Studies On Test Compression Methods Based On Equal Runlength FDR Code For Digital Circuits

With the scale of the integrated circuits(ICs)increase,the density of transistors in a chip is also increasing.Thus,the test data volume turns large,the test cost is high,and IC testing is more difficult.How to improve test data compression ratio and reduce test cost becomes one of the most important issues in IC testing.Focused on this research topic,this thesis proposes following two methods for test data compression:(1)Improved from FDR code,IFDR Code can encode both 0 runlength and 1runlength test data in a test set.The compression ratio is increased.However,there still has some room to improve.In this thesis,we propose a new coding method based on equal runlength code on the basis of IFDR,called ERFDR.Firstly,the proposed method can not only encode 0 runlengths and 1 runlengths for a test set simultaneously,but also use shorter code if the adjacent runlengths are equal.Therefore,the compression ratio can be further improved.This thesis also puts forward a new filling algorithm for a test set with don't care bits,which can enhance compression efficiency of the proposed method.Experimental results show that the proposed method can obtain a higher compression rate compared to Golomb,FDR,EFDR,IFDR codes.The test cost can be reduced effectively.(2)Facing the fact that many test vectors only have a small amount of incompatible bits,EFDR-BC code groups the vectors together which have the best compatibility each other.Therefore,only template vectors and difference vectors need to be saved.This method achieved high compression ratio.However,while many vectors are merged as a vector,more information should be saved,the compression ratio is not so high.Based on this viewpoint,this thesis proposes an improved EFDR-BC code.Firstly,we define the distance between vectors each other.Secondly,we put forward a two vectors merging algorithm.In this algorithm,we group those two vectors which have the nearest distance together.Finally,we propose an improved EFDR-BC code and a group vector code for encoding the vectors after merging respectively.Experimental results show that the proposed method can obtain a higher compression ratio compared to FDR,EFDR,EFDR-BC codes,which described the efficiency of our proposed method.On the whole,this thesis proposes two effective encoding methods for test data compression,which improve the compression ratio,reduce the test data volume as well as the test cost.