Chapter 2 Sampled Data Systems F

Chapter 2 Sampled Data Systems F - FUNDAMENTALS OF SAMPLED...

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F UNDAMENTALS OF S AMPLED D ATA S YSTEMS ANALOG-DIGITAL CONVERSION 1. Data Converter History ± 2. Fundamentals of Sampled Data Systems 2.1 Coding and Quantizing 2.2 Sampling Theory 2.3 Data Converter AC Errors 2.4 General Data Converter Specifications 2.5 Defining the Specifications 3. Data Converter Architectures 4. Data Converter Process Technology 5. Testing Data Converters 6. Interfacing to Data Converters 7. Data Converter Support Circuits 8. Data Converter Applications 9. Hardware Design Techniques I. Index
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ANALOG-DIGITAL CONVERSION
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F UNDAMENTALS OF S AMPLED D ATA S YSTEMS 2.1 C ODING AND Q UANTIZING 2.1 CHAPTER 2 FUNDAMENTALS OF SAMPLED DATA SYSTEMS SECTION 2.1: CODING AND QUANTIZING Walt Kester, Dan Sheingold, James Bryant Analog-to-digital converters (ADCs) translate analog quantities, which are characteristic of most phenomena in the "real world," to digital language, used in information processing, computing, data transmission, and control systems. Digital-to- analog converters (DACs) are used in transforming transmitted or stored data, or the results of digital processing, back to "real-world" variables for control, information display, or further analog processing. The relationships between inputs and outputs of DACs and ADCs are shown in Figure 2.1. Figure 2.1: Digital-to-Analog Converter (DAC) and Analog-to-Digital Converter (ADC) Input and Output Definitions Analog input variables, whatever their origin, are most frequently converted by transducers into voltages or currents. These electrical quantities may appear (1) as fast or slow "dc" continuous direct measurements of a phenomenon in the time domain, (2) as modulated ac waveforms (using a wide variety of modulation techniques), (3) or in some combination, with a spatial configuration of related variables to represent shaft angles. MSB MSB LSB LSB V REF V REF DIGITAL INPUT N-BITS DIGITAL OUTPUT N-BITS ANALOG OUTPUT ANALOG INPUT +FS 0 OR –FS +FS 0 OR –FS RANGE (SPAN) RANGE (SPAN) N-BIT DAC N-BIT ADC
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ANALOG-DIGITAL CONVERSION 2.2 Examples of the first are outputs of thermocouples, potentiometers on dc references, and analog computing circuitry; of the second, "chopped" optical measurements, ac strain gage or bridge outputs, and digital signals buried in noise; and of the third, synchros and resolvers. The analog variables to be dealt with in this chapter are those involving voltages or currents representing the actual analog phenomena. They may be either wideband or narrowband. They may be either scaled from the direct measurement, or subjected to some form of analog pre-processing, such as linearization, combination, demodulation, filtering, sample-hold, etc. As part of the process, the voltages and currents are "normalized" to ranges compatible with assigned ADC input ranges. Analog output voltages or currents from DACs are direct and in normalized form, but they may be subsequently post-processed (e.g., scaled, filtered, amplified, etc.).
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Chapter 2 Sampled Data Systems F - FUNDAMENTALS OF SAMPLED...

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