第一篇：12位-AD574A转换器中英文翻译资料 - 副本
英文原文
12-Bit A/D Converter
CIRCUIT OPERATION The AD574A is a complete 12-bit A/D converter which requires no external components to provide the complete successive approximation analog-to-digital conversion function.A block diagram of the AD574A is shown in Figure 1.Figure 1.Block Diagram of AD574A 12-Bit A-to-D Converter
When the control section is commanded to initiate a conversion(as described later), it enables the clock and resets the successiveapproximation register(SAR)to all zeros.Once a conversion cycle has begun, it cannot be stopped or restarted and data is not available from the output buffers.The SAR, timed by the clock, will sequence through the conversion cycle and return an end-of-convert flag to the control section.The control section will then disable the clock, bring the output status flag low, and enable control functions to allow data read functions by external command.During the conversion cycle, the internal 12-bit current output DAC is sequenced by the SAR from the most significant bit(MSB)to least significant bit(LSB)to provide an output current which accurately balances the input signal current through the 5kΩ(or10kΩ)input resistor.The comparator determines whether the addition of each successively-weighted bit current causes the DAC current sum to be greater or less than the input current;if the sum is less, the bit is left on;if more, the bit is turned off.After testing all the bits, the SAR contains a 12-bit binary code which accurately represents the input signal to within 1/2 LSB.The temperature-compensated buried Zener reference provides the primary voltage reference to the DAC and guarantees excellent stability with both time and temperature.The reference is trimmed to 10.00 volts 0.2%;it can supply up to 1.5 mA to an external load in addition to the requirements of the reference input resistor(0.5 mA)and bipolar offset resistor(1 mA)when the AD574A is powered from 15 V supplies.If the AD574A is used with 12 V supplies, or if external current must be supplied over the full temperature range, an external buffer amplifier is recommended.Any external load on the AD574A reference must remain constant during conversion.The thin-film application resistors are trimmed to match the full-scale output current of the DAC.There are two 5 kinput scaling resistors to allow either a 10 volt or 20 volt span.The 10 kbipolar offset resistor is grounded for unipolar operation and connected to the 10 volt reference for bipolar operation.DRIVING THE AD574 ANALOG INPUT
Figure 2.Op Amp – AD574A Interface
The output impedance of an op amp has an open-loop value which, in a closed loop, is divided by the loop gain available at the frequency of interest.The amplifier should have acceptable loop gain at 500 kHz for use with the AD574A.To check whether the output properties of a signal source are suitable, monitor the AD574’s input with an oscilloscope while a conversion is in progress.Each of the 12 disturbances should subside in sorless.For applications involving the use of a sample-and-hold amplifier, the AD585 is recommended.The AD711 or AD544 op amps are recommended for dc applications.SAMPLE-AND-HOLD AMPLIFIERS Although the conversion time of the AD574A is a maximum of 35 s, to achieve accurate 12-bit conversions of frequencies greater than a few Hz requires the use of a sample-and-hold amplifier(SHA).If the voltage of the analog input signal driving the AD574A changes by more than 1/2 LSB over the time interval needed to make a conversion, then the input requires a SHA.The AD585 is a high linearity SHA capable of directly driving the analog input of the AD574A.The AD585’s fast acquisition time, low aperture and low aperture jitter are ideally suited for high-speed data acquisition systems.Consider the AD574A converter with a 35 s conversion time and an input signal of 10 V p-p: the maximum frequency which may be applied to achieve rated accuracy is 1.5 Hz.However, with the addition of an AD585, as shown in Figure 3, the maximum frequency increases to 26 kHz.The AD585’s low output impedance, fast-loop response, and low droop maintain 12-bits of accuracy under the changing load conditions that occur during a conversion, making it suitable for use in high accuracy conversion systems.Many other SHAs cannot achieve 12-bits of accuracy and can thus compromise a system.The AD585 is recommended for AD574A applications requiring a sample and hold.Figure 3.AD574A with AD585 Sample and Hold
SUPPLY DECOUPLING AND LAYOUT CONSIDERATIONS It is critically important that the AD574A power supplies be filtered, well regulated, and free from high frequency noise.Use of noisy supplies will cause unstable output codes.Switching power supplies are not recommended for circuits attempting to achieve 12-bit accuracy unless great care is used in filtering any switching spikes present in the output.Remember that a few millivolts of noise represents several counts of error in a 12-bit ADC.Circuit layout should attempt to locate the AD574A, associated analog input circuitry, and interconnections as far as possible from logic circuitry.For this reason, the use of wire-wrap circuit construction is not recommended.Careful printed circuit construction is preferred.UNIPOLAR RANGE CONNECTIONS FOR THE AD574A The AD574A contains all the active components required to perform a complete 12-bit A/D conversion.Thus, for most situations, all that is necessary is connection of the power supplies(+5 V, +12 V/+15 V and –12 V/–15 V), the analog input, and the conversion initiation command, as discussed on the next page.Analog input connections and calibration are easily accomplished;the unipolar operating mode is shown in Figure 4.Figure 4.Unipolar Input Connections
All of the thin-film application resistors of the AD574A are trimmed for absolute calibration.Therefore, in many applications, no calibration trimming will be required.The absolute accuracy for each grade is given in the specification tables.For example, if no trims are used, the AD574AK guarantees 1 LSB max zero offset error and 0.25%(10 LSB)max full-scale error.(Typical full-scale error is 2 LSB.)If the offset trim is not required, Pin 12 can be connected directly to Pin 9;the two resistors and trimmer for Pin 12 are then not needed.If the full-scale trim is not needed, a 50 1% metal film resistor should be connected between Pin 8 and Pin 10.The analog input is connected between Pin 13 and Pin 9 for a 0 V to +10 V input range, between 14 and Pin 9 for a 0 V to +20 V input range.The AD574A easily accommodates an input signal beyond the supplies.For the 10 volt span input, the LSB has a nominal value of 2.44 mV;for the 20 volt span, 4.88 mV.If a 10.24 V range is desired(nominal 2.5 mV/bit), the gain trimmer(R2)should be replaced by a 50Ωesistor, and a 200Ωtrimmer inserted in series with the analog input to Pin 13 for a full-scale range of 20.48 V(5 mV/bit), use a 500 trimmer into Pin 14.The gain trim described below is now done with these trimmers.The nominal input impedance into Pin 13 is 5kΩ, and 10kΩinto Pin 14.UNIPOLAR CALIBRATION The AD574A is intended to have a nominal 1/2 LSB offset so that the exact analog input for a given code will be in the middle of that code(halfway between the transitions to the codes above and below it).Thus, the first transition(from 0000 0000 0000 to 0000 0000 0001)will occur for an input level of +1/2 LSB(1.22 mV for 10 V range).If Pin 12 is connected to Pin 9, the unit will behave in this manner, within specifications.If the offset trim(R1)is used, it should be trimmed as above, although a different offset can be set for a particular system requirement.This circuit will give approximately 15 mV of offset trim range.The full-scale trim is done by applying a signal 1/2 LSB below the nominal full scale(9.9963 for a 10 V range).Trim R2 to give the last transition(1111 1111 1110 to 1111 1111 1111).BIPOLAR OPERATION The connections for bipolar ranges are shown in Figure 5.Again, as for the unipolar ranges, if the offset and gain specifications are sufficient, one or both of the trimmers shown can be replaced by a 50 1% fixed resistor.Bipolar calibration is similar to unipolar calibration.Figure 5.Bipolar Input Connections
CONTROL LOGIC The AD574A contains on-chip logic to provide conversion initiation and data read operations from signals commonly available in microprocessor systems.Figure 6 shows the internal logic circuitry of the AD574A.The control signals CE, CS, and R/C control the operation of the converter.The state of R/C when CE and CS are both asserted determines whether a data read(R/C = 1)or a convert(R/C = 0)is in progress.The register control inputs AO and 12/8 control conversion length and data format.The AO line is usually tied to the least significant bit of the address bus.If a conversion is started with AO low, a full 12-bit conversion cycleis initiated.If AO is high during a convert start, a shorter 8-bit conversion cycle results.During data read operations, AO determines whether the three-state buffers containing the 8 MSBs of the conversion result(AO = 0)or the 4 LSBs(AO = 1)are enabled.The 12/8 pin determines whether the output data is to be organized as two 8-bit words(12/8 tied to DIGITAL COMMON)or a single 12-bit word(12/8 tied to VLOGIC).The 12/8 pin is not TTL-compatible and must be hard-wired to either VLOGIC or DIGITAL COMMON.In the 8-bit mode, the byte addressed when AO is high contains the 4 LSBs from the conversion followed by four trailing zeroes.This organization allows the data lines to be overlapped for direct interface to 8-bit buses without the need for external three-state buffers.It is not recommended that AO change state during a data read operation.Asymmetrical enable and disable times of the three-state buffers could cause internal bus contention resulting in potential damage to the AD574A.Figure 6.AD574A Control Logic An output signal, STS, indicates the status of the converter.STS goes high at the beginning of a conversion and returns low when the conversion cycle is complete.TIMING The AD574A is easily interfaced to a wide variety of microprocessors and other digital systems.The following discussion of the timing requirements of the AD574A control signals should provide the system designer with useful insight into the operation of the device.Figure 7 shows a complete timing diagram for the AD574A convert start operation.R/C should be low before both CE and CS are asserted;if R/C is high, a read operation will momentarily occur, possibly resulting in system bus contention.Either CE or CS may be used to initiate a conversion;however, use of CE is recommended since it includes one less propagation delay than CS and is the faster input.In Figure 7, CE is used to initiate the conversion.Figure 7
Once a conversion is started and the STS line goes high, convert start commands will be ignored until the conversion cycle is complete.The output data buffers cannot be enabled during conversion.Figure 8 shows the timing for data read operations.During data read operations, access time is measured from the point where CE and R/C both are high(assuming CS is already low).If CS is used to enable the device, access time is extended by 100 ns.Figure 8.Read Cycle Timing
In the 8-bit bus interface mode(12/8 input wired to DIGITAL COMMON), the address bit, AO, must be stable at least 150 ns prior to CE going high and must remain stable during the entire read cycle.If AO is allowed to change, damage to the AD574A output buffers may result.“STAND-ALONE” OPERATION
The AD574A can be used in a ―stand-alone‖ mode, which is useful in systems with dedicated input ports available and thus not requiring full bus interface capability.In this mode, CE and 12/8 are wired high, CS and AO are wired low, and conversion is controlled by R/C.The three-state buffers are enabled when R/C is high and a conversion starts when R/C goes low.This allows two possible control signals—a high pulse or a low pulse.Operation with a low pulse is shown in Figure 11.In this case, the outputs are forced into the high impedance state in response to the falling edge of R/C and return to valid logic levels after the conversion cycle is completed.The STS line goes high 600 ns after R/C goes low and returns low 300 ns after data is valid.Figure 11.Low Pulse for R/C—Outputs Enabled After Conversion
If conversion is initiated by a high pulse as shown in Figure 12, the data lines are enabled during the time when R/C is high.The falling edge of R/C starts the next conversion, and the data lines return to three-state(and remain three-state)until the next high pulse of R/C.Figure 12.High Pulse for R/C—Outputs Enabled While R/C High, Otherwise High-Z
Usually the low pulse for R/C stand-alone mode will be used.Figure 13 illustrates a typical stand-alone configuration for 8086 type processors.The addition of the 74F/S374 latches improves bus access/release times and helps minimize digital feedthrough to the analog portion of the converter.INTERFACING THE AD574A TO MICROPROCESSORS The control logic of the AD574A makes direct connection to most microprocessor system buses possible.While it is impossible to describe the details of the interface connections for every microprocessor type, several representative examples will be described here.GENERAL A/D CONVERTER INTERFACE CONSIDERATIONS A typical A/D converter interface routine involves several operations.First, a write to the ADC address initiates a conversion.The processor must then wait for the conversion cycle to complete, since most ADCs take longer than one instruction cycle to complete a conversion.Valid data can, of course, only be read after the conversion is complete.The AD574A provides an output signal(STS)which indicates when a conversion is in progress.This signal can be polled by the processor by reading it through an external three-state buffer(or other input port).The STS signal can also be used to generate an interrupt upon completion of conversion, if the system timing requirements are critical(bear in mind that the maximum conversion time of the AD574A is only 35 microseconds)and the processor has other tasks to perform during the ADC conversion cycle.Another possible time-out method is to assume that the ADC will take 35 microseconds to convert, and insert a sufficient number of ―do-nothing‖ instructions to ensure that 35 microseconds of processor time is consumed
Once it is established that the conversion is finished, the data can be read.In the case of an ADC of 8-bit resolution(or less), a single data read operation is sufficient.In the case of converters with more data bits than are available on the bus, a choice of data formats is required, and multiple read operations are needed.The AD574A includes internal logic to permit direct interface to 8-bit or 16-bit data buses, selected by connection of the 12/8 input.In 16-bit bus applications(12/8 high)the data lines(DB11 through DB0)may be connected to either the 12 most significant or 12 least significant bits of the data bus.The remaining four bits should be masked in software.The interface to an 8-bit data bus(12/8 low)is done in a left-justified format.The even address(A0 low)contains the 8 MSBs(DB11 through DB4).The odd address(A0 high)contains the 4 LSBs(DB3 through DB0)in the upper half of the byte, followed by four trailing zeroes, thus eliminating bit masking instructions.SPECIFIC PROCESSOR INTERFACE EXAMPLES Z-80 System Interface The AD574A may be interfaced to the Z-80 processor in an I/O or memory mapped configuration.Figure 15 illustrates an I/O or mapped configuration.The Z-80 uses address lines A0–A7 to decode the I/O port address.An interesting feature of the Z-80 is that during I/O operations a single wait state is automatically inserted, allowing the AD574A to be used with Z-80 processors having clock speeds up to 4 MHz.For applications faster than 4 MHz use the wait state generator in Figure 16.In a memory mapped configuration the AD574A may be interfaced to Z-80 processors with clock speeds of up to 2.5 MHz.附录E 中文翻译
12位-AD574A转换器
电路工作原理
AD574A是一个完善的12位A/D转换器，不需要外部组件提供完全的逐步逼近模拟数字转换功能。图1所示为AD574A的方块结构图。
图1 AD574A的方块结构图
当控制部分收到初始化转换命令（后边会叙述）时，会开启时钟并把连续逼近寄存器（SAR）全部置零。一旦转换周期开始，它就不能终止或重新开始，也不能从输出缓冲中读数。时钟控制SAR寄存器的时序，SAR会安排好转换周期的顺序并向控制部分返回一个“转换结束”（end-of-convert）标志。接着，控制部分停止时钟，把输出状态标志位置低，并允许控制函数，以便外部命令可以执行数据读取功能。
在转换周期期间, 内部12 位当前的产品DAC 由SAR 程序化从最高位(MSB)对最低有效位(LSB)通过5 k(或10k)输入电阻器提供准确地平衡输入信号。比较器确定位电流的连续增大是否造成了DAC当前总电流比输入电流增大或者减小;如果总电流较小，此位被留下;如果总电流较大，位被关闭。在测试完所有位以后，SAR包含了准确表示输入信号在+1/2 LSB之内的12位二进制编码。温度补偿是外部提供给DAC基准电压并保证准确的转换的时间和温度的稳定性。基准在10.000.2%伏之间平衡，当AD574A使用15伏电源时，除了按要求向参考输入电阻提供0.5mA，向双极偏移电阻提供1mA电流外，它可以给外部负载提供提供高至1.5mA的电流。如果AD574A使用12伏电源，或者外部电流必须在全部温度范围内提供，那么我们推荐使用一个外部的缓冲放大器。任何在AD574A参考手册上的外部负载都必须在转换过程中保持稳定。要调整薄膜应用电容以匹配DAC（数模转换器）的实比例输出电流。有两个5千欧的输入测量电阻允许10伏或20伏的区间。10千欧的双极偏移电容接地用于单极操作，或连接到10伏参考电压上用于双极性操作。
AD574模拟输入电压
图2 OP放大器与AD574连接
OP放大器的输出阻抗有一个开环值，在一个封闭回路中，这个值被回路增益（由增加的频率产生）等分。放大器应该至少拥有500kHz的回路增益才能和AD574A一起使用。要检查信号源的输出特性是否合适，就要在转换进行中使用示波镜监控AD574的输入端。每12个干扰应该在1秒以内衰减。
关于取样—保持器的应用，我们推荐AD585型号。我们推荐让AD711型号和AD544型号取样—保持器应在直流电下工作。
虽然AD574A的转换时间最高为35秒，但为了能够实现几个赫兹的频率的精确12位转换还是需要使用采样－保持放大器（SHA）的。如果一个驱动AD574A的模拟输入信号电压在转换所需的计时周期中变化超过LSB的一半，那么输入端就需要一个SHA。
AD585是一种高线性的采样－保持放大器（SHA），它能够直接驱动AD574A的模拟输入端。AD585的快速采集时间、低孔径和低孔径抖动都很好地使用于高速数据采集系统。考虑到AD574A的转换时间为35秒，并且拥有10Vp-p的输入信号，这是能够实现1.5Hz精确转换时所能用的最高频率。如图3所示，加上AD585后，最高频率增加到了26kHz。
AD585的低输出阻抗、快速连环反应和低损耗能够在变化的周期性负荷工况下维持12位准确性，使它适当用于高精确度转换。许多其他SHAs达不到12位转换的准确性，并且可能因而减弱系统。AD585被推荐应用于AD574A的采样与保持。
图3 带采样保持器AD585的AD574A
AD574A 电源的滤波、良好地校准和远离高频噪声是异常重要的.。噪声补偿的使用会造成不稳定的输出信号。除非特别要求滤掉输出端的电火花，交换式电源电路建议达到12比特的精确度。注意： 一点点毫伏的噪声就代表着12比特ADC（电源）的巨大误差。
电路布局应该尝试定位AD574A,与之相连的相似物输入电路,并使其从逻辑电路上尽可能连接起来.因为这个原因,不推荐使用线路电路结构.应该选择好的印刷的电路体系.AD574A处理单极性信号
AD574A包括了所有进行完全12位AD转换所需的活动组件。这样，在大多数情况下，所需的只是电源连接（+5 V, +12 V/+15 V 和 –12 V/–15 V）、模拟输入以及转换初始化命令，下页会讨论到。模拟输入连接和校准都很容易完成。单极操作模式如图4所示。
图4
AD574A所有的薄膜应用程序电阻是通过绝对刻度来衡量的。因此在许多应用程序中，并不需要刻度平衡。规格表给出了每个等级的绝对精度。例如，如果没有应用区标，AD574AK保证1LSB最大零偏移误差和0.25%(10LSB)最大满额误差。（通常满额误差是2 LSB）。如果不允许使用这个弯管平衡的话，pin 12 可以直接同pin 9连接；pin 12 的这两个电阻器和这个微调电容器就不需要了。如果不允许使用完整的平衡，应该在pin 8和pin 10之间连接一个xxxx金属薄膜微调电容器。
此器件在输入电压0到10伏连接时须接脚9和脚13,当输入电压在0到20伏之间时,应从脚14和脚9引入。AD574A提供输入信号补偿，输入电压在10伏以内时理论值是2.44mV,在输入电压在20伏以内时理论值是2.44mV
如果电压达到10.24(也就是2.5mv/bit), 增益可调电阻就必须调整为50.一个200Ω可变电阻串连到模拟输入引脚13其满刻度值为20.48V(5 mV/bit),用500Ω的可变电阻串连到模拟输入引脚14.下述增益的调整用这些可变电阻完成.引脚13的名义输入阻抗为5 kΩ, 而插脚14的名义输入阻抗为10kΩ。
单极性输入
AD574A拥有一个名义上是LSB一半的偏移量，以便对一个给定编码的准确模拟输入可以正好处于这个编码的中央（在其前后各有一半的编码转换）。这样，第一个转换（从0000 0000 0000到0000 0000 0001）会在输入电平为+1/2LSB（对于10V的范围来说是1.22mV）时发生。
如果第12脚连在第9脚上，那么单元将在规格之内按此方式工作。如果使用了偏移调整（R1），虽然可以针对特定的系统要求设置不同的偏移量，但也应该按上述方法调整。这个电路会给出大约15mV的偏移调整范围。
满量程调整适用于一个信号在满量程下产生1/2 LSB线性误差，也就是对于10V范围来说是9.9963。调整R2来实现最后一个转换（1111 1111 1110到1111 1111 1111）
双极性输入
双极的联系范围如图5。还有，就单极的范围，如果输出量与增加量的数据充足的话，一个电容器或者两个都可以拿一个50±1%的固定电阻来代替。单极标准与双极标准是相似的。
图5 逻辑控制
AD574A包含了芯片上逻辑，可以通过微处理器中通常存在的信号中提供开始转换和读取转换结果操作‖ 如图6是AD574A的内部逻辑电路。
控制信号CE、CS, 和R/C 控制交换器的操作。R/C 的状态由CE 和CS 两个信号的加入来确定进行数据读取(R/C = 1)或数据转换(R/C = 0)。记数器控制输入AO ,12/8 控制转换长度和数据格式。AO 线通常被连结到地址总线的最低有效位。如果AO置低(电位)开始, 按12 位A/D进行转换。当12/8=1时，12位数据线一次读出，主要用于16位微机系统；12/8=0时，可与8位机接口。此引脚输入为高电平时，12位数据并行输出；当此引脚为低电平时，与引脚A0配合，把12位数据分两次输出。12/8的引脚接DIGITAL COMMON输出8位数据12/8引脚接VLOGIC输出12位数据。12/8的引脚不与TTL兼容的，必须和vlogic或者digital连接，在8位模式下，当Ao置高的时候，低4位加上尾随4个0有效。在不需要内部3态缓冲器的情况下，该结构允许直接接口的8位数据流重叠。在读取转换数据操作时不建议ao改变。三态缓冲器不对称的允许与阻止时间可能造成内部总线冲突,对AD574A造成潜在危害.图6
STS这个输出信号表明了转换器的状况。STS值在转换开始时升高，在转换过程完成后降低回原样。
AD574A 容易联接于多种微处理器和其他数字化系统。下列AD574A控制信号的计时要求的讨论应该为系统设计者提供有用的对设备的操作了解。
图7
图7显示的是完整的AD574A运作时间矢量图表.坐标轴R/C在CE和CS被捕获之前都应较低;如果R/C显示较高,操作提示会立即发生,并可能引发系统争用.无论CE还是CS都能被用来转换.但是,我们推荐使用CE,因为它比CS有更少的系统延迟,并且能被较快地 输入.在图表7,CE被用来转换.一旦转换开始STS置成高位，直到转换循环完成,转换开始命令将被忽略。直到转换周期是完全的。在转换期间，输出数据缓冲无效。
图8给出了数据读取操作时间状况,在数据读取过程中, 当CE和R/C都处于高电平(假定CS已经处于低电平)的时候,开始测量访问时间.如果这时CS能够使得设备工作, 访问时间可延长100纳秒.图8 在8位的总线接线模式中（和数字公用区连线的12/8 输出），地址位AO，必须在CE升高的150毫秒之前和整个读取循环中保持稳定。如果允许AO变化，将会导致对AD574A输出缓存区的损坏。
AD5474A单机操作
AD5474A可以“独立”模式使用，它是系统里很好用的、可用的和专用的端口，以这种方式不需要用总线连接。按这方式，CE和12/8置成高位，CS和AO置成低位，而转化由RC控制。当RC置成高位时，三态缓冲器启动，当RC置成低位时开始转换。其允许两种控制信号一种高电位脉冲，低高电位脉冲。由如图11所示的低脉冲操作。在这种情况下R/C下降沿的输出响应被强制为高阻状态，在一个转换周期结束后置回有效逻辑。STS线在R/C变为低电平600ns后变为高电平，当数据有效300ns后恢复低电平。
图9
如果转换是由如图12所示的高电平脉冲所初始化的，那么在R/C为高电平时，数据链是被允许的。R/C的下降沿启动下一个转换，并且数据链返回到三态（并一直保持三态），知道下一个R/C高电平脉冲出现。
图10
通常应用R/C单机模式下的低脉冲。图13阐明了典型的8086型处理机的单机构造。额外的74F/S374 插销提高了总线的访问/放行次数并协助简化转炉数-模部分的连接线。
图11
AD574与单片机接口
AD574A的控制逻辑使得绝大多数情况下和微处理器系统总线直接连线变成可能。然而它不可能描述出每一种微处理器类型的接口连接的所有细节，下面将举几个具有代表性的例子。
典型的数模转换器接口程序序列涉及以下几步：首先, 在初始化会话的时候，地址被写进数模转换。处理器必须等待会话周期的结束，因为多数数模转换器需要一个以上的指令周期来完成会话操作。当然，有效数据只有在会话结束后才能被读取。AD574A 提供信号端输出(STS)，它能指示会话过程。这个信号可以由处理器通过读取外部三态缓冲（或其它输入端口）获得。如果系统的计时要求非常严格（请记住AD574A的最大转换时间只有35毫秒）并且处理器在ADC转换周期中有其它任务要做的话，这个STS信号同样可以用于产生一个中断信号传递给转换过程。另一种可行的延时方法是，先假设模数转换器会消耗35微秒来进行转换，然后插入足够多的空指令来保证处理器消耗掉35微秒的时间。
一旦建立,即完成转换,可以读取数据.在8位(或数位更少)ADC的情况下,单次读数运行即已足够.在转换器数位多于总线可使用数位的情况下,须选择数据格式,需进行多重读数运行.AD574A含有内部逻辑(器),允许通过选择连接12/8输入而直接到8位或多或16位数据总线界面上。在采用16位数据总线时,(12/8 高)数据总线(DB11 通过 DB0)既可以连接到数据总线的12位有效位或12位无效位。剩余4位应用软件将其掩蔽.到8位数据总线的界面是采用左优格式来实现的。在数位的上半部偶数地址(A0 低)包含 8 MSBs(DB11 通过 DB4).。奇数地址(A0 高)包含 4 LSBs(DB3 through DB0),后面跟有4个零,从而消除数位掩蔽指令.AD574A可以在输入/输出或者储存映像结构中被接线到Z-80 处理机上。图15阐明了一个输入/输出或者映像结构。Z-80使用A0–A7 地址线来解码输入/输出端口地址。
Z-80的一个有趣的特性就是当进行I/O操作时会自动插入一个等待状态，允许AD574A和时钟频率高达4MHz的Z-80处理器一起使用。对于高于4MHz的实际应用，可以使用图16所展示的等待状态发生器。在配置内存内部，AD574A可以和时钟频率高达2.5MHz的Z-80处理器通过接口相连接。
第二篇：常用临床申报资料翻译中英文对照
FDA（FOOD AND DRUG ADMINISTRATION）：（美国）食品药品管理局
IND（INVESTIGATIONAL NEW DRUG）：临床研究申请（指申报阶段,相对于NDA而 言）；研究中的新药（指新药开发阶段，相对于新药而言，即临床前研究结束）NDA（NEW DRUG APPLICATION）：新药申请 ANDA（ABBREVIATED NEW DRUG APPLICATION）：简化新药申请 EP诉（EXPORT APPLICATION）：出口药申请（申请出口不被批准在美国销售的药品）TREATMENT IND：研究中的新药用于治疗 ABBREVIATED（NEW）DRUG：简化申请的新药 DMF（DRUG MASTER FILE）：药物主文件（持有者为谨慎起见而准备的保密资料，可以 包括一个或多个人用药物在制备、加工、包装和贮存过程中所涉及的设备、生产过程或物 品。只有在DMF持有者或授权代表以授权书的形式授权给FDA，FDA在审查IND、NDA、ANDA时才能参考其内容）HOLDER：DMF持有者 CFR（CODE OF FEDERAL REGULATION）：（美国）联邦法规 PANEL：专家小组 BATCH PRODUCTION：批量生产；分批生产 BATCH PRODUCTION RECORDS：生产批号记录 POST-OR PRE-MARKET SURVEILLANCE：销售前或销售后监督 INformED CONSENT：知情同意（患者对治疗或受试者对医疗试验了解后表示同意接 受治疗或试验）
FDA（FOOD AND DRUG ADMINISTRATION）：（美国）食品药品管理局 IND（INVESTIGATIONAL NEW DRUG）：临床研究申请（指申报阶段,相对于NDA而 言）；研究中的新药（指新药开发阶段，相对于新药而言，即临床前研究结束）NDA（NEW DRUG APPLICATION）：新药申请 ANDA（ABBREVIATED NEW DRUG APPLICATION）：简化新药申请 EP诉（EXPORT APPLICATION）：出口药申请（申请出口不被批准在美国销售的药品）TREATMENT IND：研究中的新药用于治疗 ABBREVIATED（NEW）DRUG：简化申请的新药 DMF（DRUG MASTER FILE）：药物主文件（持有者为谨慎起见而准备的保密资料，可以 包括一个或多个人用药物在制备、加工、包装和贮存过程中所涉及的设备、生产过程或物 品。只有在DMF持有者或授权代表以授权书的形式授权给FDA，FDA在审查IND、NDA、ANDA时才能参考其内容）HOLDER：DMF持有者 CFR（CODE OF FEDERAL REGULATION）：（美国）联邦法规 PANEL：专家小组 BATCH PRODUCTION：批量生产；分批生产 BATCH PRODUCTION RECORDS：生产批号记录 POST-OR PRE-MARKET SURVEILLANCE：销售前或销售后监督 INformED CONSENT：知情同意（患者对治疗或受试者对医疗试验了解后表示同意接 受治疗或试验）
PREscriptION DRUG：处方药 OTC DRUG（OVER—THE—COUNTER DRUG）：非处方药 U．S．PUBLIC HEALTH SERVICE：美国卫生福利部 NIH（NATIONAL INSTITUTE OF HEALTH）：（美国）全国卫生研究所 CLINICAL TRIAL：临床试验 ANIMAL TRIAL：动物试验 ACCELERATED APPROVAL：加速批准 STANDARD DRUG：标准药物 INVESTIGATOR：研究人员；调研人员
PREPARING AND SUBMITTING：起草和申报 SUBMISSION：申报；递交 BENIFIT（S）：受益 RISK（S）：受害 DRUG PRODUCT：药物产品 DRUG SUBSTANCE：原料药 ESTABLISHED NAME：确定的名称 GENERIC NAME：非专利名称 PROPRIETARY NAME：专有名称； INN（INTERNATIONAL NONPROPRIETARY NAME）：国际非专有名称 NARRATIVE SUMMARY记叙体概要 ADVERSE EFFECT：副作用 ADVERSE REACTION：不良反应 PROTOCOL：方案 ARCHIVAL COPY：存档用副本 REVIEW COPY：审查用副本 OFFICIAL COMPENDIUM：法定药典（主要指USP、NF）． USP（THE UNITED STATES PHARMACOPEIA）：美国药典（现已和NF合并一起出 版）NF（NATIONAL formULARY）：（美国）国家药品集 OFFICIAL＝PHARMACOPEIAL= COMPENDIAL：药典的；法定的；官方的 AGENCY：审理部门（指FDA）SPONSOR：主办者（指负责并着手临床研究者）IDENTITY：真伪；鉴别；特性 STRENGTH：规格；
规格含量（每一剂量单位所含有效成分的量）LABELED AMOUNT：标示量 REGULATORY SPECIFICATION：质量管理规格标准（NDA提供）REGULATORY METHODOLOGY：质量管理方法（FDA用于考核原料药或药物产品是 否符合批准了的质量管理规格标准的整套步骤）REGULATORY METHODS VALIDATION：管理用分析方法的验证（FDA对NDA提 供的方法进行验证）Dietary supplement：食用补充品 PREscriptION DRUG：处方药 OTC DRUG（OVER—THE—COUNTER DRUG）：非处方药 U．S．PUBLIC HEALTH SERVICE：美国卫生福利部 NIH（NATIONAL INSTITUTE OF HEALTH）：（美国）全国卫生研究所 CLINICAL TRIAL：临床试验 ANIMAL TRIAL：动物试验 ACCELERATED APPROVAL：加速批准 STANDARD DRUG：标准药物 INVESTIGATOR：研究人员；调研人员 PREPARING AND SUBMITTING：起草和申报 SUBMISSION：申报；递交 BENIFIT（S）：受益 RISK（S）：受害 DRUG PRODUCT：药物产品 DRUG SUBSTANCE：原料药 ESTABLISHED NAME：确定的名称 GENERIC NAME：非专利名称 PROPRIETARY NAME：专有名称； INN（INTERNATIONAL NONPROPRIETARY NAME）：国际非专有名称 NARRATIVE SUMMARY记叙体概要 ADVERSE EFFECT：副作用 ADVERSE REACTION：不良反应 PROTOCOL：方案 ARCHIVAL COPY：存档用副本 REVIEW COPY：审查用副本 OFFICIAL COMPENDIUM：法定药典（主要指USP、NF）． USP（THE UNITED STATES PHARMACOPEIA）：美国药典（现已和NF合并一起出 版）NF（NATIONAL formULARY）：（美国）国家药品集 OFFICIAL＝PHARMACOPEIAL= COMPENDIAL：药典的；法定的；官方的 AGENCY：审理部门（指FDA）SPONSOR：主办者（指负责并着手临床研究者）IDENTITY：真伪；鉴别；特性 STRENGTH：规格；规格含量（每一剂量单位所含有效成分的量）LABELED AMOUNT：标示量 REGULATORY SPECIFICATION：质量管理规格标准（NDA提供）REGULATORY METHODOLOGY：质量管理方法（FDA用于考核原料药或药物产品是 否符合批准了的质量管理规格标准的整套步骤）REGULATORY METHODS VALIDATION：管理用分析方法的验证（FDA对NDA提 供的方法进行验证）Dietary supplement：食用补充品
第三篇：证明资料中英文翻译
证明Certificate 兹有××社区××组居民××在社区表现良好，无违法犯罪记录，也未参加任何邪教组织。It is to hereby certify that ×× ××, as a resident of Group ×× in ×× Community, behaves well and is found of no criminal record.He has never joined any evil organization.情况属实The information given above is true and correct.××派出所 ×××Police Station
2××年××月××日 April ××, 2××× ××市公安局××区分局××派出所（章）
×× Police Station of ×× District Branch of ××Public Security Bureau(Seal)
××社区×× Community
20××年××月××日April ××, 2××× ××街道办事处××社区居民委员会（章）
×× Community Neighborhood Committee of ××Sub-district Office of ×××District(Seal)
证明资料中英文翻译模板 伊莱特翻译提供
电联我们：▲〇二八■八五〇九五八〇九◆
特此证明
第四篇：中英文对照资料外文翻译文献
中英文对照资料外文翻译文献
平设计任何时期平面设计可以参照一些艺术和专业学科侧重于视觉传达和介绍。采用多种方式相结合，创造和符号，图像和语句创建一个代表性的想法和信息。平面设计师可以使用印刷，视觉艺术和排版技术产生的最终结果。平面设计常常提到的进程，其中沟通是创造和产品设计。共同使用的平面设计包括杂志，广告，产品包装和网页设计。例如，可能包括产品包装的标志或其他艺术作品，举办文字和纯粹的设计元素，如形状和颜色统一件。组成的一个最重要的特点，尤其是平面设计在使用前现有材料或不同的元素。平面设计涵盖了人类历史上诸多领域，在此漫长的历史和在相对最近爆炸视觉传达中的第20和21世纪，人们有时是模糊的区别和重叠的广告艺术，平面设计和美术。毕竟，他们有着许多相同的内容，理论，原则，做法和语言，有时同样的客人或客户。广告艺术的最终目标是出售的商品和服务。在平面设计，“其实质是使以信息，形成以思想，言论和感觉的经验”。在唐朝（618-906）之间的第4和第7世纪的木块被切断打印纺织品和后重现佛典。阿藏印在868是已知最早的印刷书籍。在19世纪后期欧洲，尤其是在英国，平面设计开始以独立的运动从美术中分离出来。蒙德里安称为父亲的图形设计。他是一个很好的艺术家，但是他在现代广告中利用现代电网系统在广告、印刷和网络布局网格。于1849年，在大不列颠亨利科尔成为的主要力量之一在设计教育界，该国政府通告设计在杂志设计和制造的重要性。他组织了大型的展览作为庆祝现代工业技术和维多利亚式的设计。从1892年至1896年威廉•莫里斯凯尔姆斯科特出版社出版的书籍的一些最重要的平面设计产品和工艺美术运动，并提出了一个非常赚钱的商机就是出版伟大文本论的图书并以高价出售给富人。莫里斯证明了市场的存在使平面设计在他们自己拥有的权利，并帮助开拓者从生产和美术分离设计。这历史相对论是，然而，重要的，因为它为第一次重大的反应对于十九世纪的陈旧的平面设计。莫里斯的工作，以及与其他私营新闻运动，直接影响新艺术风格和间接负责20世纪初非专业性平面设计的事态发展。谁创造了最初的“平面设计”似乎存在争议。这被归因于英国的设计师和大学教授Richard Guyatt，但另一消息来源于20世纪初美国图书设计师William Addison Dwiggins。伦敦地铁的标志设计是爱德华约翰斯顿于1916年设计的一个经典的现代而且使用了系统字体设计。在20世纪20年代，苏联的建构主义应用于“智能生产”在不同领域的生产。个性化的运动艺术在 2 俄罗斯大革命是没有价值的，从而走向以创造物体的功利为目的。他们设计的建筑、剧院集、海报、面料、服装、家具、徽标、菜单等。Jan Tschichold 在他的1928年书中编纂了新的现代印刷原则，他后来否认他在这本书的法西斯主义哲学主张，但它仍然是非常有影响力。Tschichold，包豪斯印刷专家如赫伯特拜耳和拉斯洛莫霍伊一纳吉，和El Lissitzky 是平面设计之父都被我们今天所知。他们首创的生产技术和文体设备，主要用于整个二十世纪。随后的几年看到平面设计在现代风格获得广泛的接受和应用。第二次世界大战结束后，美国经济的建立更需要平面设计，主要是广告和包装等。移居国外的德国包豪斯设计学院于1937年到芝加哥带来了“大规模生产”极简到美国;引发野火的“现代”建筑和设计。值得注意的名称世纪中叶现代设计包括阿德里安Frutiger，设计师和Frutiger字体大学;保兰德，从20世纪30年代后期，直到他去世于1996年，采取的原则和适用包豪斯他们受欢迎的广告和标志设计，帮助创造一个独特的办法，美国的欧洲简约而成为一个主要的先驱。平面设计称为企业形象;约瑟夫米勒，罗克曼，设计的海报严重尚未获取1950年代和1960年代时代典型。从道路标志到技术图表，从备忘录到参考手册，增强了平面设计的知识转让。可读性增强了文字的视觉效果。设计还可以通过理念或有效的视觉传播帮助销售产品。将它应用到产品和公司识别系统的要素像标志、颜色和文字。连同这些被定义为品牌。品牌已日益成为重要的提供的服务范围，许多平面设计师，企业形象和条件往往是同时交替使用。教科书的目的是本科目，如地理、科学和数学。这些出版物已布局理论设计说明和图表。一个常见的例子，在使用图形，教育是图表人体解剖学。平面设计也适用于布局和格式的教育材料，使信息更容易和更容易理解的。平面设计是应用在娱乐行业的装饰，景观和视觉故事。其他的例子娱乐设计用途包括小说，漫画，电影中的开幕和闭幕，在舞台上节目的和道具的安排。这也包括艺术品在T恤衫的应用和其他物品的出售。从科学杂志报道，提出意见和事实往往是提高图形和深思熟虑的组成视觉信息-被称为信息的设计。报纸，杂志，博客，电视和电影纪录片，可以使用平面设计通知及娱乐。随着网络，信息与经验的交互设计的工具，Adobe和Flash正越来越多地被用来说明的背景新闻。一个平面设计项目可能涉及程式化和介绍现有的文字，或者事先存在的意向或图像开发的平面设计师。例如，一家报纸的故事始于记者和摄影记者，然后成为平面设计师的工作安排到一个合理的页面布局，并确定是否有任何其他图形元素应当要求。在一本杂志的文章或广告，往往是平面设计师或艺术总监将委员会摄影师或插图创建原始文件只是被纳入设计规划。现代设计的做法已经扩展到了现代的计算机，例如在使用所见的用户界面，通常被称为交互式设计，或多媒体设计。任何图形元素用于设计之前，图形元素必须是源于通过视觉艺术技能。这些图形通常（但并不总是）被设计师开发。视觉艺术的作品主要是视觉性的东西从使用传统的传播媒介、摄影或电脑产生的艺术。平面设计原则可以适用于每一个人的版画艺术元素，并最终组成。3 印刷术是艺术，工艺和技术型，修改类型字形，并安排类型的设计。类型字形（字符）的创建和修改使用各种说明方法。这项安排的类型是选择字体、大小、线长、主要的（行距）和文字的间距。刷术是由排字工机，排字，印刷工人，图形艺术家，艺术总监，工作者和办事员。直到数字时代，印刷成为一个专业的领域。数字化开辟了新的视觉设计师和用户。排版设计师平面设计的一部分，是在网页设计中是图形设计，处理安排风格（内容）的要素。从早期的照明网页手工复制书籍的中世纪和程序，以错综复杂的现代杂志和目录布局，适当的网页设计公司长期以来一直是考虑的印刷材料，与印刷媒体，内容通常包括类型（文字，图片（照片）偶尔发生持有者图形的内容，没有印刷油墨，如模具/激光切割，烫金压印或盲目压花。平面设计师常常专心研究于界面设计，如网页设计和软件设计，最终用户的交互性是一个设计考虑的布局或接口。视觉沟通技巧、互动沟通技巧与用户互动得相结合和在线品牌推广，平面设计师往往与软件开发和网络开发人员创建的外观和风格的网站或软件应用程序，来加强用户或网络网站的访问者互动体验。版画是在纸上，其他有机材料或者表面上印刷艺术品的过程。每一张不会被复制，但时最初的因为它不是一个复制的另一艺术作品，并在技术上称为留下深刻的印象。绘画或素描，另一方面，创造了独特的原始艺术品。版画是由一个单一的原始表面创造的，在技术上已经作为基质而被已知。常见的矩阵包括：金属板，通常是铜或锌的雕刻或蚀刻石料，用于光刻;块木刻的木材，油毡和织物板的丝网印刷。但也有许多其他种类，讨论如下：作品从一个单一的印刷板创造一个版本，在现代通常每个签署和编号，形成限量。打印也可编制成册，作为艺术家的书籍。一个单一的打印可能是产品的一种或多种技术。色彩学领域是如何在打印机上和显示器上用眼睛识别颜色和如何解释和组织这些色彩。眼睛的视网膜被两个被命名为视杆和视锥的感光体涵盖。视杆对光很敏感但是对颜色不是很敏感。视锥却与视杆恰恰相反。他们对光不太敏感，但是颜色可以被感知。随着科技的发展，人们越来越认识到环境问题日益严重，大气污染、森林破坏、水土流失、土地沙漠
化、水资源污染、大量物种灭绝、石油、天然气、煤等资源枯竭。作为工业设计师，应该有强烈的环境 保护意识，使得自己的设计建立在不破坏环境及节约自然资源的基础上。
其中，温室效应、臭氧层破坏和酸雨是当今全球性的三大环境问题。
温室效应就是大气变暖的效应其形成原因是太阳短波辐射可以透过大气射入地面，而地面增暖后放
出的长波辐射却被大气中的二氧化碳就像一层厚厚的玻璃，把地球变成了一个大暖房。甲烷、臭氧、氯、氟烃以及水汽等也对温室效应有所贡献。随着人口的急剧增加和工业的迅速发展，越来越多的二氧化碳 排入大气中；
又由于森林被大量砍伐，大气中原本应被森林吸收的二氧化碳没有被吸收，致使二氧化碳 逐渐增加，温室效应也不断增强。温室效应的后果十分严重，自然生态将随之发生重大变化，荒漠将扩
大，土地侵蚀加重，森林退向极地，旱涝灾害严重，雨量增加；温带冬天更湿、夏天更旱；热带也将变 得更湿，干热的亚热带变得更干旱，迫使原有水利工程重新调整。沿海将受到严重威胁。由于气温升高，两极冰块将融化，使海平面上升，将会淹没许多城市和港口。
臭氧层破坏现象引起科学界及整个国际社会的震动。美国的两位科学家 Monila 和 Rowland 指出，正是人为的活动造成了今天的臭氧洞。元凶就是现在所熟知的氟利昂和哈龙。
酸雨目前已成为一种范围广泛、跨越国界的大气污染现象。酸雨破坏土壤，使湖泊酸化，危害动植
物生长；刺激人的皮肤，诱发皮肤病，引起肺水肿、肺硬化；会腐蚀金属制品、油漆、皮革、纺织品和 含碳酸盐的建筑。
总而言之，人类生活的环境已经日益恶化。
而恶化的原因大部分属于人类本身的不良生活方式和不 尊重客观规律，急功近利，对于地球资源的使用没有科学的计划性，而且在设计、制造产品以及日常生
活中缺乏保护环境的意识，以至于自毁家园，其危害不仅于当代，而且严重影响了子孙后代的生存。
环境问题在很大程度上是由于人们的不良设计、生活方式造成的后果。于是给设计师们提出了一个
严肃的问题：作为设计师，应肩负起保护环境的历史重任！
工业在为人类创造大量物质财富的同时，也给世界带来了灾难。工业设计在为人类创造了现代生活
方式的同时，也加速了资源、能源的消耗，并对地球的生态平衡造成了巨大的破坏。
所以，作为工业设计师，建立环境意识体现了其道德和社会责任心。设计师必须对自己的设计负责，必须把人类的健康幸福，自然与人类的和谐共存作为设计中心遵循的原则。
设计师还必须掌握必要的材料、工艺、化工、制造等方面的知识，使得其设计不对环境造成危害而 成为可能。
“可持续发展设计” 这一概念的提出，对于人性的回归及世界真正意义上的发展具有划时代的意义。他体现了设计师的道德与责任，已成为 21 世纪设计发展的总趋势。从此，人类传统工业文明发展模式
转向现代生态文明发展模式。它是社会进步，经济增长，环境保护三者之间的协同。
可持续发展是人们应遵循的一种全新的伦理、道德和价值观念。其本质在于：充分利用现代科技，大力开发绿色资源，发展清洁生产，不断改善和优化生态环境，促使人与自然的和谐发展，人口、资源 和环境相互协调。
解决可持续反展问题是一个技术创新和行为模式转变的问题。
可持续发展战略是解决在不危害未来几代人的需求前提下，尽量满足当代人的需求的问题。实现目
前利益与长远利益的统一，为子孙后代留下发展空间。
目前可持续发展战略考虑的问题有：循环性、绿色能源、生态效率。
绿色设计源于人们对于现代技术文化所引起的环境及生态破坏的反思。绿色设计着眼于人与自然的
生态平衡关系，在设计过程的每一个决策中都充分考虑到环境效益，尽量减少对环境的破坏。
对工业设计师而言，绿色设计的核心是“ 3R ”，即“减少”（Reduce）、“再循环”(Recycle)和“再 利用”（Reuse)。不仅要尽量减少物质和能源的消耗、减少有害物质的排放，而且要使产品及零件能够 5 方便的分类回收，并再生循环或重新利用。
绿色设计不仅是一种技术层面的考虑，更重要的是一种观念 上的变革。
要求设计师放弃那种过分强调产品在外观上标新立异的做法，而将重点放在真正意义上的创 新上面，已一种更为负责的方法去创造产品的形态，用更简洁、长久的造型使产品尽可能地延长其使用 寿命。
从材料方面要考虑： 原材料的存量和可再生性，获取材料时的环境能源的消耗与污染，后续加工时
环境材料的易加工性，低能耗性、低污染性，报废时的可回收性。
从加工制造方面要考虑：加工制造阶段需要将污染减至最少，或将污染消灭在生产过程初始阶段。
从包装、运输、销售等方面要考虑：包装的环境性能、绿色包装，良好的可运输性、降低自重、减 少能耗，当地化生产及减少物流过程消耗。
从产品的使用阶段考虑： 使用中的能耗、资源消耗。
产品更新换代时环境性能的模块化、可重组性、产品的使用模式等因素。
从产品的报废阶段考虑：易拆卸性，便于分解和分类，材料可回收性和可再利用性，零部件可重组 性或移作它用等因素。
清洁的能源：如考虑太阳能、水电、风力的清洁燃料；清洁的材料，涉及低污染、无毒、易降解和 可回收性；清洁的制造过程，考虑低能耗、少排放的制造；清洁的产品，涉及使用中节能、环保、报废 后的回收。
零部件的再生利用湿可持续战略的有力措施。事实证明： 报废的产品拆卸后，经分析，其中材料在
改进设计后可重用和经翻新后可重用的比例可以提高。
比如：一辆报废车中，金属材料占 80 ％，其中，有色金属占 3 ％～ 4.7 ％。世界钢产量中的 45 ％是 由废钢铁生产出的。中国钢产量的 25 ％是由废钢铁生产的。
产品全生命周期管理是指从人对产品的需求开始，到产品淘汰报废的全部生命历程。其中包括产
品需求分析产品计划、概念设计、产品设计、数字化仿真、工艺准备、工艺规划、生产测试和质量监控、销售与分销、使用、维护与维修，以及报废与回收等主要阶段。将先进的管理理念和一流的信息技术有
机融入到现代企业的工业和商业运作中，从而使企业在数字经济时代能够有效地调整经营手段和管理方式，以发挥企业前所未有的竞争优势。帮助企业进行产品创新，赢得市场，并获得额外利润，以提高企业产品的价值。
GRAPHIC DESIGN The term graphic design can refer to a number of artistic and professional disciplines which focus on visual communication and presentation.Various methods are used to create and combine symbols, images and/or words to create a visual representation of ideas and messages.A graphic designer may use typography, visual arts and page layout techniques to produce the final result.Graphic design often refers to both the process by which the communication is created and the products which are generated.Common uses of graphic design include magazines, advertisements, product packaging and web design.For example, a product package might include a logo or other artwork, organized text and pure design elements such as shapes and color which unify the piece.Composition is one of the most important features of graphic design especially when using pre-existing materials or diverse elements.Graphic Design spans the history of humankind from the caves of Lascaux to the dazzling neons of Ginza.In both this lengthy history and in the relatively recent explosion of visual communication in the 20th and 21st centuries, there is sometimes a blurring distinction and over-lapping of advertising art, graphic design and fine art.After all, they share many of the same elements, theories, principles, practices and languages, and sometimes the same benefactor or client.In advertising art the ultimate objective is the sale of goods and services.In graphic design, “the essence is to give order to information, form to ideas, expression and feeling to artifacts that document human experience.” During the Tang dynasty(618–906)between the 4th and 7th century A.D.wood blocks were cut to print on textiles and later to reproduce Buddhist texts.A Buddhist scripture printed in 868 is the earliest known printed book.In late 19th century Europe, especially in the United Kingdom, the movement began to separate graphic design from fine art.Piet Mondrian is known as the father of graphic design.He was a fine artist, but his use of grids inspired the modern grid system used today in advertising, print and web layout.In 1849, Henry Cole became one of the major forces in design education in Great Britain, informing the government of the importance of design in his Journal of Design and Manufactures.He organized the Great Exhibition as a celebration of modern industrial technology and Victorian design.From 1892 to 1896 William Morris' Kelmscott Press published books that are some of the most significant of the graphic design products of the Arts and Crafts movement, and 2 made a very lucrative business of creating books of great stylistic refinement and selling them to the wealthy for a premium.Morris proved that a market existed for works of graphic design in their own right and helped pioneer the separation of design from production and from fine art.The work of the Kelmscott Press is characterized by its obsession with historical styles.This historicism was, however, important as it amounted to the first significant reaction to the stale state of nineteenth-century graphic design.Morris' work, along with the rest of the Private Press movement, directly influenced Art Nouveau and is indirectly responsible for developments in early twentieth century graphic design in general.Who originally coined the term “graphic design” appears to be in dispute.It has been attributed to Richard Guyatt, the British designer and academic, but another source suggests William Addison Dwiggins, an American book designer in the early 20th century The signage in the London Underground is a classic of the modern era and used a font designed by Edward Johnston in 1916.In the 1920s, Soviet constructivism applied 'intellectual production' in different spheres of production.The movement saw individualistic art as useless in revolutionary Russia and thus moved towards creating objects for utilitarian purposes.They designed buildings, theater sets, posters, fabrics, clothing, furniture, logos, menus, etc.Jan Tschichold codified the principles of modern typography in his 1928 book, New Typography.He later repudiated the philosophy he espoused in this book as being fascistic, but it remained very influential.Tschichold, Bauhaus typographers such as Herbert Bayer and Laszlo Moholy-Nagy, and El Lissitzky are the fathers of graphic design as we know it today.They pioneered production techniques and stylistic devices used throughout the twentieth century.The following years saw graphic design in the modern style gain widespread acceptance and application.A booming post-World War II American economy established a greater need for graphic design, mainly advertising and packaging.The emigration of the German Bauhaus school of design to Chicago in 1937 brought a “mass-produced”minimalism to America;sparking a wild fire of “modern”architecture and design.Notable names in mid-century modern design include Adrian Frutiger, designer of the typefaces Univers and Frutiger;Paul Rand, who, from the late 1930s until his death in 1996, took the principles of the Bauhaus and applied them to popular advertising and logo design, helping to create a uniquely American approach to European minimalism while becoming one of the principal pioneers of the subset of graphic design known as corporate identity；and Josef Müller-Brockmann, who designed posters in a severe yet accessible manner typical of the 1950s and 1960s era.3 From road signs to technical schematics, from interoffice memorandums to reference manuals, graphic design enhances transfer of knowledge.Readability is enhanced by improving the visual presentation of text.Design can also aid in selling a product or idea through effective visual communication.It is applied to products and elements of company identity like logos, colors, and text.Together these are defined as branding(see also advertising).Branding has increasingly become important in the range of services offered by many graphic designers, alongside corporate identity, and the terms are often used interchangeably.Textbooks are designed to present subjects such as geography, science, and math.These publications have layouts which illustrate theories and diagrams.A common example of graphics in use to educate is diagrams of human anatomy.Graphic design is also applied to layout and formatting of educational material to make the information more accessible and more readily understandable.Graphic design is applied in the entertainment industry in decoration, scenery, and visual story telling.Other examples of design for entertainment purposes include novels, comic books, opening credits and closing credits in film, and programs and props on stage.This could also include artwork used for t-shirts and other items screenprinted for sale.From scientific journals to news reporting, the presentation of opinion and facts is often improved with graphics and thoughtful compositions of visual information-known as information design.Newspapers, magazines, blogs, television and film documentaries may use graphic design to inform and entertain.With the advent of the web, information designers with experience in interactive tools such as Adobe Flash are increasingly being used to illustrate the background to news stories.A graphic design project may involve the stylization and presentation of existing text and either preexisting imagery or images developed by the graphic designer.For example, a newspaper story begins with the journalists and photojournalists and then becomes the graphic designer's job to organize the page into a reasonable layout and determine if any other graphic elements should be required.In a magazine article or advertisement, often the graphic designer or art director will commission photographers or illustrators to create original pieces just to be incorporated into the design layout.Contemporary design practice has been extended to the modern computer, for example in the use of WYSIWYG user interfaces, often referred to as interactive design, or multimedia design.Before any graphic elements may be applied to a design, the graphic elements must be originated by means of visual art skills.These graphics are often(but not always)developed 4 by a graphic designer.Visual arts include works which are primarily visual in nature using anything from traditional media, to photography or computer generated art.Graphic design principles may be applied to each graphic art element individually as well as to the final composition.Typography is the art, craft and techniques of type design, modifying type glyphs, and arranging type.Type glyphs(characters)are created and modified using a variety of illustration techniques.The arrangement of type is the selection of typefaces, point size, line length, leading(line spacing)and letter spacing.Typography is performed by typesetters, compositors, typographers, graphic artists, art directors, and clerical workers.Until the Digital Age, typography was a specialized occupation.Digitization opened up typography to new generations of visual designers and lay users.Page layout is the part of graphic design that deals in the arrangement and style treatment of elements(content)on a page.Beginning from early illuminated pages in hand-copied books of the Middle Ages and proceeding down to intricate modern magazine and catalog layouts, proper page design has long been a consideration in printed material.With print media, elements usually consist of type(text), images(pictures), and occasionally place-holder graphics for elements that are not printed with ink such as die/laser cutting, foil stamping or blind embossing.Graphic designers are often involved in interface design, such as web design and software design when end user interactivity is a design consideration of the layout or interface.Combining visual communication skills with the interactive communication skills of user interaction and online branding, graphic designers often work with software developers and web developers to create both the look and feel of a web site or software application and enhance the interactive experience of the user or web site visitor.Printmaking is the process of making artworks by printing on paper and other materials or surfaces.Except in the case of monotyping, the process is capable of producing multiples of the same piece, which is called a print.Each piece is not a copy but an original since it is not a reproduction of another work of art and is technically known as an impression.Painting or drawing, on the other hand, create a unique original piece of artwork.Prints are created from a single original surface, known technically as a matrix.Common types of matrices include: plates of metal, usually copper or zinc for engraving or etching;stone, used for lithography;blocks of wood for woodcuts, linoleum for linocuts and fabric plates for screen-printing.But there are many other kinds, discussed below.Works printed from a single
第五篇：中英文翻译
Fundamentals This chapter describes the fundamentals of today’s wireless communications.First a detailed description of the radio channel and its modeling are presented, followed by the introduction of the principle of OFDM multi-carrier transmission.In addition, a general overview of the spread spectrum technique, especially DS-CDMA, is given and examples of potential applications for OFDM and DS-CDMA are analyzed.This introduction is essential for a better understanding of the idea behind the combination of OFDM with the spread spectrum technique, which is briefly introduced in the last part of this chapter.1.1 Radio Channel Characteristics Understanding the characteristics of the communications medium is crucial for the appropriate selection of transmission system architecture, dimensioning of its components, and optimizing system parameters, especially since mobile radio channels are considered to be the most difficult channels, since they suffer from many imperfections like multipath fading, interference, Doppler shift, and shadowing.The choice of system components is totally different if, for instance, multipath propagation with long echoes dominates the radio propagation.Therefore, an accurate channel model describing the behavior of radio wave propagation in different environments such as mobile/fixed and indoor/outdoor is needed.This may allow one, through simulations, to estimate and validate the performance of a given transmission scheme in its several design phases.1.1.1 Understanding Radio Channels In mobile radio channels(see Figure 1-1), the transmitted signal suffers from different effects, which are characterized as follows: Multipath propagation occurs as a consequence of reflections, scattering, and diffraction of the transmitted electromagnetic wave at natural and man-made objects.Thus, at the receiver antenna, a multitude of waves arrives from many different directions with different delays, attenuations, and phases.The superposition of these waves results in amplitude and phase variations of the composite received signal.Doppler spread is caused by moving objects in the mobile radio channel.Changes in the phases and amplitudes of the arriving waves occur which lead to time-variant multipath propagation.Even small movements on the order of the wavelength may result in a totally different wave superposition.The varying signal strength due to time-variant multipath propagation is referred to as fast fading.Shadowing is caused by obstruction of the transmitted waves by, e.g., hills, buildings, walls, and trees, which results in more or less strong attenuation of the signal strength.Compared to fast fading, longer distances have to be covered to significantly change the shadowing constellation.The varying signal strength due to shadowing is called slow fading and can be described by a log-normal distribution [36].Path loss indicates how the mean signal power decays with distance between transmitter and receiver.In free space, the mean signal power decreases with the square of the distance between base station(BS)and terminal station(TS).In a mobile radio channel, where often no line of sight(LOS)path exists, signal power decreases with a power higher than two and is typically in the order of three to five.Variations of the received power due to shadowing and path loss can be efficiently counteracted by power control.In the following, the mobile radio channel is described with respect to its fast fading characteristic.1.1.2 Channel Modeling The mobile radio channel can be characterized by the time-variant channel impulse response h(τ , t)or by the time-variant channel transfer function H(f, t), which is the Fourier transform of h(τ , t).The channel impulse response represents the response of the channel at time t due to an impulse applied at time t − τ.The mobile radio channel is assumed to be a wide-sense stationary random process, i.e., the channel has a fading statistic that remains constant over short periods of time or small spatial distances.In environments with multipath propagation, the channel impulse response is composed of a large number of scattered impulses received over Np different paths，Where
and ap, fD,p, ϕp, and τp are the amplitude, the Doppler frequency, the phase, and the propagation delay, respectively, associated with path p, p = 0,..., Np − 1.The assigned channel transfer function is
The delays are measured relative to the first detectable path at the receiver.The Doppler Frequency
depends on the velocity v of the terminal station, the speed of light c, the carrier frequency fc, and the angle of incidence αp of a wave assigned to path p.A channel impulse response with corresponding channel transfer function is illustrated in Figure 1-2.The delay power density spectrum ρ(τ)that characterizes the frequency selectivity of the mobile radio channel gives the average power of the channel output as a function of the delay τ.The mean delay τ , the root mean square(RMS)delay spread τRMS and the maximum delay τmax are characteristic parameters of the delay power density spectrum.The mean delay is
Where
Figure 1-2 Time-variant channel impulse response and channel transfer function with frequency-selective fading is the power of path p.The RMS delay spread is defined as Similarly, the Doppler power density spectrum S(fD)can be defined that characterizes the time variance of the mobile radio channel and gives the average power of the channel output as a function of the Doppler frequency fD.The frequency dispersive properties of multipath channels are most commonly quantified by the maximum occurring Doppler frequency fDmax and the Doppler spread fDspread.The Doppler spread is the bandwidth of the Doppler power density spectrum and can take on values up to two times |fDmax|, i.e.，1.1.3Channel Fade Statistics The statistics of the fading process characterize the channel and are of importance for channel model parameter specifications.A simple and often used approach is obtained from the assumption that there is a large number of scatterers in the channel that contribute to the signal at the receiver side.The application of the central limit theorem leads to a complex-valued Gaussian process for the channel impulse response.In the absence of line of sight(LOS)or a dominant component, the process is zero-mean.The magnitude of the corresponding channel transfer function
is a random variable, for brevity denoted by a, with a Rayleigh distribution given by
Where
is the average power.The phase is uniformly distributed in the interval [0, 2π].In the case that the multipath channel contains a LOS or dominant component in addition to the randomly moving scatterers, the channel impulse response can no longer be modeled as zero-mean.Under the assumption of a complex-valued Gaussian process for the channel impulse response, the magnitude a of the channel transfer function has a Rice distribution given by
The Rice factor KRice is determined by the ratio of the power of the dominant path to thepower of the scattered paths.I0 is the zero-order modified Bessel function of first kind.The phase is uniformly distributed in the interval [0, 2π].1.1.4Inter-Symbol(ISI)and Inter-Channel Interference(ICI)The delay spread can cause inter-symbol interference(ISI)when adjacent data symbols overlap and interfere with each other due to different delays on different propagation paths.The number of interfering symbols in a single-carrier modulated system is given by
For high data rate applications with very short symbol duration Td < τmax, the effect of ISI and, with that, the receiver complexity can increase significantly.The effect of ISI can be counteracted by different measures such as time or frequency domain equalization.In spread spectrum systems, rake receivers with several arms are used to reduce the effect of ISI by exploiting the multipath diversity such that individual arms are adapted to different propagation paths.If the duration of the transmitted symbol is significantly larger than the maximum delay Td τmax, the channel produces a negligible amount of ISI.This effect is exploited with multi-carrier transmission where the duration per transmitted symbol increases with the number of sub-carriers Nc and, hence, the amount of ISI decreases.The number of interfering symbols in a multi-carrier modulated system is given by
Residual ISI can be eliminated by the use of a guard interval(see Section 1.2).The maximum Doppler spread in mobile radio applications using single-carrier modulation is typically much less than the distance between adjacent channels, such that the effect of interference on adjacent channels due to Doppler spread is not a problem for single-carrier modulated systems.For multi-carrier modulated systems, the sub-channel spacing Fs can become quite small, such that Doppler effects can cause significant ICI.As long as all sub-carriers are affected by a common Doppler shift fD, this Doppler shift can be compensated for in the receiver and ICI can be avoided.However, if Doppler spread in the order of several percent of the sub-carrier spacing occurs, ICI may degrade the system performance significantly.To avoid performance degradations due to ICI or more complex receivers with ICI equalization, the sub-carrier spacing Fs should be chosen as
such that the effects due to Doppler spread can be neglected(see Chapter 4).This approach corresponds with the philosophy of OFDM described in Section 1.2 and is followed in current OFDM-based wireless standards.Nevertheless, if a multi-carrier system design is chosen such that the Doppler spread is in the order of the sub-carrier spacing or higher, a rake receiver in the frequency domain can be used [22].With the frequency domain rake receiver each branch of the rake resolves a different Doppler frequency.1.1.5Examples of Discrete Multipath Channel Models Various discrete multipath channel models for indoor and outdoor cellular systems with different cell sizes have been specified.These channel models define the statistics of the 5 discrete propagation paths.An overview of widely used discrete multipath channel models is given in the following.COST 207 [8]: The COST 207 channel models specify four outdoor macro cell propagation scenarios by continuous, exponentially decreasing delay power density spectra.Implementations of these power density spectra by discrete taps are given by using up to 12 taps.Examples for settings with 6 taps are listed in Table 1-1.In this table for several propagation environments the corresponding path delay and power profiles are given.Hilly terrain causes the longest echoes.The classical Doppler spectrum with uniformly distributed angles of arrival of the paths can be used for all taps for simplicity.Optionally, different Doppler spectra are defined for the individual taps in [8].The COST 207 channel models are based on channel measurements with a bandwidth of 8–10 MHz in the 900-MHz band used for 2G systems such as GSM.COST 231 [9] and COST 259 [10]: These COST actions which are the continuation of COST 207 extend the channel characterization to DCS 1800, DECT, HIPERLAN and UMTS channels, taking into account macro, micro, and pico cell scenarios.Channel models with spatial resolution have been defined in COST 259.The spatial component is introduced by the definition of several clusters with local scatterers, which are located in a circle around the base station.Three types of channel models are defined.The macro cell type has cell sizes from 500 m up to 5000 m and a carrier frequency of 900 MHz or 1.8 GHz.The micro cell type is defined for cell sizes of about 300 m and a carrier frequency of 1.2 GHz or 5 GHz.The pico cell type represents an indoor channel model with cell sizes smaller than 100 m in industrial buildings and in the order of 10 m in an office.The carrier frequency is 2.5 GHz or 24 GHz.COST 273: The COST 273 action additionally takes multi-antenna channel models into account, which are not covered by the previous COST actions.CODIT [7]: These channel models define typical outdoor and indoor propagation scenarios for macro, micro, and pico cells.The fading characteristics of the various propagation environments are specified by the parameters of the Nakagami-m distribution.Every environment is defined in terms of a number of scatterers which can take on values up to 20.Some channel models consider also the angular distribution of the scatterers.They have been developed for the investigation of 3G system proposals.Macro cell channel type models have been developed for carrier frequencies around 900 MHz with 7 MHz bandwidth.The micro and pico cell channel type models have been developed for carrier frequencies between 1.8 GHz and 2 GHz.The bandwidths of the measurements are in the range of 10–100 MHz for macro cells and around 100 MHz for pico cells.JTC [28]: The JTC channel models define indoor and outdoor scenarios by specifying 3 to 10 discrete taps per scenario.The channel models are designed to be applicable for wideband digital mobile radio systems anticipated as candidates for the PCS(Personal Communications Systems)common air interface at carrier frequencies of about 2 GHz.UMTS/UTRA [18][44]: Test propagation scenarios have been defined for UMTS and UTRA system proposals which are developed for frequencies around 2 GHz.The modeling of the multipath propagation corresponds to that used by the COST 207 channel models.HIPERLAN/2 [33]: Five typical indoor propagation scenarios for wireless LANs in the 5 GHz frequency band have been defined.Each scenario is described by 18discrete taps of the delay power density spectrum.The time variance of the channel(Doppler spread)is modeled by a classical Jake’s spectrum with a maximum terminal speed of 3 m/h.Further channel models exist which are, for instance, given in [16].1.1.6Multi-Carrier Channel Modeling Multi-carrier systems can either be simulated in the time domain or, more computationally efficient, in the frequency domain.Preconditions for the frequency domain implementation are the absence of ISI and ICI, the frequency nonselective fading per sub-carrier, and the time-invariance during one OFDM symbol.A proper system design approximately fulfills these preconditions.The discrete channel transfer function adapted to multi-carrier signals results in
where the continuous channel transfer function H(f, t)is sampled in time at OFDM symbol rate s and in frequency at sub-carrier spacing Fs.The duration
s is the total OFDM symbol duration including the guard interval.Finally, a symbol transmitted onsub-channel n of the OFDM symbol i is multiplied by the resulting fading amplitude an,i and rotated by a random phase ϕn,i.The advantage of the frequency domain channel model is that the IFFT and FFT operation for OFDM and inverse OFDM can be avoided and the fading operation results in one complex-valued multiplication per sub-carrier.The discrete multipath channel models introduced in Section 1.1.5 can directly be applied to(1.16).A further simplification of the channel modeling for multi-carrier systems is given by using the so-called uncorrelated fading channel models.1.1.6.1Uncorrelated Fading Channel Models for Multi-Carrier Systems These channel models are based on the assumption that the fading on adjacent data symbols after inverse OFDM and de-interleaving can be considered as uncorrelated [29].This assumption holds when, e.g., a frequency and time interleaver with sufficient interleaving depth is applied.The fading amplitude an,i is chosen from a distribution p(a)according to the considered cell type and the random phase ϕn,I is uniformly distributed in the interval [0,2π].The resulting complex-valued channel fading coefficient is thus generated independently for each sub-carrier and OFDM symbol.For a propagation scenario in a macro cell without LOS, the fading amplitude an,i is generated by a Rayleigh distribution and the channel model is referred to as an uncorrelated Rayleigh fading channel.For smaller cells where often a dominant propagation component occurs, the fading amplitude is chosen from a Rice distribution.The advantages of the uncorrelated fading channel models for multi-carrier systems are their simple implementation in the frequency domain and the simple reproducibility of the simulation results.1.1.7Diversity The coherence bandwidth of a mobile radio channel is the bandwidth over which the signal propagation characteristics are correlated and it can be approximated by
The channel is frequency-selective if the signal bandwidth B is larger than the coherence bandwidth.On the other hand, if B is smaller than , the channel is frequency nonselective or flat.The coherence bandwidth of the channel is of importance for evaluating the performance of spreading and frequency interleaving techniques that try to exploit the inherent frequency diversity Df of the mobile radio channel.In the case of multi-carrier transmission, frequency diversity is exploited if the separation of sub-carriers transmitting the same information exceeds the coherence bandwidth.The maximum achievable frequency diversity Df is given by the ratio between the signal bandwidth B and the coherence bandwidth，The coherence time of the channel is the duration over which the channel characteristics can be considered as time-invariant and can be approximated by
If the duration of the transmitted symbol is larger than the coherence time, the channel is time-selective.On the other hand, if the symbol duration is smaller than , the channel is time nonselective during one symbol duration.The coherence time of the channel is of importance for evaluating the performance of coding and interleaving techniques that try to exploit the inherent time diversity DO of the mobile radio channel.Time diversity can be exploited if the separation between time slots carrying the same information exceeds the coherence time.A number of Ns successive time slots create a time frame of duration Tfr.The maximum time diversity Dt achievable in one time frame is given by the ratio between the duration of a time frame and the coherence time, A system exploiting frequency and time diversity can achieve the overall diversity
The system design should allow one to optimally exploit the available diversity DO.For instance, in systems with multi-carrier transmission the same information should be transmitted on different sub-carriers and in different time slots, achieving uncorrelated faded replicas of the information in both dimensions.Uncoded multi-carrier systems with flat fading per sub-channel and time-invariance during one symbol cannot exploit diversity and have a poor performance in time and frequency selective fading channels.Additional methods have to be applied to exploit diversity.One approach is the use of data spreading where each data symbol is spread by a spreading code of length L.This, in combination with interleaving, can achieve performance results which are given for
by the closed-form solution for the BER for diversity reception in Rayleigh fading channels according to [40]
Whererepresents the combinatory function，and σ2 is the variance of the noise.As soon as the interleaving is not perfect or the diversity offered by the channel is smaller than the spreading code length L, or MCCDMA with multiple access interference is applied,(1.22)is a lower bound.For L = 1, the performance of an OFDM system without forward error correction(FEC)is obtained, 9
which cannot exploit any diversity.The BER according to(1.22)of an OFDM(OFDMA, MC-TDMA)system and a multi-carrier spread spectrum(MC-SS)system with different spreading code lengths L is shown in Figure 1-3.No other diversity techniques are applied.QPSK modulation is used for symbol mapping.The mobile radio channel is modeled as uncorrelated Rayleigh fading channel(see Section 1.1.6).As these curves show, for large values of L, the performance of MC-SS systems approaches that of an AWGN channel.Another form of achieving diversity in OFDM systems is channel coding by FEC, where the information of each data bit is spread over several code bits.Additional to the diversity gain in fading channels, a coding gain can be obtained due to the selection of appropriate coding and decoding algorithms.中文翻译 1基本原理
这章描述今日的基本面的无线通信。第一一个的详细说明无线电频道，它的模型被介绍，跟随附近的的介绍的原则的参考正交频分复用多载波传输。此外，一个一般概观的扩频技术，尤其ds-cdma，被给，潜力的例子申请参考正交频分复用，DS对1。分配的通道传输功能是
有关的延误测量相对于第一个在接收器检测到的路径。多普勒频率
取决于终端站，光速c，载波频率fc的速度和发病路径分配给速度v波αp角度页具有相应通道传输信道冲激响应函数图1-2所示。
延迟功率密度谱ρ（τ）为特征的频率选择性移动无线电频道给出了作为通道的输出功能延迟τ平均功率。平均延迟τ，均方根（RMS）的时延扩展τRMS和最大延迟τmax都是延迟功率密度谱特征参数。平均时延特性参数为
有
图1-2时变信道冲激响应和通道传递函数频率选择性衰落是权力页的路径均方根时延扩展的定义为 同样，多普勒频谱的功率密度（FD）的特点可以定义
在移动时变无线信道，并给出了作为一种金融衍生工具功能的多普勒频率通道输出的平均功率。多径信道频率分散性能是最常见的量化发生的多普勒频率和多普勒fDmax蔓延fDspread最大。多普勒扩散是功率密度的多普勒频谱带宽，可价值观需要两年时间| fDmax|，即
1.1.3频道淡出统计
在衰落过程中的统计特征和重要的渠道是信道模型参数规格。一个简单而经常使用的方法是从假设有一个通道中的散射，有助于在大量接收端的信号。该中心极限定理的应用导致了复杂的值的高斯信道冲激响应过程。在对视线（LOS）或线的主要组成部分的情况下，这个过程是零的意思。相应的通道传递函数幅度
是一个随机变量，通过给定一个简短表示由瑞利分布，有
是的平均功率。相均匀分布在区间[0，2π]。
在案件的多通道包含洛杉矶的或主要组件除了随机移动散射，通道脉冲响应可以不再被建模为均值为零。根据信道脉冲响应的假设一个复杂的值高斯过程，其大小通道的传递函数A的水稻分布给出
赖斯因素KRice是由占主导地位的路径权力的威力比分散的路径。I0是零阶贝塞尔函数的第一阶段是一致kind.The在区间[0，2π]分发。
1.1.4符号间（ISI）和通道间干扰（ICI）
延迟的蔓延引起的符号间干扰（ISI）当相邻的数据符号上的重叠与互相不同的传播路径，由于不同的延迟干涉。符号的干扰在单载波调制系统的号码是给予
对于高数据符号持续时间很短运输署<蟿MAX时，ISI的影响，这样一来，速率应用，接收机的复杂性大大增加。对干扰影响，可以抵消，如时间或频域均衡不同的措施。在扩频系统，与几个臂Rake接收机用于减少通过利用多径分集等，个别武器适应不同的传播路径的干扰影响。
如果发送符号的持续时间明显高于大的最大延迟运输署蟿最大，渠道产生ISI的微不足道。这种效果是利用多载波传输的地方，每发送符号的增加与子载波数控数目，因此，ISI的金额减少的持续时间。符号的干扰多载波调制系统的号码是给予
可以消除符号间干扰由一个保护间隔（见1.2节）的使用。
最大多普勒在移动无线应用传播使用单载波调制通常比相邻通道，这样，干扰对由于多普勒传播相邻通道的作用不是一个单载波调制系统的问题距离。对于多载波调制系统，子通道间距FS可以变得非常小，这样可以造成严重的多普勒效应ICI的。只要所有子载波只要是一个共同的多普勒频移金融衍生工具的影响，这可以补偿多普勒频移在接收器和ICI是可以避免的。但是，如果在对多普勒子载波间隔为几个百分点的蔓延情况，卜内门可能会降低系统的性能显着。为了避免性能降级或因与ICI卜内门更复杂的接收机均衡，子载波间隔财政司司长应定为
这样说，由于多普勒效应可以忽略不扩散（见第4章）。这种方法对应于OFDM的1.2节中所述，是目前基于OFDM的无线标准遵循的理念。
不过，如果多载波系统的设计选择了这样的多普勒展宽在子载波间隔或更高，秩序是在频率RAKE接收机域名可以使用[22]。随着频域RAKE接收机每个支部耙解决了不同的多普勒频率。
1.1.5多径信道模型的离散的例子
各类离散多与不同的细胞大小的室内和室外蜂窝系统的信道模型已经被指定。这些通道模型定义的离散传播路径的统计信息。一种广泛使用的离散多径信道模型概述于下。造价207[8]：成本207信道模型指定连续四个室外宏蜂窝传播方案，指数下降延迟功率密度谱。这些频道功率密度的离散谱的实现都是通过使用多达12个频道。与6频道设置的示例列于表1-1。在这种传播环境的几个表中的相应路径延迟和电源配置给出。丘陵地形导致最长相呼应。
经典的多普勒频谱与均匀分布的到达角路径可以用于简化所有的频道。或者，不同的多普勒谱定义在[8]个人频道。207信道的成本模型是基于一个8-10兆赫的2G，如GSM系统中使用的900兆赫频段信道带宽的测量。造价231[9]和造价259[10]：这些费用是行动的延续成本207扩展通道特性到DCS1800的DECT，HIPERLAN和UMTS的渠道，同时考虑到宏观，微观和微微小区的情况为例。空间分辨率与已定义的通道模型在造价259。空间部分是介绍了与当地散射，这是在基站周围设几组圆的定义。三种类型的通道模型定义。宏细胞类型具有高达500〜5000米，载波频率为900兆赫或1.8 GHz的单元尺寸。微细胞类型被定义为细胞体积约300米，1.2 GHz或5 GHz载波频率。细胞类型代表的Pico与细胞体积小于100工业建筑物和办公室中的10 m阶米室内信道模型。载波频率为2.5 GHz或24千兆赫。造价273：成本273行动另外考虑到多天线信道模型，这是不是由先前的费用的行为包括在内。
CODIT [7]：这些通道模型定义的宏，微，微微蜂窝和室外和室内传播的典型案例。各种传播环境的衰落特性是指定的在NakagamiSS）的不同扩频码L是长度，如图1-3所示的系统。没有其他的分集技术被应用。QPSK调制用于符号映射。移动无线信道建模为不相关瑞利衰落信道（见1.1.6）。由于这些曲线显示，办法，AWGN信道的一对L时，对MC-SS系统性能有很大价值。
另一种实现形式的OFDM系统的多样性是由前向纠错信道编码，在这里，每个数据位的信息分散在几个代码位。附加在衰落信道分集增益，编码增益一个可因适当的编码和解码算法的选择。
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