【正文】 結(jié)論 使 DDS和 MCU控制器組合使用，系統(tǒng)可以導(dǎo)出的數(shù)值控制消費者的需要的信號源，它具有的優(yōu)點，如良好的輸出的波形，頻率準(zhǔn)確，可靠的穩(wěn)定性和高占空比。占空比： 10％ ? 100％，差異≤ 1％。 此功能是基于數(shù)字頻率合成原則，它把輸入頻率傳送到相應(yīng)的控制字，然后一步一步結(jié)合相位預(yù)計，在記憶體中輸出波形數(shù)據(jù)表。這兩個模塊可以通過外側(cè)中斷和定時中斷被控制。一個很好的平滑的輸出波形，可以通過使用低通有源功率濾波實現(xiàn)。 連接到精確的時鐘源和寫入頻率相位控制字后， AD9850的可以產(chǎn)生可編程頻率和相位可編程的模擬正弦波輸出波，這可以用來作為直接的高頻信號源，或者通過高速比較器被轉(zhuǎn)移到矩形波。 數(shù)控 DDS 信號源系統(tǒng)設(shè)計分析 系統(tǒng)使用 STM32 作為控制核心和 AD9850作為發(fā)生器。 N 相位累加器的位數(shù)，不變。 正弦查詢表格包含一個周期正弦波，每個數(shù)字幅度信息地址對應(yīng)于 0? 360度的正弦波的相位點。其它頻率合成方法相比 , 直接數(shù)字頻率合成器（ DDS）一直以其優(yōu)良的特性在現(xiàn)代頻率合成技術(shù)中最流行的趨勢。信號發(fā)生器 。 f c external referenced clock frequency, unit: Hz。 Phase Accumulator。 DAC Abstract. Its advantage to use DDS chip is output signal frequency bigger, and precision higher, But users can39。 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 acplish 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 phaseextent 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 32bit ARMbased 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 highspeed parator. The AD9850 can realize the entire numerical frequency bining. The core of the programmable DDS is the phase accumulator, it is posed 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 frequencyprogrammable and phaseprogrammable output of analog sine wave, which can be used as the direct frequency signal source or be transferred into rectangular wave through highspeed parator. With the 125 MHz clock, 32bit frequency control word can carry out the output frequency resolution ratio of AD9850 with Hz[4]. DAC0832 module The circuit exports the phase data sheet to DAC0832 from STM32 and gets corresponding wave form by DA converting. The stepbystep adjusting phase amounts can create arbitrary frequency, the PWM signal from the STM32 transfers into the corresponding voltage by lowpass 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 DAC circuit PWM converting DA circuit The lowpass filtered PWM signal from STM32 is then stable using the voltage follower, which will yield a stable output voltage。相位累加器 。