{"title":"A monolithic companding D/A converter","authors":"J. Schoeff","doi":"10.1109/ISSCC.1977.1155668","DOIUrl":null,"url":null,"abstract":"COMPANDED PULSE CODE MODULATED (PCM) transmission of voice signals has become standardized through widespread use of the Bell system p-law and the CCITT** A-law transfer characteristics. Until now, all codecs (eoder/decoders) for these communication systems have been fabricated in either discrete or hybrid form and have been relatively expensive. This paper will present a newly developed monolithic digital-to-analog converter specifically designed for compression and expansion of signals according to the existing PCM standard. This converter, however, is not limited to PCM communication, but may be used in other areas such as data acquisition, servo controls, data recording, telemetry, voice synthesis, log attenuation, secure communications, sonar, and many other applications which require a 12-bit plus sign dynamic range and the convenience of an 8-bit digital code. When used in a telecommunications application, the companding DAC is a complete PCM decoder, with metal options for p-law and A-law. A one-half step decision level for encoding is provided within the circuit and controlled with the encode/decode logic input. This current offsets the entire transfer characteristic one half step, regardless of the value of the output current. The outputs are multiplexed for time sharing of one DAC for both encode and decode operation. The DAC settling time is 500 ns, and i t will decode more than 32 PCM channels in 125 ps, which is the sampling period at 8 kHz. In a shared encoder it will convert eight channels, assuming a 1 0 ps sample and hold acquisition time. The outputs are high impedance, high compliance current sources and will interface with most balanced loads. The reference inputs will accept a fixed reference or a positive or negative multiplying input. The transfer characteristic of the companding DAC is shown in Figure 1. The output consists of eight positive chords and eight negative chords, each containing sixteen steps. The slopes of these chords are binarily related with the chord at the origin having steps equivalent in size to those in a 12-bit converter. The step size is a nearly constant 3.2% of reading throughout most of the dynamic range, which corresponds to approximately 0.3 dB per step. Each successive chord endpoint is 6 dB below the next higher endpoint for every chord in the A-law specification, and follows this for most chords in the p-law. The dynamic range, or ratio, of the full scale to the smallest step size is 72 dB for the p-law version and 66 dB for the A-law unit. The electrical specifications for the circuit are summarized in Table I.","PeriodicalId":416313,"journal":{"name":"1977 IEEE International Solid-State Circuits Conference. Digest of Technical Papers","volume":"1 1","pages":"0"},"PeriodicalIF":0.0000,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"13","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"1977 IEEE International Solid-State Circuits Conference. Digest of Technical Papers","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1109/ISSCC.1977.1155668","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 13

Abstract

COMPANDED PULSE CODE MODULATED (PCM) transmission of voice signals has become standardized through widespread use of the Bell system p-law and the CCITT** A-law transfer characteristics. Until now, all codecs (eoder/decoders) for these communication systems have been fabricated in either discrete or hybrid form and have been relatively expensive. This paper will present a newly developed monolithic digital-to-analog converter specifically designed for compression and expansion of signals according to the existing PCM standard. This converter, however, is not limited to PCM communication, but may be used in other areas such as data acquisition, servo controls, data recording, telemetry, voice synthesis, log attenuation, secure communications, sonar, and many other applications which require a 12-bit plus sign dynamic range and the convenience of an 8-bit digital code. When used in a telecommunications application, the companding DAC is a complete PCM decoder, with metal options for p-law and A-law. A one-half step decision level for encoding is provided within the circuit and controlled with the encode/decode logic input. This current offsets the entire transfer characteristic one half step, regardless of the value of the output current. The outputs are multiplexed for time sharing of one DAC for both encode and decode operation. The DAC settling time is 500 ns, and i t will decode more than 32 PCM channels in 125 ps, which is the sampling period at 8 kHz. In a shared encoder it will convert eight channels, assuming a 1 0 ps sample and hold acquisition time. The outputs are high impedance, high compliance current sources and will interface with most balanced loads. The reference inputs will accept a fixed reference or a positive or negative multiplying input. The transfer characteristic of the companding DAC is shown in Figure 1. The output consists of eight positive chords and eight negative chords, each containing sixteen steps. The slopes of these chords are binarily related with the chord at the origin having steps equivalent in size to those in a 12-bit converter. The step size is a nearly constant 3.2% of reading throughout most of the dynamic range, which corresponds to approximately 0.3 dB per step. Each successive chord endpoint is 6 dB below the next higher endpoint for every chord in the A-law specification, and follows this for most chords in the p-law. The dynamic range, or ratio, of the full scale to the smallest step size is 72 dB for the p-law version and 66 dB for the A-law unit. The electrical specifications for the circuit are summarized in Table I.
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单片压缩D/A转换器
通过广泛使用贝尔系统p-定律和CCITT** a -定律传输特性,压缩脉冲码调制(PCM)语音信号的传输已经标准化。到目前为止,用于这些通信系统的所有编解码器(编码器/解码器)都是以分立或混合形式制造的,并且相对昂贵。本文将介绍一种新开发的单片数模转换器,根据现有的PCM标准专门设计用于信号的压缩和扩展。然而,该转换器不仅限于PCM通信,还可用于其他领域,如数据采集,伺服控制,数据记录,遥测,语音合成,日志衰减,安全通信,声纳以及许多其他需要12位加号动态范围和8位数字代码的便利的应用。当用于电信应用时,扩展DAC是一个完整的PCM解码器,具有p律和a律金属选项。电路内提供用于编码的半步决策电平,并由编码/解码逻辑输入控制。无论输出电流的值是多少,该电流都会将整个传输特性偏移半步。输出多路复用,用于一个DAC的时间共享,用于编码和解码操作。DAC的建立时间为500ns,它将以125ps的速度解码超过32个PCM通道,这是8 kHz的采样周期。在共享编码器中,它将转换8个通道,假设10ps采样并保持采集时间。输出是高阻抗,高顺应电流源,并将与大多数平衡负载接口。参考输入将接受固定参考或正或负相乘输入。扩展DAC的传输特性如图1所示。输出由8个正和弦和8个负和弦组成,每个和弦包含16步。这些和弦的斜率与原点的和弦有二元关系,其步长与12位转换器中的步长相当。在大部分动态范围内,步长几乎是读数的3.2%,相当于每步约0.3 dB。在a律中,每个连续的和弦端点比下一个更高的端点低6db,在p律中,大多数和弦都遵循这一原则。满量程到最小步长的动态范围或比率,对于p律单元为72 dB,对于a律单元为66 dB。电路的电气规格概述在表1中。
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