Electronic Design

Histograms And Feedback Improve BIST Analysis

Built-in self-test (BIST) takes on many forms, de-pending upon the type of circuit and type of analysis being performed. Two additions to the BISTMaxx software and IP from Fluence Technology offer new ways to analyze test results. These additions, the HABIST Toolkit and DACBIST Designer, also provide test support that re-quires minimal overhead and simple results analysis.

This version of the HABIST (Histogram-based Analog Built-In Self-Test) Toolkit applies histogram test analysis to analog-to-digital converter (ADC) and analog circuits. It comes with Verilog/VHDL libraries with BIST IP incorporated into the analog circuit blocks. The IP uses minimal chip area and allows real-time testing.

The HABIST IP samples a signal and builds a histogram based on this information regardless of the complexity of the signal. The signal is assumed to have a regular period, like a square or sinewave. Sample speed isn't a major issue, because multiple random samples are taken over a number of periods. The resulting histogram for a particular signal, also called a signature, is distinctive. For example, a sinewave has a U-shaped histogram. A clipped sinewave generates a distorted histogram.

HABIST pushes the histograms a step further by taking the difference between known-good results and the device under test. Ideally, the difference will be zero. Written in Java, the Toolkit software includes a copy of IBM VisualAge for Java. The Toolkit helps determine the signatures for different fault modes.

DACBIST Designer addresses digital-to-analog converter (DAC) design and test. This feature lets designers incorporate DACBIST IP to eliminate the need for mixed-signal ATE systems. A simple feedback circuit and counter provide the basis for the IP. It addresses stuck bits, shorts, and nonlinearity. Furthermore, the Designer software provides "what if" analysis to select the right BIST configurations for a simple pass/fail result. Keeping it simple is what DACBIST does best.

Contact Fluence Technology for information about pricing and availability.

Fluence Technology Inc., 8700 S.W. Creekside Place, Beaverton, OR 97008; (503) 672-8800; fax (503) 672-8700; www.fluence.com.

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