PDF《应用报告》

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4 1 INTRODUCTION The design considerations for high-speed data conversion are, in many ways, similar to those for data conversion in general.

High speed circuits may sometimes seem different because device types can be limited and only certain design techniques and architectures can be used with success. But the basics are the same. High speed circuits or systems are really those that tend to press the limits of state-of-the-art dynamic performance. This bulletin focuses on the more fundamental building blocks such as op amps, sample/holds, digital to analog and analog to digital converters (DACs and ADCs). It concludes with test techniques. Op amps, which tend to be the basic building blocks of systems, are be considered first. Sample/ holds which play an important role in data conversion are considered next followed by DACs and finally ADCs. ADCs are really a combination of the other three circuits. Emphasis is given to hybrid and monolithic design techniques since, in practice, the highest levels of performance are achieved using these processes. The material is presented from a design perspective. Theory and practical examples are of- fered so both the data conversion component designer and user will find the material useful. The concepts presented do not require extensive experience with data conversion. Fun- damental concepts are discussed allowing the subject to be understood easily. The material emphasizes high speed cir- cuit considerations―circuit theory is not treated in depth. Topics Covered in this Bulletin A. Amplifier Architectures 1. Buffer 2. Operational 3. Open Loop 4. Comparator B. Amplifier Applications 1. Sample/Hold 2. Peak Detector C. Digital to Analog Converters 1. Bipolar 2. Deglitched DAC D. Analog to Digital Converters 1. Successive Approximation 2. Flash 3. Sub-ranging E. Test Techniques 1. Settling Time 2. Aperture Jitter 3. Beat Frequency Testing 4. Servo Loop Test AMPLIFIER ARCHITECTURES Amplifiers of all types play an important role in data conversion systems. Since high speed amplifiers are both useful and difficult to design, an understanding of their operation is important. Four different types of amplifier architectures will be discussed. Buffers, op amps, open loop amplifiers, and comparators can be found in just about any signal processing application. THE BUFFER The open loop buffer is the ubiquitous modern form of the emitter follower. This circuit is popular because it is simple, low cost, wide band, and easy to apply. The open loop buffer is important in high speed systems. It serves the same purpose as the voltage follower in lower speed systems. It is often used as the output stage of wideband op amps and other types of broadband amplifiers. Consider the two buffer circuit diagrams, Figures

1 and 2. The output impedance of each buffer is about 5? and bandwidths of several hundred megahertz can be achieved. The FET buffer is usually implemented in hybrid form as very wideband FETs and transistors are usually not available on the same monolithic process. The all-bipolar form of the buffer is capable of FIGURE 1. High Speed Bipolar Buffer. VIN VOUT R4 R3 Q4 Q3 R2 Q2 VC V+ Q1 R1 R6 R5 Q6 Q5 VBIAS1 VBIAS2 HIGH SPEED DATA CONVERSION By Mike Koen (602) 746-7337

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1991 Burr-Brown Corporation AB-027A Printed in U.S.A. June,

1991 ? SBAA045 ? 应用报告高速数据转换 引言 在很多方面,高速数据转换设计需要考虑的问题与 一般数据转化十分相似,但由于芯片型号的限制,加上 只有可靠的设计技术和结构才能使用,高速电路就显得 有些不同,然而它们的基础是一样的.高速电路或系统 往往促进了前沿技术动态性能的发展. 这篇报告主要集中介绍了基本模块如运算放大器, 采样/保持,数模转换和模数转换器(DAC &