数字蜂窝系统的信号传输技术

本文介绍数字信号传输技术，着重介绍调制与解调，猝发信号传输与接收、分集接收。线性调制在移动无线电应用中日益受到重视。对于恒定包络数字ＦＭ例如ＧＭＳＫ，这是一种很好的选择，由于带宽要求更窄。采用尼奎斯特滤波的ｎ／４位移ＱＰＳＫ已作为日本的数字蜂窝标准。     

数字信号处理式摄像机头到控制单元的全数字信号传输系统（上）

本主要讨论目前数字摄像机中机头数字信号处理（DSP）到控制单元CCU的数字信号传输问题，包括摄像机数字信号在三同轴电缆和光纤中传输所要解决的信号格式、标准及速率变换，缆线特性对传输数字信号的影响及其解决办法，传输方案形式及有关参数选择的考虑。     

MPEG压缩信号的测试

在计算机成为常事的同时，经压缩的数据流也是这样。测试这些数据流的设备不仅必须能提供某种形式的读出，而且还要能分析测试中的各他层次。其过程比它初看起来复杂些，而且它需要有相当多的经验以及讲究的设备。对系统测试方法的这个根本性变化做好准备，将使向先进电视（ＡＴＶ）的过渡顺利。     

多模雷达信号重频跟踪器系统的设计

针对目前越来越多使用的多模雷达,提出一种适合跟踪多模雷达信号的重频跟踪器系统。跟踪器系统加入了跟踪雷达数据库,60通道的波门输出可以采用合成波门输出方式。跟踪器系统由数字信号处理器和现场可编程门阵列实现。     

电缆电视系统信号电平变化综合分析

就电缆电视系统信号电平变化的几种情形作系统的理论分析，并指出解决办法，供广大有线电视系统工作人员参考。     

能处理宽电压范围的快速稳定的微微安培计电路

对模拟开关、多路复用器、运算放大器和其它IC的评估是对IC测试工程师提出的挑战。典型的测试需要把测试电压或强制电压施加到器件的输入端,并测量导致的任何泄漏电流和偏移电流,这经常是在1pA或更低的级别进行的。图1、图2、图3中的低功耗测量电路与缓慢而昂贵的商品化自动测试仪形成了鲜明对比,这种电路能强制很宽的测试电压范围并提供快速稳定,使器件测试吞吐速度达到最高。表面贴装元件的广泛使用使它的印制电路板空间要求降到了最低,并使多个测量电路的封装能靠近测试夹具。     

A low-power wide dynamic range envelope detector

We report a 75-dB 2.8-/spl mu/W 100-Hz-10-kHz envelope detector in a 1.5-/spl mu/m 2.8-V CMOS technology. The envelope detector performs input dc insensitive voltage-to-current converting rectification followed by novel nanopower current-mode peak detection. The use of a subthreshold wide linear range transconductor allows greater than 1.7-V/sub pp/ input voltage swings. We show theoretically that the optimal performance of this circuit is technology independent for the given topology and may be improved only by spending more power due to thermal noise rectification limits. A novel circuit topology is used to perform 140-nW peak detection with controllable attack and release time constants. We demonstrate good agreement of experimentally measured results with theory. The envelope detector is useful in low-power bionic implants for the deaf, hearing aids, and speech-recognition front-ends.     

Linearization of receivers using envelope signal injection

This paper presents a new linearization method for receivers employing envelope signal injection. In this technique, the third-order intermodulation distortion (IM3), at the output of a mixer in IF band, is cancelled by injecting the envelope of the RF input signal to both the low noise amplifier (LNA) and the mixer. By properly adjusting the amplitude and polarity of the injected envelope signal, up to 40-dB improvement of the IM3 and 11-dB improvement of the IM5 is obtained in a two tone test with 100-kHz separation at 1.9GHz. This method operates very well over a wide range of power up to the 1-dB compression point of the receiver. The noise performance of the receiver under this linearization technique is also investigated. The noise floor at the output of the receiver is increased by 0.8 dB only when the system is optimized for linearity.     

冷链物流的变质传感信号追踪器的设计与实现

当前变质传感信号追踪器采用广播无线电波技术,不能有效对变质信号进行采集,追踪精度不高,整体性能低下。为此,设计与实现了一种新的冷链物流的变质传感信号追踪器,介绍了追踪器的硬件总体结构以及控制芯片和电源电路的设计过程,通过CMOS传感器对光子进行探测,对食物变质情况进行成像处理。为了准确获取所有子节点的环境数据,设计了一套主节点和追踪器之间的数据帧格式,给出追踪器软件的基本流程。实验结果表明该追踪器能够有效地对变质传感信号进行追踪。     

一种宽范围微弱直流信号测量的简单方法

介绍一种采用对数运算功放大器MAX4206的测量方法,可实现1 nA～1 mA直流电流的测量,电路设计简单.实验结果表明,采用该系统测量直流信号,测量精度和分辨率高,重复性好,并已成功应用于场发射测试系统,用于测量场发射电流,能满足系统测量要求.     

An envelope signal based deconvolution algorithm for ultrasound imaging

To improve the quality of medical ultrasound images, a number of restoration methods based on demodulated signals have been proposed in the literature. However, due to the shift of center frequency of transmitted ultrasound pulses at different penetration depth in a lossy medium, it is hard to determine the exact center frequency at a specified position so to achieve satisfactory demodulation. In this paper, this problem is dealt with by a novel restoration method based on envelope models of the radio frequency (RF) and the point spread function (PSF) signals. To cope with the ill inverse problem caused by the narrow band PSF, an envelop signal based sparse regularized deconvolution model is derived under a sparsity assumption of the tissue reflectivity function (TRF). Furthermore, a two-step iterative shrinkage/thresholding (TwIST) method based alternating minimization approach is applied to compute the optimal solution of the proposed deconvolution problem. Finally, the robustness and the practicability of the proposed method are demonstrated by a series of experiments on both numerical simulation and in vivo data. The experimental results show that the proposed method can achieve significant improvement of the ultrasound images in terms of the resolution gain and signal-to-noise ratio (SNR).     

Linearization of mixers using predistortion and envelope signal injection

This letter presents a new linearization method for mixers employing predistortion and envelope signal injection. In this technique the third order intermodulation distortion (IM3), at the output of a mixer in IF band, was cancelled by using a diode predistortor and injecting the envelope of the RF input signal to both the predistortor and the mixer. By properly adjusting the amplitude and polarity of the injected envelope signal, up to 26 dB improvement of the IM3 is obtained in a two tone test with 100 kHz separation at 1.9 GHz. This method operates very well over a wide range of output power up to the 1 dB compression point of the mixer.     

Multicarrier constant envelope OFDM signal design for radar applications

Orthogonal frequency division multiplexing (OFDM) radar signals have been introduced for high range resolution radars. These signals have prominent properties such as favorable ambiguity function, high bandwidth efficiency, and possibility of use in dual mode radar/communication systems. But the large amplitude fluctuations of the OFDM signal make it susceptible to system nonlinearities. To alleviate this problem, constant envelope OFDM (CE-OFDM) signal has been introduced which combines orthogonal frequency division multiplexing and phase modulation or frequency modulation. Although several works have been reported on OFDM radar signal design, there is no a systematic approach for designing CE-OFDM signals for radar applications. In this paper we will focus on CE-OFDM signal design for radar applications. Two different methods for designing a CE-OFDM signal with favorable ambiguity functions are introduced. The first one is based on modulating a complementary set of sequences on different sub-carriers while the second is based on using a proper single carrier coded signal and then extracting its most similar multicarrier OFDM or CE-OFDM coded signal.     

Retrospective shading correction algorithm based on signal envelope estimation

An additive retrospective non-parametric algorithm for the correction of the inhomogeneous intensity background of images, commonly known as shading, is presented. The algorithm assumed that an original unbiased image was corrupted by slowly-varying shading that could be estimated from the signal envelope in a process analogous to amplitude modulation detection. Unlike other filtering algorithms, the algorithm did not require pre-processing, parameter setting, user interaction, computationally intensive optimisation algorithms nor a restriction in size of the objects of interest relative to the scale of background variations. The algorithm provided satisfactory results for artificial and microscopical images.     

Reducing signal timing variations in inter-core busses

This work presents the semi-random net reordering (SRNR) technique for averaging inductive coupling in inter-core busses. The technique works by redistributing the inductive coupling from near neighbors to far neighbors through repeated semi-random net order changes at every bus turn. By utilizing the vias and layer changes that exist at the bus turn, the technique requires no additional resources. As a result, SRNR is able to significantly reduce transition speed and propagation delay variations caused by the variation in inductive coupling within the bus.