Hybrid Ring Generators for In-System Test Applications

Ring generators are high speed devices formed by transformations that alter the structure of conventional linear feedback shift registers (LFSRs) while preserving a transition function of the original circuits [8]. They feature a reduced number of levels of XOR logic, minimized internal fan-outs, and simplified layout and routing. This paper discusses hybrid ring generators – a new class of lightweight linear finite state machines. While they use the principal design rules of conventional ring generators, the new devices can reduce the number of XOR gates up to seven times compared to conventional rings implementing the same characteristic polynomial. It makes a substantial contribution toward the performance of linear circuits used in a variety of test applications. Several issues related to hybrid ring generators such as designing MISRs, programable PRPGs, or phase shifters are also discussed in the paper along with data providing architectural details of hybrid ring generators for sizes up to 256 bits.