通信工程文献翻译——数字合成的正弦波形（直接数字频率合成器DDS）是一种公知的方法已被应用到许多嵌入式应用。这种技术可以用来创建一个积极的数字正弦波形。其它频率合成方法相比, 直接数字频率合成器（DDS）一直以其优良的特性在现代频率合成技术中最流行的趋势。DDS技术实现信号源，可以进行精确控制DDS的频率，输出波形的数值控制电路等。

商业DDS芯片只能导出一个正弦波因为ROM表中的数据形式已经被凝固。如果需要进入任何波形，它可能会真正的由FPGA采用DDS的IP核或硬件描述语言等方式来实现，然而, 这种方式成本费用高;另一方面，可以任意波形通过开展数字频率结合使用的微控制器单元（MCU）和DA转换实现。实验和应用测试表明，数控信号源所组成的STM32微控制器和DDS芯片可以很好地工作。

DDS和波形编程模式

DDS系统的核心是相位累加器的框架，它是由一个ADR和一单位相位寄存器组成的。当任何时钟到来时，相位寄存器增加步长，相寄存器的输出与相位控制字相加，然后输出导入到正弦查询形成地址。

正弦查询表格包含一个周期正弦波，每个数字幅度信息地址对应于0/360度的正弦波的相位点。测绘数字信号驱动DAC并模拟输出值。

相位寄存器将返回到原来的状态时，2N/Mfc时钟；频率控制字与输出信号的频率成正比；合成所需的频率信号，它需要完成以下步骤：；1.控制每个采样相位增量和积累（频率控制字K），；2.转换成相应的正弦振幅2pi积累阶段，使用RO；3.采用DAC代码转换成模拟信号电压变化幅度；4.电压信号，DAC出口是阶梯波的形式，实现所需；数控DDS信号源系统设计分析；系统使用相位寄存器将返回到原来的状态时，2N/ M fc时钟完成。因此，DDS系统输出一个正弦波的正弦查询表时，完成一个周期。输出正弦波的周期和频率为TO - 输出正弦波周期，单位：秒; TC - 外部参考时钟周期，单位：秒; M - 相位寄存器累计步长，恒定f输出 - 输出正弦波频率，单位：赫兹; fc - 外部参考时钟频率，单位为赫兹; N - 相位累加器的位数，不变。

频率控制字与输出信号的频率成正比。为了描述清楚，正弦波的形式是一个向量转换的相位周期，相位周期与正弦波的一个周期相匹配......

The digitally synthesized sine waveform (Direct Digital Synthesis, DDS) is a well-known method and has been applied to many embedded applications [1]. This technique can be used to create a positive digital sine waveform. Compared to other frequency composing method, Direct Digital Frequency Synthesis(DDS) has been the most popular trend in modern frequency synthetic technique for its excellent characteristics. The signal source that the DDS technology realizes can carry out accurate controlling on DDS frequency , extent , phase exporting wave form's etc. by numerical control circuit, the system making use of this method has many merits such as stability, reliably and accuracy.

The commercial DDS chip can only export a sine wave for the data in the ROM form already has been solidified. If needing to come into being any wave form, it may come true by the way that FPGA adopts DDS IP core or hardware describe language etc, however, the cost of This way cost is high; on the other hand, any wave form can be achieved by making use of micro controller unit (MCU) to carryout figure frequency combining and DA converting. The experiment and applying testing have shown that the numerical control signal source composed of STM32 micro controller and DDS chip can work well.

DDS and wave form programming pattern

The core of DDS system is phase accumulator carriage, and it is composed of a ADR and one unit phase register. When any clock comes, the phase register increases by with the step length, phase register output and phase control word add together, and then the output is imported to sine inquiry form address.

The sine inquiring form includes the numeral extent information of one-period sine wave, each address corresponds to the phase dot of 0~360 degrees of the sine wave. The mapping digital Signal drives DAC and outputs analog value. 

The phase register will return to the original state when the 2N/M fc clock is finished. Accordingly, the DDS system output a sine wave when the sine inquiring form finish a circle. The output sine circle and frequency is TO --output sine wave circle, unit: s; TC --external referenced clock circle, unit: s;M --accumulated step length of phase register, constant; f out --output sine wave frequency, unit: Hz; f c --external referenced clock frequency......