接收机参数

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1、Receiver Parameters 接收机参数 云南监测站业务室 2011年3月Content目录*Receiver Parameters*接收机参数 1、 Noise Figure 噪声系数2、 MDS 最小可探测信号3、 Sensitivity 灵敏度4、 IP2/IP3 二阶截获点 / 三阶截获点5、 1dB compression 1dB压缩点6、 Oscillator phase noise 振荡器相位噪声7、 2nd / 3rd IFfilter 第2/第3中频滤波器8、 Dynamic range / Spurious free dynamic range 动态范围/无杂散动

2、态范围* Receiver Operating Modes*接收机工作模式1、Low noise mode 低噪声模式2、Normal mode 常规模式3、Low distortion mode 低失真模式Noise 噪声The physical causes for this effect ultimately lie in irregular electron movements.有电流的地方就有噪声。这种现象的产生归结为电子的不规则运动。The following principle applies: The higher the current, the more noise is

3、generated in our receiver.我们的接收机遵循下面的原则：电流越大，接收机产生的噪声就越大。We must therefore try a low-current receiver design, although this very quickly conflicts with its linearity.因此，我们将尽量采用低电流的接收机设计，尽管这与接收机的线性度形成了冲突。（接收机电流越小，接收机的线性度就越低。这就形成了一对矛盾）The requirements for low noise (NF) and high linearity (IP3) are op

4、posite in nature.对于低噪声（NF噪声系数）和高线性度（IP3三阶截获点）的要求在本质上是相反的，是一对矛盾关系。Noise is understood as the inherent noise of a receiver, which reduces the original signal-to-noise ratio of an input signal.噪声被理解为接收机的固有噪声（内部噪声），它降低了输入信号的信噪比。Inherent noise is therefore a measure of the sensitivity of the receiver. It

5、 allows conclusions as to the minimum level the signals must have to be detectable save.所以固有噪声（内部噪声）是衡量接收机灵敏度的尺度之一。由此得出结论：内部噪声是可靠检测小信号的关键。The inherent noise is usually expressed as a bandwidth-independent value: Noise Figure(NF).固有噪声通常表示为一个与带宽无关的值：噪声系数（NF）。MDS-Minimum Detectable Signal = DNL最小可探测信号M

6、DS = -174dBm + NF + 10log(RBW/1Hz) + 3dB(RBW/1Hz) Best MDS-value for RBW =1 Hz当RBW=1Hz时可以得到最好的MDS.3dB important to calculate SFDR2 and SFDR3对于计算2阶和3阶无杂散动态范围很重要MDS/dBm = minimum detectable signal 最小可探测信号 单位：dBm-174 dBm = basic noise floor at room temperature( 1 Hz BW) 室温下的最小基本噪声NF / dB = noise figure

7、 噪声系数 单位：dBRBW / Hz = used resolution band width 所用分辨力带宽3 dB = noise level + equal signal level increase power by 3dB (if signal is in phase with random noise phase ) 噪声电平 + 等信号电平增加3dB功率（如果信号相位与噪声相位同相）Sensitivity 灵敏度 The sensitivity of a receiver is calculated from 接收机的灵敏度计算方法如下：Pin, min(dBm) = -174

8、dBm / Hz + NF + 10lgBW + S/NBW e.g. demod BW=6KHz for AM 带宽 例如 AM的解调带宽为6KHz e.g. demod BW= 15KHz for FM 例如 FM的解调带宽为15KHzS/N e.g. S/N = 12dB for AM信噪比 例如 AM信噪比为12dB e.g. S/N = 20dB for FM 例如 FM信噪比为20dBDepending on the demodulation mode, a specific S/N is applied:E.g. S/N = 12 dB for AM, S/N = 20 dB f

9、or FM信噪比取决于不同的解调方式，例如AM中S/N取12dB，FM中S/N取20dBIn dBm , V or dBuV灵敏度用不同单位dBm 、V、dBuV的转换公式 With P(W)= (10P(dBm)/10)10-3 in W 用W为单位时的表达式and Vin ,min = in V W到V的转换公式Or with in dBuV.V到dBuV的转换公式。（已知噪声系数可以计算出接收机灵敏度，同样已知接收机灵敏度也可以计算出噪声系数）Intermodulation , IP2,IP3二阶、三阶交调截取点Nonlinear characteristics of the activ

10、e stages (amplifier/mixer) generate unwanted signals in the form of intermodulation products if two or more signals are applied to the input at the same time.由于有源器件（放大器或混频器）的非线性特性，当两个或更多信号同时输入有源器件（放大器/混频器）时会产生干扰信号形成互调产物。These unwanted signals should therefore be kept as low as possible. The linearit

11、y of active stages grows with increasing current or power, i.e. The more current available for amplifier stages and for LO power for mixers, the higher the linearity of the concept.因此这些不需要的（干扰）信号应该尽可能的低。有源器件的线性度是随着电流或功率的增加而增加的，即这样一个概念：放大器级的电流越大并且混频器的本振功率越大，那么线性度就越高。But remember: this directly confli

12、cts with the noise requirement.但是要记住：这与噪声要求直接冲突。（电流越大噪声也越大）Low power consumption = limited linearity低功耗 = 有限的线性度（功耗低线性度也低）IP2 and IP3 are synthetic values - can not be measured in the real worldIP2和IP3是一个合成值（人工计算结果），在现实世界中是不能被直接测量的。3rd order intermodulation - in-band -out-of-band三阶带内交调和三阶带外交调两个频率间隔近

13、的信号产生的交调产物落在中频滤波器内的叫带内交调；两个频率间隔远的信号产生的交调产物没有在中频滤波器中的叫带外交调。An out-of-band IP3 might be of interest , if the influence of very strong signals next to the frequency range of interest are present (e.g. Radar Pulses)如果三阶交调产物对邻近频率范围内的大信号产生的影响存在，那么我们可能会对这个三阶带外交调感兴趣（例如：雷达脉冲）。1dB compression point (1dB CP)1d

14、B压缩点The 1dB compression point specifies in dBm the input level at which the receiver starts to deviate from the linear amplitude behaviour.如果用dBm表示输入电平，那么1dB压缩点就是指偏离线性区1dB时的输入电平。In the linear range , each level increase by a dB at the input means the same increase in the level displayed on the recei

15、ver.在线性范围内，输入增加多少dB，接收机上的显示也增加相同的dB数。The input level at which the display deviats by 1dB from the linear behaviour is the 1dB compression point.显示结果偏离输入电平1dB时的输入电平就是1dB压缩点。High 1dB CP value = high linearity = high IP values1dB压缩点的值大线性度高交调截获点的值大Measurement is simple: apply the signal with a signal ge

16、nerator to the receiver input and increase the level until the receiver display shows 1dB less than the signal generator setting.测量1dB压缩点的值是很简单的：在接收机的输入端接入一个带有信号发生器的信号源，增加输入信号的电平值，直到接收机显示的信号小于信号发生器设置值的1dB为止（这时的输入电平就是该接收机的1dB压缩点。）Oscillator phase noise振荡器相位噪声衡量本振频率稳定性的重要指标Phase noise is a measure of

17、the short-term stability of oscillators that are used for the conversion to different IF.相位噪声是衡量振荡器的短期频率稳定度的重要指标，振荡器用于把不同的频率转换到中频。Phase noise is caused by variations of phase, frequency and amplitude. It appears as a bell-shaped noise characteristic at the oscillator signal.相位噪声是由于幅度、相位和频率的变化引起的。在振荡

18、器信号中相位噪声显示为一种钟形噪声特性。The phase noise is usually specified, depending on the carrier offset, as a single-sideband phase noise referenced to the carrier offset.相位噪声总是具体的，取决于载波偏移，作为相对于载波偏移的一个单边带噪声。Particularly critical is the phase noise of the 1st LO, the synthesizer, which we need to tune our receiver

19、.尤其关键的是第一个本振的相位噪声，我们需要调谐我们接收机的合成器。Phase noise is measured at a specific carrier offset and stated in -dBc/Hz.相位噪声的测量是在特定载频偏移下进行的，用-dBc/Hz以下。dBc specifies the (level) difference (in dB) to the carrier.dBc表示以dB为单位的载波偏移量f（载波偏移后与原来载波之差）/Hz means that the noise is reference to 1 Hz bandwidth./Hz 表示相位噪声是相

20、对于1Hz带宽而言的。For comparability, the carrier offset must always be specified, e.g. EB500: -120dBc/Hz10KHz offset.为了有可比性，载波偏移量必须始终被指定，例如：EB500的相位噪声在指定载波偏移10KHz下小于等于-120dBc/Hz。Data sheet specifications without offset cannot be compared because the phase noise decreases with increasing carrier offset.没有指定

21、偏移量的相位噪声数据表是不能进行比较的，因为相位噪声是随着载波偏移量的增加而减小的。Conversion of the oscillator signal to the IF振荡器信号转换为中频信号The input signal is mixed with the LO signal.输入信号与本振信号混合（相乘）。Direct conversion receivers avoid this effect直接变换法的接收机可以避免相位噪声的影响No LO signal needed no LO phase noise present没有引入本振信号就不会引入相位噪声Limitation: u

22、pper frequency limit around 30MHz (to keep a sufficient A/D converter solution, e.g. 16 bit)直接变换法的局限性： 上限频率限制在大约30MHz（为了保证A/D转换器的充分转换，例如 16位的A/D转换器）大于30MHz的信号就不能使用直接变换法了（A/D转换器精度位数受限）2nd or 3rd IF filter第2第3中频滤波器These are the filters of the last stage in the IF section这些滤波器是中频部分的最后一级For measurements

23、 to ITU, a bandwidth of 6dB is standard. 在ITU测量中，有一个6dB带宽的标准The more selective (steeper) the filter, the smaller the shape factor.选择性越好（越陡峭）的滤波器，它的形状因子越小。Standard values for: analog filters: 2:1 to 8:1 Digital filters: 1.2:1 to 2.5:1典型值如： 模拟滤波器：从2:1到8:1 数字滤波器：从1.2:1 到 2.5:1Digital filters are much s

24、teeper than analog filters.数字滤波器比模拟滤波器更加陡峭。3dB（6 dB） bandwidth, shape factor3dB（6 dB）带宽形状因子Shape factor (e.g. 1.7:1)OrShape factor (e.g. 1:1.7)形状因子 （例如：1.7:1）或者形状因子 （例如：1:1.7）注意：分母表示-60dB或者-3dB对应的带宽值 分子表示-3dB或者-60dB对应的带宽值 Synthesizer setting time 合成器稳定时间（到调谐稳定的时间）This parameter specifies the setting

25、 time of a synthesizer (1st LO) required for a frequency change.Data sheet specifications are for example:Synthesizer setting time 3 ms , 1 ms typ.频率合成器转换时间指频率合成器从某一个频率转换到另一个频率,并达到稳定所需要的时间。这个参数描述了合成器（第一个本振）在改变频率时稳定下来的时间。 例如，数据表这样描述：典型的合成器稳定时间=3 ms , 1ms这个时间越短，扫描速度就越快。However, we must distinguish bet

26、ween the frequency changes we are talking about.然而，我们必须要区分我们讨论的频率变化。The above value for example applies only to random (large) frequency hops in big frequency steps in FFM mode in functions like FSCAN/MSCAN上面例子中的取值只适用于随机的（大的）频率跳变，大的频率步进，如频率扫描和存储扫描模式。Spurious free dynamic range无杂散动态范围杂散是指不包括输出频率谐波的其它

27、寄生输出频率The spurious free dynamic range (SFDR) specifies the dynamic range where the receiver is free of distortion and intermodulation products.无杂散动态范围（SFDR）是指接收机在没有失真和不产生互调产物情况下的动态范围。It is defined as the difference in dB between receiver noise and the level of two equal spurious signals whose interm

28、odulation products are equal to the receiver noise.无杂散动态范围被定义为用dB表示的，接收机噪声和两个相等杂散信号的电平的差，这两个杂散信号的互调产物与接收机噪声相等。We differentiate between:我们要区分：二阶无杂散动态范围和三阶无杂散动态范围 SFDR2 = 1/2(IP2+174-NF-10lgBW)SFDR3 = 2/3(IP3+174-NF-10lgBW)SFDR2：二阶无杂散动态范围SFDR3：三阶无杂散动态范围上式中IP2表示二阶截取点的值， IP3表示三阶截取点的值，-（174-NF-10lgBW）表示M

29、DS最小可检测信号（参见前面MDS定义）。为了帮助理解，在这里解释一下SFDR3：若接收机的三阶互调产物折合到输入端恰好等于基底噪声，则此时的输入信号Pin,max规定为上限，下限输入信号规定为最小可探测信号MDS，两者之差即为SFDR3。SFDR3=Pin , max -MDS。如果输入三阶截点值为IIP3，则SFDR3表示为： SFDR3= 2/3（IIP3-MDS）Max. Input level without producing nonlinear effects by compression通过压缩输入电平不产生非线性效应的最大输入电平值Max. Input level witho

30、ut producing IP3-products不产生三阶互调产物时的最大输入电平值Max. Input level without producing IP2- products不产生二阶互调产物时的最大输入电平值Receiver operating modes接收机工作模式Low noise mode低噪声模式最高灵敏度，低线性度Normal mode常规模式适中的灵敏度和适中的线性度Low distortion mode低失真模式接收机灵敏度低，线性度较高How to calculate?任何计算？Where are the differences?各种工作模式的区别在那里？各种工作模

31、式的连接图System calculation 系统的计算Frequency: 500MHz / bandwidth: 1KHz频率：500MHz / 带宽：1KHzIntermediate data points for the calculations中间要计算的数据点1、2和3System noise figure系统噪声系数Aim of the calculations计算目的The noise figure NF has to be evaluated step by step from the receiver to the antenna interface噪声系数NF必须从接收

32、机到天线接口一步一步地求解。This overall system noise figure leads to a noise power at the system impedance (= MDS / minimum detectable signal)这个整体的系统噪声系数在系统阻抗上产生了一个噪声功率（= MDS / 最小可探测信号）Input 1dB compression point输入1dB压缩点Aim of the calculations计算目的The 1dB compression point has to be evaluated step by step from th

33、e Rx to the antenna interface1dB压缩点也必须从接收到天线接口一步一步地求解。This overall system 1dB compression point is used to calculate the max. allowed signal level at the input of the system without nonlinear effects by compression整个系统的1dB压缩点用于计算在没有非线性效应下的系统输入端最大输入电平值。Input IP2输入二阶截取点Aim of the calculations计算目的The I

34、P2 of the system has to be evaluated step by step from the Rx to the antenna interface同样地，系统的二阶截取点也必须从接收到天线接口一步一步地求解This overall system IP2 is used to calculate the max. Allowed signal level at the input of the system without producing intermodulation products above the noise level这个整体的系统IP2被用来计算不产生

35、大于噪声电平以上的互调产物时的系统最大输入电平值Input IP3输入三阶截取点 (IIP3)Aim of the calculations计算目的The IP3 of the system has to be evaluated step by step from the Rx to the antenna interface同样地，系统的三阶截取点也必须从接收到天线接口一步一步地求解This overall system IP3 is used to calculate the max. Allowed signal level at the input of the system wit

36、hout producing intermodulation products above the noise level这个整体的系统IP3被用来计算不产生大于噪声电平以上的互调产物时的系统最大输入电平值输入IP3和输入IP2的计算参数差不多，在这里就不在解释。Receiver operating modes接收机工作模式比较Low noise mode低噪声模式High gain amplifier高增益Low noise figure噪声系数低Very sensitivity具有较高灵敏度Weak IP3 (amplifier itself)较差的IP3（放大器本身）G：增益/dB NF

37、：噪声系数/dB ICP：输入1dB压缩点/dBm IP2：二阶截取点/dBm IP3：三阶截取点/dBm MDS：最小可检测信号/dBm(灵敏度下限)DR：动态范围 / dB SFDR2：二阶无杂散动态范围/dB SFDR_3：三阶无杂散动态范围/dBNormal mode 常规模式Medium gain amplifier放大器增益适中Medium noise figure中等的噪声系数Sensitivity适中的灵敏度More robust IP3 (amplifier itself)更好的三阶截取点（放大器本身）由表可以看出：相比于低噪声模式，接收机的放大器增益有所下降、噪声系数有所增

38、加、IP2和IP3增加，所以在常规模式下，接收机的灵敏度下降、增益下降但是线性度有所好转。我们推荐使用常规模式，因为在这种模式下有较为适中的各个参数。Low distortion mode低失真模式Attenuator instead of amplifier !低失真模式下衰减器取代了低噪声放大器Not sensitivity在这种模式下灵敏度非常低Robust IP3低失真模式下IP3很好，接收机线性度较好Result comparison - low noise vs. Normal mode结果比较：低噪声模式与常规模式的比较MDS：low noise mode 6 dB better

39、 than normal mode最小可监测信号：低噪声模式比常规模式高6个dBSFDR_3：normal mode 5 dB better than low noise modeSFDR_3：常规模式比低噪声模式高出5个dBResult comparison - Normal mode VS. low distortion mode结果比较：常规模式与低失真模式的比较MDS：normal mode 28dB better than low distortion mode最小可监测信号：常规模式比低失真模式高出28个dB值SFDR_3：low distortion mode 4 dB bett

40、er than normal modeSFDR_3：低失真模式比常规模式大4个dBCombination of low noise mode and low distortion mode would be the optimum低噪声模式和低失真模式的组合将是接收机的最佳工作模式but not possible, because of physical reasons但是，由于物理的因素，这种组合是不可能实现的。Therefore:因此：Normal mode, as best alternative mode for monitoring purposes常规模式是我们监测的最佳工作模式Good MDS很好的最小可监测信号Good dynamic range 很好的动态范围Good monitoring results有较好的监测结果