VCXO? Don't need 'em no more.
Voltage-controlled crystal oscillators (VCXO) are the preferred way to provide stable clock references in high-precision cellular base stations or frequency-sensitive A/D front end sensors. But VCXOs consume real estate, power, and cost…and they can be tricky to design with. National Semiconductor asserts that you don’t need them anymore, as long as you design with the PowerWise LMK04000 Family of clock jitter cleaners. Using only a simple external crystal, the new devices provide sub-200 femtosecond (fs) RMS jitter to improve system performance and accuracy; levels difficult to achieve even with high-dollar VCXOs.
There are five members of the new jitter cleaner family ranging from 24.4 mW-ps per channel to 37.4 mW-ps per channel. Each uses National’s PLLatinum architecture consisting of two cascaded PLLs, a low-noise XO, a high-perf VCO and low-noise dividers and drivers. Each also has dual-redundant inputs, 5 differential outputs, and an optional default clock at power-up which is intended to drive the FPGA used to program the clock jitter cleaner’s own power-up sequence. Multiple output options exist, but can drive clocks either up to 250 MHz (LVCMOS) or 1080 MHz (LVPECL or LVDS).