Analog ↔ digital conversion and sampling

Introduction In this chapter, we discuss the components that convert data between the digital world of the microcomputer and its I/O ports and the analog world of continuously varying voltages. These are the digital-to-analog (D/A) converter, the analog-to-digital (A/D) converter, the sample-and-hold amplifier, and the comparator. We then go on to discuss some of the fundamental limits to sampling time-varying analog signals, including the role of the sample-and-hold amplifier, and the minimum sampling frequency. Laboratory Exercise 7 is designed as an introduction to the characteristics of the D/A and A/D converters and uses an analog I/O circuit board. Laboratory Exercise 8 interfaces a D/A converter to the binary output port, measures its transfer characteristics, and uses it in waveform generation. Laboratory Exercise 9 interfaces an A/D converter to the binary input port and performs periodic sampling of sine waves. Laboratory Exercise 10 samples and recovers sine waves of various frequencies and explores the aliasing problems that arise when the input frequency is greater than one-half of the sampling frequency. Digital-to-analog converter circuits The digital-to-analog (D/A) converter changes an N-bit binary number to an analog output voltage that can have 2 N distinct values. It consists of resistors, switches, and an amplifier. Frequently, input latches are provided to retain the input number. Usually, the relationship between the input number and the output voltage is linear , but other relationships (e.g. logarithmic) are also used.