基于FPGA的DDS波形发生器的设计论文(8)

哈尔滨工业大学华德应用技术学院毕业设计（论文）

【传统信号发生器】

信号发生器又称信号源或振荡器，在生产实践和科技领域中有着广泛的应用。各种波形曲线均可以用三角函数方程式来表示。能够产生多种波形，如三角波、锯齿波、矩形波（含方波）、正弦波的电路被称为函数信号发生器。函数信号发生器在电路实验和设备检测中具有十分广泛的用途。例如在通信、广播、电视系统中，都需要射频（高频）发射，这里的射频波就是载波，把音频（低频）、视频信号或脉冲信号运载出去，就需要能够产生高频的振荡器。在工业、农业、生物医学等领域内，如高频感应加热、熔炼、淬火、超声诊断、核磁共振成像等，都需要功率或大或小、频率或高或低的振荡器。函数信号发生器的实现方法通常有以下几种：

（1）用分立元件组成的函数发生器：通常是单函数发生器且频率不高，其工作不很稳定，不易调试。

（2）可以由晶体管、运放IC等通用器件制作，更多的则是用专门的函数信号发生器IC产生。早期的函数信号发生器IC，如L8038、BA205、XR2207/2209等，它们的功能较少，精度不高，频率上限只有300kHz，无法产生更高频率的信号，调节方式也不够灵活，频率和占空比不能独立调节，二者互相影响。

（3）利用单片集成芯片的函数发生器：能产生多种波形，达到较高的频率，且易于调试。鉴于此，美国美信公司开发了新一代函数信号发生器ICMAX038，它克服了（2）中芯片的缺点，可以达到更高的技术指标，是上述芯片望尘莫及的。MAX038频率高、精度好，因此它被称为高频精密函数信号发生器IC。在锁相环、压控振荡器、频率合成器、脉宽调制器等电路的设计上，MAX038都是优选的器件。

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哈尔滨工业大学华德应用技术学院毕业设计（论文）

附录2 英文参考资料

【DDS waveform generator】

DDS The basic working principle of:

Direct digital frequency synthesizer is used digital technology, by controlling the phase the rate of change, a direct result of a variety of different frequency signals in a frequency synthesis method. The basic structure of DDS as shown in Figure 1, which is mainly from the phase accumulator, sine ROM tables, D / A converter and low-pass filter constituted.

Reference clock fr by a stable crystal oscillator. Phase accumulator by the N-bit adder with the N-bit phase register cascade structure, similar to a simple adder. Each to a clock pulse frequency control adder to the output data with the accumulated phase register phase data are added together, the sum of the results sent to the phase register of data input. Phase register will be a clock in the last adder After the effects of the new phase data generated by feedback to the adder input, so that adder in the next one under the action of the clock and frequency control data to continue to add. In this way, the reference clock phase accumulator under the effect of linear accumulation phase, when the full volume of the phase accumulator accumulating an overflow arises complete a cyclical movement, the cycle is the DDS frequency synthesis of signals in a cycle, accumulator overflow frequency is the DDS output signal frequency.

In the reference clock fr under the control of frequency control word from the accumulator to accumulate the corresponding phase data to this data as a sample address, to address the sine ROM table phase - amplitude transformation, you can at a given time to determine the output waveform amplitude. DAC digital form will be converted into the required wave amplitude of the analog form of synthesized frequency signal, low-pass filter used to filter out unwanted sample

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哈尔滨工业大学华德应用技术学院毕业设计（论文）

components, which can be determined by the frequency control word change in the output of a continuous sine wave .

DDS output frequency f0 and the reference clock fr, the phase accumulator word length N and frequency control of the relationship between the FSW as:; DDS frequency resolution as follows:; due to the output of DDS by the Nyquist sampling theorem the maximum frequency restrictions, DDS The maximum output frequency is fr / 2, but in the actual design of the DDS system, due to the non-ideal nature of the output filter, the general output signal can only reach the maximum frequency reference clock frequency fr of 40%.

【Traditional signal generator】

Signal Generator also known as source or oscillator, in the production practice and science and technology has a broad application. A variety of wave curves can be expressed in trigonometric equation. Can produce a variety of waveforms, such as the triangle wave, sawtooth, rectangular wave (including square), sine wave circuit is called the function signal generator. Function generator experiments and equipment testing at the circuit has a very wide range of uses. For example, in telecommunications, broadcasting, television systems, the need to radio-frequency (HF) emission, where the radio waves is the carrier, the audio (low frequency), video signal or pulse signal carried out, it is necessary to produce high-frequency oscillator. In industry, agriculture, bio-medical and other fields, such as the high-frequency induction heating, melting, quenching, ultrasound, magnetic resonance imaging, we need power, large or small, or high or low frequency oscillator. Function Generator implementations usually have the following:

(1) with a function generator composed of discrete components: usually is a single function generator and the frequency is not high, their work is not very stable and difficult to debug.

(2) can be transistors, such as general-purpose op amp IC device production, more than that is a function of signal generator IC specifically produced. Early in Function Generator IC, such as the

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哈尔滨工业大学华德应用技术学院毕业设计（论文）

L8038, BA205, XR2207/2209 so that they function less accuracy is not high, frequency upper limit is only 300kHz, can not generate higher frequency signals, adjustment method is also less flexible, frequency and accounted for air ratio can not be independent …… 此处隐藏：3676字，全部文档内容请下载后查看。喜欢就下载吧 ……