Linear IC Applications

UNIT-IV

OP-AMP APPLICATIONS -2
Topics to be covered:
• Oscillators: Phase shift and wien bridge oscillators,
Square, triangular and sawtooth wave generators,
Comparators, zero crossing detector, Schmitt trigger,
characteristics and limitations.
• Specialized Applications: 555 timer IC (Monostable
& Astable operation) & its applications, PLL,
operating principles, Monolithic PLL, applications,
analog multiplier and phase detection, Wide
bandwidth precision analog multiplier MPY634 and
its applications.
 Linear IC Applications

UNIT-IV
Topics Covered:
•Oscillators Introduction
•RC Phase shift oscillator using OP-AMP
Oscillators:
• The oscillator is a circuit which produces oscillations at
desired frequency without giving any input signal.

• The circuit used to generate an a.c voltage without an

ac input signal is called an oscillator.

• The circuit requires a dc source to generate ac signal.

• If the output signal is a sine wave then it is called as

sinusoidal oscillator or harmonic oscillator. Otherwise
it is called as relaxation oscillator.
Oscillators:
• Oscillator contains both active & passive
components, Passive components decides the
frequency of oscillations.

Condition for oscillations or Barkhausen criterion:

The conditions to maintain oscillations are

1. |Aβ| = 1

2. The total phase shift around the closed loop is 00

or 3600
Oscillators:

Block diagram of Oscillator

Classification of oscillators:
Oscillators are classified as

1. According to the waveforms generated

(a) Sinusoidal oscillator

(b) Relaxation oscillator

2. According to the fundamental mechanisms

(a) Negative resistance oscillators

(b) Feedback oscillators

Classification of oscillators:
3. According to the frequency generated

(a) Audio Frequency Oscillator (AFO): up to 20KHz

(b) Radio Frequency Oscillator (RFO): 20KHz to 30MHz

(c) Very High Frequency Oscillator: 30MHz to 300MHz

(d) Ultra High Frequency Oscillator: 300MHz to 3GHz

(e) Microwave Frequency Oscillator: Above 3GHz

Classification of oscillators:

4. According to the type of circuit used, sine wave

oscillators are classified as

(a) RC Oscillators

(b) LC Oscillators
RC Oscillators:
• RC oscillators are popularly used to produce low
frequencies. There are two important RC oscillators,
they are

1. RC Phase shift oscillator

2. Wien Bridge oscillator

The RC Phase Shift Oscillator:

• Circuit diagram of RC phase shift oscillator

The RC Phase Shift Oscillator:
• OP-amp provides 1800 phase shift & feedback
network provides 1800 phase shift.

• Each RC section provides a phase shift of 600 .

Derivation for frequency of oscillations:
• Consider the feedback network
• Apply KVL to the loops

--- (1)

--- (2)

--- (3)
Contd..

• Replace jw as S and using matrix form,

--- (4)

• Solving the above matrix for I3using Cramer’s rule.

--- (5)

--- (6)
Contd..
Contd..
• Equating imaginary part to zero to find the
frequency of oscillations.

Where, f is frequency of oscillations.

Contd..
• At this frequency

• For oscillations to occur, the gain of the op-amp must

be ≥29. which can be adjusted by the resistors Rf & R1
• Advantages of RC Phase Shift Oscillator:
• The circuit is simple to design.
• Can produce output over audio frequency range.
• Produces sinusoidal output waveform.
• It is a fixed frequency oscillator.
• Disadvantages of RC Phase Shift Oscillator:
• Frequency can be varied by simultaneous changing
of all RC components. Hence considered as fixed
frequency oscillator.
Problem:
1. Design a phase shift oscillator for the frequency
500Hz with +/-12V supply voltage
Contd..
 Linear IC Applications

UNIT-IV
TOPICS:
Wien Bridge Oscillator using OPAMP
Derivation for Frequency of oscillations
 Wien Bridge Oscillator :

• In wien bridge oscillator the basic amplifier is working as

non inverting amplifier, so that no phase shift is necessary
through feedback network.
Contd..

• The two arms of the bridge namely R1C1 in series

and R2 C2 in parallel are called frequency sensitive
arms.

• The type of feedback is called lead-lag network.

• The gain of the non inverting amplifier can be

adjusted using the resistor Rf and R1.
Contd..

• To satisfy the Bharkhausen condition Aβ≥ 1. it is

necessary that the gain of non inverting amplifier
must be min ‘3’.

• So the ratio of Rf and R1 must be ≥ 2.

• The frequency of oscillations is given by,

Contd..
• If the resistors and capacitors used in the bridge
are not equal then the frequency of oscillations is
given by. Hz

• Derivation for frequency of oscillations:

• The equivalent circuit of feedback network is

Contd..
• If the bridge is balanced.
Contd..
Contd..

Hz
Contd..
Contd..
• Advantages:
• Easy to adjust frequency
• Perfect sine wave oscillator
• Best audio frequency oscillations
Problem:
• Design a wien bridge oscillator for f0 = 10 kHz
 Linear IC Applications

UNIT-IV
TOPICS:
•Comparators Using OP AMP
Inverting Comparator
Non inverting Comparator
• Applications of Comparators
Zero Crossing Detector
Time Marker Generator
Window Detector
Comparator:
• A comparator as its name implies, compares a
signal voltage on one input of an op-amp with a
known voltage called a reference voltage on the
other input.

• Comparators are divided into two types:

– Non inverting Comparator

– Inverting Comparator.
 Non-inverting Comparator:

• Vin < Vref  V0 = –Vsat

• Vin > Vref  V0 = +Vsat
• Thus the V0 changes between saturation levels.
Positive Vref Negative Vref

• Vin < Vref  V0 = –Vsat

• Vin > Vref  V0 = +Vsat
Inverting Comparator:

• Vin < Vref  V0 = + Vsat

• Vin > Vref  V0 = - Vsat

• Thus the V0 changes between saturation levels.

Positive Vref Negative Vref

• Vin < Vref  V0 = + Vsat

• Vin > Vref  V0 = - Vsat
APPLICATIONS OF COMPARATORS:

1. Zero crossing detector

2. TIME MARKER GENERATOR

3. Window detector

• Zero crossing detectors are dividing into 2 types:

– Inverting zero crossing detector

– Non –inverting zero crossing detector.

 APPLICATIONS OF COMPARATORS:
• Inverting Zero Crossing Detector

• Vin < 0  V0 = + Vsat

• Vin > 0  V0 = - Vsat
 Non- Inverting Zero Crossing Detector

• Vin < 0  V0 = - Vsat

• Vin > 0  V0 = + Vsat
 TIME MARKER GENERATOR:

Used for triggering Monostable multivibrators, SCR etc.,

• Window detector:

• The window detector circuit

detects when an unknown
voltage falls within a specified
voltage band or window..
•It is also called window
comparator.
 Linear IC Applications

UNIT-IV
TOPICS:
•Schmitt Trigger
•Inverting Schmitt Trigger
•Non Inverting Schmitt Trigger
•Square wave generator
Schmitt Trigger:
• A Schmitt trigger is a special type of comparator
circuit with hysteresis implemented , used to
avoid unwanted triggering.

• It is also called Regenerative Comparator.

• The op-amp Schmitt Triggers are two types

– Inverting Schmitt Trigger

– Non-inverting Schmitt Trigger.

Inverting Schmitt Trigger:

• Vin > Vref  V0 = - Vsat

• Vin < Vref  V0 = + Vsat

• Ref . Voltage Controlled by the R1 & R2 Resistors.

Contd..

• +Vref is for positive saturation when V0 = +Vsat and

is called Upper Threshold Voltage (VUT)

• -Vref is negative saturation when Vo = - Vsat and is

called Lower Threshold Voltage (VLT)
Contd..

• Vin > VUT  V = - Vsat

• Vin < VLT  V0 = + Vsat

• VLT < Vin < VUT  V0 = Previous state

• The difference between VUT & VLT is called

width of hysteresis. Denoted as H

• Hysteresis is also called dead band or dead

zone.
Contd..

• Hysteresis Transfer characteristics.

Non-Inverting Schmitt Trigger
SQUAREWAVE GENERATOR:
• The square wave generator using op amp means
the astable multivibrator circuit using op-amp.
 SQUAREWAVE GENERATOR:

When Vo is at +Vsat, the feedback voltage is called the

upper threshold voltage VUT and is given as

When Vo is at -Vsat, the feedback voltage is called the

lower-threshold voltage VLT and is given as
Contd..
 Frequency of Oscillation:
• The voltage across the capacitor as a function of time
is given as

Where,
VC(t) is the instantaneous voltage across the capacitor.
Vinitial is the initial voltage
Vmax is the voltage toward which the capacitor is
charging.
Contd..
• Let us consider the charging of capacitor from
VLT to VUT, where VLT is the initial voltage, VUT is
the instantaneous voltage and +Vsat is the
maximum voltage.

• At t = T1, voltage across capacitor reaches VUT and

therefore equation (3) becomes
Contd..

• The time taken by capacitor to charge from VUT to VLT is same as

time required for charging capacitor from VLT to VUT . Therefore,
total time required for one oscillation is given as
Contd..

• The frequency of oscillation can be determined as

fo = 1/T, where T represents the time required for
one oscillation.

• Substituting the value of T we get,

Contd..
 Linear IC Applications

UNIT-IV

TOPIC: Triangular & Sawtooth wave

Generator
Triangular wave Generator

• It is the combination of Schmitt Trigger and integrator.

• A  Square wave (Schmitt Trigger)

• B  Triangular wave (Integrator)

Contd..

• Output wave forms of triangular wave generator

 Amplitude & Frequency Calculation:
• When comparator output is at +Vsat, the effective
voltage at point P is given by

When effective voltage at P becomes equal to zero, we can

write above equation
Contd..

Similarly, when comparator output is at -Vsat ,we can write,

The peak to peak amplitude of the triangular wave can be

given as
Contd..

•The time taken by the output to swing from – Vramp to +

Vramp (or from + Vramp to – Vramp) is equal to half the time
period T/2.
• This time can be calculated from the integrator output
equation as follows :
Contd..

Substituting value of Vo(pp) we get,

Therefore, the frequency of oscillation can be given as,

Sawtooth wave Generator:

• Unlike the triangular wave, the sawtooth wave

has unequal rise time & fall time.
Contd..

• The non inverting terminal of the integrator is

driven by voltage set between +Vcc to –VEE by
the potentiometer.

• Depending on R4 Setting, a certain DC level is

added in the output of integrator.

• If the voltage at non-inverting terminal is

• Negative  <50% (DS)  Longer Rise time

• Positive  > 50% (DS)  Longer fall time.

Contd..

• Output waveforms of Swatooth wave generator.

 Linear IC Applications

UNIT-IV
(Part-B)

Topics covered:
 Specialized Applications of OP-AMP
 IC 555 Timer
 Monostable Multivibrator using IC 555
THE 555 TIMER IC
• The 555 is a monolithic timing circuit that can
produce accurate & highly stable time delays or
oscillation.
• It can produce time delays from few micro seconds
to several hours.
• The timer basically operates in one of two modes:
– Monostable (one - shot) multivibrator
– Astable (free running) multivibrator
THE 555 TIMER IC

• The important features of the 555 timer are :

– It operates on +5v to +18 v supply voltages

– It has an adjustable duty cycle

– Timing is from microseconds to hours

– It has a current o/p (upto 200mA)

– The Output of IC is compatible with both TTL

and CMOS circuits
THE 555 TIMER IC

• Available in 3 types of packages

– 8-pin Metal can package

– 8-pin DIP ( NE/SE 555 & TLC 555)

– 14-pin DIP Package (Consist of two 555 timers)

• Good temperature stability.

• Widely available in market and less cost like op-

amp .
IC 555 –Pin Diagram:
IC 555 –Pin Diagram:

• Pin-1 is Ground

• Pin- 2 is Trigger: to give external trigger pulse.

• Pin-3 is Output

– If o/p taken b/w Pin-3 & Pin -1- Normally OFF

load (Source current)

– If o/p taken b/w Pin-3 & Pin-8 – Normally ON

load ( sink current)
IC 555 –Pin Diagram:
• Pin-4 is Reset – To reset the flip-flop or output.
• Pin-5 is Control Voltage – Given to inverting
terminal of comparator-1
• Pin-6 is Threshold – given Non-inverting pin of
op-amp comparator -1
• Pin-7 is Discharge - The collector of discharge
capacitor is given this pin.
• Pin-8 is +V - Positive supply voltage.
THE 555 TIMER IC

• APPLICATIONS:

– USED IN OSCILLATORS

– SQUARE WAVE GENERATOR

– PULSE GENERATOR
Block Diagram of 555 Timer IC:
Monostable MultiVibrator using IC 555
Monostable MultiVibrator using IC 555
Input & output waveforms
Derivation for Time Period:
• The voltage across capacitor increases exponentially
Derivation for Time Period:
Problem:
1. Design monostable multivibrator using 555 timer to
produce a pulse width of 100mSec.
• Solution:
T = 100 m Sec
T = 1.1 RC
Let us assume C = 1uF
R= T / (1.1 x C)
 Linear IC Applications
UNIT-IV
Topics covered:
 Applications of Monostable Multivibrator
 Frequency Divider
 Pulse width Modulator
 Linear Ramp Generator
 Astable Multivibrator using IC 555
 FSK generator using IC 555
 Schmitt Trigger using IC 555
 Applications of Monostable multivibrator

1. Pulse width modulator

2. Frequency divider

3. Pulse stretching

4. Linear Ramp generator

5. Missing pulse detector.

Pulse width modulator
Frequency divider
LINEAR RAMP GENERATOR:
• Linear Ramp generated by the circuit shown in
below figure.
LINEAR RAMP GENERATOR:

• The resistor R of the monostable circuit is

replaced by a constant current source.

• The capacitor is charged linearly by the constant

current source formed by the transistor Q3 .

• The capacitor voltage Vc can be written as

LINEAR RAMP GENERATOR:

• Where I is the current supplied by the constant

current source. Further the KVL equation can be
written as,

• Now sub value of current I in the above equation.

LINEAR RAMP GENERATOR:
• At time t=T, the capacitor voltage vc becomes
2/3Vcc. Then we get

• Which gives the time period of the linear ramp

generator as,
LINEAR RAMP GENERATOR:

Trigger and Ramp waveforms.

Astable Multivibtator using IC 555

• No Stable states, two- quasi stable states.

Astable Multivibtator using IC 555
Astable Multivibtator using IC 555
• The threshold input is connected to the trigger
input.
• Two external resistances RA, RB and a capacitor
C is used in the circuit.
Astable Multivibtator using IC 555
Duty Cycle & Operating frequency:

• The charging time constant is greater than the

discharging time constant. Hence at the output, the
waveform is not symmetric.

• Duty Cycle: It is defined as the ratio of ON time i.e.

high output to the total time of one cycle.
• W = time for output is high = TON
• T = time of one cycle
• D = duty cycle = W/T
• % D = W/T x 100%
Duty Cycle & Operating frequency:

• The charging time for the capacitor is given by,

Tc = Charging time = 0.693 (RA + RB) C

• While the discharge time is given by,

Td = Discharging time = 0.693 RB C

• Hence the time for one cycle is

T = Tc + Td = 0.693 (RA + RB) C + 0.693 RB C

= 0.693 (RA + 2 RB) C

Duty Cycle & Operating frequency:

• While the frequency of oscillations is given by,

Application of Astable Multivibrator using IC 555:

• The various Application of Astable Multivibrator

using IC 555 are:
– Square wave generation

– FSK generator

– Voltage controlled oscillator (VCO)

 Problem:
• A 555 timer is configured to run in astable mode with RA = 4 kΩ,
RB = 4K Ω & C= 0.01 µF. Determine the f0 and duty cycle.

• Solution: The frequency of output is given by

• Therefore , the duty cycle is given by 0.6667

 Astable Multivibrator Applications:
1. FSK Generator:
When the input is logic 1, the transistor Q1 is off. Under
the condition, 555 timer works in its normal mode as an
astable multivibrator

When the input is logic 0, (Q1 is ON

saturated) which in turn connects
the resistance Rc across RA.

fo=1.45/(RA || RC+2 RB)C

Schmitt trigger:
Schmitt trigger converts sine wave into square wave
 Linear IC Applications

UNIT-IV
TOPICS:
 PLL (PHASE LOCKED LOOP)
 IC 565 Monolithic PLL
 Capture Range
 Lock in Range
 Pull in Time
 Phase Detectors
PLL (PHASE LOCKED LOOP):

• A phase-locked loop (PLL) is a control system

that generates an output signal whose phase is
related to the phase of an input signal.
PLL:

• PLL Consist of 4 blocks:

1. Phase detector

2. Low pass filter

3. Error amplifier

4. Voltage controlled oscillator (VCO)

PLL:

• Phase detector : It compares the input frequency

fs with the feedback frequency fo & generates an
output signal (DC) which is function of difference
between the phases of the two input signals.

• Low pass filter: Removes the high frequency

components (noise)

• Error Amplifier: which amplifies the error signal

PLL:

• VCO (Voltage Controlled Oscillator): Runs in free

running mode with output frequency of fo. The
non-zero control voltage results in a shift in the
VCO frequency from its free running frequency fo
to a frequency f, given by

• f = fo + kv Vc

• Where, Kv = voltage to frequency transfer

coefficient of VCO
PLL:

• Lock Range:

• When the PLL is n lock, it can track frequency

changes in the incoming signal is called the Lock
Range or tracking range of the PLL.

• It is expressed in percentage of fo, the VCO

frequency.
PLL:

• Capture Range:

• The range of frequencies over which the PLL can

acquire lock with an input signal is called the
capture range.

• It is also expressed in percentage of fo

PLL:
• Pull-in-time:
• The capture of input signal does not take place as
soon as the signal is applied , but it takes finite time.
• The total time taken by the PLL to establish a lock is
called pull-in-time.
• This depends on the initial phase and frequency
difference between the two signals as weel as on the
overall loop gain & the bandwidth of the low pass
filter.
PLL:

• i) free running
• ii) Capture
• iii) Phase lock.
Phase comparator:
• Phase comparators are 2 types 1.analog 2 digital

• Analog phase comparators:

Digital phase comparator:
•
Monolithic phase locked loop (IC 565):

• All the different blocks of PLL are available in a

single chip of IC 565.
• 14 pin DIP package or 10 pin metal can package.

• RT, CT = external resistor & capacitor

• RT = between 2KΩ to 20 K Ω
• fo adjusted with RT, CT
Monolithic phase locked loop (IC 565):
Monolithic phase locked loop (IC 565):
Monolithic phase locked loop (IC 565):

• The loop is internally broken between Vco o/p

and the phase comparator input.

• A short circuit between pin 4 & 5 connects the

Vco output to the phase comparator so as to
compare fo with input signal fs.

• C- between pin 7 & 10 makes the LPF. (R=3.6KΩ)

• Conversion ratio of phase detector kɸ = 1.4/∏

Derivation of lock range:
Derivation of lock range:

• Output voltage of a phase detector is

• Ve = kɸ(ɸ-∏/2)  (1)

• Where, ɸ = phase error

• The output voltage of a phase detector is filtered

by the low pass filter to remove the high
frequency component.
Derivation of lock range:

• The output of the filter is amplified by a gain A

and then applied as the control voltage Vc to the
Vco as given by

• Vc = A Ve = A kɸ(ɸ-∏/2)  (2)

• This control voltage Vc will result in a shift in the

Vco frequency from its center frequency fo to a
frequency f,

• f = fo + kv Vc  (3)
Derivation of lock range:

• When the PLL is locked, the input frequency is

given by

• Sub Vc value from eq(2)

Derivation of lock range:

• The Vo(max) available from the phase detector

occurs for ɸ = ∏and 0

• Corresponding maximum control voltage is

• Sub Vc value in f equation,

Derivation of lock range:

• Where 2 ∆fL will be lock-in frequency range given

by
Derivation of lock range:
• The equation for capture range of PLL is given
by
Applications of PLL:
• Frequency multiplier:
Applications of PLL: :
• FM Demodulator:

• Frequency shift keying demodulator

• AM Detection
• Frequency translation
 Linear IC Applications
UNIT-IV
TOPICS:
 Voltage Controlled Oscillator (IC 566)

 VOLTAGE TO FREQUENCY CONVERTER

 Applications of VCO

 MPY 634
 Features & Applications

 Analog Multipliers
 Voltage Squarer, Freq Doublers, Voltage Divider
Voltage Controlled Oscillator (IC 566)
 Voltage Controlled Oscillator (IC 566)

• Block diagram of IC 566 VCO

Voltage Controlled Oscillator (IC 566)
VOLTAGE TO FREQUENCY CONVERTER:

• V-F conversion factor is a very important

parameter for VCO
VOLTAGE TO FREQUENCY CONVERTER:
• While Vc is changed by ∆Vc to achieve this,
• From expression of f’o ,

 (1)
VOLTAGE TO FREQUENCY CONVERTER:

• With no modulating input voltage,

• Control voltage Vc = (7/8)(+V)
• If fo is the original frequency then,

using the value of R1 C1 from the (1)

VOLTAGE TO FREQUENCY CONVERTER:

• Where fo is the original frequency

• This is the required voltage to frequency

conversion factor.
VCO:

• Applications of VCO:

– FM modulation

– Signal generation (Triangular & square)

– Function generation

– FSK demodulator

– Frequency multipliers
MPY 634 :

• The MPY634 is a wide bandwidth, high accuracy,

four quadrant analog multiplier.

• It has accurately laser-trimmed multiplier

characteristics.

• Its differential X, Y, and Z inputs allow configuration

as a multiplier, squarer, divider, square-rooter, and
other functions while maintaining high accuracy.
MPY 634 :
• The wide bandwidth of this new design allows
signal processing at IF, RF, and video frequencies

• The internal output amplifier of the MPY634

reduces design complexity compared to other
high frequency multipliers and balanced
modulator circuits.
MPY 634 :
• It is capable of performing frequency mixing,
balanced modulation, and demodulation with
excellent carrier rejection.

• An accurate internal voltage reference provides

precise setting of the scale factor. The differential
Z input allows user-selected scale factors from 0.1
to 10 using external feedback resistors.
MPY 634 :

• Pin Diagram
MPY 634 :

• Block Diagram of MPY 634

Wide Bandwidth PRECISION ANALOG MULTIPLIER:
(mpy634)

• FEATURES
– WIDE BANDWIDTH:
– ACCURACY
– INTERNAL WIDE-BANDWIDTH OP AMP
– EASY TO USE
– LOW COST
Wide Bandwidth PRECISION ANALOG MULTIPLIER:
(mpy634)
• APPLICATIONS
– PRECISION ANALOG SIGNAL
– PROCESSING
– MODULATION AND DEMODULATION
– VOLTAGE-CONTROLLED AMPLIFIERS
– VIDEO SIGNAL PROCESSING
– VOLTAGE-CONTROLLED FILTERS AND
– OSCILLATORS
Analog Multipliers:
• Analog multiplier is a circuit whose output
voltage at any instant is proportional to the
product of instantaneous value of two individual
input voltages.
• AD633:
• Applications of Multiplier ICs:
The multiplier ICs are used for the following
purposes:
1. Voltage Squarer
2. Frequency doublers
3. Voltage divider
4. Square rooter
5. Phase angle detector
6. Rectifier
Voltage Squarer:

• The input voltage V1 to be squared is simply

connected to both the input terminals.
• Hence we have, Vx = Vy = V1 and
• The output is V0 = Kv12
• The circuit thus performs the squaring operation.
Frequency doubler:
• A sine-wave signal Vi has a peak amplitude of Av and
frequency of f Hz. Then, the output voltage of the
multiplier circuit is double the input frequency.
Voltage Divider:
• The voltage divider circuit can be constructed using a
multiplier and an op-amp.

• This circuit produces the ratio of two input signals.