The AD9956 is Analog Devices’ newest AgileRF synthesizer. The device is comprised of DDS and PLL circuitry. The DDS features a 14-bit DAC operating at up to 400 MSPS and a 48-bit frequency tuning word （FTW）。 The PLL circuitry includes a phase frequency detector with scaleable 200 MHz inputs （divider inputs operate up to 655 MHz） and digital control over the charge pump current. The device also includes a 655 MHz CML-mode PECL-compliant driver with programmable slew rates. The AD9956 uses advanced DDS technology， an internal high speed， high performance DAC， and an advanced phase frequency detector/charge pump combination， which， when used with an external VCO， enables the synthesis of digitally programmable， frequency-agile analog output sinusoidal waveforms up to 2.7 GHz. The AD9956 is designed to provide fast frequency hopping and fine tuning resolution （48-bit frequency tuning word）。 Information is loaded into the AD9956 via a serial I/O port that has a device write-speed of 25 Mb/s. The AD9956 DDS block also supports a user-defined linear sweep mode of operation. The AD9956 is specified to operate over the extended automotive range of ?40°C to +125°C