Combining 0.18-micron CMOS with clever circuit design, Analog Devices Inc. has readied an unprecedented multichannel direct digital synthesis (DDS) device that is inherently synchronous with reduced board space and lower cost per channel. Plus, it offers independent programming of up to four inherently synchronized outputs. ADI’s new four-channel AD9959 and two-channel AD9958 deliver greater control to correct imbalances between multiple signals, enabling engineers to spend considerably less time and effort on this usually complex portion of the system design. For space-constrained systems, the AD9958 and AD9959 simplify the design process by integrating multiple DDS channels on a single chip, eliminating the need for several single-channel DDS chips and external circuitry and offering dramatic board space reduction of up to 75% over traditional solutions, claimed ADI.

Direct digital synthesis is a digital technique used for generating an analog output waveform or clocking signal from a fixed-frequency clock source. The AD9959 and AD9958 are optimized for applications that require complex high-speed synthesis up to 200 MHz, including phased-array radar/sonar systems, automatic test equipment, medical imaging and optical communications systems.

“Analog Devices is meeting the synthesizer synchronization challenge by leveraging its world-class converter technologies to develop highly integrated DDS devices that lower the cost and complexity of system design,” said Kevin Kattmann, product line director, high-speed converter group, Analog Devices. “The ability to easily achieve precision phase offset control between multiple synchronized output channels, while consuming minimal board space, enables the AD9959 and AD9958 to offer system designers significant advantages over traditional frequency synthesizer solutions and single-channel DDS products," stated Jeff Keip, product marketing manager for ADI’s high-speed converter group based in Greensboro, N.C.

Used in a wide range of applications from test and measurement equipment to wireless and satellite communications, the complete DDS solutions employ an on-chip high-performance digital-to-analog converter (DAC) to convert a reference frequency to a sampled sine wave with fine frequency control. DDS devices are increasingly becoming an attractive alternative to traditional frequency-agile analog synthesizer solutions as they offer considerable performance benefits, such as unparalleled matching of outputs, easier synchronization for obtaining quadrature and other signal phase relationships, and fast frequency transition. Digital control eliminates the need for manual system tweaking and allows output frequencies to be conveniently derived.

To alleviate the design complexities typically involved in the synchronization of multiple DDS devices, the independent channels of the AD9959 and AD9958 are internally synchronized by a common reference clock. Programmable channel control allows for correction of imbalances in external signal paths due to analog processing, such as filtering, amplification, or printed circuit board (PCB) layout mismatches. If additional channels are required, the AD9959 and AD9958 allow daisy chaining of additional DDS chips. The devices also offer low power consumption of less than 165 mW per channel.

Each channel of the four-channel AD9959 and the two-channel AD9958 incorporates a high-speed, 10-bit DAC with excellent wideband and narrowband spurious-free dynamic range (SFDR). Each fully independent programmable channel provides 14 bits of phase offset tuning, 32-bit frequency resolution and 10-bit amplitude control. The device also supports direct or linear sweep modulation, while achieving channel isolation of greater than 60 dB. The integrated 32-bit frequency tuning word enables each channel to be programmed to resolutions of 116 mHz or less with a sampling clock of up to 500 MSPS.

The AD9959 is available in production quantities now; the AD9958 is sampling now with production slated for late third quarter. Both devices are specified over the extended industrial temperature range and and are each packaged in an 8 mm × 8 mm lead-frame chip-scale package (LFCSP).