QDI Constant-Time Counters

Ned Bingham and Rajit Manohar

Counters are a generally useful circuit that appear in many contexts. Because of this, the design space for clocked counters has been widely explored. However, the same cannot be said for robust clockless counters. To resolve this, we designed an array of constant response time counters using the most robust clockless logic family, quasi-delay-insensitive (QDI) circuits. We compare our designs to their closest QDI counterparts from the literature, showing significant improvements in design quality metrics including transistor count, energy per operation, frequency, and latency in a 28nm process. We also compare our designs against prototypical synchronous counters generated by commercial logic synthesis tools.