The AD9540 is Analog Devices’ first dedicated clocking product specifically designed to support the extremely stringent clocking requirements of the highest performance data converters. The device features high performance PLL （phaselocked loop） circuitry， including a flexible 200 MHz phase frequency detector and a digitally controlled charge pump current. The device also provides a low jitter， 655 MHz CMLmode， PECL-compliant output driver with programmable slew rates. External VCO rates up to 2.7 GHz are supported. Extremely fine tuning resolution （steps less than 2.33 μHz） is another feature supported by this device. Information is loaded into the AD9540 via a serial I/O port that has a device write speed of 25 Mbps. The AD9540 frequency divider block can also be programmed to support a spread spectrum mode of operation. The AD9540 is specified to operate over the extended automotive range of ?40°C to +85°C.