EC2254 – LINEAR INTEGRATED CIRCUITS
1.1. What is an integrated circuit?
An integrated circuit (IC) is a combination of interconnected circuit elements
inseparably associated or with in continuous substrate.
1.2. Define substrate.
The substrate is the supporting material upon or with in ...
EC2254- Linear Integrated Circuits IV Semester ECE
EC2254 – LINEAR INTEGRATED CIRCUITS
1.1. What is an integrated circuit?
An integrated circuit (IC) is a combination of interconnected circuit elements
inseparably associated or with in continuous substrate.
1.2. Define substrate.
The substrate is the supporting material upon or with in which an IC is fabricated
or to which an IC is attached.
1.3. Define monolithic IC.
A monolithic IC is an IC whose elements are formed in place upon or within a
semiconductor substrate with at least one of the elements formed within the substrate.
1.4. What is a hybrid IC?
A hybrid IC consists of a combination of two or more IC types.
1.5. Define wafer.
It is the basic physical unit used in processing. It consists of large number of
identical ICs.
1.6. What are the advantages of ICs over discrete circuits?
Low cost.
There are many advantages of ICs over discrete circuits. They are:
Small size.
Improved performance.
Low power consumption.
High reliability.
Mass production capability.
Increased operating speed.
Less weight.
Easy replacement.
1.7. What are the limitations of ICs?
The limitations of ICs are as follows:
Since ICs are small and unable to dissipate large amount of power, the heat
produced by large elements may destroy the IC. The transformers and inductors cannot
be fabricated using IC technology.
1.8. What are the applications of ICs?
Integrated circuits have become part and parcel of human life. Computers cellular
phones and other digital appliances are now inextricable parts of the structure of modern
societies. That is, modern computing, communications, instrumentation, manufacturing
and transport systems, including the internet, all depend on the existence of integrated
circuits. Among the most advanced integrated circuits are the microprocessors and
Prepared By A.Devasena., Associate Professor., / Dept of ECE Page 1
,EC2254- Linear Integrated Circuits IV Semester ECE
microcontrollers which control everything from computers, cellular phones to household
appliances.
1.9. What is the classification of ICs based on complexity level?
Small scale integration (SSI).
Based on the complexity level (number of gates on a chip) ICs are classified as
Medium scale integration (MSI).
Large scale integration (LSI).
Very large scale integration (VLSI).
1.10. What is the classification of ICs based on fabrication process?
Depending on the fabrication process ICs are classified as i) monolithic IC ii)
Hybrid IC.
1.11. What is the classification of ICs based on the function performed?
Based on the functions performed integrated circuits can be classified into analog
and digital ICs.
1.12. What is meant by epitaxial growth?
The term epitaxial growth means “arranging upon”. It is the process of depositing
a thin layer (0.5 to 20 microns) of single crystal material over a single crystal substrate.
1.13. What is photolithography?
Photolithography is a process used in semiconductor device fabrication to transfer
a pattern from a photo mask to the surface of a wafer.
1.14. Define etching. What are the different types?
It is a process of removing a film or layer from the substrate in those areas not
covered with photo resist. There are two types of etching i) wet etching and ii)dry
etching.
1.15. What are the properties of the chemicals used for etching?
The chemicals used for etching (etchant) should have the following
It should react with the film etched in a smooth manner producing suitable
characteristics:
It should not react with photo resist.
products that can be carried away from the surface.
It should be act with film to be etched and not with other microelectronic
materials.
1.16. Define diffusion.
Diffusion is a process where the particles move from regions of higher
concentration to regions of lower concentrations.
1.17. What is meant by ion implantation?
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,EC2254- Linear Integrated Circuits IV Semester ECE
Ion implantation is the introduction of ionized particles atoms into targets with
enough energy to penetrate beyond surface regions.
Unlike diffusion, which is a high temperature process, ion implantation is
1.18. What are the advantages of ion implantation?
It permits greater flexibility in designing.
a low temperature process.
It is a high precision tool. It precisely controls the number of dopant
atoms.
1.19. What is meant by surface passivation?
The process of creating the protective SiO2 layer on the wafer surface is known as
surface passivation.
1.20. What is the purpose of formation of SiO 2 layer?
It serves as diffusion mask and allows diffusion impurities through
The formation of SiO2 layer serves many purposes.
It serves as an insulator in the wafer surface.
carefully defined windows etched into oxide.
It protects the junction from moisture and other atmospheric contaminants.
1.21. What is meant by metallization?
After devices have been fabricated in the silicon substrate, interconnections must
be made to link all the components on the chip. This process is called metallization.
1.22. Why aluminum is most preferred for metallization?
Aluminum is the mostly used metal for metallization. It has the following
It is a good conductor.
advantages:
It makes good mechanical bonds with silicon.
It is cheap.
It is easy to deposit aluminum films using vacuum decomposition.
1.23. What are the different IC packages?
To- glass metal.
There are three different IC packages. They are
Ceramic flat package.
Dual-in-line (ceramic or plastic type).
1.24. What are the different CMOS technologies?
The CMOS technologies are p-well process, n-well process, twin-tub process and
silicon on insulator.
1.25. What is a differential amplifier? What is the ideal value of its gain?
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A differential amplifier is one which amplifies the difference between its two
input signals. The gain with which it amplifies the difference is called its differential gain
and ideally it should be infinite.
1.26. What is common mode gain of a differential amplifier?
If the two input signals to a differential amplifier are same, then its output should
be zero. But practically it produces a small output which is proportional to the average
common level of the two input signals. The factor by which the differential amplifier
amplifies the common mode signal is called its common mode gain.
1.27. What is CMRR? State its ideal value.
The ability of the differential amplifier to reject common mode signal is expressed
by the ratio of differential gain to the common mode gain which is called its common
mode rejection ratio CMRR. The ideal value of CMRR is infinite.
Dual input, balanced output.
1.28. List out various configurations of a differential amplifier.
Dual input, unbalanced output.
Single input, balanced output.
Single input, unbalanced output.
1.29. Why practically RE cannot be selected very high?
Large RE requires higher biasing voltages to set the proper operating point
Practically RE cannot be selected very high because:
This increases the overall chip area.
of the transistor.
Smaller number of components can be installed on the same chip which is
undesirable from integrated circuit point of view.
1.30. Why constant current source is used instead of R E?
Without physically increasing the value of RE , the RE replaced by a transistor
operated at a constant current. Such a constant current source circuit gives the effect of a
very high resistance as the internal resistance of a constant current is infinite. And due to
transistorized circuit, it needs smaller supply voltage; hence it does not affect the Q point
of the basic circuit. Effect of higher value of RE is provided by a constant current source
due to which common mode gain becomes very small and due to which CMRR becomes
very high.
1.31. What is current mirror?
The circuit in which the output current is forced to equal the input current is
called current mirror.
Provides very large emitter resistance R E.
1.32. List the advantages of current mirror.
Requires lesser components than constant current bias.
Prepared By A.Devasena., Associate Professor., / Dept of ECE Page 4
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