DDS信号发生器外文资料翻译--基于DDS和单片机数字控制信号发生器的设计

Design of Digital Controlled Signal Generator Based on DDS and MCU

Yinjun Chena, Zehuai Yuan

Faculty of Electronic Information and Mechanical Electrical Engineering, Zhaoqing University,

Zhaoqing 526061, China

Keywords: DDS; MCU; Signal generator; Phase Accumulator; DAC

Abstract. Its advantage to use DDS chip is output signal frequency bigger, and precision higher, But users can't change the output signal waveforms. The MCU can produce the required arbitrary waveforms, but its program execution of the order limit the speed.So we use their Synergy to design the digital controlled signal generator. The System has the advantage of output good quality waveform, frequency of precision and stability ,and high frequency, empty, amplitude and phase is to step into the need.

Introduction

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 carry out 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 output sine circle and frequency are

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, unit: Hz; N --phase accumulator digit, constant.

The relationship among the frequency control word, and the output signal frequency and the referenced clock frequency are:

Frequency control word is directly proportional to the output signal frequency. In order to describe clearly, the sine wave form is as one vector turns around phase circle, the phase circle matches along with a cycle sine wave. Every sampling pots in wave form corresponds to a phase dot of the phase circle.

To synthesis the required frequency signal, it needs to accomplish the following steps

1. Controlling every sampling increment of phase and accumulating them (frequency control word K), output 2 pi cumulated phase (using phase accumulator).

2. Converting 2 pi accumulating phase into the corresponding sine amplitude, use ROM to store the corresponding phase-extent form of sine function in general.

3. Use DAC to change extent code into the signal simulating voltage.

4. The voltage signal that DAC exports is ladder wave form , the required simulation voltage out is achieved after LPF smoothing.

Numerical control DDS signal source system designs analysis

System uses the STM32 as control core and the AD9850 as generator. STM32 is 32-bit ARM-based micro controller with 128 K byte flash memory.

The two signal output of STM32 can be achieved by controlling AD9850 and DAC0832 output simultaneously. The system designs block diagram is shown in Fig. 1. One signal output can generate 30 MHz sine wave and rectangular wave by controlling AD9850, the other output generate any wave form with its frequency less than 10 KHz by numerical frequency mixture of DAC0832.

Fig. 1 System designs block diagram

Hardware design

AD9850 module

AD9850 contains the DDS system and high-speed comparator. The AD9850 can realize the entire numerical frequency combining. The core of the programmable DDS is the phase accumulator, it is composed of a ADR and a N bit phase register, N is for 24 ~ 32.

After connecting to the accurate clock source and writing the frequency phase control word, AD9850 can generate the frequency-programmable and phase-programmable output of analog sine wave, which can be used as the direct frequency signal source or be transferred into rectangular wave through high-speed comparator.

With the 125 MHz clock, 32-bit frequency control word can carry out the output frequency resolution ratio of AD9850 with 0.0291 Hz[4].

DAC0832 module

The circuit exports the phase data sheet to DAC0832 from STM32 and gets corresponding wave form by DA converting. The step-by-step adjusting phase amounts can create arbitrary frequency, the PWM signal from the STM32 transfers into the corresponding voltage by low-pass filter, therefore, the referenced voltage of DAC0832 is controlled, furthermore, the output wave form extent is tuned appropriately. The digital to analog conversion circuit is shown in Fig.2

Fig. 2 DAC circuit

PWM converting DA circuit

The low-pass filtered PWM signal from STM32 is then stable using the voltage follower, which will yield a stable output voltage; the voltage can be adjusted by tuning the PWM dutyfactor. The system output three PWM signals, which controls AD9850 output extent, dutyfactor and the output extent of DAC0832, respectively,. Fig. 3 shows the PWM controls DA transferring circuit.

Fig. 3 PWM controlled DA converting circuit

Fig. 4 Export amplification and the wave filtering circuit. (a) amplification circuit; (b) filtering

circuit

Amplification and wave filtering circuit

The amplification circuit will export amplified wave form and modify the factor of amplification. An excellent smooth output waveform can be achieved by using the low-pass active power filtering. The amplification circuit and the filtering circuit is showed in Fig. 4.

Software design

And the system software mainly include AD9850 driving module, DAC0832 driving module, the step-by-step automation module, PWM-converting-DA module and uC/GUI figure supporting system implanted in procedure. The operation interface is full of humanization for the

multi-window pattern is adopted. The design process of the system software is shown in Fig. 5.

Implanted uC/GUI

The numerical control signal source has used the uC/GUI software sufficiently to establish many windows and control buttons. By means of invoking the corresponding windows and control with the feedback information, the peripheral equipment operated under the control of the system.

The external equipment is mainly separated into two drivers, the drive being an AD9850 module and DAC0832 module drive, respectively. The two modules can be controlled by means of the outside interruption and timing interruption.

AD9850 Drive

AD9850 has 40 control words, among them, 32-bit is used for frequency control, 5-bit is used for the phase control, 1-bit is used for the power source dormancy control, 2-bit is used to choose operation pattern.

Fig. 5 Systematic procedure flow chart

This 40 control words may arrive at AD9850 by concurrence way or serial way, in the concurrence way, 8 data highway generals can transfer the data to a register.

After repeating 5 times, the 40-bit data is loaded into the frequency / phase data register (for refreshing DDS output frequency and phase) at the FQ-UD rising edge, meanwhile, the address pointer is reset to the first input register

Then the 8-bit data is loaded at the W-CLK rising edge, and the pointer is set to the next input register. After repeating 5 times of W-CLK rising edge, the W-CLK rising edge will work no longer until the reset signal comes or the address pointer is reset to the first input register by the FQ-UD rising edge.

The procedure operate AD9850 module through the bottom function, as

void ad9850(

double frequency, //frequency

unsigned char phase, //phase

unsigned char mode, //pattern

unsigned char power //source

)

The DAC0832 driven module

In the design of the numerical control signal source, DAC0832 is defined as single buffered pattern, when the 8 bit Parallel data D0~D7 is input, the DA will transfer data in the CS.

The bottom function of void DA0832(u8 value)can invoke Out_To_DDS0832(double Frequency,u8 type) function and control the defined wave form and frequency.

This function is based on figure frequency composes principle, it transfers the input frequency into corresponding control word, and then combing phase step-by-step expect, output wave form data sheet in memory.

The extent and dutyfactor can be tuned through invoking Adjust_Vpp() and Adjust Duty() Step-by-step automation procedure

A step-by-step automation procedure brick is added to the design to define the frequency range, step-by-step rate , step-by-step amounts , ascending or lapse, cycling pattern.

The step-by-step automation function can be realized through invoking Auto

Step(AutoStepStr*AS) and passing memory structure type to a function.

Test the experiment and data analysis

The DDS numerical control signal source can import the various changeable control words by a touching screen, and then accurately control the signal frequency, dutyfactor, extent and phase. Figure 6 shows the corresponding experimental wave forms.

Fig. 6 The oscillograph exports experiment picture (a) 1 KHz wave form output; (b) 1 MHz wave

form output; (c) 20 MHz wave form output.

With the oscillograph testing, it shows that the circuit work stably and rightly. The various parametric index exhibit fine numerical control effect.

a. Output frequency range: 1Hz—30MHz，peak-to-peak value: 50mV～10V；dutyfactor:

10%~100%, difference≤1%。

b. Export the sine wave, sawtooth wave rectangular wave, triangle wave and arbitrarily wave

form.

c. Continuous Step-by-step adjustment of frequency, dutyfactor, extent and phase.

d. The operation of the touching screen includes suppositional keyboard, sliding strip and various suppositional control carry out entering operation, and the every parameters can be

demonstrated visually.

e. Step-by-step automation, definition of: maximum value , minimum value , step-by-step rate , step-by-step amounts , ascending or lapse, cycling or not.

Numerical control reform advantage of signal source

The designed numerical control signal source is applied to the lathe reform experiment. The main targets of the numerical control system are the coordinate axis displacement (including displacement speed , direction , location etc.) , the control message originates from numerical control treating or moving control procedure mainly.

Therefore, systematic the most fundamental composition of the numerical control system should include three parts: The input/output procedure device, numerical control equipment and the servo drives.

Conclusions

Making compound use of DDS and MCU controller, the system can exported the numerical control signal source as the consumer need, it has the merits such as good exporting wave form, frequency accuracy, reliable stability and high dutyfactor. Each parameter and be easily adjusted by touching a screen, the experiments show that the various parametric indexes have fine numerical control effect.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (No: 61006075) and Guided Projects on Integration of Production, Education and Research of Guangdong Province (No：2011B090400253).

References

[1] Lygouras J. N., Tarchanidis K. N., Tsalides Ph. G., “Suspended Sediment and Dye Concentration Measurements Using a Digital Techniques”, Int. J. Electronics, 87, No.1, pp 107, (2000).

[2] Webster J. G. Ed., “Tactile Sensors for Robotics and Medicine”, Wiley, New York, (1988).

[3] Dally J. W., Rilley W. F., Mcconnel K.G., “Instrumentation for Engineering Measurements”, Wiley, New York, (1993).

[4] Tarchanidis K. N., Ioannidis I. N., Kakkalis I. K. And Lygouras J. N., “FLEXIMAT, an Integrated System Scanning the Bending of Any Matress.”, Int. Workshop on Virtual and Intelligent Measurement Systems, VIMS 2000, Annapolis, MD, USA, 29-30 April 2000, pp 115, (2000).

[5] Koukourlis C. S., Voulgaris N. C., “A Digital Method for Sinewave Generation.” Archiv fur Electrotechnik, 72, pp 327, (1989).

[6] Koukourlis Chr. S, Trigonidis V. K., Sahalos J. N., “Differential Synchronous Demodulation for Small Signal Amplitude Est imation.”, IEEE Instrumentation and Measurement, 42, No. 5, pp 926, (1993).

基于DDS和单片机数字控制信号发生器的设计

关键词: DDS; MCU;信号发生器;相位累加器;DAC

摘要:它的优点，使用DDS芯片输出信号的频率更大，精度更高，但用户不能改变输出信号的波形。MCU可以产生所需的任意波形，但其程序执行的顺序限制速度。因此，我们利用它们之间的协同设计数字控制信号发生器。该系统的优点是输出质量好的精度和稳定性，波形，频率和高频率的，空的振幅和相位是步入需要。

介绍

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[1]。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，程度，相输出波形的数值控制电路等,系统利用这种方法有许多优点，如安定，可靠和准确度。

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。输出正弦波周期和频率是:

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。频率控制字和输出信号的频率与参考时钟频率之间的关系是：

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。在波形里的每个采样点对应一个相位点的相位周期。

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），输出2 pi累计相位（使用相位累加器）。

2.转换成相应的正弦振幅2 pi积累阶段，使用ROM来存储相应的相位幅度的一般正弦函数形式。

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，实现所需的模拟电压输出低通滤波器平滑后的电压。

数控DDS信号源系统设计分析

系统使用STM32作为控制核心和AD9850作为发生器。STM32是基于ARM的32位微控制器与128 K字节的闪存。

STM32的两个信号输出，可以实现同时通过控制AD9850的和DAC0832输出。该系统的设计的框图如图1所示。一个信号输出通过控制AD9850，可产生30 MHz正弦波和矩形波，其他输出的任意波形及其频率低于10千赫是通过频率数值混合器DAC0832产生的。

图1 系统设计框图

硬件设计

AD9850的模块

AD9850包含DDS系统和高速比较器。 AD9850可以实现对整个数字频率相结合。可编程的DDS的核心是相位累加器，它是由ADR和一个N位相位寄存器组成，N为24?32。

连接到精确的时钟源和写入频率相位控制字后，AD9850的可以产生可编程频率和相位可编程的模拟正弦波输出波，这可以用来作为直接的高频信号源，或者通过高速比较器被转移到矩形波。

通过125 MHz时钟，32位频率控制字可以把AD9850的输出频率分辨率展开到0.0291赫兹[4]。

DAC0832模块

电路是通过DA从STM32向DAC0832输出相位数据表并得到相应的波形。一步一步的调节相量，可以创建任意的频率，PWM信号通过低通滤波器从STM32传输到相应的电压，因此，DAC0832的参考电压是被控制的，而且，输出的波形幅度调节适当。数字到模拟转换电路，如图2所示:

图2 DAC电路

PWM转换DA电路

低通滤波器的PWM信号从STM32到稳定使用电压跟随器，然后稳定将产生一个稳定的输出电压，通过调整PWM占空比可调节电压。该系统输出的3个PWM信号，它分别控制AD9850的输出范围，占空比和输出DAC0832的范围。图3显示出的PWM控制DA传输电路。

放大和滤波电路

放大电路将输出放大波形和修改放大的因素。一个很好的平滑的输出波形，可以通过使用低通有源功率滤波实现。放大电路和滤波电路在图4中显示。

图3 PWM控制DA转换电路

图4 导出放大和滤波电路:（a）放大电路（b）滤波电路

软件设计

系统软件主要包括AD9850的驱动模块，DAC0832驱动模块，一步一步的自动化模块，PWM转换DA模块和uC/ GUI图片支持的系统中植入程序。由于采用多窗口的图案使得操作界面充满人性化。系统软件的设计过程如图5所示。

图5系统程序流程图

植入的uC/ GUI

数控信号源已足够多的使用的uC / GUI软件建立许多窗口和控制按钮。通过调用相应的窗口和控制反馈信息，外围设备在系统的控制下操作。

外部设备主要分为两个驱动器，驱动器AD9850的模块和DAC0832模块驱动。这两个模块可以通过外侧中断和定时中断被控制。

AD9850的驱动器

AD9850具有40个控制字，其中，32位用于频率控制，5位用于的相位控制，1位用于电源休眠控制，2位用于选择运作模式。

这40个控制字可在允许的方式或串行方式到达AD9850，在允许的方式下，8位数据一般可高速将数据传送到寄存器。

重复5次后，在40位的数据被加载到频率/相位数据寄存器（用于刷新的DDS输出频率和相位），同时，上面的FQ-UD上升沿地址指针复位到第一个输入寄存器。

然后8位数据被加载在W-CLK上升沿，将指针设置到下一个输入注册。W-CLK上升沿重复5次后，在W-CLK上升沿将不再工作，直到复位信号或地址指针复位到第一个输入寄存器的FQ-UD上升沿。

程序操作AD9850模块通过底部的功能，作为：

void ad9850(

double frequency, //frequency

unsigned char phase, //phase

unsigned char mode, //pattern

unsigned char power //source

)

DAC0832驱动模块

在设计中的数字控制信号源，DAC0832被定义为单缓冲的模式，当8位并行数据D0?D7被输入，DA将在CS中传输数据。

空的DA0832（U8值）的底层函数可以调用Out_To_DDS0832（双频率，U8型）的功能和控制定义的波形和频率。

此功能是基于数字频率合成原则，它把输入频率传送到相应的控制字，然后一步一步结合相位预计，在记忆体中输出波形数据表。

通过的调用Adjust_Vpp（）的程度和占空因数可调谐和调整印花税（）

一步一步的自动化程序

一步一步的自动化程序砖被添加到设计来定义的频率范围内，一步一步的速度，一步一步的计算，递增或失效，循环模式。一步一步的自动化功能，可实现通过调用自动步骤（AutoStepStr*AS）和通过存储器结构类型的一个函数来实现。

测试实验和数据分析

DDS数字控制信号源能够通过触摸屏导入各种多变的控制字，然后准确地控制信号的频率，占空比，范围和相位。图6给出了相应的实验波形。

图6示波器出口实验图片（a）1千赫兹的输出波形（b）1兆赫兹的输出波形（c）20兆赫兹的输出

波形

用示波器测试，表明该电路工作稳定，正确。各参数指标表现出精细的数值控制效果。

一、输出频率范围：1Hz-30MHz的的峰 - 峰值值：50mV的~~10V;占空比：10％?100％，差异≤1％。

二、输出正弦波，方波，锯齿波，三角波和任意波形式。

三、连续步骤一步调整频率，占空比，幅度和相位。

四、触摸屏的操作包括虚拟键盘，滑条和各种虚拟控制进行输入操作，每一个参数都可以直观演示。

五、一步一步的自动化，定义：最高值，最低值，一步一步的速度，一步一步的计算，按升序或下降，循环或不循环。

数控改革信号源的优势

设计的数值的控制信号源被施加到车床改革实验。主要数控系统的目标是协调坐标轴的位移（包括位移，速度，方向，位置等），该控制消息来源于数控操作或运动控制程序。

因此，系统的数值控制系统的组合物，最根本的包括三个部分：输入/输出的程序的移

动设备，数控设备和伺服驱动器。

结论

使DDS和MCU控制器组合使用，系统可以导出的数值控制消费者的需要的信号源，它具有的优点，如良好的输出的波形，频率准确，可靠的稳定性和高占空比。每个参数，并通过触摸屏幕很容易地调整，实验表明，各种参数指标具有优良的数控效果。

致谢

这项工作是由国家自然科学基金会，中国（无财政支持：61006075）和指导目整合生产，教育及研究广东省（编号：2011B090400253）。

参考文献

[1] Lygouras J. N., Tarchanidis K. N., Tsalides Ph. G., “Suspended Sediment and Dye Concentration easurements Using a Digital Techniques”, Int. J. Electronics, 87, No.1, pp 107, (2000).

[2] Webster J. G. Ed., “Tactile Sensors for Robotics and Medicine”, Wiley, New York, (1988).

[3] Dally J. W., Rilley W. F., Mcconnel K.G., “Instrumentation for Engineering Measurements”, Wiley, New York, (1993).

[4] Tarchanidis K. N., Ioannidis I. N., Kakkalis I. K. And Lygouras J. N.“FLEXIMAT, an ntegrated System Scanning the Bending of Any Matress.”, Int. Workshop on Virtual and Intelligent Measurement Systems, VIMS 2000, Annapolis, MD, USA, 29-30 April 2000, pp 115,(2000).

[5] Koukourlis C. S., Voulgaris N. C., “A Digital Method for Sinewave Generation.” Archiv fur Electrotechnik, 72, pp 327, (1989).

[6] Koukourlis Chr. S, Trigonidis V. K., Sahalos J. N., “Differential Synchronous Demodulation for Small Signal Amplitude Estimation.”, IEEE Ins trumentation and Measurement, 42, No. 5,

pp926, (1993).