Wireless Systems Design

High-Clock-Speed DDSs Lower Power Dissipation


A portfolio of radio-frequency ICs (RFICs) has been expanded to welcome a new family of 14-b direct digital synthesizers (DDSs). DDS is the technique used for digitally creating and manipulating sine waves—or other continuous wave forms—in the digital domain. These new chips deliver high clock speed (400 MHz) while achieving low power dissipation. In fact, the chips have been proven to deliver one-tenth the power consumption of previous solutions. Subsequently, designers can use DDS for fast frequency hopping at higher output frequencies and in more power-sensitive applications. Typical applications might include satellite communications, broadband networking, radar, test and measurement, and instrumentation.

These new devices stand out for their ability to clock at 400 MSPS. They also can synthesize frequencies of up to 160 MHz while dissipating less than 200 mW of power. By comparison, previous DDS chips of comparable resolution could only synthesize frequencies of up to 120 MHz. They dissipated 2 W of power.

With the lower power dissipation, designers are free to use multiple chips on a single printed-circuit board (PCB) with less concern for thermal issues. Additional features of the family include an integrated 14-b digital-to-analog converter (DAC), on-chip random-access memory (RAM), phase offset and amplitude control, and multi-chip synchronization.

The new family of devices is made up of three members. The AD9951 is a basic DDS with an on-board, 14-b DAC. The AD9952 has a high-speed comparator. The AD9953 model comes equipped with RAM for nonlinear phase/frequency sweeping. The final product—the AD9954—serves as the flagship for the family. It boasts a high-speed comparator and RAM, as well as an automatic linear frequency sweep. The chip is digitally programmable. It is a complete high-frequency synthesizer capable of generating a frequency-agile, analog output sinusoidal waveform at up to 160 MHz.

The AD9954 DDS device is designed to provide fast frequency hopping and fine-tuning resolution (32-b frequency-tuning word). The frequency-tuning and control words are loaded into it via a serial-I/O port. Among the additional features of the AD9954 are an integrated 1024 x 32 static random-access memory (RAM) to support flexible frequency sweep capability in several modes. It also provides support for a user-defined linear sweep mode of operation.

The AD9954 is now available. It is specified to operate over the extended industrial temperature range of -40°C to +85°C. The AD9951, AD9952, and AD9953 are also available. All parts come in a 48-lead EPAD-TQFP package. In 1000-piece quantities, the prices per unit for the AD9951, AD9952, AD9953, and AD9954 are $13.75, $15.50, $14.75 and $17.25, respectively.

Analog Devices, Inc.
804 Woburn St., Wilmington, MA 01887; (781) 937-1989, (800) ANALOGD, www.analog.com/DDS.

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