Table of Contents
I. Overview
1. Digital and analog quantities
Analog quantities have continuous values. Digital quantities have a discrete set of values.
The temperature of my body does not suddenly change from 99°F to 97°F. The change is gradual, analog. We can quantize the graph below by sampling the temperature curve at some discrete points in time. This sampled-value representation is not digital in itself, but it can be digitized easily. Quantization comes before digitization.
Digital is better than analog in many cases. Digital data can be stored, processed and transmitted more easily. Digitized music takes less space. Noise affects analog data much more.
A microphone-speaker system is a pure analog system. Sound waves move capacitor plates creating a voltage pattern which is amplified and supplied to a speaker that converts the electrical signal back to mechanical waves. Everything in this process is analog, continuous.
A CD (compact disk) player has both digital and analog circuits. Music is stored in the disk digitally. A laser-diode optical system reads the data and supply it to a digital-to-analog converter (DAC). An analog-to-digital converter (ADC) was used while recording the music.
Both digital and analog systems are needed in the interdisciplinary field of mechatronics.
2. Binary digits, logic levels and waveforms
In digital circuits and systems there are only TWO possible states represented by two different voltage levels: HIGH and LOW. They could be represented by two current levels or bits and bumps in a CD or DVD.
States are called codes. A two-state number system is called binary, it has two digits: 0 and 1. A digit is called a bit (short for ‘binary digit’).
Positive logic: HIGH = 1 and LOW = 0. Negative logic is the opposite.