Analogue integrated circuits design-for-testability flow oriented onto OBIST strategy

© Kaunas University of Technology. Oscillation Built-In Self-Test (OBIST) strategy allows to avoid the using complex, expensive generators of input test signals during testing, and uses the oscillation frequency generated at the output of the circuit after reconfiguring into oscillator as a controlled parameter. There configuration subcircuit forms an oscillator from the original circuit in the test mode and requires an additional but insignificant area of the chip, especially against the background of stable increasing the scale of integration for the state-of-the-art integrated technologies. Selection of the efficient type of reconfiguration the original circuit into oscillator and implementation of corresponding test circuitry are the most important tasks, which, as rule, are solved nowadays based on experience of designers without automation and therefore restrict to wide use of the OBIST concept. The paper is mainly focused on the task of design-for-testability (DFT) automation with emphasis on the OBIST strategy for analog integrated circuits (IC). The design procedures according to DFT flow are proposed. Three possible structural solutions for reconfiguration of original circuit into an oscillator are considered. The necessary conditions for stability analysis of reconfigured circuit are presented. The stage of a numerical estimating the transient time before the steady-state operation after reconfiguration of original circuit into an oscillator ensuring definition of the start time point for correct calculating the oscillation frequency is proposed. The set of rules for each structural solution for reconfiguration is prepared as the formal procedures, which can support the automation during the DFT flow. The efficiency of the proposed DFT flow is demonstrated for analog circuits, for which the reconfiguration subcircuits were obtained in an automated way during design-for-testability, as well as the fault simulation has been performed. The experimental results for all cases showed the adequacy of oscillation frequency for revealing both catastrophic and parametric faults. Fault coverage for considered set of faults has consisted up to 100%

Quiescent current testing of CMOS data converters

Power supply quiescent current (IDDQ) testing has been very effective in VLSI circuits designed in CMOS processes detecting physical defects such as open and shorts and bridging defects. However, in sub-micron VLSI circuits, IDDQ is masked by the increased subthreshold (leakage) current of MOSFETs affecting the efficiency of I¬DDQ testing. In this work, an attempt has been made to perform robust IDDQ testing in presence of increased leakage current by suitably modifying some of the test methods normally used in industry. Digital CMOS integrated circuits have been tested successfully using IDDQ and IDDQ methods for physical defects. However, testing of analog circuits is still a problem due to variation in design from one specific application to other. The increased leakage current further complicates not only the design but also testing. Mixed-signal integrated circuits such as the data converters are even more difficult to test because both analog and digital functions are built on the same substrate. We have re-examined both IDDQ and IDDQ methods of testing digital CMOS VLSI circuits and added features to minimize the influence of leakage current. We have designed built-in current sensors (BICS) for on-chip testing of analog and mixed-signal integrated circuits. We have also combined quiescent current testing with oscillation and transient current test techniques to map large number of manufacturing defects on a chip. In testing, we have used a simple method of injecting faults simulating manufacturing defects invented in our VLSI research group. We present design and testing of analog and mixed-signal integrated circuits with on-chip BICS such as an operational amplifier, 12-bit charge scaling architecture based digital-to-analog converter (DAC), 12-bit recycling architecture based analog-to-digital converter (ADC) and operational amplifier with floating gate inputs. The designed circuits are fabricated in 0.5 μm and 1.5 μm n-well CMOS processes and tested. Experimentally observed results of the fabricated devices are compared with simulations from SPICE using MOS level 3 and BSIM3.1 model parameters for 1.5 μm and 0.5 μm n-well CMOS technologies, respectively. We have also explored the possibility of using noise in VLSI circuits for testing defects and present the method we have developed

Modelling methods for testability analysis of analog integrated circuits based on pole-zero analysis

Testability analysis for analog circuits provides valuable information for designers and test engineers. Such information includes a number of testable and nontestable elements of a circuit, ambiguity groups, and nodes to be tested. This information is useful for solving the fault diagnosis problem. In order to verify the functionality of analog circuits, a large number of specifications have to be checked. However, checking all circuit specifications can result in prohibitive testing times on expensive automated test equipment. Therefore, the test engineer has to select a finite subset of specifications to be measured. This subset of specifications must result in reducing the test time and guaranteeing that no faulty chips are shipped. This research develops a novel methodology for testability analysis of linear analog circuits based on pole-zero analysis and on pole-zero sensitivity analysis. Based on this methodology, a new interpretation of ambiguity groups is provided relying on the circuit theory. The testability analysis methodology can be employed as a guideline for constructing fault diagnosis equations and for selecting the test nodes. We have also proposed an algorithm for selecting specifications that need to be measured. The element testability concept will be introduced. This concept provides the degree of difficulty in testing circuit elements. The value of the element testability can easily be obtained using the pole sensitivities. Then, specifications which need to be measured can be selected based on this concept. Consequently, the selected measurements can be utilized for reducing the test time without sacrificing the fault coverage and maximizing the information for fault diagnosis

Fault simulation for structural testing of analogue integrated circuits

In this thesis the ANTICS analogue fault simulation software is described which provides a statistical approach to fault simulation for accurate analogue IC test evaluation. The traditional figure of fault coverage is replaced by the average probability of fault detection. This is later refined by considering the probability of fault occurrence to generate a more realistic, weighted test metric. Two techniques to reduce the fault simulation time are described, both of which show large reductions in simulation time with little loss of accuracy. The final section of the thesis presents an accurate comparison of three test techniques and an evaluation of dynamic supply current monitoring. An increase in fault detection for dynamic supply current monitoring is obtained by removing the DC component of the supply current prior to measurement

Analogue integrated circuits design-for-testability flow oriented onto OBIST strategy

© Kaunas University of Technology. Oscillation Built-In Self-Test (OBIST) strategy allows to avoid the using complex, expensive generators of input test signals during testing, and uses the oscillation frequency generated at the output of the circuit after reconfiguring into oscillator as a controlled parameter. There configuration subcircuit forms an oscillator from the original circuit in the test mode and requires an additional but insignificant area of the chip, especially against the background of stable increasing the scale of integration for the state-of-the-art integrated technologies. Selection of the efficient type of reconfiguration the original circuit into oscillator and implementation of corresponding test circuitry are the most important tasks, which, as rule, are solved nowadays based on experience of designers without automation and therefore restrict to wide use of the OBIST concept. The paper is mainly focused on the task of design-for-testability (DFT) automation with emphasis on the OBIST strategy for analog integrated circuits (IC). The design procedures according to DFT flow are proposed. Three possible structural solutions for reconfiguration of original circuit into an oscillator are considered. The necessary conditions for stability analysis of reconfigured circuit are presented. The stage of a numerical estimating the transient time before the steady-state operation after reconfiguration of original circuit into an oscillator ensuring definition of the start time point for correct calculating the oscillation frequency is proposed. The set of rules for each structural solution for reconfiguration is prepared as the formal procedures, which can support the automation during the DFT flow. The efficiency of the proposed DFT flow is demonstrated for analog circuits, for which the reconfiguration subcircuits were obtained in an automated way during design-for-testability, as well as the fault simulation has been performed. The experimental results for all cases showed the adequacy of oscillation frequency for revealing both catastrophic and parametric faults. Fault coverage for considered set of faults has consisted up to 100%