Digital Integrated Circuits

A microprocessor is digital is a digital circuit which is built using a combination logic functions. The microprocessor package contains an integrated circuit.

Integrated Circuit

An integrated circuit is electronic circuit or device that has electronic components on a small semiconductor chip. It has functionality of logic AND or amplifying of a signal. These are mainly two types of circuits: Digital or Analog. Analog ICs handle continuous signals such as audio signals and Digital ICs handle discrete signals such as binary values.

Types of Integrated Circuits

There are different types of integrated circuits based various criteria. Based on intended application, the Integrated Circuit (IC) can be classified as following:

  • Digital Integrated Circuits handle discrete signals such as binary values (0 and 1). These circuits use digital logic gates, multiplexers, flip flops etc.These circuits are easier to design and economical.

  • Analog Integrated Circuits handle contiguous signals. These are two types: linear integrated circuits (Linear ICs) and Radio frequency integrated circuits (RF ICs).

  • Mixed Integrated Circuits are obtained by the combination of analog and digital integrated circuits. Therefore it have digital to analog (A/D) converter, digital to analog (D/A) converter, and clock/timing integrated circuits.

General types of integrated circuits are as following: Comparators, Switching IC, Audio amplifiers, Operational amplifiers, Timers ICs.

Digital Integrated Circuit

Functions of digital integrated circuits to handle discrete signals such as binary values in which “true/false” logical operations are used. Basic Boolean functions such as AND, OR, and NOT are essential in building functionality for modern digital systems. These Boolean functions are implemented using transistors. For example, internal transistor structure of a NAND gate is given in following figure.

There might ten billion or more transistors in modern digital circuit. So, we need Integrated Circuits (ICs) that combine a small or large number of these transistors to achieve particular functionality. These circuits provide benefiting students, very low cost and higher level of reliability. Examples of integrated circuits are MOS, CMOS, TTL etc. CMOS ICs are fault tolerant, reduce risk of chip failure, use of anti-static foam for storage and transport of ICs. TTL technology requires regulated power supply of 5 volts.

Families of Integrated Circuits

A logic family is a group of electronic logic gates. A family has its own discrete logic level, power supply, individual components, characteristic, advantages and disadvantages. Within each family, there is a range of voltage which may be low level or high level.

These families are listed as following below:

Diode Logic (DL)

Registers and diodes are used to implement logic. The purpose of diode is to perform OR and AND operation, and logic switch. It is essential that diode is forward biased so that it can conduct. Disadvantages: diodes can not perform NOT operation, diode cannot work for multiple states, only one stage at a time, tend to degrade signals quickly.

Resistor-Transistor Logic (RTL)

Registers and transistors are used to implement logic. Transistors are used to combine signals which are inverted and amplified inputs. These are economical and easy to design but slower in speed. These require great amount of current from supply. RTL gates can be used as interface between linear circuits and digital.

Diode Transistor Logic (DTL)

Registers and diodes are used to implement logic. It has advantages over DL and RTL. Diode can perform AND and OR operation along with a transistor and output signal can be amplified. It has logic inversion which is signal can be restored to full logic level, if we add a transistor at output of logic gates. OR operation can be performed using diodes instead of resistors which removes interaction between input signals. Since input resistor to transistor, switching speed of transistor is limited. DTL was used in tube computers.

Transistor - Transistor Logic (TTL)

Transistors are used to implement logic and Bipolar transistors to contract integrated circuits. There are standard TTL, high speed TTL, low power TTL, and schottky TTL. It is popular logic family.

Emitter Coupled Logic (ECL)

ECL is a non-structured logic. Advantages of this logic are speed, and very low propagation delay.

Complementary Metal Oxide Semiconductor Logic (CMOS)

It is known for high fan-out, low power consumption and most reliable logic family.

Updated on: 30-Jun-2020

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