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Tue, 12/10/2013 - 2:36pm
Paul Livingstone

Technological advances are helping digital oscilloscopes keep pace with the demanding world of electronics R&D.

Rigol’s DS6104 Digital Oscilloscope uses field-programmable gate array circuitry coupled with sophisticate algorithms to allow better acquisition and data capture rates. Image: Rigol North America Inc.During the development of the transistor, which launched the computer age, oscilloscopes were a key tool for engineers and scientists who needed to understand the behavior of complex electronics. Now, computers are returning the favor by revolutionizing how test and measurement instrumentation, including oscilloscopes, is constructed and how it performs. The software-defined digitizer, which can not only perform the measurement tasks of an oscilloscope, it can be a frequency counter, ultrasonic receiver or spectrum analyzer, hints at the future direction of waveform measurement.

Factor in features like open-source software and instantaneous upgrades through software updates, and it’s not difficult to conjecture the days of traditional benchtop oscilloscopes are numbered. Not so fast. The standalone oscilloscope is still the instrument of choice for intensive and reliable waveform analysis and digital-signal processing. While the transition to digital-signal instrumentation is nearly complete, the development road for these devices is still wide open. Several key advances have transformed these instruments in areas of performance, adaptability and accessibility. These range from improvements in electronics architecture to the adoption of advanced materials and software.

Rise of the digital oscilloscope and bandwidth
A year ago, Research and Markets predicted the global digital oscilloscope market will experience market growth of nearly 20% through 2016. This growth represents more than just a transition from older technologies. More companies require sophisticated electronic test equipment to eliminate errors or bugs, and as digital oscilloscopes become more user friendly in terms of the ability to test and store electrical signals, more developers will harness their capabilities.

One of the more obvious trends in high-end digital oscilloscopes is the rise in frequency bandwidth handled by the instrument. Most of the major oscilloscope vendors carry instruments that offer 33 GHz or more of bandwidth. In 2012, the 60-GHz threshold was passed for commercial oscilloscopes, and in 2013 instruments exceeding 90 or 100 GHz have been demonstrated.

The maximum bandwidth, whether 20 MHz or 10 GHz, describes the highest frequency sine wave that can be digitized with minimal attenuation.

Delivering signal integrity to high-frequency electronics, however, is a major design challenge for oscilloscope manufacturers. Flat frequency response from direct current is difficult at frequencies of 63 GHz or more. When designing its Infiniium 90000 oscilloscope series, Agilent Technologies, Billerica, Mass., had to develop a new set of technologies, called RealEdge, that preserved signal integrity to the oscilloscope’s graticule.

The X-Series, introduced in 2011, incorporated several advances that replaced the three key chips in the oscilloscopes front-end: the pre-amplifier, sampler and trigger chips. By elevating the capabilities of all three (32 GHz for the pre-amplifier, 20 GHz for the trigger and 80 GS/sec for the sampler), Agilent was able to preserve the input electronic waveform at higher frequencies. The key to these improvements was transistor speed, up to 200 GHz, made possible with the use of indium phosphide in the chips, packaged using a new technology.

These chips played a part in Agilent’s next advance, the 2013 R&D 100 Award-winning Q-Series oscilloscope. This 63-GHz update to the 90000 Infiniium line also incorporates RealEdge, which uses a hybrid filter bank to accurately capture rise times as fast as 5 psec and data rates up to 120 Gbit/sec. This permits applications in gigabit Ethernet development.

Sample rates and visualization
Bandwidth alone does not dictate the most appropriate digital oscilloscope for a given application. The buyer must make a host of considerations for specifications like sample rate, sampling modes, memory, dynamic range, resolution, and special capabilities, such as multi-instrument synchronization.

Sample rate is one of the most important, and plays a big part in determining how much of an oscilloscope’s bandwidth offers useful information.

Teledyne LeCroy’s HDO Series oscilloscopes incorporate several new design features to allow the instrument to make the most of new, high-acquisition 12-bit analog-to-digital converters. Image: Teledyne LeCroyThis rate, which is clocked to digitize the incoming signal to either the digitizer or the ADC in a digital oscilloscope, determines how effectively an oscilloscope can accurately reproduce time-domain signals.

One way to achieve a higher sampling rate is to expand the bandwidth of the instrument’s analog-to-digital converter (ADC). In 2012, Teledyne LeCroy, Chestnut Ridge, N.Y., introduced a 12-bit ADC in its HDO4000 and HDO6000 oscilloscopes, which offer bandwidths from 200 MHz to 1 GHz. The goal of a higher acquisition rate for the ADC is a clean, crisp waveform display. This allows a higher sampling (up to 2.5 GS/sec), deeper memory (250 Mpt/sec) and lower noise.

The new ADCs were deployed as part of Teledyne LeCroy’s High Definition Technology, which includes high signal-to-noise amplifiers and low-noise system architecture along with the new ADCs. The combination of improvements is able to deliver a 16-fold improvement in resolution compared to prior oscilloscopes of similar bandwidth.

Flexibility in circuitry
Power alone does not dictate success in the test and measurement space. Vendors must adapt to emergent electronics technologies and take advantage of opportunities presented in logic circuit design. Field-programmable gate arrays (FPGAs) have helped revolutionize customized test applications, and has increasingly found its way into OEM test equipment. Like Agilent’s adoption of indium-phosphide transistors to improve cooling and increase cycle speed, the introduction of FPGA technology to the oscilloscope gives the test instrument a competitive advantage over digitizers and imparts some of the flexibility offered by software-defined oscilloscopes. Designing FPGA-based systems for high-frequency oscilloscopes has required the development of new, more rigorous algorithms for signal sampling, manipulation and display. After several years of work, Rigol North America Inc., Oakwood, Ohio, made the move in 2010 into 1-GHz-plus FPGA-based oscilloscope technology with its Rigol DS6104 Digital Oscilloscope. A 2011 R&D 100 Award winner, the oscilloscope represented a fundamental shift from a limited ASICs-based instrument to an adaptable “smart” platform that quickly showed the benefits of FPGAs: a greatly elevated acquisition rate and a memory depth that allowed much longer data capture rates.

The capability offered by FPGAs has been expanded in subsequent years to several of Rigol’s oscilloscope series, and has given rise to complementary technologies and features. Because of the large number of single measurement points captured by the FPGA-based instruments, Rigol’s up to 110,000 waveforms per second could be recorded, forming the basis of high-resolution waveforms that can be analyzed closely.

This technology has spread throughout Rigol’s range to include more economical desktop models such as the DS1000Z Series and mixed-signal MSO4000 Series. The DS1000Z is a four-channel digital oscilloscope available in 70 to 100 MHz bandwidths that is capable of 60,000 frames real-time waveform recording.

The more capable MSO4000 features 16 digital channels at bandwidths up to 500 MHz, as well as four analog channels. Designed for extensive testing and debugging this oscilloscope is capable of 1 GS/sec in digital and 4 GS/sec in analog with 140 Mpts of memory depths in analog and 28 Mpts in digital. This series of oscilloscopes gets the benefits of UltraVision as well, allowing replay and analysis of up to 200,000 frames analog (64,000 frames digital) and a low-noise floor with vertical sensitivity of just 1 mV/div.

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