William S. Coates

Two FIFO ring performance experiments

Asynchronous circuits are often perceived to operate slower than equivalent clocked circuits. We demonstrate with fabricated chips that asynchronous circuits can be every bit as fast as clocked circuits. We describe two high-speed first-in-first-out (FIFO) circuits that we used to compare the performance of asynchronous FIFOs with that of conventionally clocked shift registers. The first FIFO circuit uses a pulse-like protocol, which we call the Asynchronous Symmetric Persistent Pulse Protocol (asP*), to advance data along a pipeline of conventional latches. Use of this protocol requires careful management of circuit delays. The second FIFO circuit uses a transition signaling protocol and special transition latches to store data. These transition latches are fast, but they are about 50% larger than conventional latches. Measurements obtained from chips fabricated in 0.6 /spl mu/m CMOS and from SPICE simulations show that the throughput of the first FIFO design matches that of a conventionally clocked shift register design, with a maximum throughput of 1.1 Giga data items per second. The throughput of the second design exceeds the performance of the asP* design and achieves a maximum throughput of 1.7 Giga data items per second. We have extensively tested the chips and have found them to operate reliably over a very wide range of conditions.