Equivalent Time Sampling Oscilloscope vs. Real-Time Oscilloscope

Application Notes

Introduction

In the past, deciding between an equivalent time sampling oscilloscope and a real-time oscilloscope was a matter of determining your bandwidth requirements; but with today’s high-performance instruments that distinction isn’t as clear. This document will discuss how each type of scope samples the incoming waveform and explain the trigger requirements. A summary detailing the advantages of each scope is provided at the end.

Table of contents

  • Real-Time Oscilloscope
    • Real-time oscilloscope as an ADC
    • Triggering the real-time oscilloscope
  • Equivalent Time Sampling Oscilloscope
    • One sample per cycle
    • Sampling methodology
    • Triggering the equivalent time sampling scope
  • Eye Diagram
    • Creating an eye diagram
    • Real-time eyes
  • Advantages of Real-Time Scopes
  • Advantages of Equivalent Time Sampling Scopes
  • Related Literature

Real-Time Oscilloscope

Real-time oscilloscope as an ADC

A real-time oscilloscope, sometimes called a “single-shot” scope, captures an entire waveform on each trigger event. Put another way, this means that a large number of data points are captured in one continuous record. To better understand this type of data acquisition, imagine it as an extremely fast analog-to-digital converter (ADC) in which the sample rate determines the sample spacing and the memory depth determines the number of points that will be displayed. In order to capture any waveform, the ADC sampling rate needs to be significantly faster than the frequency of the incoming waveform. This sample rate, which can be as fast as 80 GSa/s, determines the bandwidth which currently extends to 63 GHz.

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