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Interfacing to the Analog World
Chapter 15 Interfacing to the Analog World William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Digital and Analog Representations
See Figure 15-1 Four binary positions = 4-bit resolution 16 different representations Eight binary positions = 8-bit resolution 256 different representations William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-1 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Operational Amplifier Basics
Very high input impedance Very high voltage gain Very low output impedance See Figure 15-2 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-2 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Binary-Weighted Digital-to-Analog Converters
Sum of the currents from the input resistors Binary weighting factor See Figure 15-4 Accurate resistances is difficult Practical for 4-bit conversions maximum William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-4 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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R/2R Ladder Digital-to-Analog Converters
Only two resistor values 8, 10, 12, 14, 16 bits and higher resolutions See Figure 15-5 R/2R ladder See Figure 15-7 analog output versus digital input William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-5 Figure 15-7 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Integrated-Circuit Digital-to-Analog Converters
DAC0808 See Figure 15-8 block diagram pin configuration typical application See Figure 15-9 testing the 256-step output William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-8 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-9 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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IC Data Converter Specifications
See Figure 15-10 differential nonlinearity gain error missing codes nonmonotonic offset error relative accuracy settling time 3-bit ADC transfer characteristic William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-10 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure (continued) William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Parallel-Encoded Analog-to-Digital Converters
Parallel encoding simultaneous multiple comparator flash See Figure 15-11 three-bit parallel encoded ADC priority encoder William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-11 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Counter-Ramp Analog-to-Digital Converters
Counter in conjunction with a D/A converter See Figure 15-12 For continuous conversions end-of-conversion line back to clear input Disadvantage slow conversion time speed depends on steps necessary to convert William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-12 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Successive-Approximation Analog-to-Digital Conversion
See Figure 15-13 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-13 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Integrated-Circuit Analog-to-Digital Converters
NE5034 See Figure 15-15 block diagram pin configuration Successive-Approximation Three-state output buffer William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-15 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Integrated-Circuit Analog-to-Digital Converters
ADC 0801 See Figure 15-17 block diagram pin configuration successive-approximation differential measurements William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-17 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Data Acquisition System Application
See Figure 15-19 Analog Multiplexer Switch (AM3705) Sample-and-Hold Circuit (LF198) Programmable-Gain Instrumentation Amplifier (LH0084) Analog-to-Digital Converter (ADC0801) William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-19 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Transducers and Signal Conditioning
Physical quantities to electrical quantities Must be conditioned Thermistors resistance dependant on temperature response is nonlinear See Figure characteristic curve See Figure circuit William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Figure 15-20 Figure 15-21 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Transducers and Signal Conditioning
Linear IC Temperature Sensors See Table temperature versus binary output The Strain Gage resistance changes when stretched William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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William Kleitz Digital Electronics with VHDL, Quartus® II Version
Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Summary Any analog quantity can be represented by a binary number. Longer binary numbers provide higher resolution, which gives a more accurate representation of the analog quantity. The binary-weighted D/A converter is the simplest to construct, but it has practical limitations in resolution (number of input bits). William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Summary Operational amplifiers are important building blocks in analog-to-digital (A/D) and digital-to-analog (D/A) converters. They provide a means for summing currents at the input and converting a current to a voltage at the output of converter circuits. The R/2R ladder D/A converter uses only two different resistor values, no matter how many binary input bits are included. This allows for very high resolution and ease of fabrication in integrated-circuit form. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Summary The DAC0808 (or MC1408) IC is an 8-bit D/A converter that uses the R/2R ladder method of conversion. It accepts 8 binary input bits and outputs an equivalent analog current. Having 8 input bits means that it can resolve up to 256 unique binary values into equivalent analog values. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Summary Applying an 8-bit counter to the input of an 8-bit D/A converter will produce a 256-step sawtooth waveform at its output. The simplest way to build an analog-to-digital (A/D) converter is to use the parallel encoding method. The disadvantage is that it is practical only for low-resolution applications. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Summary The counter-ramp A/D converter employs a counter, a D/A converter, and a comparator to make its conversion. The counter counts from zero up to a value that causes the D/A output to exceed the analog input value slightly. That binary count is then output as the equivalent to the analog input. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Summary The method of A/D conversion used most often is called successive approximation. In this method, successive bits are tested to see if they contribute an equivalent analog value that is greater than the analog input to be converted. If they do, they are returned to zero. After all bits are tested, the ones that are left ON are used as the final digital equivalent to the analog input. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Summary The NE5034 and the ADC0804 are examples of A/D converter ICs. To make a conversion, the start-conversion pin is made LOW. When the conversion is completed the end-of-conversion pin goes LOW. Then to read the digital output, the output enable pin is made LOW. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Summary Data acquisition systems are used to read several different analog inputs, respond to the values read, store the results, and generate reports on the information gathered. Transducers are devices that convert physical quantities such as heat, light, or force into electrical quantities. Those electrical quantities must then be conditioned (or modified) before they can be interpreted by a digital computer. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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