UNIT 2 CHARACTERISTICS OF OP-AMP

UNIT-II

CHARACTERISTICS OF OP-AMP

OPERATION AMPLIFIER
An operational amplifier is a direct coupled high gain amplifier consisting of one or more
differential amplifiers, followed by a level translator and an output stage.

It is a versatile device that can be used to amplify ac as well as dc input signals & designed
for computing mathematical functions such as addition, subtraction ,multiplication,
integration & differentiation.

Op-amp symbol

Ideal characteristics of OPAMP

1. Open loop gain infinite
2. Input impedance infinite
3. Output impedance low
4. Bandwidth infinite
5. Zero offset, ie, Vo=0 when V1=V2=0

Inverting Op-Amp

Vout = -Vin(Rf/Ri)

Voltage follower

Vout = Vin

DC characteristics

Input offset current

The difference between the bias currents at the input terminals of the op- amp is called as input
offset current. The input terminals conduct a small value of dc current to bias the input transistors.
Since the input transistors cannot be made identical, there exists a difference in bias currents

Input offset voltage

A small voltage applied to the input terminals to make the output voltage as zero when the
two input terminals are grounded is called input offset voltage

Input bias current

Input bias current IB as the average value of the base currents entering into terminal of
an op-amp
IB=IB(+) + IB(-)


AC characteristics

Frequency Response

HIGH FREQUENCY MODEL OF OP-AMP

Need for frequency compensation in practical op-amps
• Frequency compensation is needed when large bandwidth and lower closed loop gain is
desired.
• Compensating networks are used to control the phase shift and hence to improve the stability

Frequency compensation methods
• Dominant- pole compensation
• Pole- zero compensation


Slew Rate
• The slew rate is defined as the maximum rate of change of output voltage caused by a step
input voltage.
• An ideal slew rate is infinite which means that op-amp’s output voltage should change
instantaneously in response to input step voltage.

UNIT 1 IC FABRICATION

UNIT-I

IC FABRICATION

INTEGRATED CIRCUITS

An integrated circuit (IC) is a miniature ,low cost electronic circuit consisting of active and
passive components fabricated together on a single crystal of silicon. The active components are
transistors and diodes and passive components are resistors and capacitors.

Advantages of integrated circuits
1. Miniaturization and hence increased equipment density.
2. Cost reduction due to batch processing.
3. Increased system reliability due to the elimination of soldered joints.
4. Improved functional performance.
5. Matched devices.
6. Increased operating speeds.
7. Reduction in power consumption

Basic processes involved in fabricating Monolithic ICs
1. Silicon wafer (substrate) preparation
2. Epitaxial growth
3. Oxidation
4. Photolithography
5. Diffusion
6. Ion implantation
7. Isolation technique
8. Metallization
9. Assembly processing & packaging

Silicon wafer (substrate) preparation

1.Crystal growth &doping
2.Ingot trimming & grinding
3.Ingot slicing
4.Wafer policing & etching
5.Wafer cleaning

Epitaxial growth

Epitaxy means growing a single crystal silicon structure upon a original silicon substrate, so that
the resulting layer is an extension of the substrate crystal structure.
The basic chemical reaction in the epitaxial growth process of pure silicon is the hydrogen
reduction of silicon tetrachloride.

Oxidation

SiO2 is an extremely hard protective coating & is unaffected by almost all reagents except by
hydrochloric acid. Thus it stands against any contamination.
By selective etching of SiO2, diffusion of impurities through carefully defined through windows in
the SiO2 can be accomplished to fabricate various components.

Photolithography
The process of photolithography makes it possible to produce microscopically small circuit
and device pattern on si wafer
Two processes involved in photolithography
a) Making a photographic mask
b) Photo etching

Photographic mask


The development of photographic mask involves the preparation of initial artwork and its diffusion.
reduction, decomposition of initial artwork or layout into several mask layers.

Photo etching
Photo etching is used for the removal of SiO2 from desired regions so that the desired2impurities can
be diffused

Diffusion
The process of introducing impurities into selected regions of a silicon wafer is called diffusion. The
rate at which various impurities diffuse into the silicon will be of the order of 1μm/hr at the
temperature range of 9000 C to 11000C .The impurity atoms have the tendency to move from regions
of higher concentrations to lower concentrations

Ion implantation technique
It is performed at low temperature. Therefore, previously diffused regions have a lesser tendency for
lateral spreading.
In diffusion process, temperature has to be controlled over a large area inside the oven, where as in
ion implantation process, accelerating potential & beam content are dielectrically controlled from
outside

Dielectric isolation
In dielectric isolation, a layer of solid dielectric such as SiO2 or ruby completely surrounds each
components thereby producing isolation, both electrical & physical. This isolating dielectric layer is
thick enough so that its associated capacitance is negligible. Also, it is possible to fabricate both pnp
& npn transistors within the same silicon substrate

Metallization
The process of producing a thin metal film layer that will serve to make interconnection of the various
components on the chip is called metallization.

Aluminium is preferred for metallization
1. It is a good conductor
2. it is easy to deposit aluminium films using vacuum deposition.
3. It makes good mechanical bonds with silicon
4. It forms a low resistance contact

IC packages available
1. Metal can package.
2. Dual-in-line package.
3. Ceramic flat packages.

LINEAR INTEGRATED CIRCUITS AND APPLICATIONS

AIM
To introduce the concepts for realizing functional building blocks in ICs, fabrications & application of
ICs.

OBJECTIVES
i. To study the IC fabrication procedure.
ii. To study characteristics; realize circuits; design for signal analysis using Op-amp ICs.
iii. To study the applications of Op-amp.
iv. To study internal functional blocks and the applications of special ICs like Timers, PLL
circuits, regulator Circuits, ADCs.

UNIT I IC FABRICATION 9
IC classification, fundamental of monolithic IC technology, epitaxial growth, masking and etching,
diffusion of impurities. Realisation of monolithic ICs and packaging. Fabrication of diodes,
capacitance, resistance and FETs.

UNIT II CHARACTERISTICS OF OPAMP 9
Ideal OP-AMP characteristics, DC characteristics, AC characteristics, offset voltage and current:
voltage series feedback and shunt feedback amplifiers, differential amplifier; frequency response of
OP-AMP; Basic applications of op-amp – summer, differentiator and integrator


UNIT III APPLICATIONS OF OPAMP 9
Instrumentation amplifier, first and second order active filters, V/I & I/V converters, comparators,
multivibrators, waveform generators, clippers, clampers, peak detector, S/H circuit, D/A converter (R-
2R ladder and weighted resistor types), A/D converter - Dual slope, successive approximation and
flash types.

UNIT IV SPECIAL ICs 9
555 Timer circuit – Functional block, characteristics & applications; 566-voltage controlled oscillator
circuit; 565-phase lock loop circuit functioning and applications, Analog multiplier ICs.

UNIT V APPLICATION ICs 9
IC voltage regulators - LM317, 723 regulators, switching regulator, MA 7840, LM 380 power
amplifier, ICL 8038 function generator IC, isolation amplifiers, opto coupler, opto electronic ICs.

L = 45 TOTAL = 45PERIODS

TEXT BOOKS
1. Ramakant A.Gayakward, ‘Op-amps and Linear Integrated Circuits’, IV edition, Pearson
Education, 2003 / PHI. (2000)
2. D.Roy Choudhary, Sheil B.Jani, ‘Linear Integrated Circuits’, II edition, New Age, 2003.

REFERENCES
1. Jacob Millman, Christos C.Halkias, ‘Integrated Electronics - Analog and Digital circuits system’,
Tata McGraw Hill, 2003.
2. Robert F.Coughlin, Fredrick F.Driscoll, ‘Op-amp and Linear ICs’, Pearson Education, 4th edition,
2002 / PHI.
3. David A.Bell, ‘Op-amp & Linear ICs’, Prentice Hall of India, 2nd edition, 1997