Texas Instruments SN74LS297

the sn54ls297 and sn74ls297 devices are designed to provide a simple cost-effective solution to high-accuracy digital phase-locked-loop applications. these devices contain all the necessary circuits with the exception of the divide-by-n counter to build first order phase-locked loops as described in figure 1. both exclusive-or (xorpd) and edge-controlled (ecpd) phase detectors are provided for maximum flexibility. proper partitioning of the loop function with many of the building blocks external to the package makes it easy for the designer to incorporate ripple cancellation or to cascade to higher order phase-locked loops. the length of the up/down k counter is digitally programmable according to the k counter function table.