bist内建自测试

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1、内建自测试（BIST）1主讲内容nBIST概念介绍nBIST测试向量生成nBIST体系结构nBIST应用举例2BIST介绍nBIST研究的提出：降低成本、可靠要求nBIST的概念：使用部分电路测试电路本身nBIST的分类：测试的形式离线测试在线测试功能结构并发非并发3Test ControllerSystemBoardTest ControllerBoardTest ControllerBoardTest ControllerChipChipTest ControllerTPGCUTORAChipTest ControllerTPGCUTORAChipTest ControllerTPGCUT

2、ORA4BIST介绍nTPG generates pseudo random test vectorsnInput Isolation Circuitry isolates the normal system inputs from the CUTnOutput Response Analyzer performs polynomial division for test data compaction(signature analysis)Test Pattern Generator Circuit Under TestTest Controller Output Response Anal

3、yzerInput IsolationCircuitrySystem InputsSystem OutputsNormal OperationTest Mode5BIST优点n减少输入输出引脚n可重复测试n不需要大量的测试图形产生n减少测试时间n执行全速测试n在生产时就执行测试6BIST带来的问题n面积开销n性能缺失n故障覆盖率n易于实现n支持系统级测试n提供诊断能力7BIST实现技术分类n基于存储向量的测试产生基于存储向量的测试产生l 微指令支持l 测试向量存储在ROM中n硬件算法产生测试向量硬件算法产生测试向量l 计数器l 线性移位反馈寄存器（LFSR)l 细胞自动机（CA）8LFSR（线

4、性反馈移位寄存器）9LFSR（线性反馈移位寄存器）n产生的函数可用下列多项式表示：n对于外接型电路，按下式生成的序列：10n初始值：lC1=1,C2=0,C3=0,C4=1lA1=0,A2=0,A3=0,A4=1LFSR（线性反馈移位寄存器）11Cellular Automata(CA)n线性CA（冯诺依曼邻或称3-邻）Rule 90 xi(t+1)=xi-1(t)xi+1(t)Rule 150 xi(t+1)=xi-1(t)xi(t)xi+1(t)Rule 150Rule 90Rule 90Rule 9012CA规则表13零边界CA14周期边界CA15LFSR VS CACharacteri

5、stic LFSR CA Area OverheadLeastLess than one Gate/nodeHigher than LFSROne Gate/nodeMax.Length SequenceEasy to implementWell defined P(x)Harder to implementCombination of rules not well definedPerformanceLower External FeedbackXOR gates in FeedbackHigher Internal Feedback Max.one gate/pathHighNo gate

6、s in feedbackParallel Pattern RandomnessLowShifting of DataHighLogical relation with neighborsStuck-at-fault detectionHigh HighStuck-open and Delay fault Detection LowLess number of transitionsHighHigher number of transitions due to higher randomnessCAD friendlinessNoNodes cannot be cascadedYesNodes

7、 can be easily cascadedSignature AliasingHigher ProbabilityShifting of DataLower Probability16BIST 测试向量生成n加权伪随机测试加权伪随机测试l被测电路输入端取“1”的概率即为权值。l保障故障覆盖率的前提下压缩测试长度。l改变输入端“0”，“1”的概率以使得故障更容易出现。l影响权值的因素：输入端在内部电路中所关联的逻辑单元数量来计算。l加权逻辑的实现：17随机不可测故障LFSR18加权逻辑的实现n每个寄存器 原始输出的 权值为1/2LFSR1/83/41/27/81/219BIST 测试向量生成

8、n穷举测试穷举测试l提供所有可能输入组合l实现完整的功能测试l100%可能的故障覆盖率l大量的输入引脚给电路 带来很大测试时间和 硬件的开销20BIST 测试向量生成n伪穷举测试生成l逻辑分段 锥分段 敏化路径分段 (4-2)-CUTl物理分段x1x2x3x4y1y2y3y4C1C2FABn1n2CD2122Pseudoexhaustive test-1.Pseudoexhaustive-exhaustive on submodule and pseudoexhaustive on CUT2.Partition the CUT into several smaller submodules3.

9、as 1 in the slide4.as 2 in the slide5.give a example for a 40-input circuit,the testing time is 2*40 or 100,000 seconds on 10MHz test clock.If the circuit is partitioned into 10 subcircuits and each have 20 inputs,the testing time is only 1 second.6.However,partition is a difficult task.Most researc

10、h emphasize on the partitioning algorithm.23figure:Cheng-Wen Wu,NTHU 24“X”问题n未知逻辑值“X”会对MISR中的异或逻辑产生影响，造成对MISR特征的损害n未知逻辑值“X”产生的原因：三态总线竞争，没有初始化的非扫描触发器，RAM存储，无驱动的原始输入，组合环。25BIST体系结构之BILBO26STUMPS 结构Test Pattern GeneratorBIST controllerCombinational part of the CUTMISRChain 1Chain 2Chain n.0 1primary inputsprimary outputs27figure:Cheng-Wen Wu,NTHU 28BIST 应用案例29