中英文资料外文翻译文献Design of Digital Controlled Signal Generator Based on DDS and MCU Keywords: DDS; MCU; Signal generator; Phase Accumulator; DAC
Abstract. Its advantage to use DDS chip is output signal frequency bigger, and precision higher, Butusers 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 designthe digital controlled signal generator. The System has the advantage of output good qualitywaveform, frequency of precision and stability ,and high frequency, empty, amplitude and phase is tostep into the need.
Introduction
The digitally synthesized sine waveform (Direct Digital Synthesis, DDS) is a well-known method andhas been applied to many embedded applications [1]. This technique can be used to create a positivedigital sine waveform. Compared to other frequency composing method, Direct Digital FrequencySynthesis(DDS) has been the most popular trend in modern frequency synthetic technique for itsexcellent characteristics. The signal source that the DDS technology realizes can carry out accuratecontrolling 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 hasbeen solidified. If needing to come into being any wave form, it may come true by the way that FPGAadopts DDS IP core or hardware describe language etc, however,the cost of This way cost is high; onthe 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 shownthat the numerical control signal source composed of STM32 micro controller and DDS chip canwork 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 unitphase register. When any clock comes, the phase register increases by with the step length, phaseregister output and phase control word add together, and then the output is imported to sine inquiryform 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 signaldrives 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 circleand 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 describeclearly, the sine wave form is as one vector turns around phase circle, the phase circle matche
s alongwith a cycle sine wave. Every sampling pots in wave form corresponds to a phase dot of the phasecircle.
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 thecorresponding 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
isachieved 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-basedmicro controller with 128 K byte flash memory.
The two signal output of STM32 can be achieved by controlling AD9850 and DAC0832 outputsimultaneously. The system designs block diagram is shown in Fig. 1. One signal output can generate30 MHz sine wave and rectangular wave by controlling AD9850, the other output generate any waveform with its frequency less than 10 KHz by numerical frequency mixture of DAC0832.
controller翻译中文
Fig. 1 System designs block diagram
Hardware design
AD9850 module
AD9850 contains the DDS system and high-speed comparator. The AD9850 can realize the entirenumerical frequency combining. The core of the programmable DDS is the phase accumulator, it iscomposed 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 sinewave, which can be used as the direct frequency signal source or be transferred into rectangular wavethrough 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 waveform by DA converting. The step-by-step adjusting phase amounts can create arbitrary frequency, thePWM 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 tunedappropriately. 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, whichwill yield a stable output voltage; the voltage can be adjusted by tuning the PWM dutyfactor. Thesystem output t
hree PWM signals, which controls AD9850 output extent, dutyfactor and the outputextent 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. Anexcellent smooth output waveform can be achieved by using the low-pass active power filtering. Theamplification circuit and the filtering circuit is showed in Fig. 4.
Software design
And the system software mainly include AD9850 driving module, DAC0832 driving module, thestep-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-windowpattern 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 manywindows and control buttons. By means of invoking the corresponding windows and control with thefeedback 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 moduleand DAC0832 module drive, respectively. The two modules can be controlled by means of the outsideinterruption 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 chooseoperation pattern.

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