When Oscilloscopes Went Digital

By David Herres

The major players in oscilloscope development have been Tektronix Inc., Teledyne LeCroy Corp. and Agilent Technologies (originally Hewlett-Packard, now Keysight Technologies). These giants watch each other closely, each trying to outdo the others in delivering quality and innovation. It would be an understatement to say they are fiercely competitive, although the rivalry appears to be good-natured by-and-large. Certainly each has benefited from the others’ research.

Tektronix introduced the idea of triggering in 1947 when the company brought out its model 511. The result was a stable display that made meaningful measurements possible.

LeCroy is credited with introducing the digital oscilloscope. Walter LeCroy, a gifted photographer and founder of LeCroy Corp., invented the digital storage oscilloscope (DSO), based on his expertise in engineering high-speed digitizers for CERN, Switzerland’s venerable research institution.

The DSO is generally considered equivalent to a digital oscilloscope. By the mid-1980s it had come to dominate the oscilloscope scene. This analog-digital distinction has nothing to do with whether analog or digital signals can be viewed. It pertains to the way in which the signals are processed after initial attenuation/amplification. Following this first unit in the block diagram, the analog signal goes to an analog-to-digital converter (ADC) where it is sampled at a predetermined rate in accordance with an internally synthesized clock signal. Then the now-digitized waveform moves to memory chips. This makes for the great diverse functionality that digital oscilloscopes exhibit. Signals can be preserved for future review and analysis, sent via Internet to remote computers and mobile devices and manipulated in a variety of interesting ways.

Analog oscilloscopes have a certain simplicity that is appealing, and for that reason they are still used in niche applications such as in educational institutions. With the digital scope’s extensive post processing possibilities, however, there can be no turning back from the digital revolution that has taken place.

Digital oscilloscopes are encumbered with a new set of specifications. Like analog scopes, they have a bandwidth spec, the frequency range in which accurate measurements are possible. But a key specification for digital versions is the sampling rate, the number of samples-per-second that the ADC can process and send to memory. Additionally, we must consider the record length. That refers to the number of points that comprise each waveform record.

The major oscilloscope manufacturers offer models with various specifications at widely differing prices. So in acquiring a digital instrument it is important to evaluate the anticipated workload and proceed accordingly.