191EE332 - INTEGRATED ELECTRONICS

UNIT 4 - OPERATIONAL AMPLIFIER AND ITS

APPLICATIONS
Introduction – Classification – IC chip size and circuit
complexity, Ideal OP-AMP characteristics – DC characteristics
– AC characteristics, differential amplifier, Basic op-amp
applications - Inverting and non-inverting amplifiers – summer
and Subtractor – Differentiator – Integrator, V/I and I/V
converter, Instrumentation amplifier, Precision rectifier, Schmitt
Trigger, Multi-vibrators
 Unit 1- Operational amplifies
• What is an Integrated Circuit?

• Where do you use an Integrated Circuit?

• Why do you prefer an Integrated Circuit to the circuits made by

interconnecting discrete components?
What is an Integrated Circuit?

Def: The “Integrated Circuit “ or IC is a miniature, low cost

electronic circuit consisting of active and passive components that
are irreparably joined together on a single crystal chip of silicon.

In 1958 Jack Kilby of Texas Instruments invented first IC

Applications of an Integrated Circuit

• Communication

• Control

• Instrumentation

• Computer

• Electronics
Advantages:

• Small size
• Low cost
• Less weight
• Low supply voltages
• Low power consumption
• Highly reliable
• Matched devices
• Fast speed
 Classification

• Digital ICs
• Linear ICs Integrated circuits

Monolithic circuits Thick &Thin Hybrid circuits

film
Bipolar Uni polar

Pn junction Dielectric JFET

MOSFET
isolation isolation

Classification of ICs
 Chip size and Complexity
• Invention of Transistor (Ge) - 1947

• Development of Silicon - 1955-1959

• Silicon Planar Technology - 1959

• First ICs, SSI (3- 30gates/chip) - 1960

• MSI ( 30-300 gates/chip) - 1965-1970

• LSI ( 300-3000 gates/chip) -1970-1975

• VLSI (More than 3k gates/chip) - 1975

• ULSI (more than one million active devices are integrated on single chip)
 IC Package types
• Metal can Package
• Dual-in-line
• Flat Pack
 Metal can Packages
• The metal sealing plane is at the bottom over
which the chip is bounded
• It is also called transistor pack
 Doul-in-line Package
• The chip is mounted inside a plastic or ceramic
case
• The 8 pin Dip is called MiniDIP and also available
with 12, 14, 16, 20pins
 Flat pack
• The chip is enclosed in a rectangular ceramic case
 Selection of IC Package
Type Criteria

Metal can 1. Heat dissipation is important

package 2. For high power applications like power
amplifiers, voltage regulators etc.

DIP 1. For experimental or bread boarding purposes as

easy to mount
2. If bending or soldering of the leads is not
required
3. Suitable for printed circuit boards as lead
spacing is more
Flat pack 1. More reliability is required
2. Light in weight
3. Suited for airborne applications
 Packages

The metal can (TO) The Flat Package

Package

The Dual-in-Line (DIP)

Package
 Factors affecting selection of IC package

• Relative cost

• Reliability

• Weight of the package

• Ease of fabrication

• Power to be dissipated

• Need of external heat sink

 Temperature Ranges

1. Military temperature range : -55o C to +125o C (-55o C to +85o C)

2. Industrial temperature range : -20o C to +85o C (-40o C to +85o C )

3. Commercial temperature range: 0o C to +70o C (0o C to +75o C )

 Manufacturer’s Designation for Linear ICs
• Fairchild - µA, µAF

• National Semiconductor - LM,LH,LF,TBA

• Motorola - MC,MFC

• RCA - CA,CD

• Texas Instruments - SN

• Signetics - N/S,NE/SE

• Burr- Brown - BB
191EE332 - INTEGRATED ELECTRONICS

UNIT 4 - OPERATIONAL AMPLIFIER AND ITS

APPLICATIONS
Introduction – Classification – IC chip size and circuit
complexity, Ideal OP-AMP characteristics – DC
characteristics – AC characteristics, differential amplifier,
Basic op-amp applications - Inverting and non-inverting
amplifiers – summer and Subtractor – Differentiator –
Integrator, V/I and I/V converter, Instrumentation amplifier,
Precision rectifier, Schmitt Trigger, Multi-vibrators
 Operational Amplifier

An “Operational amplifier” is a direct coupled high-gain amplifier

usually consisting of one or more differential amplifiers and usually
followed by a level translator and output stage.

The operational amplifier is a versatile device that can be used to

amplify dc as well as ac input signals and was originally designed for
computing such mathematical functions as addition, subtraction,
multiplication and integration.
 Op Amp
Positive power supply
(Positive rail)

Non-inverting
Input terminal
Output terminal

Inverting input
terminal
Negative power supply
(Negative rail)
 Characteristics and performance parameters of Op-amp

• Input offset Voltage

• Input offset current
• Input bias current
• Differential input resistance
• Input capacitance
• Open loop voltage gain
• CMRR
• Output voltage swing
 Characteristics and performance parameters of Op-amp

• Output resistance
• Offset adjustment range
• Input Voltage range
• Power supply rejection ratio
• Power consumption
• Slew rate
• Gain – Bandwidth product
• Equivalent input noise voltage and current
 Characteristics and performance parameters of Op-amp

• Average temperature coefficient of offset parameters

• Output offset voltage

• Supply current
 1. Input Offset Voltage

The differential voltage that must be applied between the two input
terminals of an op-amp, to make the output voltage zero.

It is denoted as Vios

For op-amp 741C the input offset voltage is 6mV

 2. Input offset current

The algebraic difference between the currents flowing into the two input
terminals of the op-amp

It is denoted as Iios = | Ib1 – Ib2|

For op-amp 741C the input offset current is 200nA

 3. Input bias current

The average value of the two currents flowing into

the op-amp input terminals

It is expressed mathematically as
I b1  I b 2
2

For 741C the maximum value of Ib is 500nA

 4. Differential Input Resistance

It is the equivalent resistance measured at either the inverting or non-

inverting input terminal with the other input terminal grounded

It is denoted as Ri

For 741C it is of the order of 2MΩ

 5. Input capacitance

It is the equivalent capacitance measured at either the inverting or non-

inverting input terminal with the other input terminal grounded.

It is denoted as Ci

For 741C it is of the 1-4 pF

 6. Open loop Voltage gain

It is the ratio of output voltage to the differential input voltage, when

op-amp is in open loop configuration, without any feedback. It is

also called as large signal voltage gain

It is denoted as AOL AOL=Vo / Vd

For 741C it is typically 200,000

 7. CMRR

It is the ratio of differential voltage gain Ad to common mode

voltage gain Ac

CMRR = Ad / Ac

Ad is open loop voltage gain AOL and Ac = VOC / Vc

For op-amp 741C CMRR is 90 dB

 8. Output Voltage swing
The op-amp output voltage gets saturated at +Vcc and –VEE
and it cannot produce output voltage more than +V cc and –
VEE. Practically voltages +Vsat and –Vsat are slightly less than
+Vcc and –VEE .

For op-amp 741C the saturation voltages are + 13V for supply voltages + 15V
 9. Output Resistance

It is the equivalent resistance measured between the output

terminal of the op-amp and ground
It is denoted as Ro

For op-amp 741 it is 75Ω

 10. Offset voltage adjustment range

The range for which input offset voltage can be adjusted using the
potentiometer so as to reduce output to zero

For op-amp 741C it is + 15mV

 11. Input Voltage range

It is the range of common mode voltages which can be applied for

which op-amp functions properly and given offset specifications
apply for the op-amp

For + 15V supply voltages, the input voltage range is + 13V

 12. Power supply rejection ratio

PSRR is defined as the ratio of the change in input offset voltage due to the
change in supply voltage producing it, keeping the other power supply
voltage constant. It is also called as power supply sensitivity (PSV)

PSRR= (Δvios / ΔVcc)|constant VEE PSRR= (Δvios / ΔVEE)|constant Vcc

The typical value of PSRR for op-amp 741C is 30µV/V

 13. Power Consumption

It is the amount of quiescent power to be consumed by op-amp with

zero input voltage, for its proper functioning

It is denoted as Pc

For 741C it is 85mW

 14. 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 signal is applied.
 Slew rate

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
 Slew rate equation

Vs = Vm sinωt dVo
= Vm ω cosωt
Vo = Vm sinωt dt
dVo
S =slew rate = dt max

S = Vm ω = 2 π f Vm For distortion free output, the

S = 2 π f Vm V / sec maximum allowable input frequency

This is also called full power fm can be obtained as

S
bandwidth of the op-amp fm 
2 V m
 15. Gain – Bandwidth product

It is the bandwidth of op-amp when voltage gain is unity (1). It is

denoted as GB.

The GB is also called unity gain bandwidth

(UGB) or closed loop bandwidth

It is about 1MHz for op-amp 741C

 16. Equivalent Input Noise Voltage and Current

The noise is expressed as a power density

Thus equivalent noise voltage is expressed as V2 /Hz while the

equivalent noise current is expressed as A2 /Hz
 17. Average temperature coefficient of offset parameters

The average rate of change of input offset voltage per unit change in temperature
is called average temperature coefficient of input offset voltage or input offset
voltage drift
It is measured in µV/oC. For 741 C it is 0.5 µV/oC

The average rate of change of input offset current per unit change in temperature
is called average temperature coefficient of input offset current or input offset
current drift
It is measured in nA/oC or pA/oC . For 741 C it is 12 pA/oC
 18. Output offset voltage ( Voos )

The output offset voltage is the dc voltage present at the output

terminals when both the input terminals are grounded.

It is denoted as Voos
 19. Supply current

It is drawn by the op-amp from the power supply

For op-amp 741C it is 2.8mA

Op amp equivalent circuit
 The Ideal Operational Amplifier
• 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
 Ideal Op-amp
1. An ideal op-amp draws no current at both the input terminals
I.e. I1 = I2 = 0. Thus its input impedance is infinite. Any
source can drive it and there is no loading on the driver stage

2. The gain of an ideal op-amp is infinite, hence the differential

input Vd = V1 – V2 is essentially zero for the finite output
voltage Vo

3. The output voltage Vo is independent of the current drawn

from the output terminals. Thus its output impedance is zero
and hence output can drive an infinite number of other
circuits
 Op-amp Characteristics
• DC Characteristics
Input bias current
Input offset current
Input offset voltage
Thermal drift

• AC Characteristics
Slew rate
Frequency response
 Ideal Voltage transfer curve

+Vsat

AOL = ∞

-Vd +Vd
0

+Vsat ≈ +Vcc
-Vsat
 Practical voltage transfer curve
1. If Vd is greater than corresponding to b, the output attains +Vsat

2. If Vd is less than corresponding to a, the output attains –Vsat

3. Thus range a-b is input range for which output varies linearily
with the input. But AOL is very high, practically this range is very
small
 Transient Response Rise time

When the output of the op-amp is suddenly changing like pulse type,
then the rise time of the response depends on the cut-off frequency
fH of the op-amp. Such a rise time is called cut-off frequency limited
rise time or transient response rise time ( tr )

0.35
tr 
fH
 Op-amp Characteristics
• DC Characteristics
Input bias current
Input offset current
Input offset voltage
Thermal drift

• AC Characteristics
Slew rate
Frequency response
 DC Characteristics
Thermal Drift

The op-amp parameters input offset voltage Vios and input offset
current Iios are not constants but vary with the factors

1. Temperature

2. Supply Voltage changes

3. Time
 Thermal Voltage Drift

It is defined as the average rate of change of input offset voltage per unit
change in temperature. It is also called as input offset voltage drift

Vios
Input offset voltage drift =
T

∆Vios = change in input offset voltage

∆T = Change in temperature
It is expressed in μV/0 c. The drift is not constant and it is not uniform
over specified operating temperature range. The value of input
offset voltage may increase or decrease with the increasing
temperature
Slope can be of Input Offset Voltage Drift
2
either polarities
Vios
1
in
mv 0
-1
-2
TA , ambient temp
-55 in oc
-25 0 25 50 75
 Input bias current drift
It is defined as the average rate of change of input bias current per unit
change in temperature

Thermal drift in input bias current =

I b
T
It is measured in nA/oC or pA/oc. These parameters vary randomly with temperature.
i.e. they may be positive in one temperature range and negative in another
 Input bias current drift

100

80
Ib in
nA 60
40
TA ambient temp.
20
in oC
-55
-25 0 25 50 75
 Input Offset current drift

It is defined as the average rate of change of input offset current per

unit change in temperature

I ios
Thermal drift in input offset current =
T

It is measured in nA/oC or pA/oc. These parameters vary randomly with temperature.

i.e. they may be positive in one temperature range and negative in another
 Input Offset current Drift

2 Slope can be of
either polarities
Iios in
1
nA
0
-1
-2
TA , ambient temp
-55 in oc
-25 0 25 50 75
 AC Characteristics
Frequency Response

Ideally, an op-amp should have an infinite bandwidth but practically op-amp gain
decreases at higher frequencies. Such a gain reduction with respect to
frequency is called as roll off.

The plot showing the variations in magnitude and phase angle

of the gain due to the change in frequency is called frequency
response of the op-amp
When the gain in decibels, phase angle in degrees are plotted against
logarithmic scale of frequency, the plot is called Bode Plot

The manner in which the gain of the op-amp changes with variation
in frequency is known as the magnitude plot.

The manner in which the phase shift changes with variation in

frequency is known as the phase-angle plot.
 Obtaining the frequency response

To obtain the frequency response , consider the high frequency model of the op-amp
with capacitor C at the output, taking into account the capacitive effect present

Where
AOL
AOL ( f )  AOL(f) = open loop voltage gain as a
1  j 2 fRo C function of frequency
AOL AOL = Gain of the op-amp at 0Hz
AOL ( f ) 
f
1  j( ) F = operating frequency
fo
Fo = Break frequency or cutoff frequency
of op-amp
For a given op-amp and selected value of C, the frequency f o is constant. The
above equation can be written in the polar form as

AOL
AOL ( f ) 
2
 f 
1   
 fo 

 f 
AOL ( f )  ( f )   tan 
 f 

1

 0
Frequency Response of an op-amp
 The following observations can be made from the frequency response of an op-amp
i) The open loop gain AOL is almost constant from 0 Hz to the break frequency fo .
ii) At f=fo , the gain is 3dB down from its value at 0Hz . Hence the frequency fo is also
called as -3dB frequency. It is also know as corner frequency
iii) After f=fo , the gain AOL (f) decreases at a rate of 20 dB/decade or 6dB/octave. As the
gain decreases, slope of the magnitude plot is -20dB/decade or -6dB/octave, after f=fo .
iv) At a certain frequency, the gain reduces to 0dB. This means 20log|AOL | is 0dB i.e. |AOL
| =1. Such a frequency is called gain cross-over frequency or unity gain bandwidth
(UGB). It is also called closed loop bandwidth.

UGB is the gain bandwidth product only if an op-amp has a single breakover frequency,
before AOL (f) dB is zero.
For an op-amp with single break frequency f o , after fo the
gain bandwidth product is constant equal to UGB
UGB=AOL fo

UGB is also called gain bandwidth product and denoted as f t

Thus ft is the product of gain of op-amp and bandwidth.
The break frequency is nothing but a corner frequency f o . At this
frequency, slope of the magnitude plot changes. The op-amp for which
there is only once change in the slope of the magnitude plot, is called
single break frequency op-amp.
For a single break frequency we can also write

UGB= Af ff

Af = closed loop voltage gain

Ff = bandwidth with feedback

v) The phase angle of an op-amp with single break frequency varies between 0 0
to 900 . The maximum possible phase shift is -900 , i.e. output voltage lags input
voltage by 900 when phase shift is maximum
vi) At a corner frequency f=fo , the phase shift is -450.

F = UGB / AOL
o
191EE332 - INTEGRATED ELECTRONICS

UNIT 4 - OPERATIONAL AMPLIFIER AND ITS

APPLICATIONS

Introduction – Classification – IC chip size and circuit

complexity, Ideal OP-AMP characteristics – DC
characteristics – AC characteristics, differential amplifier,
Basic op-amp applications - Inverting and non-inverting
amplifiers – summer and Subtractor – Differentiator –
Integrator, V/I and I/V converter, Instrumentation
amplifier, Precision rectifier, Schmitt Trigger, Multi-
vibrators
 Inverting Amplifier Analysis
Iin R If Rf
in

Vin
+
Vout

Due to virtual ground:

Iin= Vin / Rin= If = – ( Vout / Rf )
Vout= – (Rf / Rin ) Vin
Rf > Rin →multiplier Rf < Rin→ divider
 Non-inverting Amplifier
+
Vin
If
Vin Vout
Iin Rf
Rin

Due to virtual ground:

VINV = VNI = Vin
If = (Vout–Vin) / Rf = Iin= Vin / Rin
Vout = [1+ (Rf / Rin )] Vin
Subtractor Analysis

Vout= Rf (V2–V1)/ Rin

Instrumentation Amplifier
An instrumentation amplifier is used to amplify very low-level signals, rejecting noise and
interference signals. Examples can be heartbeats, blood pressure, temperature,
earthquakes and so on. Therefore, the essential characteristics of a good instrumentation
amplifier are as follows.

Inputs to the instrumentation amplifiers will have very low signal energy. Therefore the
instrumentation amplifier should have high gain and should be accurate.

 The gain should be easily adjustable using a single control.

 It must have High Input Impedance and Low Output Impedance to prevent loading.

 The Instrumentation amplifier should have High CMRR since the transducer output will
usually contain common mode signals such as noise when transmitted over long wires.

 It must also have a High Slew Rate to handle sharp rise times of events and provide a
maximum undistorted output voltage swing.
Instrumentation Amplifier using Op Amp
The instrumentation amplifier using op-amp circuit is shown below. The op-amps 1 & 2 are
non-inverting amplifiers and op-amp 3 is a difference amplifier. These three op-amps
together, form an instrumentation amplifier. Instrumentation amplifier’s final output Vout is
the amplified difference of the input signals applied to the input terminals of op-amp 3.Let
the outputs of op-amp 1 and op-amp 2 be Vo1 and Vo2 respectively.
Then, Vout = (R3/R2)(Vo1-Vo2)
Look at the input stage of the instrumentation amplifier as shown in the figure below.
The instrumentation amplifier derivation is discussed below.
The potential at node A is the input voltage V1. Hence the potential at node B is also
V1, from the virtual short concept. Thus, the potential at node G is also V1.

The working of the instrumentation amplifier is, Ideally

the current to the input stage op-amps is zero. Therefore
the current I through the resistors R1, Rgain, and R1
remain the same.
Applying Ohm’s law between nodes E and F,
I = (Vo1-Vo2)/(R1+Rgain+R1) ……………………….(1)
I = (Vo1-Vo2)/(2R1+Rgain)
Since no current is flowing to the input of the op-amps 1 & 2, the current I between the nodes G and H can
be given as,
I = (VG-VH) / Rgain = (V1-V2) / Rgain……………………….(2)
Equating equations 1 and 2,
(Vo1-Vo2)/(2R1+Rgain) = (V1-V2)/Rgain
(Vo1-Vo2) = (2R1+Rgain)(V1-V2)/Rgain ……………………….(3)
The output of the difference amplifier is given as,
Vout = (R3/R2) (Vo1-Vo2)
Therefore, (Vo1 – Vo2) = (R2/R3)Vout
Substituting (Vo1 – Vo2) value in equation 3, we get
(R2/R3)Vout = (2R1+Rgain)(V1-V2)/Rgain
i.e. Vout = (R3/R2){(2R1+Rgain)/Rgain}(V1-V2)
This above equation gives the output voltage of an instrumentation amplifier.
The overall gain of the amplifier is given by the term (R3/R2){(2R1+Rgain)/Rgain}.
The overall voltage gain of an instrumentation amplifier can be controlled by adjusting the value of resistor
Rgain.
The common mode signal attenuation for the instrumentation amplifier is provided by the difference
amplifier.
Advantages of Instrumentation Amplifier

The advantages of the instrumentation amplifier include the following.

The gain of a three op-amp instrumentation amplifier circuit can be easily varied by
adjusting the value of only one resistor Rgain.
The gain of the amplifier depends only on the external resistors used.
The input impedance is very high due to the emitter follower configurations of amplifiers 1
and 2
The output impedance of the instrumentation amplifier is very low due to the difference
amplifier3.
The CMRR of the op-amp 3 is very high and almost all of the common mode signal will be
rejected.
Applications of Instrumentation Amplifier

The applications of the instrumentation amplifier include the following.

These amplifiers mainly involve where the accuracy of high differential gain is required,
strength must be preserved in noisy surroundings, as well as where huge common-mode
signals are there. Some of the applications are
Instrumentation amplifiers are used in data acquisition from small
o/p transducers like thermocouples, strain gauges, measurements of Wheatstone bridge,
etc.
These amplifiers are used in navigation, medical, radar, etc.
These amplifiers are used to enhance the S/N ratio (signal to noise) in audio applications
like audio signals with low amplitude.
These amplifiers are used for imaging as well as video data acquisition in the conditioning
of high-speed signal.
These amplifiers are used in RF cable systems for amplification of the high-frequency
signal.
Difference between Operational Amplifier and Instrumentation Amplifier

The key differences between the operational amplifier and instrumentation amplifier
include the following:

 An operational amplifier (op-amp) is one kind of an integrated circuit.

The instrumentation amplifier is one type of differential amplifier.

 Instrumentation amplifier can be built with three operational amplifiers.

The differential amplifier can be built with a single operational amplifier.

 The output voltage of difference amplifier gets affected because of the mismatch
resistors
Instrumentation amplifier offers gain with a single resistor of its primary phase which
does not need a resistor matching.
 Precision Rectifier:
The ordinary diodes cannot rectify voltages below the cut-in-voltage of the diode. A circuit
which can act as an ideal diode or precision signal – processing rectifier circuit for rectifying
voltages which are below the level of cut-in voltage of the diode can be designed by placing
the diode in the feedback loop of an op-amp.
Figure shows the arrangement of a precision diode. It is a single diode arrangement and functions as a non-
inverting precision half– wave rectifier circuit. If V1 in the circuit of figure is positive, the op-amp output
VOA also becomes positive. Then the closed loop condition is achieved for the op-amp and the output
voltage V0 = Vi . When Vi < 0, the voltage V0A becomes negative and the diode is reverse biased. The loop
is then broken and the output V0 = 0.

Consider the open loop gain AOL of the op-amp is approximately 104 and the cut-in voltage Vγ for silicon
diode is ≈ 0.7V. When the input voltage Vi > Vγ / AOL, the output of the op-amp VOA exceeds Vγ and the
diode D conducts. Then the circuit acts like a voltage follower for input voltage level Vi > Vγ / AOL ,(i.e.when
Vi > 0.7/104 = 70μV), and the output voltage V0 follows the input voltage during the
positive half cycle for input voltages higher than 70μV as shown in figure.

When Vi is negative or less than Vγ / AOL, the output of op-amp VOA becomes negative, and the diode
becomes reverse biased. The loop is then broken, and the op-amp swings down to negative saturation.
However, the output terminal is now isolated from both the input signal and the output of the op-amp
terminal thus V0 =0.
No current is then delivered to the load RL except for the small bias current of the op-amp and the reverse
saturation current of the diode.
This circuit is an example of a non-linear circuit, in which linear operation is achieved over the remaining
region (Vi < 0). Since the output swings to negative saturation level when Vi <0, the circuit is basically of
saturating form. Thus the frequency response is also limited.
Applications: The precision diodes are used in
 half wave rectifier,
 Full-wave rectifier,
 peak value detector,
 Clipper and clamper circuits.
Disadvantage:
It can be observed that the precision diode as shown in figure operated in the first quadrant
with Vi
> 0 and V0 > 0. The operation in third quadrant can be achieved by connecting the diode in
reverse
direction.
Voltage to Current Converter with floating loads (V/I):

Voltage to current converter in which load resistor RL is floating (not connected to ground).
Vin is applied to the non- inverting input terminal, and the feedback voltage across R1
devices the inverting input terminal. This circuit is also called as a current – series negative
feedback amplifier. Because the feedback voltage across R1 (applied Non-inverting terminal)
depends on the output current i0 and is in series with the input difference voltage Vid.
Current to Voltage Converter (I –V):

Open – loop gain A of the op-amp is very large. Input impedance of the op amp is very
high.
Sensitivity of the I – V converter:
1. The output voltage V0 = -RF Iin.
2. Hence the gain of this converter is equal to -RF. The magnitude of the gain (i.e.) is
called as sensitivity of I to V converter.
3. The amount of change in output volt ΔV0 for a given change in the input current ΔIin is
decide by the sensitivity of I-V converter.
4. By keeping RF variable, it is possible to vary the sensitivity as per the requirements.
A multivibrator is an electronic circuit used to implement a variety of simple two-
state devices such as relaxation oscillators, timers and flip-flops. It consists of two amplifying
devices cross-coupledby resistors or capacitors. The first multivibrator circuit, the astable
multivibrator oscillator, was invented by Henri Abraham and Eugene Bloch during World War
I. They called their circuit a "multivibrator" because its output waveform was rich
in harmonics.
Astable multivibrator, in which the circuit is not stable in either state —it continually
switches from one state to the other. It functions as a relaxation oscillator.

Monostable multivibrator, in which one of the states is stable, but the other state is
unstable (transient). A trigger pulse causes the circuit to enter the unstable state. After
entering the unstable state, the circuit will return to the stable state after a set time. Such a
circuit is useful for creating a timing period of fixed duration in response to some external
event. This circuit is also known as a one shot.

Bistable multivibrator, in which the circuit is stable in either state. It can be flipped from one
state to the other by an external trigger pulse. This circuit is also known as a flip-flop. It can
store one bit of information, and is widely used in digital logic and computer memory.
Astable Multivibrator
The two states of circuit are only stable for a limited time and the circuit switches
between them with the output alternating between positive and negative saturation
values.
Analysis of this circuit starts with the assumption that at time t=0
the output has just switched to state 1, and the transition would
have occurred.

An op-amp Astable multivibrator is also called as free running

oscillator. The basic principle of generation of square wave is to
force an op-amp to operate in the saturation region (±Vsat).

A fraction β =R2/(R1+R2) of the output is feedback to the positive

input terminal ofop-amp. The charge in the capacitor increases &
decreases upto a threshold value called ±βVsat.

The charge in the capacitor triggers the op-amp to stay either at

+Vsat or –Vsat. Asymmetrical square wave can also be generated
with the help of Zener diodes. Astable multi vibrator do not require
a external trigger pulse for its operation & output toggles from one
state to another and does not contain a stable state.

Astable multi vibrator is mainly used in timing applications &

waveforms generators.
Design

1. The expression of fo is obtained from the charging period t1 & t2

of capacitor as
T=2RCln (R1+2R2)/R1
2. To simplify the above expression, the value of R1 & R2 should be
taken as R2 = 1.16R
Such that fo simplifies to fo =1/2RC.
3. Assume the value of R1 and find R2.
Assume the value of C & Determine R from fo =1/2R C
5. Calculate the threshold point from βVSATl = R1lVTl/ R1-R2
l/βVSATl w h e r e β is the feedback ratio.
Monostable Multivibrator using Op-amp: circuit diagram
Input Output Waveform:
A multivibrator which has only one stable and the other is quasi stable state is
called as Monostable multivibrator or one-short multivibrator. This circuit is useful for
generating signal output pulse of adjustable time duration in response to a triggering signal.
The width of the output pulse depends only on the external components connected to the
opamp.
Usually a negative trigger pulse is given to make the output switch to other state. But, it
then return to its stable state after a time interval determining by circuit components. The
pulse
width T can be given as T = 0.69RC. For Monostable operation the triggering pulse width Tp
should be less then T, the pulse width of Monostable multivibrator. This circuit is also called
as
time delay circuit or gating circuit.
191EE332 - INTEGRATED ELECTRONICS

UNIT 4 - OPERATIONAL AMPLIFIER AND ITS

APPLICATIONS

Introduction – Classification – IC chip size and circuit

complexity, Ideal OP-AMP characteristics – DC characteristics
– AC characteristics, differential amplifier, Basic op-amp
applications - Inverting and non-inverting amplifiers – summer
and Subtractor – Differentiator – Integrator, V/I and I/V
converter, Instrumentation amplifier, Precision rectifier, Schmitt
Trigger, Multi-vibrators
 SSI MSI LSI VLSI ULSI

< 100 active 100-1000 1000-100000 >100000 active Over 1 million

devices active devices active devices devices active devices

Integrated BJT’s and MOSFETS 8bit, 16bit Pentium

resistors, Enhanced Microprocessor Microprocessor
diodes & BJT’s MOSFETS s s