1、外文翻译（原文） 毕业设计 （外文翻译材料） 学 院 ： 专 业 ： 学生姓名 ： 指导教师 ： 电气与电子工程学院 电子信息工程 外文翻译（原文） All About Direct Digital Synthesis By Eva Murphy Colm Slattery What is Direct Digital Synthesis? Direct digital synthesis (DDS) is a method of producing an analog waveformusually a sine waveby generating a time-varying sign
2、al in digital form and then performing a digital-to-analog conversion. Because operations within a DDS device are primarily digital, it can offer fast switching between output frequencies, fine frequency resolution, and operation over a broad spectrum of frequencies. With advances in design and proc
3、ess technology, todays DDS devices are very compact and draw little power. Why would one use a direct digital synthesizer (DDS)? Arent there other methods for easily generating frequencies? The ability to accurately produce and control waveforms of various frequencies and profiles has become a key r
4、equirement 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 industrial or biomedical test equipment applications, convenience, compactness, and low
5、 cost are important design considerations. Many possibilities for frequency generation are open to a designer, ranging from phase-locked-loop (PLL)-based techniques for very high-frequency synthesis, to dynamic programming of digital-to-analog converter (DAC) outputs to generate arbitrary waveforms
6、at lower frequencies. But the DDS technique is rapidly gaining acceptance for solving frequency- (or waveform) generation requirements in both communications and industrial applications because single-chip IC devices can generate programmable analog output waveforms simply and with high resolution a
7、nd accuracy. Furthermore, the continual improvements in both process technolog y and design have resulted in cost and power consumption levels that were previously unthinkably low. For example, the AD9833, a DDS-based programmable waveform generator (Figure 1), operating at 5.5 V with a 25-MHz clock
8、, consumes a Figure 1. The AD9833-a one-chip waveform generator. 外文翻译（原文） maximum power of 30 milliwatts. What are the main benefits of using a DDS? DDS devices like the AD9833 are programmed through a high speed serial peripheral-interface (SPI), and need only an external clock to generate simple s
9、ine waves. DDS devices are now available that can generate frequencies from less than 1 Hz up to 400 MHz (based on a 1-GHz clock). The benefits of their low power, low cost, and single small package, combined with their inherent excellent performance and the ability to digitally program (and re-prog
10、ram) the output waveform, make DDS devices an extremely attractive solutionpreferable to less-flexible solutions comprising aggregations of discrete elements. What kind of outputs can I generate with a typical DDS device? DDS devices are not limited to purely sinusoidal outputs. Figure 2 shows the s
11、quare-, triangular-, and sinusoidal outputs available from an AD9833. How does a DDS device create a sine wave? Heres a breakdown of the internal circuitry of a DDS device: its main components are a phase accumulator, a means of phase-to-amplitude conversion (often a sine look-up table), and a DAC.
12、These blocks are represented in Figure 3. A DDS produces a sine wave at a given frequency. The frequency depends on two variables, the reference-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 used, the phase accumulator computes Figure 2. Square-, triangular-, and sinusoidal outputs from a DDS. Figure 3. Components of a direct digital synthesizer.
