【正文】 RAM 中，配置完成后， FPGA 進(jìn)入工作狀態(tài)。 ALTERA FLEX10K 系列 FPGA,規(guī)模從一萬(wàn)門到十萬(wàn)門 ,可提供 720～ 5392 個(gè)觸發(fā)器及 6144～ 24576 位 RAM,提供 30ns、 40ns 及 50ns 等幾個(gè)速率等級(jí) ,可適應(yīng)18～ 105MHz 的信號(hào)處理速率。 (3） FPGA 內(nèi)部有豐富的觸發(fā)器和 I／ O 引腳。 AD9850 接口控制簡(jiǎn)單，可以用 8 位并行口或串行口直接輸入頻率、相位等控制數(shù)據(jù)。這些芯片集成度高，內(nèi)部都集成了 D／ A 轉(zhuǎn)換器，精度最高可達(dá) 12bit。當(dāng)然一味靠增加波形ROM 的深度和字長(zhǎng)的方法來(lái)減小雜散對(duì)性能的提高總是有限的。 當(dāng) DDS 相位累加器采用 32 位字長(zhǎng)，時(shí)鐘頻率為 30MHz 時(shí)，它的輸出頻率間隔可達(dá)到 ΔfDDS =fc/2N =50*106≈ =10mHz。 相位累加器利用 Nbit 二進(jìn)制加法器的模溢出特性來(lái)模擬理想正弦波的 2π相位周期。累加寄存器將加法器在上一個(gè)時(shí)鐘脈沖作用后所產(chǎn)生的新相位數(shù)據(jù)反饋到加法器的輸入端，以使加法器在下一個(gè)時(shí)鐘脈沖的作用下繼續(xù)與頻率控制字相加。 DDS 的基本原理及性能特點(diǎn) 直接數(shù)字頻率合成 (Direct Digital Synthesis,簡(jiǎn)稱 DDS)技術(shù)是頻率合成領(lǐng)域中的一項(xiàng)新技術(shù)。利用頻 率合成技術(shù)制成的信號(hào)發(fā)生器，通常被稱為頻率合成器。 直接數(shù)字式頻率合成（ DirectDigitalFrequencySynthesis，簡(jiǎn)稱 DDS 或 DDFS）是近年來(lái)發(fā)展起來(lái)的新的頻率合成技術(shù)。目前在各種無(wú)線電臺(tái)中使用的頻率合成器普遍采用可變數(shù)字式鎖相環(huán)頻率合成器，通過(guò) CPU 控制可獲得不同的頻點(diǎn)。頻率合成器既要產(chǎn)生所需要的頻率 ,又要獲得純凈的信號(hào)。但其取樣時(shí)頻率較高 ,對(duì)硬件的要求也較高 ,而且常需多級(jí)分頻或采用高性能的鎖相環(huán) ,其中分頻式的任意波形發(fā)生器頻率分辨率低 ,鎖相式的任意波形發(fā)生器頻率切換速度慢。 程序控制輸出方式 計(jì)算機(jī)根據(jù)波形的函數(shù)表達(dá)式，計(jì)算出一系列波形數(shù)據(jù)瞬時(shí)值，并定時(shí)地逐個(gè)傳送給 D／ A 轉(zhuǎn)換器，合成出所需要的波形。s products more representative. Such as the AD7008, AD9850, AD9851, AD9852, AD9858 and so on. The system clock frequency ranging from 30MHz to 300MHz, in which the system clock of the AD9858 is reached lGHz. The chips also have the modem function. Such as the AD7008 quadrature modulation signal can be generated, while the AD9852 can also be generated FSK, PSK, amplitude modulation and linear frequency modulation signal. These highly integrated chips, are integrated within the D / A converter, the accuracy of up to 12bit. At the same time have adopted a number of optimization designed to improve performance. because these chips are mostly used in water technology, water technology through the use of the phase accumulator to increase the operating frequency, allowing the output frequency of DDS chip can be further improved. Water through the use of technology in the phase accumulator to ensure that the premise of the operating frequency, the phase accumulator word length can be designed for longer, such as the AD9852 has reached the phase accumulator 48. Models rather than 32 before, so that the output signal of the frequency resolution significantly improved. The use of DDS technology to produce the DDS arbitrary waveform signal generator is a relatively new type of signal source, and has been widely put into use. It is not only capable of producing the traditional function of the signal generator can produce sine, square, triangle wave, sawtooth wave, but also can generate arbitrary waveform editor. Due to the characteristics of the DDS can also be very easy to produce some digital modulation signals, such as FSK, PSK, etc.. Some highend signal generator can even have a munication signal. At the same time, the frequency resolution of the output waveform, frequency and other indicators of accuracy are greatly improved. HP33120 panies such as HP can generate the lOmHz15MHz sine and square wave, but also can produce lOmHz5MHz of arbitrary waveform, but also have the modulation function, can be AM, FM, FSK, Burst, Sweep signal. HP39?？梢?jiàn)，基于 DDS 技術(shù)的波形發(fā)生器能實(shí)現(xiàn)高穩(wěn)定度、高精度、高分辨率的波形輸出，具有頻率切換速度快、體積小、價(jià)格便宜的特點(diǎn) ,是一種很有發(fā)展前途的信號(hào)源。并且具有了和 PC 機(jī)良好的接口，可以通過(guò) WINDOWS界面的程序進(jìn)行任意波形的編輯。它不僅能產(chǎn)生傳統(tǒng)函數(shù)信號(hào)發(fā)生器能產(chǎn)生的正弦波、方波、三角波、鋸齒波，還可以產(chǎn)生任意編輯的波形。這些芯片還具有調(diào)制功能。為了提高信號(hào)源輸出頻率穩(wěn)定度，可以采用晶體振蕩器等方法來(lái)解決。為了滿足頻率個(gè)數(shù)多 的要求，可以采用頻率合成技術(shù)，即通過(guò)對(duì)頻率進(jìn)行加減乘除運(yùn)算，可從一個(gè)高穩(wěn)定度和高精確度的標(biāo)準(zhǔn)頻率源，產(chǎn)生大量的具有同一穩(wěn)定度和精確度的不同頻率。如 AD7008 可以產(chǎn)生正交調(diào)制信號(hào)，而 AD9852 也可以產(chǎn)生 FSK、 PSK、線性調(diào)頻以及幅度調(diào)制的信號(hào)。由于 DDS 的自身特點(diǎn)，還可以很容易的產(chǎn)生一些數(shù)字調(diào)制信號(hào)，如 FSK、 PSK 等。 除了在儀器中的應(yīng)用外， DDS 在通信系統(tǒng)和雷達(dá)系統(tǒng)中也有很重要的用途。 所以本設(shè)計(jì)采用此方案。s HP33250 can have the 1uHz80MHz sine and square wave, resulting in the 1uHz to 25MHz arbitrary waveform. BK PRECISION pany level 4070A Arbitrary Waveform function generator sine wave and square wave output frequency , frequency resolution 10mHZ. At the same time, also has AM, FM, PM, SSB, BPSK, FSK, Burst, DTMFGeneration and DTMFDetection function. And have a good machine and the PC interface, the interface can process WINDOWS arbitrary waveform editor. In addition to the application of instruments, DDS in munications systems and radar systems are also very important purposes. DDS can be more easily adopted by some of the monly used modulation munication signal, such as: frequency shift keying (FSK), binary phase shift keying (BPSK) and Quadrature Phase Shift Keying (QPSK) and so on. DDS can generate two quadrature phase signal strictly in the quadrature modulator and demodulator in a wide range of applications, this is a good local oscillator. In addition with the integrated circuit manufacturing process of gradual improvement through the use of advanced technology and lowpower design, digital integrated circuits have a speed greatly improved. Now, its latest operating frequency of the DDS chip can reach 1GHz, so that could have a relatively wide frequency band of the output signal. To further enhance the DDS output frequency, resulting in a lot of DDS technology and other methods of frequency synthesis. Such as when the output signal is a highfrequency narrowband signal can be used when the method of filtering expansion mixer output DDS, the DDS can also be used to generate highfrequency spec