关于信号英语作文

human creativeness is boundless. with the advance of science and technology, a completely new means of communication the mobile phone -- came to the world, which, being not fixed in one place like ordinary phones, greatly facilitates telephone communication.the mobile phone spreads so rapidly, first businessmen to office workers, then to township enterprise managers,then to journalists and then nowadays to people of all trades and professions. at present,it seems that nowhere we do not hear the musical ringing of the mobile phone. people at first buy phones for convenience and later for fashion. to occupy this increasingly big market, the manufacturers are worrying their brains into making various types of phones, large or small, colorful or black and white, multi-functional or with video cameras,to satisfy the needs. new fashions appear almost every day.however, it is a great pity that the inventors of the mobile phone did not expect the negative effects caused by their scientific merits. because of the abuse of the mobile phone,aircraft mechanism refuses to work properly, libraries are no longer so quiet, restaurants are filled with noisy phone talk,teaching is incessantly interrupted by the signals.....人类的创造力是无限的。随着科学技术的发展,一种全新的沟通方式移动电话,来到这个世界上的时候,它 不被固定在一个地方不像普通手机,极大地方便电话沟通。手机传播如此之快,首先是商人 ，上班族,然后乡镇企业经理,然后记者,然后现在各行各业的人。目前,似乎没有我们听不见手机的音乐铃声的时候。人们第一次买手机为了方便,后来为时尚。占据越来越大的市场,制造商们担心他们的大脑在各种类型的手机,大或小,彩色或黑白,多功能或摄像机,以满足需求。几乎每天都出现新的时尚。然而,遗憾的是一个伟大的发明家手机没有期望他们的科学价值造成的负面影响。由于滥用手机,飞机机制不正常工作,图书馆不再是那么安静,餐厅充满了嘈杂的电话谈话,教学是不停地打断.....信号

1.等红灯wait for the green light许多人是不是脱口而出：wait for a red ligh，哈哈，其实错得很离谱哦。Traffic lights tell drivers and pedestrians what they must do at intersections and along roads. They tell road users when to stop and go, when and how to turn and when to drive with extra caution.交通灯告诉司机和行人在十字路口和沿路应该做什么。他们告诉道路使用者什么时候该停车，什么时候该转弯，什么时候该开车，要格外小心。Lights红绿灯或者 city lights或traffic signalsThe idea that red means stop and green means go has influenced our lives in more ways than just traffic signals.红灯停绿灯行这一观念对我们生活的影响远不止于交通信号。

点拨：交通信号灯主要是红黄绿，我们都知道红灯停，绿灯行，黄灯不要急，这也是我们基本的道路交通规则。In order to keep the road orderly and people safe everyone should follow the traffic rules.When you walk you should walk at the side of the road.Always be careful and look left and right before you cross the road.If you like riding don't run through the red traffic lights.Don'tride too fast.If you driveyou should slow down at the traffic lights you must always wear a seat belt and you must never drink wine.When many passengers are wait-ing for the bus please stand in line and wait for your turn don't push others.Don't get off the bus until it has stop red.Remember:Don't break the trafficrules.为了保持道路的秩序和人们的安全，每个人都应该遵守交通规则。当你走路的时候，你应该走在路边。在过马路之前，你要注意左右。如果你不喜欢在红色交通灯上骑车，不要太快。如果你开车时要在红绿灯处减速，你必须始终系安全带，千万不要喝酒。当许多乘客在等公共汽车时，请排队等候，不要推其他人。记住：不要下车，直到它停下来。记住：不要违反交通规则。

DDS and converter form signal generatorMany applications require low-frequency signal generators that can deliver high-performance, high-resolution signals. This Design Idea presents a circuit that generates frequencies of 0 to 1 MHz. Sinusoidal, triangular, and square-wave outputs are available. You can achieve frequency resolution of better than 0.1 Hz and phase resolution of better than 0.1°; thus, you can program exact coherent frequencies. This feature is useful in digital modulation and frequency-tuning applications. The circuit uses the ADµC831 and AD9834 to generate the required frequencies (Figure 1). You can program the microcontroller from either a PC or a Unix-based workstation. You then program the AD9834 using a three-wire serial interface via the microcontroller. The interface word is 16 bits long.You can program the AD9834 to provide sinusoidal, triangular, and square-wave outputs using the DDS (direct-digital-synthesis) architecture. The chip operates as an NCO (numerically controlled oscillator) using an on-chip, 28-bit phase accumulator, sine-coefficient ROM, and a 10-bit D/A converter. You typically consider sine waves in terms of their magnitude form, A(t)=sin(ωt). The amplitude is nonlinear and is, therefore, difficult to generate. The angular information, on the other hand, is perfectly linear. That is, the phase angle rotates through a fixed angle for each unit in time. Knowing that the phase of a sine wave is linear, and, given a reference interval (clock period), you can determine the phase rotation for that period: ΔPhase=ω dt; ω=ΔPhase/dt=2πf, and f=(ΔPhase×fMCLK)/(2π), where dt=1/fMCLK, and fMCLK is the master clock.Using this formula, you can generate output frequencies, knowing the phase and master-clock frequency. The phase accumulator provides the 28-bit linear phase. The amplitude coefficients of the output sine wave are stored in digital format in the sine-coefficient ROM. The DAC converts the sine wave to the analog domain. If you bypass the ROM, the AD9834 delivers triangular waveforms instead of sinusoidal waveforms. A square-wave output is also available on the part. Figure 2 shows the various waveforms available from the system. As shown in Figure 1, the sinusoidal/ triangular output waveforms are available on the IOUT pin (Pin 19); and the square wave output is available on the SIGN_BIT_OUT pin (Pin 16). You program the DDS by writing to the frequency registers. The analog output from the part is then: fOUT=fMCLK/228×(frequency-register word).The outputs of the DDS have 28-bit resolution, so effective frequency steps on the order of 0.1 Hz are possible to a maximum of approximately 1 MHz. Figure 2 shows the typical waveform outputs. Two phase registers are available that allow 12-bit phase resolution. These registers phase-shift the signal by: Phase shift=2π/4096×(phase-register word).A 50-MHz crystal oscillator provides the reference clock for the DDS. The output stage of the DDS is a current-output DAC loaded by an external resistor. A 200Ω resistor generates the required peak-to-peak voltage range. The output is ac-coupled through capacitor C1. The MicroConverter contains two on-chip, 12-bit DACs. DAC1 varies the current through R5, adjusting the full-scale current of the DDS via the FSADJUST pin. The equation to control the full-scale current of the DDS DAC is: IOUT (full-scale)=18×I×R5.DAC0, the internal reference of the MicroConverter, and op amp 2 allow for offset control of the output voltage of the DDS. You can program this dc offset to ±10V at 10-bit resolution. When R1=R2 and the gain of op amp 2=8, then the output of op amp 2 is: VOUT=(DAC output–(VREF/2))×8, yielding a ±10V range.Resistors R6 through R9 allow for control of gain through op amp 3. The gain of the op amp is a function of resistor switching, which you enable using the RDRIVE pin available on the MicroConverter. This operation allows for an effective programmable-output amplitude of approximately ±10V p-p. Thus, the circuit allows for programmable sinusoidal and triangular waves, including dc offsets, and the ability to set peak-to-peak amplitude of approximately ±10V. The square wave output on the SIGN_BIT_OUT pin has 0 to 5V amplitude. For low-frequency operation, a lowpass filter normally serves to filter reference-clock frequencies, spurs, and other images. For applications in which the output signal needs amplification, you should use a narrowband filter to filter out unwanted noise before the gain stage. A third-order filter would be good enough to remove most of the unwanted noise. Figure 3 shows a typical spectral plot of the output. Applications for this circuit range from signal-waveform generation to digital modulation. You can use the system in frequency-sweeping and -scanning applications and in resonance applications that use the frequency as an excitation signal to determine circuit resonance. Another useful application is as a reference oscillator for a PLL system.