Oscilloscopes evolve from modest displays to powerful tools
This article is part of Then and now in our library of series and part of Electronic Design 70th Anniversary Series.
What you will learn:
- What is an electromechanical oscillograph?
- Which model ushered in the era of the real-time digital oscilloscope?
- Examples of the latest powerful equipment.
Capable of graphically displaying a range of information about electronic circuit performance as a two-dimensional plot over time, oscilloscopes produce waveforms that are too fast and transient to be seen by the human eye alone. Not only is it a primary tool for the electronics design engineer, but the oscilloscope can also be found in the military/aero, science, medical, and telecommunications, among other spaces.
Waveform analysis of properties such as amplitude, frequency, rise time, time interval, distortion, and other aspects is an important force multiplier in the design process. At first, calculating these values required manually measuring the waveform against scales built into the instrument’s display.
Genesis of the Oscilloscope
The first high-speed visualizations of electrical voltages were made with an electromechanical oscillograph (Fig.1). These were eventually replaced by oscilloscopes based on cathode ray tube (CRT) technology to display the results. Once called cathode ray oscilloscopes, CROs have been superseded by digital storage oscilloscopes (DSOs) with thin LCD displays, fast analog-to-digital converters (ADCs), and digital signal processors (DSPs).
1. An electromagnetic oscillograph measures variations in electric current by passing it through a magnetic coil. (Credit: Rama, CC BY-SA 2.0 FR, via Wikimedia Commons; public domain image scanned by Dale Mahalko, firstname.lastname@example.org)
The electromagnetic oscillograph, invented by William Duddell, measured changes in electric current flowing through a magnetic coil, which induces a momentum in the coil that can be directly measured. Some designs used a mirror to reflect a beam of light to allow minute movements of the coil to be measured. Others had a pointer, often fitted with a pen, to record the values. A modern oscilloscope may have a built-in display, or it may be an electronic module that plugs into a computer or laptop to process, display, and record waveforms.
The first CRO was created by German physicist Ferdinand Braun, and VK Zworykin developed a waterproof high-vacuum CRT with a thermionic transmitter in 1931, allowing General Radio to manufacture an oscilloscope that could be used outside of a laboratory.
The first dual-beam oscilloscope came in the late 1930s from a British company called ACCossor, which was later acquired by Raytheon. Widely used during World War II to work on radar equipment, the CRT in the uncalibrated device did not produce a true double beam, but rather a split beam consisting of an additional plate between the vertical deflection plates.
Early oscilloscopes had a synchronized sawtooth waveform generator to provide the time axis. Charging a capacitor with a constant current creates an increasing voltage, which is then transmitted to the horizontal deflection plates to create the sweep. When the capacitor reaches a certain point, it discharges; the track would return to the left to begin another journey. The load current could be adjusted so that the sawtooth generator has a longer period than a multiple of the vertical axis signal.
The first real-time digital oscilloscope
Providing a digital solution with analog driving, the 9400 Dual 175 MHz oscilloscope challenged the industry with a display that shows both the real-time input signal in the upper trace and its calculated Fourier spectrum in the trace lower. (Fig.2). Released in 1971, the screen used a standard, mass-produced television tube.
2. The 9400 Dual 175 MHz oscilloscope had a display showing both the real-time input signal in the upper trace and its calculated Fourier spectrum in the lower trace.
The 9400 was notable for leveraging LeCroy’s long-acquisition memory technology for convenient long-memory analysis capabilities at a time when other solutions focused on recreating the viewing experience of a analog oscilloscope.
A few years later, LeCroy released the WD 2000 Waveform Digitizer (Fig.3). With a real-time ADC, memory, and display in a single package, the device captured point-in-time events in real time. It didn’t have much memory depth—only 20 samples—and it provided no input signal conditioning (50 Ω, 1 V full scale only), and it sold for around $20,000. However, it had all the basic functionality of a digital oscilloscope and it was fast. These 20 samples were 1 ns apart in real time.
3. The WD 2000 waveform digitizer incorporated real-time ADC, memory, and display into a single package.
Sampling (or “equivalent time”) oscilloscopes had been around for a while, offering much higher sampling rates for repetitive signals only, but the WD 2000 was a real-time oscilloscope with a small CRT. It achieved its speed through a current-sampling technique derived from the company’s particle physics ADCs, known as the “Wilkinson Run-Down” ADC. They were quite slow, but very accurate, and there were 20 of them compared to more modern designs based on a single “flash” type ADC.
An interesting note concerns Mike Bedesem, the president of LeCroy Research Systems (the company’s name at the time), who allegedly hand painted the text on the front panels of WD 2000s. The WD2000 was a harbinger of the company’s 9400 digital oscilloscope, in the sense that it was a convergence of High Energy Physics technology applied to signal visualization. It too, like the 9400, introduced in 1984, was a physicist’s oscilloscope.
The electronics industry has always sought to develop more and better solutions, and the oscilloscope world must stay one step ahead. The Infiniium UXR developed by Keysight Technologies was the first series of real-time oscilloscopes to offer high-performance data acquisition with 10-bit resolution (Fig.4). The solution offers four simultaneous channels with real-time analog bandwidth from 5 to 110 GHz, each simultaneously sampling at 256 Gsample/s.
4. Keysight Technologies’ Infiniium UXR provides high performance data acquisition with 10-bit resolution.
Offering advanced performance, ultra-low noise, and high signal fidelity, the Infiniium UXR enabled engineers to capture and examine very fast phenomena. One, two and four channel models feature a 10-bit ADC and deep memory of up to 2 Gpoints per channel.
Claiming the highest effective bit count (ENOB) at full bandwidth, the Infiniium UXR has a noise floor of less than 1 mVrms vertical noise at 110 GHz. The device also guarantees the accuracy of its measurements with a jitter of less than 25 fs (rms) of intrinsic jitter and less than 10 fs (rms) of inter-channel jitter. In addition, the solution allows precise operation with the available auto-calibration modules.
On top of that, there’s a metering acceleration ASIC and a memory controller capable of 5 trillion integer operations per second (IOPS). This is made possible using Keysight’s indium phosphide ASIC technology for low noise and high signal integrity through time-interleaved sampling across the full bandwidth. The oscilloscope’s 16 GB of RAM, 3.0 GHz quad-core processor and hardware acceleration enable fast processing. And a 15.4 inch. The capacitive touchscreen highlights the Infiniium UXR’s ability to measure edges as fast as 2.8ps.
A multifaceted tool
Convergence and integration have been major drivers in the electronics industry, and the test and measurement space is no stranger to this force. The latest oscilloscopes are more than mere display mechanisms: they are powerful development tools in their own right with multiple functions.
For example, Tektronix’ latest solution, the Series 2 Mixed-Signal Oscilloscope (MSO), is not only powerful, fast and accurate, it’s also a sleek, lightweight design that includes a high-resolution display of 10.1 inches. touchscreen (Fig.5).
5. The Series 2 Mixed Signal Oscilloscope has a sleek, lightweight design with a 10.1 inch high resolution display. touchscreen.
Measuring 1.5” thick and weighing less than four pounds, the bezel can fit in a laptop bag. It is available in battery-powered configurations, allowing engineers to use the same instrument on the bench or in the field. An entry-level oscilloscope with a common tablet-like user interface, the Series 2 MSO is an accessible device for both experienced and novice users. With a bandwidth of up to 500 MHz, it claims the widest bandwidth in its class.
An ecosystem of ready-to-use software includes TekScope PC, TekDrive and VNC. With TekScope PC, viewing and analysis capabilities can extend beyond the oscilloscope to the PC and waveform analysis can be performed anywhere and anytime. A collaborative data cloud workspace allows uploading, storing, organizing, searching, downloading and sharing any type of file from any connected device, and an integrated VNC server allows connection, control and visualization Remote MSO Series 2 from anywhere, on any device.
The 2-Series MSO features up to four analog channels with 500 MHz bandwidth, 2.5 G/s sample rate, 16 channels, 50 MHz AFG, 4-bit digital pattern generator , advanced triggers, protocol decoding, DVM and frequency counter. The capacitive touchscreen and intuitive user interface make it easy to use. An offering of compatible probes and accessories makes the 2 Series MSO capable and versatile to meet a variety of applications.
Oscilloscopes have come a long way from electromechanical display mechanisms to advanced digital products with high bandwidth, fast capture, and high fidelity. From their earliest iterations which could not even store their data for later analysis, to the latest multi-tool solutions, oscilloscopes have become an even more vital tool for electronic design. The next generation of devices on the horizon promises to be even more powerful, functional and useful.
Read more articles in Then and Now in our series library and in the Electronic Design 70th Anniversary Series.