Introduction to Electronic Circuits - Computing System - Lecture Slides, Slides of Computer Science

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Introduction to Electronic

Circuits

CT101 – Computing Systems

Overview

• Review the definition of voltage, electric current,

resistance and power.

• Introduction to various electronic components

• Introduction to FET transistor design and principle

of operation.

• Use of FET transistor in logic circuits

• Understand a logic gate function

Voltage

• A positive electric field surrounding a group of one or more protons will exert a repelling

force on other groups of protons, and an attracting force on groups of electrons.

• Since an electric field can cause charged particles to move, it can do some amount of

work, and so it is said to have electrical potential energy.

• The amount of energy an electric field can impart to unit charge is measured in joules

per coulomb, more commonly known as voltage. Voltage is commonly used as a short

name for electrical potential difference.

• Voltage is a way of using numbers to describe an electric field
  • Voltage may be thought of as the “electromotive force” that can cause charged particles to move.
• A power supply is a device containing imbalance of electrons:
  • One side (the negative side) has material containing an abundance of electrons
  • The other side (positive side) has material containing a relative absence of electrons.
• The electrical potential energy available in the power supply, measured in volts, is

determined by the number of electrons it can store, the separation distance between

negative and positive materials, the properties of the barrier between the materials, and

other factors.

• Some power supplies (like small batteries) output less than a volt, while others (like power generation stations) can output tens of thousands of volts.

Resitance

• Electrons carry the smallest possible amount of negative charge, and billions of

them are present in even the tiniest piece of matter.

• Insulators - electrons are held firmly in place by heavier, positively charged protons. Electrons cannot move freely between atoms.
• Conductors - electrons can move more easily from atom to atom.
• The movement of electrons in a conductor is called electric current , measured in

amperes.

• If a power supply is used to impress a voltage across a conductor, electrons will

move from the negative side of the supply through the conductor towards the

positive side.

• All materials, even conductors, exhibit some amount of resistance to the flow of electric current. The amount of resistance determines how much current can flow – the higher the resistance, the less current can flow.
• A conductor has very low resistance, so a conductor by itself would never be

placed across a power supply because far too much current would flow,

damaging either the supply or the conductor itself. Rather an electronic

component called a resistor would be used in series with the conductor to limit

current flow

Power

• As current flows through the resistor, collisions occur between the

electrons flowing from the power supply and the materials in the

resistor. These collisions cause electrons to give up their potential

energy, and that energy is dissipated as heat.

• In electric circuits, power , measured in Watts , is defined as (voltage

x current) or P = V·I. The power transferred to the resistor at any

given time results in resistor heating. The more power transferred to

the resistor, the hotter it gets.

• For a given voltage, a smaller-valued resistor would allow more current to flow (see Ohm’s law), and therefore more energy would be dissipated as heat (and the resistor would get hotter).

• The total energy consumed in an electric circuit is simply the time

integral of power, measured in Watts per second, or Joules. Thus,

in the circuit above, the electric power delivered to the resistor is P

= 3.3V x 1A, or 3.3Watts and in one second, 3.3W x 1second or

3.3J of energy is dissipated. Docsity.com

Electric and Electronic Circuits

• A collection of electronic components that have been assembled

and interconnected to perform a given function is commonly

referred to as a circuit

• The word circuit derives from the fact that electric power must flow from the positive terminal of a power source through one or more electronic devices and back to the negative terminal of a power source, thereby forming a circuit.

• If the connections between an electronic device and either the

positive or negative terminals of a power supply are interrupted, the

circuit will be broken and the device will not function

• Many different types of components and devices can be found in

modern circuits, including resistors, capacitors, and inductors,

semiconductor devices like diodes, transistors, and integrated

circuits

• Devices in a circuit are connected to one another by

means of electrical conductors or wires. Docsity.com

Review of Zeros and Ones

• A signal in a digital circuit is a circuit net that transports an output voltage from one device to one or more inputs connections of other devices.
• In a digital circuit, signals are constrained to be at one of two voltages, either Vdd or GND. The set of voltage values {Vdd, GND} that define the state of a signal wire in a digital system are commonly represented by the numeric symbols {1, 0}, with ‘1’ representing Vdd and ‘0’ representing GND.
• Since digital systems can only represent two-state data, and since we have already assigned those states the numeric symbols ‘0’ and ‘1’, it follows that data in digital symbols can be represented by binary (base two) numbers. One signal wire in a digital circuit can carry one binary digit ( “bit”) of information;
• Groupings of signal wires (called “bus”) can carry multiple bits that can define a binary number.
• Using bits to represent data in digital systems makes is easy to adopt existing logical and numerical techniques to the study of digital circuits. For example, an AND relationship can be logically described as “true” when all inputs are “true” If we assign the symbol “1” to “true”, then the AND relationship yields a “1” when the inputs are all “1”, concisely demonstrated by the truth table. Since a’1’ represents Vdd and a ‘0’ GND, this logical AND truth table can define a logic circuit that outputs a ‘1’ (or Vdd) whenever all inputs are a ‘1’.

Electronic Circuit Components

• Resistors

• Capacitors

• Input Devices

• Output Devices

• Connectors

• Printed Circuit Boards

• Integrated Circuits

Capacitors

• A capacitor is a two-terminal device that can store electric energy in the form of charged particles. You can think of a capacitor as a reservoir of charge that takes time to fill or empty. The voltage across a capacitor is proportional to the amount of charge it is storing – the more charge added to a capacitor of a given size, the larger the voltage across the capacitor. It is not possible to instantaneously move charge to or from a capacitor, so it is not possible to instantaneously change the voltage across a capacitor. It is this property that makes capacitors useful on many applications.
• Capacitance is measured in Farads. A one Farad capacitor can store one Coulomb of charge at one volt. For engineering on a small scale (i.e., hand-held or desk-top devices), a one Farad capacitor stores far too much charge to be of general use (it would be like a car having a 1000 gallon gas tank).
• More useful capacitors are measured in micro-farads (uF) or pico- farads (pF). The terms "milli-farad“ and "nano-farad" are rarely used. Large capacitors often have their value printed plainly on them, such as "10 uF" (for 10 microfards).

Capacitor Symbol

SMD ceramic at top left; SMD tantalum at bottom left; Through-hole tantalum at top right; Through-hole electrolytic at bottom right;

Input Devices (Buttons & Switches)

• Circuits often require inputs that come directly from users (as opposed to inputs that come from other devices).
• User-input devices can take many forms, among them keyboards (as on a PC), buttons (as on a calculator or telephone), rotary dials, switches and levers, etc.
• Since digital circuits operate with two voltage levels (LHV or Vdd, and LLV or GND), input devices like buttons and switches should be able to produce both of these voltages based on some user action.
• The slide switches are also known as “single throw-double pole” (STDP) switches, because only one switch (or throw) exists, but two positions (or poles) are available (a pole is an electrical contact to which the switch can make contact). These switches can be set to output either Vdd (when the actuator is closest to the board’s edge) or GND.
• The push button switches are also known as “momentary” contact buttons, because they only make contact while they are actively being.The figure below shows typically pushbutton and slide switch circuits used in demo boards

Push Button Switch STDP Switch Docsity.com

Connectors

• They all communicate electronic information between the board and outside devices.
• Since connectors come in so many different sizes and shapes, they are usually shown on

the PCB silk screen and on circuit schematics as just rectangular boxes using a “J”

labeling.

• Some examples:

Printed Circuit Board

• Electronic components are often assembled and interconnected on a flat surface known as a circuit board.
• The several types of existing circuit boards may be divided into two broad categories: - those intended for prototype or experimental circuits; - and those intended for production and/or commercial sale.
• Circuit boards used for experimental work are often referred to as breadboards or protoboards.
• Production circuit boards are design usually using specialised CAD software (e.g. OrCAD, Protel, etc..). Once the design is completed, the PCB has to be manufactured. Typical steps are shown in the picture.

Digital Circuits

• A digital circuit represents and manipulates information

encoded as electric signals that can assume one of two voltages

• logic-high voltage (or Vdd) and logic-low voltage (or GND)
• If a given circuit net is at Vdd, then that signal is said to carry

a logic ‘1’; if the net is at GND, then the node carries a logic

• The components in digital circuits are simple on/off switches

that can pass logic ‘1’ and logic ‘0’ signals from one circuit net

to another. Most typically, these switches are arranged to

combine input signals to produce an output signal according to

basic logic relationships

• Assuming a logic ‘1’ is closing the switch and a logic ‘0’

opens the switch, in the example the combination of switches

can implement logic functions

• One well-known logic circuit is an NAND gate that combines two input signals to produce an output that is the logic NAND (negative AND) of the inputs (i.e., if both input1 and input2 are a ‘1’, then the output is a ‘0’).
• Another well-known logic circuit is OR gate that combines two input signlas to produce an output that is the logic OR of the inputs (i.e. if input1 or input2 are ‘1’, then the output is a ‘1’ )

Transistors

• …. ARE SWITCHES!!!

• are arranged so that they can be turned on or off by signals carrying

either VDD (LHV) or GND (LLV)

• The transistor switches used in modern digital circuits are called

“Metal Oxide Semiconductor Field Effect Transistors”, or

MOSFETs (or just FETs).

• FETs are three terminal devices that can conduct current between

two terminals (the source and the drain) when a third terminal (the

gate) is driven by an appropriate logic signal.

• In the simplest FET model (which is appropriate for our use here),

the electrical resistance between the source and the drain is a

function of the gate-to-source voltage – the higher the gate voltage,

the lower the resistance (and therefore, the more current that can

flow). In analog circuits (like audio amplifiers), the gate-to-source

voltage is allowed to assume any voltage between GND and Vdd;

but in digital circuits, the gate-to-source voltage is constrained to be

either Vdd or GND Docsity.com