ANALOG INTEGRATED CIRCUITCS
UNIT-3
OP-AMP AND ITS APPLICATIONS
TOPICS
• Basic Operational Amplifier
• Characteristics of Op-Amp
• Functional Block Diagram
• Open and Closed loop configuration
• DC characteristics and AC characteristics
• Widlar Current Source
• Wilson Current Source
• Instrumentation amplifier
• Log and Antilog amplifiers
• Differentiator, Integrator
• Comparators
• Schmitt Trigger
• Precision Rectifier
• First order Low pass filter.
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
Classification of ICs
Integrated Circuits
Monolithic Circuits Hybrid Circuits
Bipolar Unipolar
P-n- junction Dielectric MOSFET JFET
isolation isolation
IC CHIP SIZE & CIRCUIT COMPLEXITY
Parameter Gate Level Year
Invention of 1947
transistor (Ge)
Development of 1955 – 1959
silicon transistor
Silicon planar 1959
technology (Si)
SSI 3 to 30 gates/chip approx. or 1960 – 1960
100 transistor/chip
(Logic gates, Flip-
flops)
MSI 30 to 300 gates/chip approx. or 1965 – 1970
1000 transistor/chip
(Counters, Multiplexers, Adders)
LSI 300 to 3000 gates/chip approx. 1970 – 1980
or
1000 – 20,000 transistor/chip
(8-bit Microprocessor, ROM,
RAM)
IC CHIP SIZE & CIRCUIT COMPLEXITY
Parameter Gate Level Year
VLSI More then 3000 gates/chip 1980 – 1990
approx. or 20,000 – 1,00,000
transistor/chip
(16 and 32 bit Microprocessors)
ULSI 106 – 107 transistors/ Chip 1990 - 2000
(Special Processors, Virtual
reality, Smart sensors)
GSI > 107 transistors/ Chip 2000
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
package.
Packages
The metal can (TO) The Flat Package
Package
The Dual-in-Line (DIP)
Package
Characteristics of Op-
Amp
OPERATIONAL 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
+5v
Non-inverting input
2
7 0utput
6
inverting input 4
3
-5v
PIN DIAGRAM
Ideal characteristics of OPAMP
Open loop voltage gain AOL =∞
Input Impedance Ri =∞
Output Impedance Ro =0
Bandwidth BW =∞
Zero offset (Vo = 0 when V1 = V2 = 0) Vios =0
CMRR ρ =∞
Slew rate S =∞
No effect of temperature
Power supply rejection ratio PSRR = 0
Inverting Op-Amp
Rf
VO I
VU T N R1
16
Non-Inverting Amplifier
R1
VO U T INV
R
1 2
Voltage follower
Comparison of the ideal inverting and non-inverting op-
amp
Ideal Inverting amplifier Ideal non-inverting amplifier
1. Voltage gain=-Rf/R1 1. Voltage gain=1+Rf/R1
2. The output is inverted with 2. No phase shift between input
respect to input and output
3. The voltage gain can be 3. The voltage gain is always
adjusted as greater than, equal to greater than one
or less than one
4. The input impedance is R1 4. The input impedance is very
large
Functional block diagram
V1(-)
Vo
Differential Differential Buffer and Output
Amplifier Amplifier Level shifter Stage
V2(+)
1.Dual input balanced output differential amplifier.
2. Dual-input unbalanced output differential
amplifier.
3.Emitter follower with constant current source.
4. Complementary symmetry push pull amplifier
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
DC characteristics
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
DC characteristics
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
DC characteristics
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
+ -
DC characteristics
THERMAL DRIFT
Bias current, offset current and offset
voltage change with temperature. A circuit
carefully nulled at 25oc may not remain so when
the temperature rises to 35oc. This is called drift.
AC characteristics
Frequency Response
HIGH FREQUENCY MODEL OF OPAMP
AC characteristics
Frequency Response
OPEN LOOP GAIN VS FREQUENCY
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
Po l e - zero compensation
Slew rate
It is defined as the maximum rate of change of
output voltage with time. The slew rate is
specified in V/µsec
Slew rate = S = dVo / dt |max
It is specified by the op-amp in unity gain condition.
The slew rate is caused due to limited charging rate of the
compensation capacitor and current limiting and saturation of the
internal stages of op-amp, when a high frequency large amplitude
It is given by dVc /dt = I/C
For large charging rate, the capacitor should be
small or the current should be large.
S = Imax / C
For 741 IC the charging current is 15 µA and
the internal capacitor is 30 pF. S= 0.5V/ µsec
The modes of using an
op-amp
Open Loop : (The output one the
assumes
possibleoutput states, that two
is +Vsat
of or – and
amplifier acts as a switch only).
Closed Loop: ( The utility of an op-amp can be
Vsat the
greatly increased by providing negative feed
back. The output in this case is not driven into
saturation and the circuit behaves in a linear
manner).
Open loop configuration of
op-amp
The voltage transfer curve indicates the
inability of op- amp to work as a linear small
signal amplifier in the open loop mode
Such an open loop behavior of the op-amp finds
some rare applications like voltage comparator,
zero crossing detector etc.
Open loop op-amp configurations
The configuration in which output depends on
input, but output has no effect on the input is
called open loop configuration.
No feed back from output to input is used
in such configuration.
The op-amp works as high gain amplifier
The
op-amp can be used in three modes in
open loop configuration they are
Differential
amplifier
Inverting
Why op-amp is generally not used in open loop mode?
As open loop gain of op-amp is very large, very
small input voltage drives the op-amp voltage
to the saturation level. Thus in open loop
configuration, the output is at its positive
saturation voltage (+Vsat ) or negative saturation
voltage (-Vsat ) depending on which input V1 or V2 is
more than the other. For a.c. input voltages,
output may switch between positive and
This indicates the inability of op-amp to work as a linear small signal
amplifier in the open loop mode. Hence the op-amp in open loop
configuration is not used for the linear applications
Closed loop operation of
op-amp
The utility of the op-amp can be increased
considerably by operating in closed loop mode.
The closed loop operation is possible with the
help of feedback. The feedback allows to feed
some part of the output back to the input
terminals.
In the linear applications, the op-amp is always
used with negative feedback.
The negative feedback helps in controlling
gain, which otherwise drives the op-amp out of
WIDLAR AND WILSON CURRENT SOURCE
INSTRUMENTATION AMPLIFIER
An instrumentation amplifier is used to
measure and control physical quantities
such as temperature, humidity, light
intensity, and waterflow.
Instrumentation amplifier is the front end component of every
measuring instrument which improves the signal to noise ratio of
the input electrical signal from the transducer
DIFFERENTIATOR
OUTPUT WAVEFORMS
IMPROVED OP-AMP DIFFERENTIATOR
INTEGRATOR
PRACTICAL INTEGRATOR
COMPARATOR
If A0 is large, practical response can be
approximated as :
VIN > 0 V+ > V-
VOUT = +VSAT VIN <
0 V+ < V- VOUT
= -VSAT
NON INVERTING COMPARATOR
A comparator compares a signal voltage applied at the input of
an op-amp with a known reference voltage V ref given at the other
input.
It is an open-loop operation, i.e., there is no feedback path in the
case of a comparator
INVERTING COMPARATOR
-
SCHMITT TRIGGER
• The Schmitt trigger is an op-amp comparator
circuit featuring hysteresis.
• The inverting variety is the most commonly
used.
OPERATION
It is obvious from the circuit that positive
feedback is employed in the circuit.
The feedback factor
β =Vf / Vo = R2/(R2+R1).
HYSTERISIS
Hysteresis = V upper threshold- Vlower threshold
= β*Vcc-(- β*Vcc) = 2* β*Vcc= 2*Vcc*R2/(R2+R1)
LOG AMPLIFIER
•Logarithmic amplifier gives the output proportional to the logarithm of
input signal.
•If Vi is the input signal applied to a differentiator then
output is Vo = K*ln(Vi)+l
•where K is gain of logarithmic amplifier,l is constant.
ANTI LOG AMPLIFIER
Anti log amplifier is one which provides output proportional to the anti log i.e.
exponential to the input voltage.
If Vi is the input signal applied to a Anti log amplifier then the output is
Vo=K*exp(a*Vi) where K is proportionality constant, a is constant.
The current equation of diode is given as Id =
Ido*(exp (V/Vt)-1)
Ido is reverse saturation current, V
is voltage applied across diode;
Vt is the voltage equivalent of
temperature
Applying KCL at
inverting node of opamp
Id = (0-Vo)/R =
Io*(exp (Vin/Vt))
PRESICION RECTIFIER
Vi > 0 v ; D1, D2 ON ;Vo = 0
Vi < 0 v ; D1, D2 OFF ;Vo = –(Rf/R1)*Vi
PRECISION FULL WAVE RECTIFIER
FULL WAVE RECTIFIER WITH TWO OP-AMPS
FILTERS
Filter is a frequency selective circuit that passes
signal of specified Band of frequencies and
attenuates the signals of frequencies outside
the band
Type of Filter
1. Passive filters
2. Active filters
•Active filters use op-amp(s) and RC components.
• Advantages over passive filters:
– op-amp(s) provide gain and overcome circuit losses
– increase input impedance to minimize circuit loading
– higher output power
– sharp cutoff characteristics some commonly used
FIRST ORDER LOW PASS FILTER
FREQUENCY RESPONSE
THANK
YOU
