A 240 MHz 8-trap programmable FIR filter for disk-drive read channels

The 240 MHz digital FIR equalizer addresses the needs of magnetic disk drive applications. The FIR has low latency (3 cycles including input and output latches) to allow sufficient gain and stability in the channel timing and gain feedback loops. Programmable coefficients are supported so that the filter response can be modified in real time according to the demands of zone bit recording. (ZBR means that d is constant even as r varies in the data-rate equation.) Demands on accuracy as well as the number of taps vary, so the design is modular in the number of taps and bits to allow reuse in multiple applications. Tap counts in the range 3-10 are common. Complete testability is provided by scanmux-type static latches in all storage elements.