Integrated Circuits

Integrated Circuits, tiny electronic circuits used to perform a specific electronic function, such as amplification; it is usually combined with other components to form a more complex system.

It is a small silicon semiconductor crystal, called a chip, containing electrical components such as transistors, diodes, resistors, and capacitors. IC's come in two types of packages viz:

• Flat package
• DIP package(Dual Inline Package)

                                                                                 

Fig: Flat Package                                                                                                     

   Fig: DIP Package

The DIP is most widely used because of the low price and easy installation on circuit boards. Most ICS have a standard size and the number of pins ranges from 8-64. The size of the IC package is very small but offers a wide variety of advantages;

• Low cost/Economical
• Reduce power consumption
• High reliability against failure. So, digital systems need lesser pairs.
• High Operating Speed and suitable for high-speed operation.
• Reduce the use of external wiring connections as the connection is internal to the package.

IC's are classified into two general categories:

1. Linear ICs: It operates with continuous signals to provide electronic functions such as amplifiers and voltage comparators.
2. Digital ICs: It operates with binary signals and is made up of interconnected digital gates.

Level of Integration

With the advent of technology, the number of gates used in an IC has increased considerably. Hence, on the basis of gates used, Ics can be either small, medium, or large-scale integration devices. Fixed function digital ICs are classified and listed below according to their complexity from the least complex to the most complex.

1. Small Scale Integration(SSI):

SSI is a fixed-function ICs that contain only a few equivalent gate circuits( transistors numbering in the tens) on single chips. It includes basic gates, flip-flops, transistors, etc.

2. Medium Scale Integration(MSI);

MSI is a fixed-function ICs that contain 10-100 equivalent gate circuits(hundreds of transistors) on each chip. It includes encoders, decoders, counters, registers, multiplexers, arithmetic circuits, etc.

3. Large Scale Integration(LSI):

LSI is a fixed-function ICs that contain 100-1000 equivalent gate circuits (tens of thousands of transistors) on each chip. It includes large memories, 1KB RAM, calculator chips, first microprocessors, etc.

4. Very Large Scale Integration(VLSI):

VLSI is a fixed-function ICs that contain 1000-10000 equivalent gate circuits (hundreds of thousands of transistors) on each chip. It includes 1MB RAM, second-generation and later microprocessors chips, etc.

5. Ultra Large Scale Integration(VLSI):

ULSI is a fixed-function ICs that contain more than a million equivalent gate circuits (more than a million of transistors) on each chip. It includes very large memories, large microprocessors, large single-chip computers, etc.

IC Digital Logic Families

Digital IC gates are not only classified by their logic operation but also by the specific logic circuit family to which they belong. Each logic family has its own basic electronic circuit upon which more complex digital circuits and functions are developed. The basic circuit in each family is either a NAND or a NOR gate. Each family has its capabilities and limitations, its advantages and disadvantages. The following list describes the main logic families.

1. Diode Logic(DL)

2. Resistor-Transistor Logic(RTL) Family

3. Diode-Transistor Logic(DTL)

4. Transistor-Transistor Logic(TTL) Family

5. Emitter-Coupled Logic(ECL) Family

6. Complementary Metal Oxide Semiconductor (MOS) Family

Characteristics of digital logic families

• Fan-in: the number of inputs to a gate.
• Fan-out: the number of standard loads driven by a gate output. Power Dissipation: the amount of power needed by the gate.
• Propagation delay: The signals through a gate take a certain amount of time to propagate from the inputs to the output. This interval of time is defined as the propagation delay of the gate.
• Noise Margin: Noise margin is the maximum noise voltage added to an input signal of a digital circuit that does not cause an undesirable change in the circuit output.