The advent of zero-intermediate-frequency transmitter architectures is limited by the choice of digital-to-analog converters available. Current parts consume up to 2 W to achieve a few hundred megahertz operation in direct digital synthesis (DDS). Now, the AD995x family of RF ICs for DDS from Analog Devices is tackling that problem.
Base specifications include 400-MHz maximum clock, less than 200-mW power consumption, a 25-Mbit/s serial I/O port for read/write operations, 14-bit resolution, and 1.8-V operation with outputs that interface directly to 3.3-V systems. The parts all have a built-in crystal-controlled oscillator and clock multiplier, which can be synchronized to other AD995x parts within the system through the synchronization inputs and outputs.
The top device, the AD9954, features 1024 × 32 bits of RAM, a frequency accumulator that enables automatic frequency sweeping, and a separate high-speed comparator. The chip generates sinusoids up to 160 MHz. Users can configure the RAM to drive either the frequency tuning word (for frequency modulation) or the phase offset word (for phase modulation). Due to process and design innovations, the part consumes less than 200 mW of power when operating at 400 Msamples/s.
Unit pricing for 1000 pieces ranges from $13.75 for the AD9951, which is the base DDS part, up to $17.25 for the AD9954. Units are available in 48-lead EPAD-QFPs.
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