Research On Testability Design Of Digital - Analog Hybrid Circuit

Nowadays, because of the high cost and low efficiency, traditional design method is no longer appropriate for current electronic circuit design. As a new design technique, Design for Test (DFT) has been considered as one of the appropriate technologies in test area. Based on correlative regulations and standards, DFT working on circuit design improves the controllability and observablity of the products. The cost of the whole process could be reduced at the same time. There are several requests for the design of a certain Mixed-Signal Circuits in an electronic control system such as high reliability, high fault detection rate and high fault isolation rate. The simulation results show that the current circuits can not meet the above requests. Hence, the research of testability analysis, testability design and testability verification technology was studied in order to improve the testability.The major contributions of this thesis are summarized as follows:(1) A whole scheme which is appropriate for a Mixed-Signal Circuits in an electronic control system was put forward. The ad-hoc DFT and the structure DFT were introduced. The basic theory and function of Boundary Scan were analyzed in detail. Aiming at the feature of the functional structure of certain Mixed-Signal Circuits, a typical scheme of DFT based on testability modeling, analysis, Boundary Scan and testability verification technology was proposed with detailed procedures presented.(2) A testability model based on multi-signal model was built up and the research of testability analysis was completed for the circuits. Several testability analysis methods based on model were introduced, such as logic model, information flow mode, hybrid diagnostic mode and multisignal flow graphs mode. Depending on the analysis of function and the fault model of the circuits, a testability model based on multisignal flow graphs mode was built up. According to the simulation results conducted by Testability Engineering and Maintenance System (TEAMS), the the circuits was evaluated and the design was improved by the direction.(3) An improved algorithms which is appropriate for the circuits was given. Based on the comparison of several Boundary Scan algorithms including walk"1" or walk"0" algorithm, modified counting sequence algorithm(MCSA), equal-weight algorithm and equal-weight wrong-estimate algorithm, an improved method of walk"1" was given. The study illustrated that the new algorithm had better performance on compactness and completeness.(4)The testability verification platform for the circuits was designed. The software and the hardware system was built up, which was composed of fault injection, test controller, Boundary Scan chain, MCU program and interface software.(5)Testing experiments based on fault injection were carried out on the platform, including the integrity test, the interconnect test, the cluster test, the MOSFET test, etc. The results of the experiments showed that the system based on DFT worked properly.The fault detection rate and fault isolation rate of the system were effectively enhanced as well. In a word, the method of testability analysis and DFT are valid and feasible tools in the process of Mixed-Signal Circuits design and application.