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  Linear Integrated Circuits, Physics tutorial

Introduction:

To understand what the linear integrated circuit is, it is significant to first understand what the integrated circuit, or IC, is. The IC is possibly better called as chip or microchip. It is a kind of semiconductor which has series of resistors, capacitors, and transistors built in it. Every IC can have hundreds or millions of these. Integrated circuits are frequently utilized as microprocessors, computer memory, oscillators, amplifiers, or timers.

Linear integrated circuit (linear IC) is the solid-state analog device classified by theoretically infinite number of possible operating states. It functions over continuous range of input levels. On the contrary, digital IC has finite number of discrete input and output states.

Within certain input range, amplification curve of linear IC is straight line; input and output voltages are directly proportional. Best known and most common, linear IC is operational amplifier or op amp that includes resistors, diodes, and transistors in conventional analog circuit. There are two inputs, called as inverting and non-inverting. Signal applied to inverting input results in signal of opposite phase at output. Signal applied to non-inverting input produces signal of identical phase at output. Connection, through variable resistance, between output and inverting input is used to control amplification factor.

A linear integrated circuit is utilized in the variety of modern electronic equipment. Circuit is able to receive, process and produce a variety of different levels of energy as the device operates. Devices that require amplifiers and oscillators often make use of this type of circuit, which is characterized by equal input and output signal levels.

Such circuits can be either analog or digital. Linear integrated circuits are analog ICs. They are different than digital ICs as they are able to create large variety of levels of output. In fact, in theory, this circuit must be able to provide the infinite number of different signal levels. The digital integrated circuit, on the contrary, is able to generate only few different levels of output.

Analog ICs are known as linear integrated circuits as the signal output level of circuit is the linear function of signal input level. Graphing input and output levels shows this fact visually. If output is graphed at same moment as input, connecting points would generate the straight line. In other words, as input changes, output of circuit changes proportionately.

When the signal is applied at inverting input, corresponding and opposite phase is generated at output. Applying the signal to non-inverting input of circuit results in the identical phase produced at output. Variable resistance produces connection between inverting input and output that controls amplification of signal.

Digital ICs:

Digital ICs have circuits whose input and output voltages are restricted to two possible levels - high or low. It is thus as digital signals are generally binary. Examples of Digital ICs comprise:

  • Logic gates
  • Flip-flop
  • Calculator chip
  • Memory chip
  • Amongst others.

LICs have extensive use in military and industrial applications and in consumer products. They are often utilized in:

1. Operational amplifiers

2. Small-signal amplifiers

3. Power amplifiers

4. RF and IF amplifiers

5. Microwave amplifiers

6. Multipliers

7. Voltage comparators,

8. Voltage regulators etc.

Advantages of Integrated Circuits:

1. Small in size. As fabrication procedure is utilized for integration of active and passive components on to silicon chip, IC becomes lot smaller.

2. Weight of IC also decreases, when compared to discrete circuit.

3. Production of hundreds of IC's the cost of production will be extremely low and less time consuming.

4. PCB comprising soldered joints will be less reliable. This problem is omitted in IC's due to no soldered joints, with fewer interconnections, and therefore highly reliable.

5. Increased operating speed due to absence of parasitic capacitance effect.

6. As IC's are made in bulk temperature coefficients and other parameters will be strongly matching.

7. All IC's are tested for operating ranges in very low and very high temperatures.

8. As all components are fabricated inside chip, there won't be any external projections.

Disadvantages of Integrated Circuits:

1. Few complex IC's maybe costly. If such integrated circuits are utilized roughly and become faulty, they have to be exchanged by the new one. They can't be repaired as individual components inside IC are very small.

2. Power rating for most of IC's doesn't exceed more than 10 watts. Therefore it isn't possible to produce high power IC's.

3. Few components such as transformers and inductors can't be integrated in IC. They have to be joined externally to semiconductor pins.

4. High grade P-N-P assembly isn't possible.

5. IC won't work properly if wrongly handled or exposed to excessive heat.

6. It is hard to get low temperature coefficient.

7. It is hard to fabricate IC with low noise.

9.  There is large value of saturation resistance of transistors.

Integrated Circuit - Classification:

ICs can be categorized on basis of their chip size as given below:

  • Small scale integration (SSI)-3 to 30 gates/chip.
  • Medium scale integration (MSI)-30 to 300 gates/chip.
  • Large scale integration (LSI)-300 to 3,000 gates/chip.
  • Very large scale integration (VLSI)-more than 3,000 gates/chip

Some other classification of integrated circuits based on fabrication techniques used are given below:

1. Monolithic Integrated Circuits: Monolithic IC's refer to the single stone or single crystal. Single crystal refers to the single chip of silicon as semiconductor material, on top of which all active and passive components required are interconnected.

2. Thin and Thick Film Integrated Circuit: Thick and thin film IC's are relatively larger than monolithic IC's and smaller than discrete circuits. They locate their use in high power applications. Although it is a little large in size, these IC's can't be integrated with transistors and diodes.

3. Hybrid or Multi-chip Integrated Circuits: The circuit is fabricated by interconnecting the number of individual chips. Hybrids ICs are frequently utilized for high power audio amplifier applications from 5 Watts to more than 50 Watts. Active components are diffused transistors or diodes. Passive components may be group of diffused resistors or capacitors on the single chip, or they may be thin-film components.

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