Advantages of Digital Techniques

Advantages of Digital Techniques      An increasing majority of applications in electronics, as well as in most other technologies, use digital techniques to perform operations that were once performed using analog methods. The chief reasons for the shift to digital technology are:

1. Digital systems are generally easier to design. This is because the circuits that are used are switching circuits, where exact values of voltage or current are not important, only the range (HIGH or LOW) in which they fall.
2. Information storage is easy. this is accomplished by special switching circuits that can latch onto information and hold it for as long as necessary.
3. Accuracy and precision are greater. Digital systems can handle as many digits of precision as you need simply by adding more switching circuits. In analog systems, precision is usually limited to three or four digits because the values of voltage and cureent are directly dependent on the circuit component values.
4. Operation can be programmed. It is fairly easy to design digital systems whose operation is controlled by a set of stored instructions called a program. As technology progresses, this is becoming even easier. Analog systems can also be programmed, but the variety and complexity of the available operations is severely limited.
5. Digital circuits are less affected by noise. Spurious fluctuations in voltage (noise) are not as critical in digital systems because the exact value of a voltage is not important, as long as the noise is not large enough to prevent us from distinguishing a HIGH from a LOW.
6. More digital circuitry can be fabricated on IC chips. It is true that analog circuitry has also benefited from the tremendous development of IC technology, but its relative complexity and its use of devices that cannot be economically integrated (high-value capacitors, precision resistors, inductors, transformer) have prevented analog systems from achieving the same high degree of integration.

1-1 NUMERICAL REPRESENTATIONS

1-1 NUMERICAL REPRESENTATIONS

In science, technology, business, and, in fact, most other fields of endeavor, we are constantly dealing with quantities. Quantities are measured, monitored, recorded, manipulated arithmetically, observed, or in some other way utilized in most physical systems. It is important when dealing with various quantities that we be able to represent their values efficiently and accurately. There are basically two ways of representing the numerical value of quantities: analog and digital.

Analog Representations     In analog representation a quantity is represented by a voltage, current, or meter movement that is proportional to the value of that quantity. An example is an automobile speedometer, in which the deflection of the needle is propotional to the speed of the auto. The angular position of the needle represents the value of the auto’s speed, and the needle follows any changes that occurs as the auto speeds up or slow down.

Another example is the common room thermostat, in which the bending of the bimetallic strip is proportional to the room temperature. As the temperature changes grdually, the curvature of the strip changes proportionally.

Still another example of an analog quantity is found in the familiar audio microphone. In this device an output voltage is generated in proportion to the amplitude of the sound waves that impinge on the microphone. The variations in the output voltage follow the same variations as the input sound.

Analog quantities such as those cited above have an important characteristic: they can vary over a continuous range of values. The automobile speed can have any value between zero and, say, 100 mph. Similarly, the microphone output might be anywhere within a range of zero to 10 mV (e.g., 1mV, 2.3724 mV, 9.9999 mV).

Digital Representations     In digital representation the quantities are represented not by proportional quantities but by symbols called digits. As an example, consider the digital watch, which provides the time of day in the form of decimal digits which represent hours and minutes (and sometimes seconds). As we know, the time of day changes continuously, but the digital watch reading does not change continuously; rather, it changes in steps of one per minute (or per second). In other word, this digital representation of the time of day changes in discrete steps, as compared with the representation of time provided by an analog watch, where the dial reading changes continuously.

     The major difference between analog and digital quantities, then, can be simply stated as follows:

                               analog=continuous

                               digital=discrete (step by step)

Because of the discrete nature of digital representations, there is no ambiguity when reading the value of a digital quantity, whereas the value of an analog quantity is often open to interpretation.

Introductory Concepts

Introductory Concepts

Numerical Representations                            

Digital Circuits

Digital and Analog Systems                            

Parallel and Serial Transmission

Digital Number Systems                                  

Memory

Representing Binary Quantities                    

Digital Computers

OBJECTIVES

 

Upon completion of this chapter, you will be able to:

• Distinguish between analog and digital representations.
• Name the advantages, disadvantages, and major differences among analog, digital, and hybrid systems.
• Understand the need for analog-to-digital converters (ADCs) and digital-to-analog converters (DACs).
• Converts between decimal and binary numbers.
• Identify typical digital signals.
• Cite several integrated-circuit fabrication technologies.
• Identify a timing diagram.
• State the differences between parallel and serial transmission.
• Describe the property of memory.
• Describe the major parts of a digital computer and understand their functions.