Clock IC Harnesses GPS Signal For Synchronization

The AD9548 clock generator/synthesizer is the first clock IC that lets designers use the standard, free 1-pulse/s signal of GPS satellites to generate and synchronize clock signals for communications infrastructure equipment, according to the manufacturer. The device eliminates the dedicated oscillators, phase-locked loops, and other clock recovery circuitry communications systems previously required to generate clock signals synchronized to the widely available GPS standard. The AD9548 includes a digital PLL that up-converts the 1-pps GPS signal while reducing input-time jitter or phase noise associated with the external references to as little as 300 fs. The clock distribution section provides four output drivers, each programmable either as a single differential LVPECL/LVDS output or as pairs of single-ended CMOS outputs. Each output has a dedicated 30-bit programmable post divider, enabling the generation of different output frequencies. An integrated reference clock multiplier allows for system clock references as low as 4 MHz while still supporting outputs of up to 450 MHz. The AD9548 also includes a digitally controlled loop filter programmable to as low as 1-mHz, as well as manual and automatic holdover circuitry that continuously generates a low-jitter, valid output clock even when some, or all, references have failed. The AD9548 comes in an 88-lead LFCSP and is specified over ?40°C to 85°C. The device is available now for $$24.82 in quantities of 1000. ANALOG DEVICES INC., Norwood, MA. (781) 328-4700.