超强功能PCM1738 D/A变换器--支持SACD/DSD和DVD的PCM音频组件

目前正处在数字影音技术更新换代的关键时期。人们已熟视了姗姗来迟的DVD,而高清晰度的数字电视,还处于“只听雷声响,未见雨下来”的状况。但数字音频技术先声夺人,以此为基础的集成电路已纷纷投放市场。其中最闪亮的一块PCM1738D/A变换器就是范例。     

日本PCM录音机的现状

本文简要地回顾了PCM录音机的历史。对PCM录音机和模拟录音机在主要性能方面进行了比较,指出了PCM化的优点。叙述了PCM录音机的构成框图和纠错、检错方法。介绍了日本PCM录音机的现状,最后对SONY和松下两家公司为了适应录像机伴音高保真化、视频唱片和直播电视卫星伴音PCM化的形势而新研制的两种录像机电视伴音PCM化的VTR作了重点介绍。     

D型全塑PCM电缆及应用

本文介绍2Mb/s传输系统选用PCM电缆的考虑,它的结构及其中继段长度计算,并提出PCM电缆应用与施工中的几个问题。     

传送数据的PCM电路为何会自动振铃

山东省青岛卫星地球站的数据网采用MDT－30型PCM终端机的音频话路作为数据传输信道,把甲、乙两地的E－08分组交换机经MODEM与PCM终端机的音频话路相接,使处于不同地区的数据网连接起来,见图1所示。　　曾有一段时间,发现这条电路的信息传输中断,且出现频繁的自动振铃现象。正常工作的分组交换机和MODEM均不会发出铃流信号,那么是什么原因使电路自动振铃呢？ 　　分析后认为这种现象可能是以下某种原因造成的： 　　（1）　MDT－30型PCM终端机信令系统故障。　　（2）　MDT－30型PCM终端机话路的电路稳定度不合格,电路自…     

4200测试系统在PCM参数测试中的应用

为了使4200型半导体特性描述系统（以下简称4200系统）能够最大限度地发挥作用，根据工作需要将该系统首次用于PCM参数测试。同时，与使用传统的晶体管图示仪测试的PCM参数进行了对比。结果表明，4200系统在PCM参数测试中具有很高的实用性，为稳定工艺提供了可靠监控手段。     

什么叫PCM

PCM是Pulse Code Modulation的简写,译为脉码调制,但通常叫PCM较方便.PCM信号是真正的数字信号,数字通信网就是利用PCM信号.所以,谈起数字通信,必然提到PCM.怎样形成PCM信号呢?约略地说,从模拟信号变成PCM信号,须经历三个主要步骤,它们是:(1)取样——对模拟信号每隔一定时间取它的幅度值.(2)量化——看取样得到的幅度值落在某一层次附近.(3)编码——按照取样量化的层次,     

高性能PCM1794解码器的制作

工作之余，历时半年，经历了3次打样．我的PCM1794DAC电路PCB终于完成了。本电路主要以同轴解码，兼顾PCHi—Fi，DAC芯片采用的是PCM1794，数字接收采用的是目前公认基抖最小的DIR9001，USB接收用的是PCM2706。     

中兴ZXSM—10智能PCM系统及其应用

描述了中兴ZXSM－10智能PCM系统的系统结构、应用范围、性能特点及其在电力网和铁路上的组网应用。     

基于混沌序列的遥测PCM数据加密算法

指出了在遥测系统中应用信息保密技术的必要性。结合遥测数据加密的基本要求,提出对遥测PCM数据进行混沌加密的方法,着重分析了遥测PCM系统的信息加密方案和密钥同步实现措施。该措施有助于遥测信号中断后的密钥重新准确同步,另外还对收发两端密钥同步的可靠性进行了理论计算,同时分析讨论了该遥测PCM混沌加密系统的安全性能。仿真结果表明,该方法没有引起收端的误码扩散,而且能够确保遥测PCM系统的加密强度要求。     

用瞬时测频法实现PCM/DPSK遥测信号的软件解调

根据PCM／DPSK遥测信号的特点，介绍了一种通过数字信号瞬时测频实现PCM／DPSK遥测信号的软件解调的方法。该方法处理速度快、误码率低，能够有效地抑制多普勒频率对解调的影响，便于软件编程实现。同时给出了解调过程的仿真流程图和仿真结果。     

Integrated PCM codec

Describes a one-chip PCM codec circuit which has been implemented in the CMOS process. The design uses two separate linear digital-to-analog converters, made with charge redistribution techniques. Experimental results show the circuit to meet accepted requirements and operate with very low power requirements.     

Proposed electrooptical PCM multiplexer-demultiplexer

A reciprocal time multiplexer-demultiplexer for optical PCM is proposed. The device is based on the coincidence of an optical pulse and a modulating voltage pulse in an electrooptic crystal. Both a lumped and a traveling-wave configuration are described.     

A single-channel PCM codec

A single channel PCM codec is described which is being manufactured for use in the new British Post Office range of digital PABXs. The codec works on the principle of converting to and from PCM using an intermediate delta sigma modulation code format. This technique allows relatively simple analog circuitry to be used in conjunction with a digital LSI chip to perform the conversion between the intermediate code and PCM. The codec meets all the relevant CCITT Recommendations with significant operating margins.     

一种脉冲间隔编码的实现方法

脉冲编码主要有重频编码、周期编码、脉冲间隔编码(PCM编码)及伪随机码4种码型样式,各种脉冲编码中脉冲间隔编码的应用最为广泛。文中以基础频率为5～50 Hz、1～12 bits可变码位的脉冲间隔编码为研究对象,对脉冲间隔编码的特点及生成机理进行分析,并通过实际的硬件、软件设计讨论其实现方法,最终给出几种脉冲间隔编码的输出结果。     

PCM Jitter Suppression by Scrambling

Jitter suppression in a chain of baseband PCM repeaters is studied. It is shown that a scrambler is very effective for systematic jitter suppression and that beyond 5 stages little additional suppression results. The probability of mark in the scrambler output converges to 0.5, independently of that in the input PCM signal. Experimental results confirm the analysis and show the ability of the scrambler to reduce the systematic jitter. The timing information disappearance of PCM repeatered lines when the scrambler is applied is also discussed.     

Optimum PCM Codes for DPSK

The effect of digital errors in PCM systems for speech signals depends on the PCM code used. The standard binary folded PCM code is superior to the natural binary code but it is not optimum. This paper considers PCM codes especially designed to be insensitive to the double error patterns produced by DPSK. It is concluded that the dynamic range with especially designed PCM codes is considerably extended compared to standard binary folded PCM. Special simplified interleaving schemes and optimum PCM codes for coherent PSK are also considered. The dynamic behavior of various PCM codes is calculated and compared, e.g., asymptotically optimum PCM codes for DPSK, binary folded PCM with and without interleaving, asymptotically optimum PCM codes for coherent PSK, etc. We conclude that the best scheme for DPSK is simplified interleaving and an optimum PCM code for PSK. This paper also gives analytical formulas for double errorA-factors for standard PCM systems.     

An integrated interpolative PCM decoder

Discusses the technique of time averaging interpolation which provides a means for obtaining telephone quality digital-to-analog conversion using conventional digital integrated-circuit processing. Describes a monolithic circuit that decodes the 8-kHz companded PCM commonly used in voiceband communication systems. The circuit, realized in a standard buried collector bipolar technology, contains 300 integrated injection logic (I/SUP 2/L) gates together with a current-driven resistive ladder network. The performance of the decoder exceeds typical toll network objectives.     

A single-chip CMOS PCM codec

Describes a single-chip full duplex per channel PCM codec implemented in a metal gate CMOS process. An 8-bit companding DAC, a novel autozeroed analog subsystem, and a 3.5-MHz frame interface control logic comprise the 175/spl times/195-mil integrated circuit. The DAC is implemented with matched n channel devices and utilizes redundancy and feedback to achieve the required accuracy. The analog subsystem contains two sample and hold circuits, autozeroing circuitry, CMOS amplifiers, and a fast CMOS comparator.     

PCM Subckannels for Video Microwave

A PCM subcarrier system has been developed which will permit video microwave to carry 24 6-kHz channels along with the normal video signal. The channels may be used directly or split into 48 3-kHz voice channels. The subcarrier system uses a differentially coherent quadraphase approach and has a data rate of 3 Mbit.