直接数字合成(DDS)是一种利用数字数据处理块作为一种手段来产生频率和相位可调的输出信号，参考固定频率的精密时钟源的技术

Copyright  1999 Analog Devices, Inc.

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Section 1. Fundamentals of DDS Technology

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 reference 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

attractive alternative to analog-based PLL synthesizers. For many applications, the DDS solution

holds some distinct advantages over the equivalent agile analog frequency synthesizer employing

PLL circuitry.

DDS advantages:

• Micro-Hertz tuning resolution of the output frequency and sub-degree phase tuning

capability, all under complete digital control.

• 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.

• 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.

clock, an address counter, a programmable read only memory (PROM), and a D/A converter (see

Figure 1-1).