Overview
Direct digital synthesis (DDS) is a technique for using digital data processing blocks as a means to generate a frequency - and phase-tunable output signal referenced to a fixed-frequency precision clock source. In essence, the referenced clock frequency is "divided down" in a DDS architecture by the scaling factor set forth in a programmable binary tuning word. The tuning word is typically 24-48 bits long which enables a DDS implementation to provide superior output frequency tuning resolution.
Today's cost-competitive, high-performance, functionally-integrated, and small package-sized DDS products are fast becoming an alternative to traditional frequency-agile analog synthesizer solutions. The intergration of a high-speed, high-performance, D/A converter and DDS archetecture onto a single chip (froming what is commonly known as a Complete-DDS solution) enabled this technology to target a wider range of applications and proved, in many cases, an attrantive alternative to analog-based PLL synthesizers. For many applications, the DDS solution holds some distinct advantages over the equivlent agile frequency synthesizer employing PLL circuitry.
DDS Advantages:
1. Micro-Hertz tuning resolution of the output frequency and sub-degree phase tuning capability, all under complete digital control.
2. Extremely fast "hopping speed" in tuning output frequency (or phase), phase-continuous frequency hops with no over/undershoot or analog-related loop settling time anomalies.
3. The DDS digital architecture eliminates the need for the manual system tuning and tweaking associated with component aging and temperature drift in analog synthesizer solutions.
4. The digital control interface of the DDS architecture facilitates an environment where systems can be remotely controlled, and minutely optimized, under processor control.
5. When utilized as a quadrature synthesizer, DDS afford unparalleled matching and control of I and Q synthesized outputs.
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