Introduction to Logic Design & Circuits

Asst. Prof. Mohanad Alayedi

Department of Software Engineering
Haliç University
mohanadysalayedi@halic.edu.tr

CEN203, Fall 2024

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 Course Content
Digital Design:
➢ Number Systems
➢ Boolean Functions
➢ Functions of logic gates
➢ Combinational logic
➢ Synchronous sequential logic
➢ Storage elements
➢ Registers and counters
➢ Memory and programmable logic

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 Integrated Circuit

➢ Until 1960s, logic circuits were constructed with bulky

components, such as transistors and resistors that came as
individual parts.
➢ An integrated circuit is a where we can place a number of
transistors, thus an entire circuit.

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 Integrated Circuit

➢ In 1965, Gordon Moore, co-founder chairman of Intel,

observed that the number of transistors that can be placed on
a unit area doubles every 1.5 to 2 years.
➢ This is known as Moore’s law.

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 Moore’s Law – 2x transistors per 1.5yrs

An Osborne Executive portable computer, from 1982 with a Zilog Z80 4MHz CPU, and a 2007 Apple iPhone
with a 412MHz ARM11 CPU.
The Executive weighs 100 times as much, is nearly 500 times as large by volume, costs approximately 10 times
as much (inflation adjusted), and has 1/100th the clock frequency of the smartphone. (Wikipedia)

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 Digital Hardware Design

➢ Logic circuits can be implemented on a single chip or, more likely, through combining
multiple chips placed on a printed circuit board (PCB).

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 Digital Hardware Design

➢ There are three types of chips:

– Standard chips
– Programmable Logic Devices (PLDs)
– Custom-Designed Chips

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 Digital Hardware Design

➢ Standard chips
– Performs a simple function, such as an AND operation.
– Each chip contains a small number of circuitry (typically less than 100 transistors).
– Complex functions are implemented by connecting these chips.
– Disadvantages:
• They are inefficient (they don’t utilize the space on a PCB well).
• The functionality of each chip is fixed and cannot be changed.

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 Digital Hardware Design

➢ Programmable Logic Devices (PLDs)

– In contrast to standard chips, PLDs can be configured by the user to implement a wide range of
different logic circuits.
– These chips have a general structure and include a collection of programmable switches that
allow the chip to configured in many different ways.
– It is the end user that programs the chip; most PLDs are re- programmable.
– Field-programmable gate array (FPGA) is a sophisticated PLD that contains several hundred
million transistors.

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 Digital Hardware Design

➢ Custom-Designed Chips
– PLDs are available as off-the-shelf components, and can be used to implement most
logic circuits through programming.
– However, the drawback of PLDs is that programmable switches consume valuable chip
area and limit the speed of operations.
– Application-specific integrated circuits (ASICs) are designed from scratch to perform a
specific task. They are optimized to perform the task and hence lead to better
performance.

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 A Binary Switch

“open” “closed”

x = 0 x = 1

(a) Two states of a switch

Variable x
indicates the
state of the
switch
S

(b) Symbol for a switch

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 Variables and Functions

S
Battery x Light

➢ L: state of the light

➢ L = 1 the light is on;

➢ L = 0 the light is off;
➢ The state of the light can be described as a function of the
input variable x:
➢ – L(x) = x

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 AND Function

S S
Power
x1 x2 Light
supply

The state of the light, L, is a function of both x1 and x2: L(x1,x2)

L(x1,x2)=1, (the light is on), when both x1 and x2 are 1.

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 OR Function

x1

Power
supply S Light

x2

L(x1,x2)=1, (the light is on), when at least one of x1 and x2 is 1.

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 NOT Function (Inverter Function)

Power
supply x S Light

L(x)=1, (the light is on), when x is 0.

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 An Example of Logic Network

X1
S
Power
supply S X3 Light

X2

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 Logic Circuits

➢ This course is about logic circuits – the building blocks from which computers and
all sorts of electronic devices are built.

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 Logic Circuits

➢ In this course, we will learn how to build very complex functions from elementary
logic circuits.

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 Digital System
➢ Digital System: A system that uses discrete sets of values to describe information. Example:
Discrete sets of 10 Decimal digits, 26 letters in English, Binary Values
➢ In computers information is defined by discrete level of currents or voltages that are
described by discrete set of symbols on paper. Present day digital computers use “Binary”
codes, where it uses symbols of “1” and “0”
➢ In decimal system we use symbols of “0, 1, 2, 3, 4, 5, 6, 7, 8, 9”
➢ Important part is the understanding the common protocol that are used in digital system.
➢ In this lecture we start with concept of digitization. Then we use number systems that can be
used for discretization. Then we follow the subject with binary logic and combinational devices.

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 Example Digital Systems

➢ General Purpose Desktop/Server Digital Computer

- Often designed to maximize performance. Optimized for speed

• Handheld Calculator

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 Example Digital Systems

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 Basic Design Tradeoffs

➢ You can improve on one at the expense of worsening one or both of the others.
➢ These tradeoffs exist at every level in the system design – every sub-piece and
component.
➢ Design Specification:
- Functional Description.
- Performance, cost, power constraints.

➢ As a designer, you must make the tradeoffs necessary to achieve the function
within the constraints.
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 Design Space & Optimally

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 Analog vs. Digital
➢ Everything in the world is an Analog system. That means they can be described by
continuous sets of numbers.
Ex. Temperature reading of 32.36546 oC if you have enough sensitivity in your
measurement and you have two readings of 32.36546 oC and 32.36547 oC
➢ Example Digital Representation: Music waveform (Discrete time and amplitude)

➢ A series of numbers is used to represent the waveform, rather than a voltage as in

analog systems
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