Logic Families Electronics

INTRODUCTION TO LOGIC FAMILIES

What is a logic Family

It is the way to describe the internal circuitry of the I.C.

Types of logic Families

We have 7 Basic Logic Families

1) RTL – Resistor Transistor Logic

2) DTL – Diode Transistor Logic

3) IIL – Integrated injection Logic

4) TTL – Transistor – Transistor Logic (Ex 7400 & 5400

Series)

5) ECL – Emitter Coupled Logic (Ex 10000 series)

6) MOS – Metal Oxide Semiconductor

7) CMOS – Complementary Metal Oxide Semiconductor

(Ex. 4000 Series)

Presentation By Anant Shrivastava (E.I. Fourth Sem)

RTL & DTL – Not used in new design

But act as a useful starting point

RTL was the first Commercial Family

DTL is now Completely replaced by TTL TTL – It is a modified form of DTL

it is formed by replacing each diode with a transistor

Basic Gate is NAND

IIL,MOS – Used in Large Scale Integration ECL – Used in High Speed Operations

Basic Gate is NOR

CMOS – Where power requirement is low Basic Gate is inverter

Some Information on each Logic Family


Characteristics Fan-out – Maximum number of standard

load a gate can drive without disparity Power Dissipation – Power Required to operate the gate

Expressed in mW. Propagation Delay – Time taken by the signal to

propagate from input to output when a signal change occur

Noise Margin – Maximum Noise voltage that can be added to circuit without unwanted effect on output

(Two Types : - AC & DC Noise)

Represented in V and represent max level


Family Type

Voltage Supply

High Level Voltage Low Level Voltage

Range Typical Range Typical

TTL Vcc = 5 2.4 – 5 3.5 0 - 0.4 0.2

ECL VEE = -5.2 -0.95 – -0.7 -0.8 -1.9 – -1.6 -1.8

CMOS VDD = 3 – 10 VDD VDD 0 - 0.5 0

Common Logic Levels

Characteristic TableFamily Fan-out aPower

DissipationPropagation

delayNoise Margin

TTL 10 10 10 0.4

Schottky TTL 10 22 3 0.4

Low power Schottky TTL

20 2 10 0.4

ECL 25 25 2 0.2

CMOS 50 0.1 25 3


Technology

Logic Families Electronics