Pulse and Digital Techniques
EEE507: MEASUREMENT AND INSTRUMENTATION II
LECTURE NOTES ADCs AND DACs
By: Olorunniwo O. Dept. of Electronic & Electrical Engineering Obafemi Awolowo University Ile-Ife Page. | 1
1.
ADCs and DACs • Basic DAC Architecture: -binary weighted; -R-2R ladder • Basic ADC: -flash; -dual-slope ; and -successive approximation • Sample and Hold Circuit • Aperture Error • ADC/DAC specifications: -INL; -DNL; -dynamic range. • Oversampling • Noise-shaping and sigma-delta converters 1.1 INTRODUCTION
It is observed that most physical quantities in nature are analog signals. These quantities include: temperature, pressure and speed—to mention a few. Further, these quantities assume an infinite number of possible values other than 1’s and 0’s. Understandably, these analog quantities must be converted into binary strings, representative of their values. The process of conversion of analog signals into their equivalent digital form is termed analog-to-digital conversion. The reverse form of the process is digital-to-analog conversion. Often, computers utilize these important processes for control of analog devices. To that end, for analog-to-digital (A/D) and digital-to-analog (D/A) converters to be useful, there has to be a meaningful representation of the analog and signal quantity. Starting points of the conversion processes are with devices called transducers. Transducers are devices that convert physical quantities into electrical quantities. What are the major building blocks in ADC and DAC circuits? The operational amplifiers are common features in A/D and D/A converters. It provides means of: 1. Summing currents at the input; and 2. Converting a current to voltage at the output of the converter circuit. The basic operations of an ideal op-amp are illustrated in Figure 1 and 2.
Figure1 Page. | 2
Figure2 Note: The three (3) notable characteristics of an op-amp are: (a) Very high input impedance; (b) Very high voltage gain; and (c) Very low output impedance.
LECTURE NOTES ADCs AND DACs
By: Olorunniwo O. Dept. of Electronic & Electrical Engineering Obafemi Awolowo University Ile-Ife Page. | 1
1.
ADCs and DACs • Basic DAC Architecture: -binary weighted; -R-2R ladder • Basic ADC: -flash; -dual-slope ; and -successive approximation • Sample and Hold Circuit • Aperture Error • ADC/DAC specifications: -INL; -DNL; -dynamic range. • Oversampling • Noise-shaping and sigma-delta converters 1.1 INTRODUCTION
It is observed that most physical quantities in nature are analog signals. These quantities include: temperature, pressure and speed—to mention a few. Further, these quantities assume an infinite number of possible values other than 1’s and 0’s. Understandably, these analog quantities must be converted into binary strings, representative of their values. The process of conversion of analog signals into their equivalent digital form is termed analog-to-digital conversion. The reverse form of the process is digital-to-analog conversion. Often, computers utilize these important processes for control of analog devices. To that end, for analog-to-digital (A/D) and digital-to-analog (D/A) converters to be useful, there has to be a meaningful representation of the analog and signal quantity. Starting points of the conversion processes are with devices called transducers. Transducers are devices that convert physical quantities into electrical quantities. What are the major building blocks in ADC and DAC circuits? The operational amplifiers are common features in A/D and D/A converters. It provides means of: 1. Summing currents at the input; and 2. Converting a current to voltage at the output of the converter circuit. The basic operations of an ideal op-amp are illustrated in Figure 1 and 2.
Figure1 Page. | 2
Figure2 Note: The three (3) notable characteristics of an op-amp are: (a) Very high input impedance; (b) Very high voltage gain; and (c) Very low output impedance.