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PWM脉冲信号

www.bysj580.com / 2016-11-30
PWM脉冲信号
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1878年,爱迪生开始研究电灯,提出由位于中央的电站向四周地区提供照明的想法。1879年10月,他进一步改进了他的电灯的设计,1882年9月4,纽约Peral街电站的运行标志着电力工业的开始。在Pearl街,由蒸汽机驱动直流发电机向1平方里范围内的59个用户的110V的白炽灯供电,供电负荷最初为30kW。从1882年至1972年,电力工业成长速度惊人,电能价格持续下降,主要原因是由于科技上不断取得的成就和工程界创造性的成果。
由Sprague电力引进的实用的直流电机及白炽灯的发展推动了爱迪生的直流系统的发展。3线220V直流系统的发明在一定程度上提高了供电负荷,但是当输电距离和负荷继续增加,电压成为一大问题。1885年William Stanley发明的经济可行的变压器解决了这一在输电距离和负荷上的限制问题。Stanley在Massachusetts的Great Barrington建立了一个交流配电系统,为150盏灯供电。变压器使得电能可以在更高电压和更低电流传输,降低了线路电压降,使交流系统比直流系统跟具吸引力。美国第一条单相交流线路1889年在Oregon运行,该线路21公里,电压等级为4kV,连接Oregon和Portland。
1888年Nikola Tesla在美国电气工程师协会的会议上,提交了一篇讲解两相感应和同步电机的论文,使得多相系统相对单相系统的优势更加明显了,这更加推进了交流系统的发展。1891年,第一条三相线路在德国运行,传输距离179km,电压等级12kv。在1893年美国(加利福尼亚)的第一条三相线路开始运行,传输距离12km,电压等级2.3kv。Tesla所设想的三相感应电动机逐渐成为工业的主力。
蒸汽电厂的主要燃料是煤,天然气,石油和铀。其中,由于储量丰富,煤是在美国使用最广泛的燃料。虽然,在20世纪70年代早期很多以煤为燃料的电厂都转化为以石油为燃料,然而由于1973年至1974年石油禁运而导致的石油短缺,这一趋势又被反转以燃煤为主,以减少对外国石油的依赖。1957年,相当于90MW汽轮机装机容量,以铀为燃料的核电机组投建,如今,具有1312MW汽轮机装机容量的核电机组在使用中。但是,由于建设费用的增加,申请许可的拖延和公众的舆论阻碍了美国核电容量的增长。
自从20世纪90年代以来,美国新建电厂的燃料一直是天然气。燃气轮机安全,干净,一致认为比其他技术更有效率。截至2001年,天然气的发展趋势一直在加快。据估计,200个大型燃气电厂正在发展中,占据了美国电源规划的75%-90%。然而,天然气价格的提高可能会减慢燃气电厂的发展。
其他类型的电力发电也在使用中,包括风力涡轮发电机;从地壳获得蒸汽或热水形式能源的地热发电厂,太阳电池阵列和潮汐发电厂。这些能源不容忽视,但预计它们不能满足世界未来的大部分能源需求。相反,核聚变能源却能够满足这一需求。大量的研究已经表明,因核聚变能源生产安全,无污染并且节约(经济)电力能源,其将是21世纪后期及以后一项大有可为的技术。核聚变反应消耗的氚,海水是其几乎取之不尽的补给。
最早的交流系统以25Hz, 50Hz, 60Hz和133Hz各种频率运行。1891年60Hz成为美国的标准频率。1893年,通过采用同步换流器,开始使用25Hz系统。但是,这些系统主要用于铁路电气化(很多现在已经退役),因为它们有造成白炽灯闪烁的缺点。加利福尼亚的水利电力部采用50Hz,但是,当1937年Hoover大坝开始运作,频率就转换为60Hz。1949年南加利福尼亚的Edison公司也将频率从50Hz转变为60Hz。今天,60Hz(在美国,加拿大,日本和巴西使用)和50Hz(在欧洲,前苏联,除巴西以外的南美洲,印度以及日本使用)是世界上发电,输电和配电的两个标准频率。60Hz系统的优点在于系统中的发电机,电动机和变压器通常比同等级50Hz系统的设备小。50Hz系统的优点是传输线和变压器的电抗在50Hz时较60Hz时小。
从1902年到1972年美国电力能源以每年大约7%的速度增长。这相当于在70年中每10年电能消耗就增加了一倍。换而言之,每10年电力工业新增的容量等于初始时所建容量的总和。1973/1974的石油禁运之后,每年的增长率就比较缓慢了。1972到1980年美国的千瓦时消耗每年增长3.4%,而1980至2000年每年增长2.1%。
随着负荷的增长,发电机组的规模也在不断的增加。投建较大机组的主要目的就是规模效应,即减少了每千瓦容量的安装成本。不过,发电效率也在稳步的提高。由于机组规模和蒸汽温度、压力的改进,还有蒸汽再加热的使用,使得热效率得到提高,节约了燃料费用和总的运行费用。
传输电压也在不断地提高。从爱迪生的220V三相直流电网到单相4kV和三相2.3kV输电,美国的交流输电电压已经逐步上升到150,230,345,500和现在的765kV。并且1000kV以上的超高压正在研究当中。提高传输电压的目的是为了:(1)提高传输距离和传输容量,(2)线电压下降较小,(3)降低线路损耗,(4)减小每MW输电用地费用,(5)减少输电的投资和运行费用。如今,一条三相765kV的线路能将数千兆瓦的功率输送至几百公里以外。
信号发生器历史:在测试、研究或调整电子电路及设备时,为测定电路的一些电参量,用来模拟在实际工作中使用的待测设备的激励信号。信号源按工作原理可以分为: LC 源、锁相源、合成源等。LC源是直接产生正弦信号,合成源是DDS发展过程:直接频率合成,锁相式频率合成,直接数字频率合成。
信号发生器发展:1、通常分类是按照产生信号产生的波形特征来划分:音频信号源、函数信号源、功率函数发生器、脉冲信号源、任意函数发生器、任意波形发生器、标准高频信号源、射频信号源、电视信号发生器、噪声信号源、调制信号发生器、数字信号源 等。这种分类基本覆盖了航空航天、电子、电力等领电参数测量仪域的每一个角落。2、正弦信号发生器原理:RC,LC等回路产生正弦波。3、方波都是通过正弦波和电压比较器通过比较产生的;脉冲信号发生器:能产生宽度、幅度和重复频率可调的矩形脉冲的发生器可用以测试线性系统的瞬态响应,或用作模拟信号来测试雷达、多路通信和其他脉冲数字系统的性能。函数/任意波形发生器:它综合了各种信号源的优点于一身主要用于模拟输出自然界的一些不规则信号生成标准波形如正弦波、方波、三角波、脉冲波,还可以生成"实际环境"信号,包括在被测试信号发生器设备离开实验室或车间时可能遇到的所有毛刺、漂移、噪声和其它异常事件。
信号源按照应用领域分类: 低频信号发生器(音频),高频信号发生器(射频通信信号),电视信号发生器(电视信号),电视扫频信号发生器(电视信号)等。纵观信号发生器的发展,直接合成数字信号发生器是近几年的发展趋势。Rigol的产品即使采用直接合成技术信号发生器。函数(波形)信号发生器能产生某些特定的周期性时间函数波形(正弦波、方波、三角波、锯齿波和脉冲波等)信号,频率范围可从几个微赫到几十兆赫。除供通信、仪表和自动控制系统测试用外,还广泛用于其他非电测量领域。在现代通讯设备测试中,常常需要一种信号源,既能产生各种模拟和数字调制信号,同时也能根据测试要求改变信号变频电源特征,如电平特性、调制特性、噪声特性、失真特性、互调、串音等,以便对通讯设备的各项接受和发送性能做全面的测试。从目前来看,在如此宽范围内产生复杂的调制信号只能借助于任意波形发生器。
另外,在军用雷达接受机测试中,常常需要多种能模拟现实情况中出现的各种调制现象,以确保其各种接受性能。例如当存在有噪声和杂散回波时,为了实现更精确的信号处理,许多雷达都采用了Barker编码,而利用任意波形发生器做调制源,可以对Barker编码进行模拟,从而产生所需要的测试信号。总之,由于任意波形发生器具有方便产生任意波形的能力,现在已经成为现代军用测试领域内最常用的测试仪器之一。
正弦波: 正弦波发生电路能产生正弦波输出,它是在放大电路的基础上加上正反馈而形成的,它是各类波形发生器和信号源的核心电路,正弦波发生电路也称为正弦波振荡电路或正弦波振荡器
方波:方波是通过电压比较器产生的:比较电压信号(被测试信号与标准信号)大小
三角波:方波电压作为积分运算电路的输入,积分运算电路的输出得到三角波电压
任意波:直接数字合成(DDS)技术信号源的任意波产生方法:直接从波表提取N个点,这N个点是用户自定义的点。DDS:同传统的频率合成技术相比:DDS技术具有极高的频率分辨率,极快的变频速度,变频相位连续,相位噪声低,易于功能扩展和便于全数字化集成,容易实现对输出信号的多种调制。1971年3月美国学者J.Tierncy,C.M.Rader和B.Gold首次提出了直接数字频率合成(Direct Digital Synthesis)技术。这是一种从相位概念出发直接合成所需要的波形的新的全数字频率合成技术。DDS信号发生器原理:原理如同一个CD音乐播放器,存储在光盘上数字信息被读出,转换成模拟波形最后通过扬声器输出。直接数字合成原理:直接数字频率合成(DDS)是采用数字化技术,通过控制频率控制字直接产生所需的各种不同频率信号。DDS主要由参考时钟、相位累加器、正弦查找表、D/A转换器和滤波器等组成。
参考时钟由一个高稳定的晶体振荡器产生,来同步整个频率合成器的各个组成部分。N位加法器与N位相位寄存器级联构成相位累加器,每来一个时钟脉冲,加法器就将频率控制字K与相位寄存器中的数据相加。相位寄存器可以将加法器在上一个时钟作用后产生的新相位数据反馈到加法器的输入端,以使加法器在下一个时钟的作用下继续将相位数据与频率控制字相加。这样,相位累加器在参考时钟的作用下进行线性相位累加。当相位累加器达到上限时,就会产生一次溢出,完成一个周期性的动作,这个周期就是合成信号的一个周期,累加器的溢出频率也就是DDS的合成信号频率。在参考时钟的控制下,频率控制字送入相位累加器。用相位累加器的输出作为正弦查找表的查找地址对正弦表进行查找。查找表中的每个地址代表一个周期正弦波的一个相位点,每个相位点对应一个量化振幅值。因此,这个查找表相当于一个相位/振幅变换器,它将相位累加器的相位信息映射成数字振幅信息。查找后的振幅数据再经过D/A转换器得到相应的阶梯波,最后经低通滤波器对阶梯波进行平滑处理,即可得到由频率控制字决定的连续变化的输出正弦波。正弦波和三角波都可以存在波表中,而方波的实现是有波表中的正弦波经过和一个电压比较器后得出,然后有另一个通道直接简单滤波处理,然后输出。脉冲波也是两种实现方式:现成的DDS单芯片,可编程逻辑和DAC搭建DDS基于"FPGA"的技术设计实现DDS(FPGA,是英文Field Programmable Gate Array,可翻为现场可编程逻辑阵列。它是一种半定制的专用集成电路(ASIC),既具有ASIC的优点,同时也具有可编程逻辑器件的灵活性。2、FPGA的基本特点主要有:1)采用FPGA设计ASIC电路,用户不需要投片生产,就能得到合用的芯片。 --2)FPGA可做其它全定制或半定制ASIC电路的中试样片。3)FPGA内部有丰富的触发器和I/O引脚。4)FPGA是ASIC电路中设计周期最短、开发费用最低、风险最小的器件之一。5)FPGA采用高速CHMOS工艺,功耗低,可以与CMOS、TTL电平兼容。可以说,FPGA芯片是小批量系统提高系统集成度、可靠性的最佳选择之一。
目前FPGA的品种很多,有XILINX的XC系列、TI公司的TPC系列、ALTERA公司的FIEX系列等。)
调制原理的介绍:把基带信号变换成可传输信号的技术。基带信号:是原始的电信号,一般是指基本的信号波形,在数字通信中则指相应的电脉冲。用来控制高频载波参数的基带信号称为调制信号。载波:未调制的高频电振荡(可以是正弦波,也可以是非正弦波)。已调信号:被调制信号调制过的载波信号称为已调波或已调信号。1、在无线遥测遥控系统和无线电技术中调制就是用基带信号控制高频载波的参数(振幅、频率和相位),使这些参数随基带信号变化。2、一般载波的信号都高于基带信号的频率。3、在输入基带信号时,注意信号频率不要超过仪器对应调制要求的最大范围。调制分类:调制方式按照调制信号的性质分为模拟调制和数字调制两类。模拟调制:调幅(AM)、调频(FM) 、调相(PM)、脉宽调制(PWM),数字调制:振幅键控(ASK)、移频键控(FSK)、移相键控(PSK)。1、调制信号为二进制数字信号时,这种调制称为二进制数字调制。在二进制数字调制中,载波的幅度、频率或相位只有两种变化状态。2、ASK:数字幅度调制又称幅度键控。2ASK:二进制幅度键控。FSK:数字频移键控是用载波的频率来传送数字消息,即用所传送的数字消息控制载波的频率。2FSK:二进制数字频移键控。PSK:相移键控。2PSK:二进制相移键控AM(调幅):用调制信号控制载波的振幅,使载波的振幅随着调制信号变化调幅波的频率仍是载波频率调幅波包络的形状反映调制信号的波形。FM(调频):用调制信号控制载波的振荡频率,使载波的频率随着调制信号变化。调频波的振幅保持不变调频波的瞬时频率偏离载波频率的量与调制信号的瞬时值成比.补充:(角度调制是非线性调制,已调信号频谱不再是原调制信号频谱的线性搬移,而是频谱的非线性变换,会产生与频谱搬移不同的新的频率成分。2、角度调制可分为频率调制(FM)和相位调制(PM)。即载波的幅度保持不变,而载波的频率或相位随基带信号变化。3、FM分为窄带调频与宽带调频根据调制后载波瞬时相位偏移的大小,可将频率调制分为宽带调频(WBFM)与窄带调频(NBFM)。
PM(调相)用调制信号控制载波的相位,使载波的相位随着调制信号变化。调相波的振幅保持不变,调相波的瞬时相角偏离载波相角的量与调制信号的瞬时值成比例。PWM(脉宽调制)用调制信号控制脉冲序列中各脉冲的宽度,使每个脉冲的持续时间与该瞬时的调制信号值成比例脉冲序列的幅度保持不变,被调制的是脉冲的前沿或后沿,或同时是前后两沿,使脉冲持续时间发生变化。PWM广泛应用于电源开关电路。如开关电源中,脉宽宽度调制式(PWM)开关型稳压电路是在控制电路输出频率不变的情况下,通过电压反馈调整其占空比,从而达到稳定输出电压的目的。PWM管理电路:需要PWM电路来驱动电机。   
步进电机是一种将电脉冲转化为角位移的执行机构。当步进驱动器接收到一个脉冲信号,它就驱动步进电机按设定的方向转动一个固定的角度(称为"步距角"),它的旋转是以固定的角度一步一步运行的。可以通过控制脉冲个数来控制角位移量,从而达到准确定位的目的;同时可以通过控制脉冲频多路测试仪率来控制电机转动的速度和加速度,从而达到调速的目的。步进电机可以作为一种控制用的特种电机,利用其没有积累误差(精度为100%)的特点,广泛应用于各种开环控制。PWM广泛应用于电源开关电路。如开关电源中,脉宽宽度调制式(PWM)开关型稳压电路是在控制电路输出频率不变的情况下,通过电压反馈调整其占空比,从而达到稳定输出电压的目的。 
PWM只适用于脉冲信号。PWM广泛应用于电源开关电路。如开关电源中,脉宽宽度调制式(PWM)开关型稳压电路是在控制电路输出频率不变的情况下,通过电压反馈调整其占空比,从而达到稳定输出电压的目的。FSK(移频键控):用数字调制信号的0/1控制载波的频率,当数字信号的振幅为高(1)时载波频率为f1当数字信号的振幅为低(0)时载波频率为f2。Burst(突发模式):可为用户提供多种波形函数的脉冲串输出可持续特定数目的波形周期(N循环脉冲串)或应用外部门信号时(为门控脉冲串),可使用任何波形函数。主要应用领域:适用于脉冲电路、逻辑电路的研究、半导体器件参数的测试、电子计算机等。Sweep (扫频)信号发生器产生的信号的频率是连续变化的,它可用来测量系统对频率响应情况主要应用领域:电源的设计检验、放大器设计检测等等。扫频应用范围:高/低频信号接受机和发送机测试,电视信号测试,通信网络测试。垂直分辨率(幅度分辨率):信号源的垂直分辨率是指信号源中可以编程的最小电压增量是仪器数模转换器的二进制字宽度,单位为位,它规定了波形的幅度精度奈奎斯特取样定理规定,取样频率或时钟速率必须至少是生成的信号中最高频谱成分的两倍,以保证精确的复现。采样速率:取样速率通常用每秒兆样点或者千兆样点表示,表明仪器可以运行的最大时钟或取样速率。取样速率影响着主要输出信号的频率和保真度。奈奎斯特取样定理规定,取样频率或时钟速率必须至少是生成的信号中最高频谱成份的两倍,以保证精确的复现输出信号带宽:表明能够输出的信号最高频率分量,常用输出的正弦波最高频率表示。波形存储深度:存储深度是指用来记录波形的采样点数,它决定着波形数据的最大采样样点数量。最高输出频率=采样率×0.4输出信号的带宽常用正弦波输出的最高频率表示。带宽(Fw):带宽是所有测量交流仪器必须考虑的技术指标,指仪器输出或能测量的信号幅度衰减 -3dB 处的最高频率。直接数字合成信号源的带宽一般用正弦波的最高频率表示。
在一些军事、航空、交通制造业等领域中,有些电路运行环境很难估计,在实验设计完成之后,在现实环境还需要作更进一步实验,有些实验的成本很高或者风险性很大(如火车高速实验时铁轨变换情况、飞机试机时螺旋桨的运行情况等),人们不可能长期作实验判断所设计产品(例如高速火车、飞机)的可行性和稳定性等。
 
 英文
In 1878, Thomas A. Edison began work on the electric light and formulated the concept of a centrally located power station with distributed lighting serving a surrounding area. He perfected his light by October 1879, and the opening of his historic Pearl Street Station in New York city on September 4, 1882, marked the beginning of the electric utility industry. At Pearl Street, dc generators, then called dynamos, were driven by steam engines to supply an initial load of 30kW for 110-V incandescent lighting to 59 customers in a 1-square-mile area. From this beginning in 1882 through 1972, the electric utility industry grew at a remarkable pace – a growth based on continuous reductions in the price of electricity due primarily to technological accomplishment and creative engineering.
The introduction of the practical dc motor by Sprague electric, as well as the growth of incandescent lighting, promoted the expansion of Edison’s dc systems. The development of three-wire 220-V dc systems allowed load to increase somewhat, but as transmission distances and loads continued to increase, voltage problems were encountered. These limitations of maximum distance and load were overcome in 1885 by William Stanley’s development of a commercially practical transformer. Stanley installed an ac distribution system in Great Barrington, Massachusetts, to supply 150 lamps. With the transformer, the ability to transmit power at high voltage with corresponding lower current and lower line-voltage drops made ac more attractive than dc. The first single-phase ac line in the United States operated in 1889 in Oregon, between Oregon city and Portland – 21 km at 4 kV.
The growth of ac systems was further encouraged in 1888 when Nikola Tesla presented a paper at a meeting of the American Institute of Electrical Engineers describing two-phase induction and synchronous motors, which made evident the advantages of polyphase versus single-phase systems. The first three-phase line in Germany became operational in 1891, transmitting power 179 km at 12 kV. The first three-phase line in the United States (in California) became operational in 1893, transmitting power 12 km at 2.3 kV. The three-phase induction motor conceived by Tesla went on to become the workhorse of the industry.
In the same year that Edison’s steam-driven generators were inaugurated, a waterwheel-driven generator was installed in Appleton, Wisconsin. Since then, most electric energy has been generated in steam-powered and in water-powered (called hydro) turbine plants. Today, steam turbines account for more than 85% of U.S. electric energy generation, whereas hydro turbine account for about 7%. Gas turbines are used in some cases to meet peak loads.
Steam plants are fueled primarily by coal, gas, oil, and uranium. Of these, coal is the most widely used fuel in the United States due to its abundance in the country. Although many of these coal-fueled power plants were converted to oil during the early 1970s, that trend has been reversed back to coal since the 1973/74 oil embargo, which caused an oil shortage and created a national desire to reduce dependency on foreign oil. In 1957, nuclear units with 90MW steam-turbine capacity, fueled by uranium, were installed, and today nuclear units with 1312 MW steam-turbine capacity ware in service. However, the growth of nuclear capacity in the United States has been halted by rising construction costs, licensing delays, and public opinion.
Starting in the 1990s, the choice of fuel for new power plants in the United States has been natural gas. The gas-fired turbine is safe, clean, more efficient than competing technologies, and uncontroversial. As of 2001, the tread toward natural gas has accelerated. It is estimated that 200 large gas-fired plants are being developed, accounting for 75-90% of planned U.S. Expansion. However, increasing natural gas prices may slow this trend.
Other types of electric power generation are also being used, including wind-turbine generators; geothermal power plants, wherein energy in the form of steam or hot water is extracted from the earth’s upper crust; solar cell arrays; and tidal power plants. These sources of energy cannot be ignored, but they are not expected to supply a large percentage of the world’s future energy needs. On the other hand, nuclear fusion energy just may. Substantial research efforts have shown nuclear fusion energy to be a promising technology for producing safe, pollution-free, and economical electric energy later in the 21st century and beyond. The fuel consumed in a nuclear fusion reaction in deuterium, of which a virtually inexhaustible supply is present in seawater.
The early ac systems operated at various frequencies including 25, 50, 60, and 133 Hz. In 1891, it was proposed that 60 Hz be the standard frequency in the United States. In 1893, 25-Hz systems were introduced with the synchronous converter. However, these systems were used primarily for railroad electrification (and many are now retired) because they had the disadvantage of causing incandescent lights to flicker. In California, the Los Angeles Department of Power and Water operated at 50 Hz, but converted to 60 Hz when power from the Hoover Dam became operational in 1937. In 1949, Southern California Edison also converted from 50 to 60 Hz. Today, the two standard frequencies for generation, transmission, and distribution of electric power in the world are 60 Hz (in the United States, Canada, Japan, Brazil) and 50 Hz ( in Europe, the former Soviet republics, South America except Brazil, India, also Japan). The advantage of 60-Hz systems is that generators, motors, and transformers in these systems are generally smaller than 50-hz equipment with the same ratings. The advantage of 50-Hz systems is that transmission lines and transformers have smaller reactances at 50 Hz than at 60 Hz.
The rate of growth of electric energy in the United States was approximately 7% per year from 1902 to 1972. This corresponds to a doubling of electric energy consumption every 10 years over the 70-year period. In other words, every 10 years the industry installed a new electric system equal in energy-producing capacity to the total of what it had built since the industry began. The annual growth rate slowed after the oil embargo of 1973/74. Kilowatt-hour consumption in the United States increased by 3.4% per year from 1972 to 1980, and by 2.1% per year from 1980 to 2000.
Along with increases in load growth, there have been continuing in creases in the size of generating units. The principal incentive to build larger units has been economy of scale – that is, a reduction in installed cost per kilowatt of capacity for larger units. However, there have also been steady improvements in generation efficiency. For example, in 1934 the average heat rate for steam generation in the U.S. electric industry was 17,950 BTU/kWh, which corresponds to 19% efficiency. By 1991, the average heat rate was 10,367 BTU/kWh, which corresponds to 33% efficiency. These improvements in thermal efficiency due to increases in unit size and in steam temperature and pressure, as well as to the use of steam reheat, have resulted in savings in fuel costs and overall operating costs.
There have been continuing increases, too, in transmission voltages. From Edison’s 220-V three-wire dc grid to 4-kV single-phase and 2.3-kV three-phase transmission, ac transmission voltages in the United States have risen progressively to 150, 230, 345, 500, and now 765 kV. And ultra-high voltages (UHV) above 1000 kV are now being studied. The incentives for increasing transmission voltages have been: (1) increases in transmission distance and transmission capacity, (2) smaller line-voltage drops, (3) reduced line losses, (4) reduced right-of-way requirements per MW transfer, and (5) lower capital and operating costs of transmission. Today, one 765-kV three-phase line can transmit thousands of mega watts over hundreds of kilometers.
In the test, or adjustment of electronic circuits and devices for the determination of some of the electrical parameters of the circuit, the excitation signal of the device under test is used to simulate the actual work.The source can be divided according to the principle: the LC source, phase-locked source, synthetic source.LC source : directly generate a sinusoidal signal.Synthetic source: the DDS development process: direct frequency synthesis, phase-locked frequency synthesis, direct digital frequency synthesis.usually classification is divided in accordance with the characteristics of the waveform of the generated signal generating:
Audio signal source, function signal source, the power function generator, pulse signal source, arbitrary function generator, arbitrary waveform generator,
Standard frequency signal source, the RF signal source, a television signal generator, the noise signal source, the modulation signal generator, a digital signal source.
This classification is basically covering every corner of the aerospace, electronics,electricity and other collar electrical parameter measuring instrument domain. sinusoidal signal generator principle: RC, LC circuit produces sine wave.
The square wave is generated by the comparison of a sine wave and the voltage comparator;Can generate rectangular pulses of adjustable width, amplitude and repetition frequency generator pulse signal generator:Can be used to test the linear system transient response, or as analog signals to test the radar, multi-way communication, and the other pulses digital system performance.It combines a variety of signal source advantages of a mainly for the irregular nature of the analog output signal.
Generate standard waveforms such as sine wave, square wave, triangle wave, pulse wave.Can also generate a signal of the physical environment, including all the glitches that you may encounter when you leave the lab or workshop in the measured signal generator equipment, drift, noise and other abnormal events.
In modern communications device testing, and often the need for a signal source, both to produce a variety of analog and digital modulation signals, and also according to the test requirements change signal power inverter characteristics, such as the level characteristic, modulation characteristics, noise characteristics, the distortion characteristic intermodulation, crosstalk, etc., in order to do comprehensive testing of communications equipment to receive and send performance. Judging from the current situation, in such a wide range of complex modulated signals can only be by means of an arbitrary waveform generator.
Further, in military radar receiving machine test, often requires a variety of can simulate various modulation phenomenon appears in reality, to ensure a variety of accepted performance. For example, when the presence of noise and spurious echoes, in order to achieve a more accurate signal processing, many radar using a Barker coded using an arbitrary waveform generator to do modulation source, Barker coding can be simulated, thereby generating the required test signal. In short, arbitrary waveform generator has the convenient ability to generate arbitrary waveforms, and now has become the most commonly used test instruments in the field of modern military test.
Sine wave:The sine wave generating circuit can generate a sine wave output, which is coupled with positive feedback on the basis of the amplification circuit is formed.It is the core circuit the various waveform generator and the signal source.The sine wave generating circuit is also referred to as a sine wave oscillator circuit, or a sine wave oscillator
Square wave:The square wave is generated by the voltage comparator: the size of the comparison voltage signal (the test signal with the standard signal)
Triangle wave:Square-wave voltage as the input to the integral calculation circuit, the output of the integral calculation circuit to obtain the voltage of the triangular wave
Arbitrary wave:Arbitrary waveform generation method: direct digital synthesis (DDS) technology source extracted directly from the wave table N points, the N is a user-defined point.
DDS:Compared with traditional frequency synthesizer technology.DDS technology has a very high frequency resolution, fast frequency conversion speed, frequency phase continuous, phase noise is low, easy-to-function expansion and ease of a fully digital integrated and easy to implement a variety of modulation of the output signal.The March 1971 American scholar J.Tierncy, CMRader and B.Gold first proposed the direct digital frequency synthesis (Direct Digital Synthesis) technology.
This is a departure from the concept phase direct synthesis of the required waveforms of a new all-digital frequency synthesis technique.
DDS signal generator principle:Principle match a CD music player, and the digital information stored on the disc is read out, converted into an analog waveform to last through speaker output.
Direct digital synthesis principle:The direct digital frequency synthesis (DDS) is the use of digital technology, directly required various frequency signal by controlling the frequency control word. DDS is composed mainly by the reference clock,the phase accumulator, sine lookup table, and D / A converters and filters, etc., FIG Diagram 1.
The reference clock generated by a high stability of the crystal oscillator, to synchronize the entire of the various components of the frequency synthesizer. N-bit adder with N-bit phase registers cascaded phase accumulator, each to a clock pulse adder will frequency control word K phase registers are added.Phase register can be fed back to the new phase data generated by the adder on one clock after the input terminal of the adder, the adder on the next clock to continue to be added to the phase data and the frequency control word. Thus, the phase accumulator linear phase accumulation in the reference clock.When the phase accumulator reaches the upper limit, it will generate an overflow, completion of a periodic operation of, the cycle is a cycle of the synthesized signal, the accumulator overflow frequency is synthesized signal of the DDS frequency.
Under control of the reference clock, the frequency control word is fed to the phase accumulator. The output of the phase accumulator as a sine lookup table lookup address lookup sine table. Find each address in the table is representative of one cycle of a sine wave of a phase point, each phase point corresponds to a quantized amplitude value. Therefore, the lookup table is the equivalent of a phase / amplitude converter, it the phase information of the phase accumulator is mapped into a digital amplitude information. Find the amplitude data and then after a D / A converter to obtain the corresponding ladder wave ladder wave smoothing treatment, and finally through the low pass filter can be obtained by the frequency control word determines the continuous variation of the output of the sine wave. The sine wave and triangular wave may be present in the wave form, the realization of the square wave is a sine wave in the wave form derived through and a voltage comparator, and then another channel straightforward filtering process, and then output. Pulse wave is also
Implemented in two ways:Off-the-shelf DDS single-chip, programmable logic and DAC structures DDS Based on the technical design of the "FPGA" DDS(FPGA, the English Field Programmable Gate the Array, can be turned as field programmable logic arrays, it is a semi-custom ASIC (ASIC), has both the advantages of an ASIC, but also has the flexibility of programmable logic devices. basic characteristics:1) ASIC circuit FPGA design, users do not need to cast film production, will be able to get the combination chip. - 2) FPGA can do other full-custom or semi-custom ASIC circuits in the sample sheet.3) FPGA internal trigger and I / O pins.4) FPGA ASIC circuits in the shortest design cycle, the lowest development costs, one of the least risky devices.5) FPGA with high-speed CHMOS process, low power consumption, can be compatible with CMOS, TTL level.It can be said that the FPGA chip is a small batch systems to improve system integration, the reliability of one of the best choice.
The many varieties of FPGA, the XC series XILINX, TI's TPC series, ALTERA company FIEX series. )
Modulation principle the introduction:The baseband signal is converted into a signal technology can transmit.The baseband signal: the original electrical signal, generally refers to the basic signal waveforms in digital communication means corresponding to the electrical pulses. The baseband signal is used to control the high-frequency carrier parameters referred to as a modulated signal.
Carrier: the un-modulated high-frequency electrical oscillations (may be a sine wave,can also be a non-sine wave).The modulated signal: the modulation signal modulated carrier signal is called a modulated wave or a modulated signal.1 in the wireless the telemetering remote control system and radio technology to control the parameters (amplitude, frequency and phase) of the high-frequency carrier modulation baseband signal, so that the variation of these parameters with the base band signal.2 the general carrier signal is higher than the frequency of the baseband signal.3 in the input baseband signal, the attention signal frequency not exceed the instrument corresponding to the maximum range of the modulation requirements.
Modulation:The modulation method according to the nature of the modulation signal is divided into two types of analog modulation and digital modulation.
Analog modulation: amplitude modulation (AM) and frequency modulation (FM), phase modulation (PM), pulse width modulation (PWM)Digital modulation: amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK)1 the modulated signal is a binary digital signal, this modulation is called binary digital modulation.In binary digital modulation, the amplitude, frequency or phase of the carrier only two changes state.2 ASK: digital amplitude modulation, also known as amplitude shift keying.2ASK: binary amplitude shift keying.FSK: digital frequency shift keying is used the frequency of the carrier wave to send a digital message, which uses a digital message sent by the control of the frequency of the carrier.2FSK: binary digital frequency shift keying.PSK: Phase Shift Keying.2PSK: Binary Phase Shift KeyingAM (amplitude modulation): So that the amplitude of the carrier wave with the modulating signal changes with the amplitude of the modulation signal control carrierThe AM wave frequency carrier frequency.
The shape of the envelope of the amplitude modulated wave reflects the waveform of the modulation signal.FM (frequency modulation) So that the frequency of the carrier wave with the modulating signal changes with the oscillation frequency of the modulation signal control carrier.
The amplitude of the FM wave unchanged,The instantaneous value proportional to the instantaneous frequency of the FM wave departing from the amount of the carrier frequency of the modulation signal.NOTE: (angle modulation is a non-linear modulation, the modulated signal spectrum is no longer a linear move of the original modulation signal spectrum, but the non-linear transformation of the spectrum, will produce a different spectrum move the new frequency components.2 angle modulation may be divided into a frequency modulated (FM) and phase modulation (PM). I.e. the amplitude of the carrier remains constant, the carrier frequency or phase with the baseband signal changes.3 FM divided into narrowband FM and wideband FM.
According to the size of the offset of the instantaneous phase of the modulated carrier, the frequency modulation can be divided into wideband FM (WBFM) and narrowband FM (NBFM). PM (phase modulation)
With the phase of the carrier of the modulation signal to control, so that the phase of the carrier wave with the modulating signal changes.The phase modulation amplitude of the wave remains unchanged.Instantaneous value proportional to the instantaneous phase angle deviation of the phase-modulated wave with a modulation signal of the carrier phase angle.PWM (Pulse Width Modulation)So that each pulse has a duration of each pulse width modulated signal control pulse sequence, with the instantaneous value of the modulation signal is proportional to the amplitude of the pulse sequence remains unchanged, being modulated pulse the leading or trailing edge, or both before and after the both edges, so that the pulse duration changes.PWM is widely used in power switching circuits. Such as switching power supplies, pulse-width-width modulated (PWM) switching regulator circuit is in the case of the control circuit outputs a constant frequency, voltage feedback to adjust its duty cycle, so as to achieve a stable output voltage.PWM circuit: need the PWM circuit to drive the motor.
The stepper motor is an electrical pulse into the angular displacement of the implementing agencies.When the the stepper driver receives a pulse signal, it will drive the stepper motor to set the direction of rotation of a fixed angle (referred to as "step angle"), its rotation in a fixed angle step by step operation. The amount of angular displacement may be controlled by controlling the number of pulses so as to achieve accurate positioning purposes; while tester rate of the multi-channel temperature control by controlling the pulse frequency of the motor rotation speed and acceleration, so as to achieve the speed control purposes. The stepper motor can be used as a special motor control, the use of the characteristics of its accumulated error (100% accuracy), widely used in a variety of open-loop control. PWM is widely used in power switching circuits. Such as switching power supplies, pulse-width-width modulated (PWM) switching regulator circuit is in the case of the control circuit outputs a constant frequency, voltage feedback to adjust its duty cycle, so as to achieve a stable output voltage.PWM is only applicable to the pulse signal. PWM is widely used in power switching circuits. Such as switching power supplies, pulse-width-width modulated (PWM) switching regulator circuit is in the case of the control circuit outputs a constant frequency, voltage feedback to adjust its duty cycle, so as to achieve a stable output voltage.FSK (frequency shift keying)Controlling the frequency of the carrier with the digital modulation signal of 0/1.
When the amplitude of the digital signal is high (1) when the carrier frequency is f1.When the amplitude of the digital signal is low (0) when the carrier frequency is f2.Burst (Burst Mode)Pulse train output can provide users with a variety of waveform function,Sustainable waveform of a specific number of cycles (N cycle burst),Outside the department or application signal (gated burst), you can use any waveform function.The main application areas: applied to pulse circuits, logic circuits, semiconductor test device parameters, and computer.Sweep (sweep),The frequency of the signal generated by the signal generator is continuously changed, it can be used to measure the response of the system to the frequency.
Main application areas: design verification of the power amplifier design, detection,etc.Test of the sweep range of applications: high / low frequency signal receiver and transmitter, TV signal testing, communication network testVertical resolution (amplitude resolution):the vertical resolution of the signal source means the minimum voltage of the signal source can be programmed to increment.Instrument binary word width of the digital-to-analog converter unit for a bit, it specifies the waveform amplitude accuracy
Nyquist Sampling Theorem states that the sampling frequency or the clock rate must be at least twice the highest spectral component of the generated signal, in order to guarantee accurate reproducibility.Sampling rate:Sampling rate is usually Msamples per second, or Gigabit samples said, that the instrument can operate the clock or sampling rate.The sampling rate affect the frequency of the output signal and fidelity.Nyquist Sampling Theorem states that the sampling frequency or the clock rate must be at least twice the highest spectral component of the generated signal, in order to guarantee accurate reproducibility.Output signal bandwidth:The highest frequency component to indicate that a signal can be output, the highest sine wave frequency of the common output.Waveform memory depth:Memory depth is used to record the waveform sampling points, it determines the the maximum sampling the number of samples of the waveform data.Maximum output frequency = sampling rate × 0.4,The highest frequency of the output signal of the bandwidth of common sine wave output.Bandwidth (Fw):Bandwidth is a measure AC instrument must consider the technical indicators, refers to the instrument output signal amplitude can be measured attenuation of-3dB at the highest frequency.The bandwidth of the direct digital synthesis signal source is generally the highest frequency of the sine wave.
In the military, aerospace, transportation, manufacturing and other fields, some of the circuit is difficult to estimate the operating environment, after the completion of the experimental design, the need for further experiments in the real environment, high cost or risk of some experiments (such as tracks transform the situation train high-speed experimental aircraft test machine when the propeller operation, etc.), it is impossible for long-term experiments to determine the design of the product (for example, high-speed trains, aircraft), the feasibility and stability.Electronic circuit design and semiconductor analog clock signal, you need a high clock stability, load change test, Analog Devices, a microprocessor interface, AD and DA circuit, data and wireless communications, modems signal simulation, system fault simulation functional testing of the base station equipment .
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