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Bench Talk for Design Engineers

Bench Talk

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Bench Talk for Design Engineers | The Official Blog of Mouser Electronics


Simplify Mixed Signal Design Testing Jon Gabay

(Source: Nischaporn - stock.adobe.com)

The landscape of test and measurement tools has evolved significantly from the era dominated by discrete devices. Once, meters were simply meters, scopes were scopes, and logic analyzers were only that, each with its unique capabilities and limitations. Interconnectivity was often limited to triggers for analog scope tracing or logic analyzer data gathering, making setups a complex task involving extensive cabling and interconnect alterations for different measurements or verification tests. However, this scenario has largely shifted.

Today, while discrete tools like digital oscilloscopes, signal generators, digital multimeters, emulators, and logic analyzers are still available, contemporary test labs favor integrated tools catering to mixed signal designs and verifications. Integrating these tools with workstations and PCs facilitates smoother transitions of test and verification tasks across departments, manufacturers, and test/certification houses.

The Debate: To Probe or Not to Probe

One of the key advancements in modern embedded systems is the ability to perform self-tests and employ serial boundary scan technologies to verify signal integrity and continuity. Although primarily confined to the digital domain, most large-scale integrated circuits integrate boundary-scan technologies such as J-Tag for code loading and testing and exercising I/O lines.

This advancement has reduced printed circuit board sizes as the need for multiple discrete test points has largely been eliminated. It also significantly saves design, test, and debug time, as continuity or short probing can be executed using a serial network for testing. This is particularly beneficial given the fine-pitch pinouts of modern processors, which make it challenging to reliably use continuity testers to verify the integrity of the high pin count.

Modern multifunction and mixed-signal test and measurement tools efficiently handle digital realm testing, including debugging and verifying serial networks for communications. This encompasses chip-to-chip communications like I Square C, UART, and SPI, as well as machine-to-machine communications like Ethernet and fiber optics.

Wireless technology exemplifies the challenges of mixed-signal verification, as it encapsulates digital, analog, and transmission line testing. Probing these circuits can alter their characteristics, making non-intrusive probing a specialized subject involving wireless RF detection and signal processing. Despite the capabilities of modern PCB layout tools, real-world results often deviate, necessitating several iterations of circuit boards for desired performance levels. Each of these design applications has specific requirements for design and functional verifications, prompting the question—Where does an engineering team begin to identify the best tools for their needs?

The Choice: All-in-One or Modular

Quality manufacturers offer several integrated test tools that are excellent starting points. If a single piece of equipment can perform most of the required tests, it simplifies connectivity and synchronization. The first step in this process is to determine the number of channels required, considering analog and digital channels separately as they are typically not interchangeable.

The type of display incorporated with the tools can also influence size and price. Self-contained mixed signal scopes like the Tektronix Mixed Domain MDO4000C Series are robust, versatile scopes that can address many complex applications (Figure 1). The integrated XGA display allows users to visually inspect waveforms and measurements, while the integrated Ethernet and USB connectivity facilitates integration into a flexible and expandable test bench.

Figure 1: The combination of an oscilloscope, logic analyzer, spectrum analyzer, arbitrary function generator, protocol analyzer, DVM, and more make this single tool acquire analog and digital data simultaneously with synchronization. (Source: Mouser Electronics)

However, for more demanding applications requiring higher functionality than an all-in-one unit can provide, premier tools like the PicoScope 9404-16 CDR 4 channel modular scope from Pico Systems, featuring a 5 Tsample/sec resolution, may be necessary (Figure 2). This module uses a PC or laptop for data display, making it an ideal candidate for field service and calibration purposes.

Figure 2: As a modular digital oscilloscope, the PicoScope 9404-16 CDR has an astounding 5 Tsample/sec sampling rate. It uses a PC or laptop for data display, making it an ideal candidate for field service and calibration purposes. (Source: Mouser Electronics)

On the Road Considerations

With various designs, deciding between an integrated display on a test gear or networking with other equipment and computers can be challenging. This choice becomes particularly crucial if the test bed needs to be mobile.

Field service often has stringent requirements for both scheduled maintenance and repair. Advanced designs may require calibration, and cost constraints may prohibit including stable calibration references inside the designs. All-in-one units like the Tektronix unit provide a comprehensive solution, eliminating the need to transport and set up various tools. However, specialized modules might be required for on-the-road testing.

A significant advantage of all-in-one units is that they enable a test engineer, whether mobile or in a lab, to master a single tool that satisfies the requirements. Furthermore, with everyone having access to laptops and tablets, setup macros can quickly and accurately program and configure a flexible piece of gear for multiple tests, reducing human errors and saving valuable time.

Conclusion

There is no universal solution for test and measurement. Different disciplines have unique needs. For instance, IC designers may require pin leakage testing, which is not required for equipment designs. High voltage testing is also limited to specific equipment.

Designers must carefully consider adding test points when necessary and least intrusive. Testing DACs, ADCs, audio and video systems, and wireless RF may require specialized tools. However, mixed-signal testers now offer well-engineered solutions for many of these needs, providing accurate and reliable reporting.



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After completing his studies in electrical engineering, Jon Gabay has worked with defense, commercial, industrial, consumer, energy, and medical companies as a design engineer, firmware coder, system designer, research scientist, and product developer. As an alternative energy researcher and inventor, he has been involved with automation technology since he founded and ran Dedicated Devices Corp. up until 2004. Since then, he has been doing research and development, writing articles, and developing technologies for next-generation engineers and students.


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