The AD9558 is a low loop bandwidth clock multiplier that provides jitter cleanup and synchronization for many systems, including synchronous optical networks (SONET/SDH). The AD9558 generates an output clock synchronized to up to four external input references. The digital PLL allows for reduction of input time jitter or phase noise associated with the external references. The digitally controlled loop and holdover circuitry of the AD9558 continuously generates a low jitter output clock even when all reference inputs have failed. The AD9558 operates over an industrial temperature range of −40°C to +85°C. If a smaller package is required, refer to the AD9557 for the two-input/two-output version of the same part.