NI LabVIEW SignalExpress Interactive Measurement Software Connects Design and Test

As electronics products become more and more complex, driving more and more functionality into smaller and cheaper devices, the design and testing process gets more difficult. In the design space, there is tremendous pressure on the design tool vendors to open their products, so users can have a streamlined and connected design tool chain. Electronic design automation (EDA) software can incorporate more and more technology into their basic schematic modeling and simulation tools, and then automate the conversion of these electrical designs into physical chips or boards. In the manufacturing space, more companies are adopting a flexible modular hardware and software approach based on virtual instrumentation, so they can easily add measurement components to their modular test architecture to match the growing functionality of their products. Both of these trends, toward more open, modular, and compatible software tools in the design and test areas, represent progress for the design engineer and test engineer respectively. However, these two basic functions – design and test – must work together to get a product from concept to delivery. It is the gap between design and test that remains neglected by the tool vendors.

This document explains the impact of the widening productivity gap between design and test software and how National Instruments LabVIEW SignalExpress and virtual instrumentation alleviates these challenges by connecting design and test tools.

Introduction

Test plays a critical role in the design and manufacture of today’s electronic devices. Measurements taken throughout the product development cycle provide invaluable feedback on the functionality and performance of a product design. Engineers rely on timely, accurate measurements in design and manufacturing to deliver a product as quickly as possible without sacrificing quality.

The engineering community has experienced tremendous advances in technology over the past decade. EDA tools must continually evolve and provide abstraction layers around this technology so that engineers can deal with the increasing complexity. Test tools have also evolved to allow a more modular approach to managing a production test strategy.

Technology Impact on Design and Test

Rapid product development cycles and declining engineering productivity are forcing many electronic manufacturers to reevaluate their test strategies to ensure they are able to perform the necessary testing to improve product designs and maintain good quality. Integrating new features into a product design is becoming increasingly streamlined through evolving semiconductor and design automation tools. Conversely, the time needed to properly acquire measurements for modeling, verification, validation, and manufacturing test of the new designs increases on the order of several magnitudes. For instance, through the simple addition of an 802. 11 wireless feature to a mobile phone, more than 100 more tests must be performed in design, validation, and manufacturing without adding significant time to the project.

For engineers this equates to higher workloads and longer hours to maintain a consistently shorter product release schedule. In fact, a recent survey among test engineers indicated that more than 50 percent have experienced an increased workload compared to two years ago with an average of nine projects per year lasting approximately eight months each (Profile of an Engineer Survey, Test & Measurement World, 2003). The survey also indicates one of the primary causes of the increasing workloads is due to a growing gap between design and test throughout the product development cycle.

Role of Measurement in Design

Test and measurement tools serve many different roles across the product development cycle. The diverse role of test in design provides the best illustration of the varying requirements on test in the product development cycle. Unfortunately, testing in the design phase is not always as simple as making a pass or fail determination. Design engineers must typically perform a variety of measurements with different requirements during the three phases of the design flow – modeling, verification, and characterization.


During the modeling phase, engineers may require a mix of measurements to assist them in building more accurate behavioral models for certain components or subcomponents used in their design. Once initial prototypes are built, designers need to quickly perform measurements on their prototypes and compare against the expected results from their simulation tools. After the design is fixed and the prototypes have been tested, engineers characterize it by testing the outer limits of the design to establish the published operational specifications for the product.

Obviously, design engineers already use physical measurements in the process of creating and verifying a design prototype. Even though their primary tool is a software tool, or set of tools, for designing and simulating the electrical, thermal, and mechanical aspects of their designs, the average design engineer will spend time huddled over a laboratory bench making measurements with a digital multimeter, oscilloscope, or logic analyzer to ensure that what they are designing actually works. This the primary use case for many of the traditional instruments built today. Although they are programmable through GPIB or other interfaces, a large percentage of these instruments are used primarily on the bench in an interactive, as opposed to programmatic sense. Design engineers, already experts in advanced design software, many times do not have the time nor desire to learn the remote commands to automate some of the more complex or repetitive measurements by programming their instruments in C, Visual Basic, or LabVIEW. Instead, they are content to make the measurements themselves by turning knobs and dials on their instruments, or rely on engineers from outside groups who are dedicated to test programming to help them automate their complex measurements.

Bridging the Gap in Design and Test

Clearly, there is a trend toward a more connected design tool chain. The fundamental goal of these tools is to enable the design engineer to build something. After days, weeks, or months of designing (depending on the product), the design engineer first sees the fruition of his/her labor when the first prototype (chip, board, system) is built. It is at this prototype stage that physical measurements begin on the laboratory bench, usually with traditional benchtop instruments. First making simple sanity-check measurements on the prototype to see if it operates at all, followed by more strenuous measurements to characterize its performance under more varied conditions, the design engineer moves from a very software-centric design environment, to a very hardware/instrument-centric measurement environment. Many times, the measurements on the physical world reveal behavior that did not show up in the ideal design simulation environment. In these cases, the first prototype may not be the last. Iterating through this process of designing and building a prototype, checking it with physical measurements, and then tweaking the design is a common experience for many design engineers.

After this design process iterates enough to generate a functioning design within specification, the software engineers responsible for building the automated systems for testing the product take over. Developing a very fast, easy-to-operate test software approach run at the end of the production line is the primary goal of the test engineers at this point. In many cases, the time scheduled for developing these test systems has been squeezed significantly because of unforeseen hitches in the design phases. As designers add more complexity and functionality to their designs, and spend more time iterating through the design process and validating its performance, the test engineers many times are not given any extra time to develop their test programs.

Interactive or Automated Measurements – Why Not Both?

The design engineer using a set of traditional instruments on a laboratory benchtop to make measurements on a design is flanked by software-dominated processes on both sides. The design and simulation process is driven by EDA software tools. The automated test process is driven by virtual instrumentation software. But the benchtop instruments sitting in a design lab sit right between these two evolving, yet isolated islands of automation. Traditional instruments give the design engineer fast and easy measurements at your fingertips, but they can be tedious and time-consuming to program for automated measurements. If the interactivity and ease of use of an instrument could be preserved while simplifying the process of plugging these instruments into a software environment, engineers could further streamline the electronic design and development process. If the benchtop measurement process of testing and characterizing a prototype chip or board, where the performance and functionality of the product is most closely scrutinized and measured, was driven from a software standpoint, engineers could achieve faster design iterations and better overall productivity. Specifically, by leading all phases of the development process with a software mindset, engineers could:

• Share data from design tools with test and measurement tools
• Drive physical measurements with stimulus signals defined in a simulation tool
• Set up measurement parameters directly from simulation runs to automate the process of programming a test
• Directly compare a measured result against the expected result from simulation
• Drive simulation runs from signals acquired in the physical world that more accurately represent the stimulus
• More easily acquire physical measurement data on a component or subsystem and format it for use as a behavioral model in simulation
• Make more complex measurements, such as voltage, current, or temperature sweeps, automated so they can be repeated faster and more reliably
• Measurements defined in the design lab could be more easily transferred into the validation and production teams
• Signals from the final design and simulation iterations could be transferred from design directly into production systems to be used as final go/no-go test limit comparisons

LabVIEW SignalExpress, a new interactive measurement tool from National Instruments, bridges the gap between design and test with a software perspective.

NI LabVIEW SignalExpress – Interactive Measurement Software

NI LabVIEW SignalExpress is a new software environment that provides a truly interactive measurement experience for design and test engineers performing benchtop measurements. LabVIEW SignalExpress is designed around the needs detailed earlier by design and test engineers from leading electronic companies. Specifically, LabVIEW SignalExpress provides the following core features for increasing measurement productivity in design and test applications:

• Instantly acquire, compare, automate and store measurements
• No programming required
• Use built-in steps for measurement, processing, and analysis operations
• Import simulation data from design software (SPICE, PSpice, and Multisim)
• Convert projects to NI LabVIEW for validation and manufacturing test

Short Time to Measurement
National Instruments LabVIEW SignalExpress is designed to meet the needs of design and test engineers who need to measure and analyze electronic signals quickly. LabVIEW SignalExpress introduces an innovative approach to configuring measurements using intuitive drag-and-drop steps that do not require any programming. Engineers can instantly measure a signal, compare the signal against simulated results, and automate the sweeping of a characterization test using a variety of built-in measurement, processing, analysis, and data storage steps in LabVIEW SignalExpress. Unlike traditional benchtop measurements, LabVIEW SignalExpress combines the optimal balance of measurement functionality and ease of use to assist engineers in streamlining design and test processes.

NI LabVIEW SignalExpress is the ideal interactive measurement software for a variety of applications such as:

• Design modeling
• Design verification
• Design debugging
• Device characterization
• Validation test prototyping/debugging
• Automated test prototyping/debugging

Rapid Measurement Configuration
There are many built-in steps available for immediate use in LabVIEW SignalExpress. Engineers can quickly perform a measurement on a signal by selecting a step from the following step menus:

• Signal Input/Output – Generation and acquisition of signals from a variety of hardware
• Processing – Interactive alignment, filtering, averaging, and scaling
• Time Domain – Amplitude and level measurements, timing and transition, and histogram
• Frequency Domain – Measurements for power, frequency response, tone, and distortion
• Test Operations – Ability to perform sweeping operations and limit testing
• User-Defined Step – Call any LabVIEW VI measurement or analysis function

Each step in an NI LabVIEW SignalExpress project can be configured using intuitive Step Setup panels. For example, by inserting a signal acquisition step, the user can readily configure the appropriate device and corresponding input channel, sample size, sample rate, timing, and triggering without writing a single line of code. Engineers can also quickly browse the settings for each step by leaving the step setup panel open and selecting different steps.

In addition, they can select from three run modes while configuring LabVIEW SignalExpress steps.

• Idle – No signals are being acquired or generated
• Run Once – Execute steps once and return to idle state
• Run – Execute steps continuously until stop button is pressed. This mode delivers the “always on” experience of a benchtop instrument

Comparing Measurements with Simulated Results

National Instruments LabVIEW SignalExpress provides unprecedented measurement integration with common EDA software tools. LabVIEW SignalExpress provides steps for importing design simulation files from Berkely SPICE-compliant simulators, PSpice, and Electronic Workbench Multisim to compare actual measurement signals directly to the simulated results. Interactive comparison can be performed using the Interactive Alignment step. This step provides a variety of automatic resampling algorithms to autoalign two input signals which most often consist of a simulation signal loaded from a file and an actual measured signal from a data acquisition device or modular instrument. This step also features an innovative manual alignment feature that provides a way to grab the signal with a mouse, interactively align the two signals together, and immediately visualize the difference between the two signals.

Storing Measurement Data to File

NI LabVIEW SignalExpress offers several ways to capture and store measurement and test results to file. The first method enables users to intuitively drag a particular signal from a LabVIEW SignalExpress step into an open Microsoft Excel worksheet as shown in the figure below. Users can also right-click on any signals displayed in LabVIEW SignalExpress to print the actual picture for data collection purposes. NI LabVIEW SignalExpress also offers steps for saving measured signals to a variety of file formats including LabVIEW data files (*. lvm) and standard ASCII data files (*. txt).

Automatic Sweeping and Limit Testing

LabVIEW SignalExpress provides several major time-saving features, such as automatic measurement sweeping and limit testing, to assist engineers with automating a variety of measurements. The sweep step can be inserted and used to instantly sweep through steps in a project. The sweep step automatically calculates the data points for the built-in linear and exponential sweeping. Alternatively, engineers can load their sweep points manually or from an ASCII file.

The limit test step further reduces the overall development time by providing a built-in step for measuring a signal against a predefined guard band or waveform available as a signal in the existing project or load from file. This step can be used for testing time and frequency-domain signals. The limit test step automatically calculates the pass or fail status of the signal at any given time based upon the signal or scalar limit specified by the user.

Repeatable, Consistent Measurements

National Instruments LabVIEW SignalExpress offers useful project management features in addition to an intuitive, short-time-to-measurement experience. LabVIEW SignalExpress users can quickly configure a measurement application and save the project (*. wbp) for later use. With LabVIEW SignalExpress you can also open several projects at once to quickly browse among them.

The LabVIEW SignalExpress measurement task management features save engineers significant time on repeated measurements. Engineers or technicians can simply open and run a LabVIEW SignalExpress project without requiring any programming or addition instrument configuration and setup. This readily facilitates the sharing of measurement projects with other engineers to increase productivity, broaden measurement expertise, and ensure consistent, repeatable measurements during the important design phase of the product development cycle.

Creating User-Defined Steps

In the event a specific measurement, analysis, or comparison step is not available in the LabVIEW SignalExpress menu, engineers can use NI LabVIEW to create user-defined steps for LabVIEW SignalExpress. User-defined steps provide the ideal solution for adding measurements with GPIB and VXI instruments, in addition to situations where application-specific analysis routines are needed. LabVIEW SignalExpress provides a variety of tools to assist users in creating and inserting user-defined steps.

Connecting LabVIEW SignalExpress to LabVIEW

Many test applications developed during the design and verification phases are often reused in the validation and manufacturing test phases later in the product development cycle. LabVIEW SignalExpress and LabVIEW help reinforce this good practice through seamless connectivity and reuse. Using LabVIEW, any LabVIEW SignalExpress user can convert his/her LabVIEW SignalExpress project to a LabVIEW VI as shown. This greatly assists engineers in saving test development time later in the product development cycle. It also helps ensure that consistent measurements are being made on a product during the remaining phases.

Using LabVIEW SignalExpress in Validation and Manufacturing Test

National Instruments LabVIEW SignalExpress is a very powerful interactive measurement software tool that can be used to acquire, compare, automate, and store measurements through the entire product development cycle. Many LabVIEW SignalExpress features are developed around bridging the gap in design and test. LabVIEW SignalExpress is also a very valuable tool for validation and manufacturing test engineers building systems with virtual instrumentation. LabVIEW SignalExpress can save tremendous amounts of time in prototyping, debugging, and troubleshooting measurements in the more automated test systems found in validation and manufacturing test applications. LabVIEW and NI TestStand are recommended as the primary software tools for use in these areas accompanied by LabVIEW SignalExpress as a powerful, exploratory tool for test engineers and technicians.

Summary

Until now, electronic design and test engineers spent hours acquiring and analyzing electronic measurements manually with traditional benchtop instruments. The advancing complexity of today’s electronic devices requires more tests to verify and validate a design without introducing additional time in the product development cycle. National Instruments delivers a simple, interactive solution through LabVIEW SignalExpress. With LabVIEW SignalExpress, engineers now can use virtual instrumentation on the benchtop to save valuable time by automating measurements for modeling, verification, characterization, validation, and manufacturing test.

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