外文翻譯-關(guān)于直接數(shù)字頻率合成器

1、外文翻譯（原文）- 1 -All About Direct Digital SynthesisBy Eva Murphy [eva.murphy@analog.com]Colm Slattery [colm.slattery@analog.com]What is Direct Digital Synthesis? Direct digital synthesis (DDS) is a method of producing an ana

2、log waveform—usually a sine wave—by generating a time-varying signal in digital form and then performing a digital-to-analog conversion. Because operations within a DDS device are primarily digital, it can offer fast swi

3、tching between output frequencies, fine frequency resolution, and operation over a broad spectrum of frequencies. With advances in design and process technology, today’s DDS devices are very compact and draw little power

4、. Why would one use a direct digital synthesizer (DDS)? Aren’t there other methods for easily generating frequencies? The ability to accurately produce and control waveforms of various frequencies and profiles has become

5、 a key requirement common to a number of industries. Whether providing agile sources of low-phase-noise variable-frequencies with good spurious performance for communications, or simply generating a frequency stimulus in

6、 industrial or biomedical test equipment applications, convenience, compactness, and low cost are important design considerations. Many possibilities for frequency generation are open to a designer, ranging from phase-lo

7、cked-loop (PLL)-based techniques for very high-frequency synthesis, to dynamic programming of digital-to-analog converter (DAC) outputs to generate arbitrary waveforms at lower frequencies. But the DDS technique is rapid

8、ly gaining acceptance for solving frequency- (or waveform) generation requirements in both communications and industrial applications because single-chip IC devices can 外文翻譯（原文）- 3 -sinusoidal outputs. Figure 2 shows the

9、 square-, triangular-, and sinusoidal outputs available from an AD9833.How does a DDS device create a sine wave? Here’s a breakdown of the internal circuitry of a DDS device: its main components are a phase accumulator,

10、a means of phase-to-amplitude conversion (often a sine look-up table), and a DAC. These blocks are represented in Figure 3.A DDS produces a sine wave at a given frequency. The frequency depends on two variables, the refe

11、rence-clock frequency and the binar y number programmed into the frequency register (tuning word). The binary number in the frequency register provides the main input to the phase accumulator. If a sine look-up table is

12、used, the phase accumulator computes a phase (angle) address for the look-up table, which outputs the digital value of amplitude—corresponding to the sine of that phase angle—to the DAC. The DAC, in turn, converts that

13、 number to a corresponding value of analog voltage or current. To generate a fixed-frequency sine wave, a constant value (the phase increment—which is determined by the binary number) is added to the phase accumulator wi

14、th each clock cycle. If the phase increment is large, the phase accumulator will step quickly through the sine look-up table and thus generate a high frequency sine wave. If the phase increment is small, the phase accumu

15、lator will take many more steps, accordingly generating a slower waveform.What do you mean by a complete DDS? The integration of a D/A converter and a DDS onto a single chip is commonly Figure 3. Components of a direct d