Generation de vecteurs de test pour les circuits.

摘要

Testing mixed signal circuits is known to be a very difficult task. This is mainly due to the nature of analog signal and its interaction with digital signals. Usually mixed-signal circuits are tested using functional vectors. Since there is no stopping criteria, mixed signal circuits are either over-tested or under-tested.;Mixed signal circuits are partitioned into purely analog and purely digital parts and each part is tested alone. This technique has its drawbacks, since it is not practical in most of the cases. In fact, circuit partitioning means degradation of performances especially for analog circuits. Also, the access of all the analog performances is not possible.;In order to overcome these problems, a test vector generation technique for analog and mixed signal circuits is presented. This technique considers the coverage of the circuit structure as a stopping criteria for analog circuit functional testing. The sensitivity is used as a first order estimation of the relation between functionality and circuit structure. Thus analog circuit is modeled by a graph representing the relation between performances and components. Then, the test vector generation problem is formulated as a minimum cost flow problem in graph theory. Simple and multiple fault models are considered in the problem formulation.;We propose to test a mixed-signal circuit as an entity and without any modification. In this case, the constraints imposed by each block on the other are taken into consideration while generating test vectors. In order to cover all the kinds of mixed-signal circuits, we considered two kinds of circuits, an analog digital circuit which is made of analog, digital and ADC (analog to digital converter) blocks and a digital-analog circuit which is made of a digital block, an analog block and a DAC (digital to analog converter). Thus any mix can be considered using these two kinds of mixed circuits. Also, in order to have a complete ADC test, a functional and structural testing of embedded ADC is presented.;The digital part of a mixed signal circuit is tested for stuck-at faults and using boolean function manipulation, and the analog part is tested by measuring a minimum number of performances that cover the circuit structure. The main problems of mixed signal circuit testing without modification is error propagation from one block to another and analog signal control from digital block and vice-versa. In order to overcome these problems, the constraints imposed by each block on the others are taken into consideration in the test generation procedure. These constraints are considered as a constraint function that reduces the test vector search-space.