Oscilloscopes have evolved from 50 MHz to 100 GHz and from benchtop to wristwatch models

Today, oscilloscopes come in numerous shapes and sizes—from devices as small as a wristwatch to pocket-sized and benchtop variants. They even have diverse bandwidths—from the entry level 50 MHz models to the high-end 100 GHz devices

By Richa Chakravarty

Wednesday, August 13, 2014: Today’s complex embedded designs have enabled oscilloscopes to evolve technologically, breaking into a new level of functionality to cater to changing industry needs. Miniaturisation of equipment is pushing vendors to incorporate multiple measurement tools within an oscilloscope—both in benchtop and portable models. Today, the market offers some of the most advanced oscilloscopes, which are typically available in the three categories of low-end, mid-market and high-end instruments. Keeping up with the trends in the market, there has been a transition from conventional to digital oscilloscopes and, finally, to mixed domain variants.

However, the high price of these instruments had earlier hindered users from owning them. But with the demand for oscilloscopes increasing, companies like Tektronix, Agilent, Teledyne LeCroy and Scientech have introduced low-priced oscilloscopes that promise reasonable quality and performance.

What’s new in the market

Today, oscilloscopes come in numerous shapes and sizes—from models that are as small as a wristwatch to pocket-sized and bench-top variants. They even have diverse bandwidths—from the entry-level 50 MHz to the high-end 100 GHz. Let’s study some of the new types available in the market.

Oscilloscopes integrated with other instruments: In response to the growing demand from consumers (particularly design engineers), manufacturers have started integrating important test and measurement (T&M) devices into an oscilloscope.

“Oscilloscopes that integrate multiple instruments in one, provide cost effective measurement solutions and, at the same time, save bench space. Ultra high bandwidth oscilloscopes have analogue-to-digital conversion up to 160 GS/s and have high technology indium phosphide (InP),” opines Sanchit Bhatia, applications engineer, electronic measurement group, Agilent Technologies India Pvt Ltd. In April 2014, Agilent launched two new series­ – the 6000X and Infiniium S-series. The 6000X series integrates six instruments in one — an oscilloscope, logic analyser (MSO), protocol analyser, dual-channel WaveGen function/arbitrary waveform generator and a digital voltmeter. It is also the industry’s first 10-digit counter totaliser, which has 3.2 GHz bandwidth. It includes 2- and 4-channel DSO models as well as MSO models with 16 digital channels in bandwidths ranging from 1 GHz to 6 GHz at a 20-GS/s sample rate.

The Infiniium S-series sets a new standard for signal integrity in bandwidths up to 8 GHz at 10-bit resolution. “Compared to the traditional scopes with 8-bit analogue-to-digital converters (ADCs), the S-series has four times the vertical resolution for the precise viewing of signal details. Coupled with a new low-noise front end, the S-series delivers an effective number of bits (ENOB) for the system, which is more than eight, the highest in the industry,” shares Sanchit Bhati.

Tektronix’s 3000 series mixed domain oscilloscopes (MDO) integrate instruments like a logic analyser, protocol analyser, spectrum analyser, function generator and digital voltmeter. These oscilloscopes feature two or four analogue input channels with bandwidths ranging from 100 MHz to 1 GHz, 16 digital channels (optional) and one RF input channel matching the bandwidth of the oscilloscope (9 kHz up to analogue bandwidth). “Debugging and verification of designs are crucial from the customer’s perspective. While the other features in an MDO are used only on an intermittent basis, it’s always a hassling and time consuming task for designers to find a piece of equipment, other than the scope, for any given debugging task. With the integration provided by the MDO3000 series, customers can stay focused on the task at hand, regardless of the debug tools required,” shares Naresh Narasimhan, country marketing manager, Tektronix India.

In June 2014, Rohde and Schwarz launched a series of oscilloscopes that features a high waveform update rate and high vertical sensitivity. The oscilloscopes in this series are available with bandwidths of 50 MHz, 70 MHz and 100 MHz. The fanless instrument offers a sampling rate of 1 GS/s and a memory depth of 1 MS/s. The integrated pattern generator to generate protocol messages at up to 50 Mbit/s is ideal for embedded users. In addition to using predefined messages, developers can program their own signal patterns for supported serial protocols. The integrated three-digit digital voltmeter enables service technicians to simultaneously perform voltage measurements on both analogue channels with two values each. “Thanks to 128k test points and analysis functions in the frequency domain, this series keeps pace with significantly larger oscilloscopes. The time domain signal, measurement window, FFT analysis range and measurement results are displayed on a single screen, which makes it easier to measure the spectra,” informs Srinivasa Appalla, manager, product support and application, Rohde & Schwarz India Pvt Ltd.

Designed for plug-in options, Good Will Instrument’s GDS-2000A series of oscilloscopes offers users the flexibility to upgrade the DSO with field-installable options. Hence, two modules can be used simultaneously to the maximum capacity, including the 8-channel logic analyser, 16-channel logic analyser, DDS function generator, and the LAN/SVGA interface module or GPIB interface module. With a 20.32 cm (8-inch) 800 x 600 high-resolution TFT LCD display, a 1mV/div to 10V/div vertical range and 1ns/div to 100s/div time base, the GDS-2000A series is able to demonstrate waveforms of complicated and obscure signals. “The GDS-2000A series is equipped with all the features a high-tech DSO should have today. The abundant trigger functions—including edge, pulse width, runt, rise/fall time, video, alternate, event-delay, time delay, bus and logic triggers—enable waveform capture under various test circumstances. The advanced math function allows the user to do post-acquisition signal processions to meet the requirements of particular tasks. It also provides the flexibility of easy conversion from a DSO into an MSO, due to the use of a plug-and-play concept,” informs Sumit Sharma, marketing manager, Good Will Instrument Co Ltd.

PC USB-based digital oscilloscopes: A PC-based oscilloscope is attached to a computer to acquire the signal and show it on the computer’s display. In most cases the power supply, too, is derived from the computer’s USB port, which makes these devices handy. A lot of multifunction options are also available in these scopes, such as an additional signal generator, logic analyser, multimeter, 5V DC supply, digital I/Os and spectrum analyser. These oscilloscopes are ideal for production testing, research, design and all other applications involving analogue circuit tests and troubleshooting. They display not only the wave form but also the frequency of the wave form, the duty cycle of the wave form, rise time, fall time, P-P voltage, RMS voltage, average voltage, etc. These oscilloscopes provide bandwidth signal analysis anywhere between 10-20 MHz to as high as 20 GHz. These USB-based, modular devices typically have one, two, four or eight channels with a USB 2.0 or USB 3.0 interface, depending on the model. Some of them are even loaded with memory capacity.

Scientech offers one of the smallest PC-based oscilloscopes. “Its 700 series has a bandwidth of up to 100 MHz, 10 channels (2 analogue, 8 digital) and comes with an inbuilt spectrum analyser, waveform and clock generator, and data recorder, all in one instrument,” says Vivek Mantri, country manager, Scientech Technologies Pvt Ltd.

Metro Electronic Products offers Owon’s latest VDS 1022 and VDS 1022I PC-based oscilloscopes of 25 MHz. Launched in March 2014, these oscilloscopes come with isolated channels that can be connected to any laptop and have easy plug-and-use software. An estimated cost that is half that of traditional DSOs, and the fact that they physically fit into a user’s pocket, make these PC-based oscilloscopes extremely ‘pocket friendly’.

Pocket-sized oscilloscopes: Small pocket-sized oscilloscopes are very useful for field engineers. Most of these are low-priced, but their accuracy is not as good as other scopes and hence they are used just for basic analysis. The frequency range of these oscilloscopes is also limited. Some expensive variants do support signals in the MHz range, but the low-budget models are normally for the kHz range only and cannot be used for debugging high-frequency signals. However, Scientech’s 700 series in this range can support up to 100 MHz with SPI, CAN and i2c protocol. Its networking feature supports OSs like Windows, Linux, Mac, etc. Some of these oscilloscopes also come with wireless connectivity, such as Bluetooth.

High-speed oscilloscopes: Some oscilloscopes offer higher speed serial standards that work beyond 10 GBps and require a high bandwidth to capture the signal content. Teledyne LeCroy has introduced a 100GHz real-time oscilloscope targeting applications such as CEI-25/28, CEI-56, optical coherent modulation communication systems, defence and radar applications.

Smart touch scopes: Today, smart touch interfaces can be used to define areas where you want the oscilloscope to trigger. These interfaces are fully configurable. The latest digital scopes incorporate touchscreen displays, enabling new operating concepts and enhancing ease of use. Good touchscreen implementations support drag-and-drop functionality for organising the display with multiple waveform diagrams and to select predefined operations. Agilent’s 6000X series has a 30.73 cm (12.1-inch) multi-touch capacitive touchscreen that helps engineers visualise and isolate more anomalies with its 450,000 waveform per second update rate.

Launched in April 2014, Scientech’s 403 DSO gives the user great operability. This DSO can test 32 different electrical parameters and display the results simultaneously on the screen. “To meet the educational and industry customers’ application needs, the 403 DSO offers innovative technology, unique specifications, powerful trigger functions, wide auto measurement functions, wide memory depth and broad analysis capabilities,” informs Vivek Mantri, country manager, industrial segment, Scientech Technologies Pvt Ltd.

How to choose the right oscilloscope

Users have many options available in the market. Oscilloscopes are used in various industries, from education and research labs, to defence and industrial usage. Thus, buyers should always check their requirements and, accordingly, choose an oscilloscope with the right parameters. “With a variety of channels available, purchasers should decide how many are actually needed, and the bandwidth needs should also be ascertained. Triggering capabilities, memory, display capabilities, and sample rates need also to be considered when buying an oscilloscope. Price is another key aspect that users should keep in mind,” advises Manish Kwatra, managing director, Metro Electronic Products.

Other important parameters include vertical sensitivity, acquisition memory and sampling rate. Opines Srinivasa Appalla, “In order to capture very low level signals, the user should ensure that vertical sensitivity is 1 mV/div. Also, a high sampling rate with deeper acquisition memory is required to capture long duration of signals without compromising on sample rate. Users should also check whether the bandwidth can be upgraded, since this protects the investment in the scope and prevents the need to buy yet another device.”

The role of each specification is described below.

Bandwidth: This determines the maximum frequency signal that an oscilloscope can accurately measure. The accuracy decreases with the increase in the signal’s frequency.

Rise time: This is the time taken by a signal to change from a specified low value to a specified high value. Typically, these values are 10 per cent and 90 per cent of the step height. As a thumb rule, similar to bandwidth, the rise time of the oscilloscope should be less than 1/5th the fastest rise time of the signal to accurately measure it.

Sample rate: This refers to how frequently a digital oscilloscope takes a sample of the signal. The faster an oscilloscope samples, the fewer the details that get lost while reconstructing the signal. The sampling rate that you might require to accurately read the signal will depend a lot on the method used for reconstructing the signal, which is also called interpolation.

Record length: Record length determines the time that can be captured by each channel of the oscilloscope. An entry-level oscilloscope comes with 2k to 2.5k points.

External trigger: External triggers allow users to stabilise repetitive waveforms and make them appear static on the display by continuously displaying the same section of the input signal. Generally, oscilloscopes are available with edge and pulse width trigger.

Waveform capture rate. The sample rate indicates how fast the oscilloscope samples the input signal within one waveform, but the waveform capture rate refers to how quickly an oscilloscope captures a waveform. The oscilloscopes with better waveform capture rates capture fast transients better.

Probe specifications: The probe’s specifications are as important as that of an oscilloscope’s. The probe’s bandwidth should match the bandwidth of the oscilloscope. The probe will be in direct contact with the circuit and should not overload it. Otherwise, the measurements will not be correct.

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