The AD9549 provides synchronization for many systems, including synchronous optical networks (SONET/SDH). The AD9549 generates an output clock, synchronized to one of two external input references. The external references may contain significant time jitter, also specified as phase noise. Using a digitally controlled loop and holdover circuitry, the AD9549 continues to generate a clean (low jitter), valid output clock during a loss of reference condition, even when both references have failed. The AD9549 operates over an industrial temperature range of −40°C to +85°C. Applications * Network synchronization * Reference clock jitter cleanup * SONET/SDH clocks up to OC-192, including FEC * Stratum 3/3E reference clocks * Wireless base stations, controllers * Cable infrastructure * Data communications * Flexible reference inputs * Input frequencies: 8 kHz to 750 MHz * Two reference inputs * Loss of reference indicators * Auto and manual holdover modes * Auto and manual switchover modes * Smooth A-to-B phase transition on outputs * Excellent stability in holdover mode * Programmable 16 + 1-bit input divider, R * Differential HSTL clock output * Output frequencies to 750 MHz * Low jitter clock doubler for frequencies of >400 MHz