An adaptively-pipelined mixed synchronous-asynchronous digital FIR filter chip operating at 1.3 GigaHertz

A high-throughput low-latency digital finite impulse response (FIR) filter has been designed for use in partial-response maximum-likelihood (PRML) read channels of modem disk drives. The filter is a hybrid synchronous-asynchronous design. The speed critical portion of the filter is designed as a high-performance asynchronous pipeline, sandwiched between synchronous input and output portions, making it possible for the entire filter to be dropped into a clocked environment. A novel feature of the filter is that the degree of pipelining is dynamically variable, depending upon the input data rate. This feature is critical in obtaining a very low filter latency throughout the range of operating frequencies. The filter was fabricated in a 0.18 μm CMOS process. Resulting chips were fully functional over a wide range of supply voltages, and exhibited throughputs of over 1.3 Giga items/second, and latencies as low as four clock cycles. The internal asynchronous pipeline was estimated to be capable of significantly higher throughputs, around 1.8 Giga items/second. With these performance metrics, the filter has better performance than that reported for existing digital read channel filters.