Hybrid Ring Generators for In-System Testing

Ring generators (RGs) are devices obtained by transforming conventional linear feedback shift registers in several steps that preserve the original transition functions. They feature feedback nets with the depth of a single XOR gate, and have reduced propagation times, increased throughput, minimized internal fan-outs, and simplified layout and routing. This paper presents hybrid ring generators (HRGs) that take RGs on the next evolutionary step in the development of their ecosystem. While using the principal design rules of RGs, the new devices are structurally improved and capable of circulating internal data faster than their predecessors. Practical aspects related to HRG-based test response compactors, programable pseudorandom test pattern generators, or phase shifters are discussed in the paper along with data providing architectural details of maximum-length (primitive) HRGs for sizes up to 1184 bits. It is also observed that XOR gate counts of HRGs can be much smaller than those of the conventional RGs producing the same output sequences.