • Short pulse trigger;
  • Pulse Slope Trigger;
  • logical trigger
  • Build/Hold Time Trigger ......

Digital Oscilloscope Roll Mode

Scroll mode is a way that can be applied to the full continuous display, in which the oscilloscope acquires sample points and immediately copies the acquired data to the display memory. These new samples are displayed on the right side of the screen, and the existing waveforms on the screen are scrolled to the left. The old sample points disappear once they are moved to the left side of the screen. In this way, the waveforms displayed on the screen always reflect the latest signal to the time change.

Thanks to the scroll mode, it is possible to use an oscilloscope instead of a chart recorder to display slowly changing phenomena, such as chemical processes, battery charge/discharge cycles, or the effect of temperature on system performance.

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