19 December 2001
Extended real time
When is a real time oscilloscope more real time?
It's an analogue world, so everyone keeps telling us. But there is a shift towards digital technology in every aspect of our lives, and oscilloscopes –seen as a universal tool to investigate signal quantity and quality – are becoming more popular in digital form.
Digital oscilloscopes come in three flavours: digital storage (dsos); digital phosphor (dpos); and sampling. A conventional dso allows you to capture and view events that may happen only once – transients. Because the waveform information exists in digital form as a series of stored binary values, it can be analysed, archived, printed and otherwise processed within the oscilloscope itself or by an external computer. The waveform need not be continuous. A dso uses a serial processing architecture to capture, display and analyse signals. Meanwhile, a dpo employs a parallel processing architecture to perform these functions.
The performance increases of the dpo architecture means there is a higher probability of witnessing transients – such as runts, glitches and transition errors. A digital sampling oscilloscope can capture, sequentially, signals whose frequency components are much higher than the oscilloscope's sample rate. This allows it to measure signals of up to an order of magnitude faster than other oscilloscopes. The advantage of a sampling oscilloscope is that bandwidths up to 50GHz are available, but the trade off is that it relies on the signal being repetitive, so if there are infrequent random events, you may not be able to capture them.
Dean Miles, Tektronix' business development manager for Europe, the Middle East and Africa, explained: "The choice for many of our customers is between dpos and sampling oscilloscopes. The additions to the CSA7000 family fill the gap between dpos and sampling techniques.
"The CSA8000 series was the first instrument to be launched as a communications signal analyser, based on sampling techniques. This type of solution is ideal for design evaluation and manufacturing test in telecommunications.
"The CSA8000 and other communications signal analysers have sampling speeds of 20kbit/s. In comparison, the CSA7000 samples at 20Gbit/s – suitable for the telecoms and datacoms market. Applications span engineers needing to troubleshoot ic components sold to network equipment vendors, designers of network communications equipment and production test engineers for compliance testing of network communications equipment systems.
The additions to Tektronix' CSA7000 family – relatively low cost, mid range instruments – are the flagship CSA7404 and the CSA7154. The CSA7404 is billed as the 'first and only real time digital oscilloscope to specifically address the design of high speed electrical and optical systems with data rates up to 2.5Gbit/s'.
Miles stated that the CSA7404 is real time, compared to 'scopes using sequential techniques. "It is remarkable for a number of qualities; for its optical capabilities and because it integrates many functions in software that would previously have needed an additional module. For example, the use of an integrated optical reference receiver means that compliance testing for multiple standards and data rates is simple. By putting standards characteristics into software, the CSA7000 series allows software to be updated when standards change." This compares to alternative systems which introduce standards in a hardware format; when standards change, the modules are obsolete and new ones must be purchased.
"The limitation on the CSA7404 is bandwidth: until semiconductor technologies and component parts improve, it will be hard to improve on this."
Miles says the CSA7000 series was designed in response to the needs of telecommunications customers. "Designers were saying they needed a cross between an optical and general purpose 'scope and that eight out of ten signals they needed to test were at 2.5Gbit/s.
The trends we are seeing is designs moving toward serial bus and there is a move towards multiplexing to achieve higher bit rates."
With these products, Tektronix is enforcing its emphasis on the potentially lucrative telecommunications industry. A recent Frost & Sullivan report has determined the telecoms market is a $1trillion business and still growing. Telecoms depends on the ability of its infrastructure and equipment to process signals and relies on oscilloscopes as robust and effective signal analysers.
Tektronix, Agilent and LeCroy have strong positions in different segments. Agilent categorises the market at six levels. Agilent's European oscilloscope specialist, Peter Kasenbacher, explains: "At the low end are service models, typically handhelds; with economy 'scopes at less than 100MHz bandwidth at the next level. At the mid range are compact, relatively low cost devices, typically in the 100 to 500MHz and 500MHz to 1GHz bandwidth ranges. At the high end are performance level devices, running at 1GHz and faster; with the highest level featuring sampling oscilloscopes, which can range from 20GHz to 50GHz."
Agilent has focused primarily on the mid to high range of the market and is similarly targeting telecoms. LeCroy focuses on the very high performance end, whilst Tektronix meets specific market needs with a broad range of oscilloscopes.
Kasenbacher says Agilent is the only company to offer mixed signal oscilloscopes. "These typically fall into the compact (60 to 100MHz) category and are proving the most popular of our offering. This is because most consumer products incorporate 8bit microcontrollers with analogue inputs, but need to process the signal digitally. If you want to debug these systems, you need an instrument which can synchronise a slow analogue signal with a digital signal running at a couple of MHz. Agilent has achieved analogue/digital synchronisation with Megazoom: a deep memory technology. Deep memory can slow the instrument significantly when enabled, but Megazoom, based on a specific Agilent architecture, does not impair functionality. Therefore, Megazoom runs as an always on facility, unlike other deep memories which are operated as a special mode. Says Kasenbacher: "Mixed signal is everywhere and will continue to be an important market for us. High end versions of this will be something for the near future."
There are two important application areas for Agilent, says Kasenbacher. "The first is R&D, where the most sophisticated and highest accuracy instruments are needed. Agilent makes use of its strong position in the logic analyser market and offers solutions which combine logic and oscilloscopes."
The second major stream is manufacturing, where speedy remote set up and high data throughput are key drivers. Agilent and Tektronix similarly view the telecoms and datacoms market as having the biggest potential for oscilloscopes, but have taken a different approach to catering for these customers' needs. Tektronix takes an integration approach – for example, incorporating communications analysis from OC-3/STM-1 to OC-768/STM-256 as software in a 'straight from the box' solution. Meanwhile, Agilent uses the same hardware for different applications but makes the software upgrades an additional cost.
As for the future, Miles says Tektronix is focusing on improving data rate towards STM-64 and is pushing the 2.5Gbit/s boundaries. Agilent, meanwhile, has invested in deep memory oscilloscopes – which it believes are essential for analysing the long and complex data streams associated with sophisticated communications and computing applications – and will shortly launch new members of its Infiniium family, which currently addresses this market.