Sampling oscilloscope

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A sampling oscilloscope captures the time domain waveform at discrete time intervals using a sampling circuit. These captured voltages are then either stored in an analog fashion (integrator circuits and CRTs) or digitized and processed digitally. Through the 1960s, the sampling group at Tektronix was led by Al Zimmerman.

A distinction is made between real-time and equivalent time sampling. Real-time sampling requires a sampling rate of at least twice the highest signal bandwidth to capture the signal without aliasing artifacts. It is rare with analog oscilloscopes, but the method of choice for low to medium speed digital storage oscilloscopes, and allows for single shot waveform acquisition.

Equivalent time sampling requires repetitive signals but allows to capture a fast signal with a sampling rate much slower than the signal bandwidth. When talking about a "Sampling Oscilloscope" this approach is usually referred to. For digital instruments the term "Digital Sampling Oscilloscopes" is used. However the lines are blurry, since many instruments utilizing sampling concepts switch between different acquisition modes depending on the timebase setting.

RealTimeSampling Fig29 XYZs of Oscill.png EquivTimeSampling Fig32 XYZs of Oscill.png
Real-Time Sampling Equivalent Time Sampling

Equivalent time sampling is further divided into sequential, and random sampling. Instruments that have a random sampling mode usually also have a sequential sampling mode, e.g., the 7T11.

RandomTimeSampling Fig33 XYZs of Oscill.png SequentialTimeSampling Fig34 XYZs of Oscill.png
Random equivalent-time sampling: the sampling clock runs asynchronously with the input signal and the trigger. Sequential equivalent-time sampling: the single sample is taken for each recognized trigger after a time delay which is incremented after each cycle.