A Low-Cost, Expandable PXI-Based Solution for Mixed-Signal ASIC Test

Author(s):
N.D Smith - Cal. Bay Systems, Inc.
M. Cem Karahan - Cal. Bay Systems, Inc.

Industry:
Industrial Controls/ Devices/ Systems, Research, Machines/Mechanics

Products:
PXI/CompactPCI, LabVIEW

The Challenge:
Developing a flexible test system for characterizing new application-specific integrated circuits (ASICs).

The Solution:
Building a PXI-based system complete with software written with NI LabVIEW software that enables easy channel-count expansion by using the NI Synchronization and Memory Core (SMC) architecture.

The Solution:
Building a PXI-based system complete with software written with NI LabVIEW software that enables easy channel-count expansion by using the NI Synchronization and Memory Core (SMC) architecture.

Timely characterization and debuging data is critical to quickly getting new ASIC designs to market. With PXI instruments and LabVIEW, it is easy to create custom characterization systems that would previously have been difficult to build. We used several NI PXI-6552 digital waveform generator/analyzers to put together a custom scan-chain test system, facilitating rapid debuging of an ASIC design.

A fabless semiconductor startup company challenged National Instruments and Cal-Bay Systems to develop a verification platform to test their mixed-signal ASICs. Debugging a new ASIC is an iterative process; test results may determine the requirements of the next test. Delays associated with running custom test protocols on traditional automated test equipment (ATE) at the foundry resulted in unacceptable delays in time to market. Placing the design validation test system in the hands of the design engineers reduced ASIC debuging time by a factor of five.

After the initial test system was deployed, test data showed that more channels were needed to debug the ASIC design. The LabVIEW and PXI platforms allow channel expansion by adding modular instruments configured to work together as one instrument through the NI SMC device.

Deep On-Board Memory, Hardware Comparison, and Low-Level Control via Bidirectionality

Scan-chain testing of ASICs allows designers to access many registers inside an ASIC via the scan-chain interface, which typically has only a few I/O pins. Scan-chain testing requires the generation of millions of digital waveforms (stimuli) to the ASIC while simultaneously acquiring and comparing the actual response of the ASIC to the expected response. The NI PXI-6552 module can be used for both generation and acquisition in scan-chain tests.

Each digital line of a PXI-6552 module has tristate capability that allows for dual-mode operation. With tristate operation, the possible states associated with a digital line are not limited to the traditional 1 (drive high) and 0 (drive low). For lines configured as inputs, a comparison engine measures the ASIC’s response to the given stimuli and compares this response to the expected value in the hardware. These capabilities make it possible to tightly control the individual registers in the ASIC on a per-cycle basis. With the PXI-6552, the programmer can compensate for transmission line delays by applying a fixed delay to a selected list of channels. 

Finally, the ASIC test design is not limited to a single logic family, as programmable logic levels are allowed. All of these features make it possible to design a flexible and customized test for an ASIC.

Efficient and Effective Software Development with NI LabVIEW

The key requirement in this application was giving test engineers the tools to quickly define digital waveforms to generate and compare. The customer wanted to use text files to accomplish this task. Thus, the system software used native LabVIEW file I/O libraries to read millions of “vectors” from text files. Next, NI-HSDIO driver libraries were used to implement the digital waveform generation and hardware compare features. Hardware compare functionality reduces the overhead associated with the comparison task allowing comparisons to be made spontaneously with no coding and little post-processing. Design engineers can review test results via intuitive waveform graph controls, text-based reports, and mismatched vector displays. Displays of mismatched vectors permit design engineers to quickly “drill down” into the large data sets. 

Easy Expandability with NI SMC
A main cost factor in automated test hardware is channel count. Generally speaking, more channels increase the cost of a data acquisition system. Adding more channels after the initial design may be expensive or impossible. The NI T-Clock Technology for Timing and Synchronization solves this problem by synchronizing multiple devices with minimal modifications to existing hardware and software, giving test design engineers the ability to add more channels seamlessly. Cal-Bay engineers were also challenged to put this technology to use during this project. 

After the initial development phase was completed for 20 digital I/O channels, the customer expressed a desire to use the same software architecture with a total of 40 channels. This upgrade was completed seamlessly and in short order thanks to NI SMC technology on the hardware front. On the software side, as the original software design employed principles of a modular architecture, addition of extra channels to the system was a relatively minor task.

Conclusion

Per-cycle bidirectional control of individual digital I/O lines coupled with features such as tristate operation, hardware comparison, programmable voltage level support, and channel time delay make the NI PXI-655x modular instruments formidable alternatives to traditional high-cost ATEs.

LabVIEW native software libraries and free drivers that ship with NI modular instruments reduce the time and risk associated with the usual software development process. NIs SMC technology allows for easy introduction of additional digital I/O channels, seamlessly expanding the existing system in short order.

For more information, contact:

 

M. Cem Karahan

 

Cal. Bay Systems, Inc.

 

3070 Kerner Blvd., Suite B

 

San Rafael, CA 94901

 

Tel: (415) 258 - 9400

 

Fax: (415) 258-9288

 

E-mail: cem@calbay.com

 

 

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