时间同步系统短波校时失败分析及解决方法

针对时间同步系统短波校时失败的现象,给出了一种数模结合实现的相关自动增益控制(AGC)电路模型。短波校时接收机采用超外差接收机方案,结合短波授时的特点,找到校时失败的原因。介绍了短波授时的信号格式,分析了模拟非相关自动增益控制电路对接收机的影响——模拟的自动增益控制电路容易使传输信号的幅度和相位发生畸变,并且对输入信号的响应时间慢。最后通过分析计算,建立了数模结合的相关自动增益控制电路模型。实验测试结果表明,采用此设计的短波校时接收机能解决信号格式及信道失真引起的短波校时的不同问题,对短波校时接收机的设计具有指导作用。     

解析1～40GHz短距离设备电磁兼容欧洲标准

对短距离设备（SRD）欧洲标准ETSI EN300 440-1 V1.6.1进行解读,介绍了测试模型的选取、测试环境条件,同时较详尽地分析了发射机和接收机的参数要求,其中发射机参数主要包括有效全向辐射功率、工作带宽、杂散发射和占空比。接收机参数主要有临近信道选择性、阻塞性能和接收机杂散。最后,对传导和辐射测试场地和试验布置,以及SRD设备中常用的几种频谱访问机制进行了概括说明。     

NEBS认证—传导发射

介绍了 NEBS 认证测试中对待认证设备对外端口传导发射的要求,其中有电源端口、信号端口、模拟音频端口和通信端口的传导发射要求。交流端口的传导发射要求测试噪声电压和噪声电流,其他端口要求测试噪声电流,不能用测试噪声电压代替噪声电流的测试。     

Multitone Feedback Through Demodulating Log Detector for Detection of Spurious Emissions in Software Radio

This paper provides an analysis of a log detector in order to determine its response to a multitone input for detection of spurious emissions in a radio frequency transmitter. Treatment is given to the single tone response of the log detector and extended to a two-tone log detector system, where a large signal and a small signal are present. The large signal is observed to experience logarithmic processing with an output at zero frequency. The small signal produces an output at the difference frequency of the large signal frequency and small signal frequency that is approximately proportional to the ratio of the small signal voltage to the large signal voltage. The two-tone results are generalized to an m-tone input. Experimental results are presented to show the accuracy of the model. The log detector circuit analyzed is able to detect a spurious emission within 45 MHz of the main signal with plusmn1 dB of accuracy.     

AGC系统抗干扰方法改进

以VHF系统接收机AGC电路为例介绍了传统自动增益控制电路工作原理,针对VHF系统接收出现杂音情况,阐明了传统AGC电路缺乏强干扰措施,影响VHF系统后续信号处理,造成通信中断。通过分析带内强干扰在传统AGC电路内的作用机制和无线电系统带内强干扰的AGC电压表现的规律,提出了在传统AGC电路上增加数字比较电路,自动识别带内强干扰,调整放大增益并在输出端进行放大限幅,进而消除带内强干扰。     

A VHF Implementation of a LINC Amplifier

LINC is a technique that uses signal processing to produce Linear amplification of bandpass signals with grossly Nonlinear circuit Components. The important signal processing functions in LINC are forming two constant envelope phase modulated signal components from the bandpass input signal and recombining the amplified components to produce an amplified replica of the input signal. Two- and three-tone laboratory tests of a complete LINC amplifier show that, at full output, spurious levels 40 dB below tone level are achievable for tone spacings of 100 kHz. Because the laboratory model is operated at relatively low frequencies (hundreds of MHz), scaling up in frequency should result in a LINC with < 40 dB spurious over a considerably wider band. Lower spurious levels or bandwidths of several tens of MHz will require asin^{-1}phase modulator that is less sensitive to delay in a feedback loop and a wider-bandwidth lower-distortion input limiter.     

一种用于软件无线电的接收机射频前端电路设计与实现

设计了一种用于软件无线电的射频前端电路,该电路可工作于短波、超短波频段（3～89MHz）。电路将天线接收的信号经过前端滤波、AGC、放大处理后,将输出信号稳定到2V,直接送给下级进行A/D采样及基带处理。设计的核心是宽带AGC电路,采用了一种级联VGA的形式,较大地提高了AGC电路的动态范围和线性范围。经过硬件实测,该接收电路灵敏度能够达到-90dBm,动态范围为70dB,并且具有线性度高、噪声系数小等特点。     

3G系统中AGC的FPGA设计实现

详细介绍了数字AGC的基本原理,3G接收机需要采用AGC电路处理输入的无线信号,从而给无线环路中的可变增益放大器或数控衰减器提供外部控制信号,使得无线链路输出基本恒定且与输入信号电平无关的信号给基带部分处理,同时在很宽的范围内保持线性。RF输入电压经IF放大后,检波器检测出该电压的包络。该包络电压经AGC处理后,产生增益可变器件的控制电压,从而减小IF的输入和增益。     

船载卫星天线中AGC参考信号的提取方法

在船载卫星天线系统中,需要一个能反映天线接收信号强弱的参考量.笔者在分析了数字卫星电视接收机中AGC产生的原理以及其可作为参考信号的可行性后,利用TMS320F2812 DSP的I/O接口模拟I2C总线时序,控制BS2F7HZ0194一体化调谐解调器,成功提取出卫星天线控制器所需的AGC参考信号.试验表明,该AGC信号能如实地反映天线接收信号的强弱.     

基于Simulink的数字AGC系统设计与仿真

在Simulink环境下搭建了数字自动增益控制（AGC）系统的仿真平台,该平台由中频信号模型、可控增益放大器、A/D采样与I、Q分离模型及峰值提取和AGC控制算法部分组成,各个部件与真实器件、模块相对应,且参数可变。该平台按照真实AGC系统的信号流程进行仿真,能够为数字AGC算法的性能进行预测和评估,为AGC系统的参数选择提供了分析工具。     

The application of automatic gain control to microwave radiometers

An automatic gain control system for stabilizing the gain of microwave radiometers is described. System analysis sets forth the requirements for gain and bandwidth of the AGC loop. Two systems are described. One is a continuous AGC system that maintains a constant detector voltage and, as a result, the system gain is a function of the input signal. For input signals which are small compared to the system noise temperatures the nonlinearity due to the AGC system is negligible. In the second system, the output of the detector is sampled when the receiver comparison switch is connected to the reference termination. Therefore, the gain of the system is not affected by the signal and no nonlinearity is caused by the AGC system. The effect of noise in the AGC loop is analyzed and it is shown that the time constant of the AGC system can be made shorter than the final system output filter without increasing the over-all system noise.     

Wavelet-based nonlinear AGC method for hearing aid loudnesscompensation

Hearing impairment can often be corrected by medical or surgical treatment, provided the loss is not due to cochlear pathology (sensorineural loss). For sensorineural loss, the only corrective action is to wear a hearing aid. Many perceptual differences between normal and sensorineural hearing-impaired listeners are due to differences in the dB levels at which sound is detected by the ear (auditory threshold) and the associated dynamic range over which it is comfortable to listen to (loudness sensation). To adequately compensate for this, the processing of the auditory signal should be nonlinear and time-varying. Two wavelet-based compression algorithms have been developed: automatic gain control (AGC) with linear amplification and nonlinear compression AGC. The nonlinear AGC is a compression algorithm, which models loudness sensation. The wavelet transform separates the input into seven frequency bands corresponding to the critical bands of the human auditory system. For each frequency band, multiplying the wavelet coefficients by the gain can amplify or compress nonlinearly and smoothly, depending on the signal level, time and spectrum. Results suggest that the nonlinear approach, while maintaining the general spectral structure of the signal, is perceptually superior to linear AGC and compensates better for audibility loss     

A four-port scattering matrix formalism for p-i-n traveling-wavephotodetectors

This paper presents a full four-port characterization for traveling-wave optoelectronic devices, in particular, traveling-wave photodetectors (TWPDs), resulting in a scattering matrix formalism, which can be used for passive as well as active devices. A set of coupled distributed equivalent circuits is proposed for modeling the device, taking into account the wanted detection and spurious emission of light. A scattering matrix formalism is established, predicting the performances of the device at microwaves, when a microwave signal is used either for modulating the intensity of the optical power (forward detection mode) or for biasing the p-i-n junction (reverse emission mode). Hence, the obtained four-port device is nonreciprocal. Some symmetry properties are induced by the physical symmetry of the device. It has matched inputs, when symmetric electrical and optical reference loads are used. The scattering matrix satisfies power conservation laws. The formalism may be used to optimize the designs of TWPD's by varying the loads at each of the four ports     

基于FPGA的大动态数控AGC系统设计

自动增益控制(AGC)是接收机的重要问题,传统模拟实现精度不高、灵活性差、调试复杂。介绍了一种大动态数控AGC实现方法,直接累加均方值估算信号功率,经对数运算后与参考值比较,得到对应需放大或缩小的功率值,通过查表再反馈控制前端,全过程由程序控制实现,执行元件为DVGA芯片AD8370。仿真及实测结果表明,该方法对信号功率变化响应迅速、控制精度较高,且适合FPGA实现,动态范围可达70dB。     

基于AGC算法的音频信号处理方法及FPGA实现

在语言通信系统中,为准确、清晰地接收到语音信息,需要克服语音接受中的干扰和音频信息源不稳定等因素。文中研究了基于实现AGC算法的音频信号处理方法以及FPGA实现,通过对AGC算法、音频AGC算法的设计、音频AGC算法FPGA的实现等研究,总结出基于实用AGC算法的音频信号处理方法及FPGA的实现,可降低音频信号失真程度,大幅提升了音频信号输出的稳定性。实验结果表明,实用AGC算法在音频信号处理和FPGA实现中的应用,具有良好的性能。     

基于VC＋＋信号源自动测试软件设计

在信号的频率、功率、相位噪声和杂散测试中，传统的人工测试方法往往要花费大量时间，已不满足现代快速测试要求，因此，对于信号频率、功率、相位噪声、杂散自动化快速测试是十分必要的。本文基于VC＋＋6．0开发平台，设计了信号源自动测试软件，实验证明，该软件界面友好，操作简单，能快速测试信号各项指标。     

Analog AGC Circuitry for a CMOS WLAN Receiver

The IEEE 802.11a standard uses orthogonal frequency division multiplexing (OFDM) to allow high data rates in multipath WLAN environments. The high peak-to-average power ratio (PAPR) of OFDM signals, along with stringent settling-time constraints, make conventional closed-loop automatic gain control (AGC) schemes impractical for WLAN receivers. In a direct conversion receiver, AGC and channel-select filtering are performed by analog baseband circuitry. A baseband signal processor using a new open-loop analog gain-control algorithm for OFDM is described. The new AGC algorithm uses switched coarse gain-setting steps followed by an analog open-loop fine gain-setting step to set the final gain of variable gain amplifiers (VGAs). The AGC was implemented in a 0.18-$muhbox m$CMOS process using newly designed circuits including linear VGAs, RMS detectors, and current-mode computation circuitry. Simulation and measurement results verify that the new AGC circuit converges with gain error less than 1dB to the desired level within 5.6$muhbox s$.     

A Floating-Point ADC with Variable Gain Pipeline Stages

Typically an automatic gain control (AGC) amplifier is needed in a receiver to control the amplitude of the signal at the input of the ADC. To get rid of the AGC, a floating-point pipelined analog-to-digital converter (FP-ADC), which consists of variable gain stages, is presented. The frontend pipeline stages of the ADC use a larger gain if the value of the signal is small. If the value of the signal is large, they act as typical pipeline stages. Thus, the small values of the signal are converted using higher resolution than larger values. The dynamic range of the ADC is increased and a separate AGC is not needed.     

解析315～600kHz短距离设备电磁兼容欧洲标准

介绍了短距离设备欧洲标准ETSI EN 302 536-1 V1.1.1的测试模型选取方法,测试条件,以及电源和环境要求。同时,分析了辐射测试场地和测试布置。最后,详尽解读了315～600 kHz频段短距离设备的载波输出电平、调制带宽、杂散发射和占空比等发射机参数,以及接收机杂散等接收机参数。     

手机杂散干扰控制方法

结合测试结果与产品设计,总结了排查问题的流程。分析了手机中出现杂散干扰的不同原因,比如由手机的发射机、功率切换、等效天线和电源芯片等引起的杂散发射,并分别提出了滤波、调整信号上升沿/下降沿时间、消除等效天线等整改措施。整改后,手机杂散测试合格。