Engineering Lecture1:

Logic Circuits & Concepts about basic

Electrical Engineering Devices

by Christin Sander

Overview

1) Logic Circuits Analogue vs Digital Binary Numbers Logic Gates Boolean Algebra Flip-Flops & Clocks Counters Data Storage

2) Electrical Engineering Overview of Transistors Amplifiers Operational Amplifiers

Analogue versus Digital

Analogue: Digital:

ANALOGUE signals vary in a continuous way, can take any values

DIGITAL signals represent information as a sequence of discrete varying physical quantities, encode values into binary numbers (0 or 1)

Analogue to Digital Conversion In nature, signals normally occur in an

analogue way To convert them into a digital signal, a

threshold value is selected. For values below the threshold: 0For values above the threshold: 1

Binary Numbers

Binary Number System The binary number system is the base 2 number system Uses 2 different symbols (0 and 1) A BInary digiT("BIT") in each position

Binary logic circuits are useful for making controllers A binary system can also represent numbers of any magnitude Logic circuits can be realised which will perform arithmetical operations

on these binary numbers This is the principle behind almost all digital calculators and computers

Decimal Number System The decimal number system is the base 10 number system Uses 10 different symbols (0,1,2,…..9)

In General, any number system can be used

Logic Gates Electronic circuits with one

or more input wires and one output wire

The voltage on the output depends on the voltages on the inputs

The relationship between inputs and output is a logical function, determined by the circuit arrangement inside the gate.

Circuit

(made up of transistors used as switches)

Logical Functions

Boolean Algebra

Flip-flops

D Flip-flop Divide-by-2-circuit

Ripple-Down Counter

J-K Flip-flop

Q+ indicates the value of Q after the next clock pulse

If J and K are different, Q takes on the value of J

If J and K are both 0, Q remains unchanged

If J and K are both 1, Q changes to its inverse (it "toggles")

Information from J and K is read in on the rising edge of the clock, and is translated into action at the Q outputs on the FALLING edge of the clock

Synchronous Counter

Synchronous Counter (8-bits)

Data Register

A circuit which can store temporarily all bits of a binary number

A 3-bit register

(a typical personal computer will have several 16-bit and 32-bit data registers in its arithmetic unit)

Storage Devices: ROM

A ROM cell

Typical m-ROM device

Transistors

Small input current controls a large output current

Can act as a switch if in saturation or cut-off region

Amplifiers

An amplifier is a device that accepts a small signal and outputs a larger signal that generally matches the waveform characteristics of the input

It amplifies the input signal Factors affecting amplification

Gain: Relationship of input and output signal Efficiency Bandwidth Settling time Noise

Operational Amplifiers

An opamp is a device that takes an analogue signal and amplifies it

Output voltage depends on difference of input voltage

Applications: Analogue to digital converters Filters Comparators