Oscilloscopes mainly rely on sampling the signal under test to be displayed on the screen, so understanding the sampling technology of oscilloscopes can understand the principles and methods of oscilloscopes. From the sampling process to understand the difference between digital real-time sampling and digital equivalent sampling.

Digital Oscilloscope Sampling Techniques

Digital Equivalent Sampling

Digital real-time sampling

Different sampling techniques complicate the definition of digital oscilloscope bandwidth:

Repetitive signal bandwidth i.e. analog bandwidth (amplifier bandwidth)

Single Signal Bandwidth

Sampling rate versus single signal bandwidth

Nyquist sampling principle

Sampling on a sinusoidal waveform requires a minimum of two or more points in a cycle to reproduce the waveform.

fs (sampling rate) > 2BW (signal frequency)

Example: 100M sine wave signal, minimum sampling rate?

2X100M = 200MS/s

Definition of Single Bandwidth for Digital Oscilloscopes

is the maximum bandwidth available for a single (transient) signal measurement

BWs = fs (sampling rate) ÷ kR (interpolation factor related to reproduction technique)

2.5 . 4 . 10 .

Example: Interpolation factor is 4, sampling rate is 100MS/s, oscilloscope single bandwidth?

100MS/s ÷ 4 = 25MHz

Digital Equivalent Sampling Technique

After many single samples from different cycles of a repetitive signal, enough sample points are obtained to reconstruct the waveform of this repetitive signal. Equivalent sampling must fulfill two prerequisites:

The signal must be repetitive

Must be able to stabilize the trigger

Digital equivalent sampling techniques require multiple triggering of the signal

Digital equivalent sampling techniques require multiple triggering of the signal

Digital Real-Time Sampling (DRT)

Real-time sampling is the most intuitive sampling method, with sample rates exceeding the analog bandwidth by a factor of 4-5 or more.

Same performance per channel, single bandwidth, repeat bandwidth = single bandwidth

Not only is it suitable for capturing repetitive signals, but it is also an effective method for capturing single signals as well as burrs and anomalies hidden in repetitive signals.

Digital real-time sampling requires only one trigger to acquire all the information of the signal.

Digital real-time sampling requires only one trigger to acquire all the information of the signal.

Single acquisition bandwidth

The single-sample bandwidth, which is also often referred to as the real-time bandwidth, is determined by the combination of the analog bandwidth, the sampling rate, and the method of waveform reconstruction, and thus it determines the integrity of the constructed single-sample waveform .

The methods of waveform reconstruction mainly refer to interpolation algorithms for waveform reproduction.

Single acquisition bandwidth

Single acquisition bandwidth

For a single event, the oscilloscope must have a sufficient sampling rate to recover the waveform from a single capture. Nyquist's sampling law states that the sampling rate should be at least two times the highest frequency bandwidth of the signal to ensure that the signal is recovered without mixing.

Digital Equivalent Sampling vs. Real-Time Sampling

Digital Equivalent Sampling vs. Real-Time Sampling

Sampling:

Sampling was done at equal intervals;

The sampling rate is expressed in "points/second".

sampling interval

sampling interval

What happened during the sampling?

Oscilloscope Sampling Process

Oscilloscope Sampling Process

The analog signal is converted into a digital signal by transforming it and eventually restoring it to an analog waveform displayed on an oscilloscope. In layman's terms, sampling is actually using points to depict the analog signal entering the oscilloscope.

"Deadband" refers to the time during which the instrument does not capture a signal, e.g., digitizing process, data processing process, analog oscilloscope sweepback process ......

The data is stored in the memory, and pre-trigger, post-trigger observation and analysis are also possible.

Summary - Oscilloscope Sample Rate Selection Methods

After we determine the bandwidth of the oscilloscope, we also have to choose a sufficient sampling rate to match it, so that we can obtain a real-time bandwidth suitable for actual measurements, thus obtaining satisfactory measurement results.

If, in practical measurements, more importance is attached to precise information about a single signal, we recommend that the sampling rate be more than five times the bandwidth, preferably eight to ten times.

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