Electrical signal processing and transmission

CHAPTER-4
ELECTRICAL SIGNAL PROCESSING
AND TRANSMISSION
Er. Bishal Rimal
Lecturer
Kantipur Engineering College
Lalitpur, Nepal

OPERATIONAL AMPLIFIER
 An operational amplifier (Op-Amp) is a differential amplifier
that amplifies the difference of voltages applied to its two
input terminals (differential input), and provides a single-
ended output.
 Amplifiers are devices which take a relatively weak
signal as an input and produce a much stronger signal
as an output.
 V+: non-inverting input
 V−: inverting input
 Vout: output
 VS+: positive power supply
 VS−: negative power supply

• Input stage provides most of the voltage gain of OP-AMP and
decides input resistance.
• Intermediate stage is another differential amplifier which is
driven by the output of input stage.
• Due to direct coupling between the first two stages, the input of
level shifting is an amplified signal with some non zero dc level.
• Level shifting stage is used to bring this dc level to zero volts
with respect to ground.
• Output stage increase the current supplying capability of OP-
AMP and also provides low output resistance.

IDEAL AND PRACTICAL CHARACTERISTICS
OF OP-AMP

• Open loop voltage gain-It is the differential gain of an OP-
AMP in the open loop mode of operation.
• Input resistance-It is defined as the equivalent resistance which
can be measured at either at inverting or non- inverting terminal
with the other terminal connected to ground.
• Output resistance-It is the resistance measured by looking
into the output terminal of OP-AMP, With the input source short
circuited.
• Bandwidth-It is the range over which all signal frequencies
are amplified almost equally.
• Common mode rejection ratio-It is defined as the ratio
of differential gain to common mode gain.

CNTD..
• Slew rate-It is defined as the maximum rate of change of
output voltage per unit time i.e maximum rate at which amplifier can
respond to an abrupt change in input level.
• Power supply rejection ratio-It is the change in an OP-AMPs input
offset voltage caused by variation in the supply voltage.
• Input offset voltage-Ideally, for a zero input voltage output should be
zero. But practically it is not so. This is due to unavoidable unbalances
inside the OP- AMP.
• Input bias current-It is the average of the currents flowing into the
two input terminal of the OP-AMP.
• Input offset current- It is the algebraic difference between the currents
flowing into the inverting and non-inverting terminal of OP-AMP

SIGNAL AMPLIFICATION
 Signal amplification is carried out when the typical
signal output level of a sensor is considered to be
too low (as for instance in the case of a weak
thermocouple signal, which is of the order of
microvolts).
 Hence the strength of weak signal needs to be
increased, this boosting function is done by signal
amplifier.
 Some major applications of op amp in signal
amplification is discussed below.

INVERTING AMPLIFIER
 Inverting amplifier is one
in which the output is
exactly 180 degree out of
phase with respect to
input(i.e. if you apply a
positive voltage, output
will be negative).
 Output is an inverted(in
terms of phase) amplified
version of input.

NON INVERTING AMPLIFIER
 Non Inverting amplifier is
one in which the output is
in phase with respect to
input(i.e. if you apply a
positive voltage, output
will be positive ).
 Output is an Non
inverted(in terms of
phase) amplified version
of input.

VOLTAGE FOLLOWER/ BUFFER
Here if R2=0, Av=1
i.e V0=Vi
• Used to isolate stages from each other.
• Used as an impedance transformer.
• Reduce power consumption of the source
• Reduce distortion from overloading, distortion and other electromagnetic
interference.

SUMMER/ ADDER
If Rf=R1=R2=R3
Then, V0= -(Vi1+Vi2+Vi3 )
Thus,
Output signal is the sum of all input signals.

DIFFERENTIAL
(SUBTRACTER)
Thus,
Output signal is difference of two input signals

DIFFERENTIAL/SUBTRACTER
Using superpossition theorm
Alternative method
+
Hints:
Eq 3 is obtained using voltage divider rule.
i.e voltage across V+ is volltage on Rfp deu to V2 source
+

• It is used as a series negative feedback circuit by using op amplifier
• Generally, we use differential amplifier that acts as a volume control circuit.
• The differential operational amplifier can be used as an automatic gain
control circuit.
• Some of the differential operational amplifier can be used for Amplitude
modulation.

INTEGRATER
 An integrator in measurement and control applications
is an element whose output signal is the time integral of
its input signal.
 It accumulates the input quantity over a defined time to
produce a representative output.
 used to perform calculus operations in analogue
computers.
 used in analogue-to-digital converters, ramp generators
and also in wave shaping applications.
 This application of an integrator is sometimes called a
totalizer in the industrial instrumentation trade.

DESIGN OF INTEGRATER TO PRODUCE RAMP
VOLTAGE OF -5V/MILISEC.
 Let Vin=5v
 We know
 Then, Vo=-5t/RC
 Now, Vo/t=-5/RC v/s…………………………A
 From question, Vo/t=-5v/ms= -5000v/s…….B
 Equating A and B we get;
RC=10-3
Now we have to chose value R and C such that its
multiple is 10-3 ,so let R=1000 ohm then C=10-6 F
The designed ckt is shown alongside.

DIFFERENTIATOR
 It is the circuit that perform
mathematical differentiation of input
signal.
 Eg. If input is triangular wave, output is
square wave.
 Used most widely in process
instrumentation i.e used to monitor the
rate of change of various points.

ASSIGNMENT 1
1.List out the ideal characteristics of Op-Amp.
2.Design an integrator circuit with output ramp voltage
of -20V/ms.
3.Derive the expression for gain and list out application of
op-amp under following configuration
 Inverting
 Nonverting
 Summer
 Subtracter
 Integrator
 Differentiater

INSTRUMENTATION AMPLIFIER
 The output signal produced by transducers is very weak
so need to be amplified before further processing which is
done by instrumentation amplifier.
 An instrumentation amplifier is a differential op-amp circuit
providing high input impedances with ease of gain
adjustment through the variation of a single resistor(Rgain)
in figure aalongside.
 .Instrumentation amplifiers are
used where great accuracy and
stability of the circuit both short
and long-term are required.

FEATURE OF INSTRUMENTATION AMPLIFIER
 Single resistor gain adjustment u with high
accuracy.
 High CMRR so that it eliminates the distortion
 High stability of gain due with low temperature
coefficient.
 Low dc offset and drift error reffered to input
 Low output impedance

Fig Instrumentation amplifier
First stage is carefully matched op-amps
Second stage is generally unity gain differential amplifier.
Changing the value of Rg will change its gain.

As the second stage is unity gain
differential amplifier, output is
given by:
Thus by changing the value of
Rg, gain of the amplifier can
be changed.

APPLICATIONS
 Strain-gauge bridge interfaces for pressure and temperature
sensing.
 Thermocouple temperature sensing.
 A variety of low-side and high-side current-sensing applications.
 Data acquisition from low output transducers
 Medical instrumentation
 Current/voltage monitoring
 Audio applications involving weak audio signals or noisy
environments
 High-speed signal conditioning for video data acquisition and
imaging
 High frequency signal amplification in cable rf systems

NETWORK ISOLATION
Here if R2=0, Av=1
i.e V0=Vi
• Used to isolate stages from each other electrically.
• Used as an impedance transformer.
• Reduce power consumption of the source
• Reduce distortion from overloading, distortion and other electromagnetic
interference.
Same as isolation buffer

WAVE SHAPER
 Modification of time varying electrical signals (V,I)
using combination of electronics devices
 May be linear or non-linear
 E.g Clipper circuit clips out the certain portion of
waveform. They are non linear wave shaping as
they involve transistors or diodes.

SIGNAL ATTENUATION
 Attenuation is a reduction of signal strength during
transmission.
 Attenuation occurs with any type of signal, whether
digital or analog. (db)
 Sometimes called loss, attenuation is a natural
consequence of signal transmission over long distances.
 Attenuation is a natural phenomenon that cannot be
prevented while transmitting signals but we can use
repeater to amplify the signal again.
 Op-amp with Av <1 are attenuator

NOISE
 Unwanted signal introduced upon desired signal is
noise.
 Degrades the quality of desired signal.
 Electronic component produces some noise when
assembled to build a combine system. These noise
might get superimposed with the desired signal.
These noise may get interfaced with the information
contained in the circuit.
 E.g Thermal noise, Shot noise, Flicker noise, Burst
noise, Transient time noise

REDUCTION OF NOISE IN ELECTRONIC CIRCUIT
 Keep the signal wires short.
 Keep the wires away from electrical machinery.
 Use twisted together wires.
 Use differential inputs to remove noise common the
both wires.
 Filter the signal.

ANALOGUE AND DIGITAL FILTERING
 Analogue filter
 Process continuous
time signal
 Low accuracy
 Difficult to simulate and
design
Types
 Active filter
More common at lower
frequencies
 Passive filter
More common at higher
frequencies
 Digital Filter
 Process discrete time
signal
 High accuracy
 Easy design and
simulation
Types
 IIR( Infinite Impulse
Response)
 FIR (Finite Impulse
Response)
Filters are frequency selective circuits

COMMUNICATION SYSTEM
 Communication system is a system designed to
send information from a source to destination.
Information may be voice, data, video etc.
Fig: Block diagram of General communication system

OPTICAL COMMUNICATION SYSTEM
 Communication through light
 Transmission medium is Optical fibre.
Fig: Block Diagram of Optical Fiber communication system

WORKING OF OPTICAL FIBRE
 Works on the principle of total internal reflection (i.e.
Incident angle is greater than critical angle in denser
medium) at core cladding interference.
 When light enters core at small angle, it suffers refraction
and strike core cladding interface.
 Then light suffers total internal reflection.
 After suffering such repeated total internal reflection, ray of
light will reach at other end.
 At the end it suffers refraction and emerge out from optical
fiber.
 Thus light inside the fiber travels in a guided manner so
also known as optical waveguide.

Electrical signal processing and transmission

ADVANTAGE OF OPTICAL COMMUNICATION
SYSTEM
 Increased Bandwidth and Channel Capacity
 Low Signal Attenuation
 Immune to Noise
 No Crosstalk
 Lower Bit Error Rates
 Signal Security
 Electrical Isolation
 Reduced Size and Weight of Cables
 Radiation Resistant and Environment Friendly
 Resistant to Temperature Variations etc.

DISADVANTAGE OF OPTICAL COMMUNICATION
SYSTEM
 Specialist skills needed
 Cost of installation
 Cost of transmission equipment from electrical to
optical signals
 Optical fibers can not carry electrical power
 Mechanically weak

APPLICATION
 As fibers are very flexible, they are used in flexible digital cameras.
 Fibers are used in mechanical imaging i.e. for inspection of mechanical welds
in pipes and engines of rockets, space shuttles, airplanes.
 Fibers are used in medical imaging such as endoscopes and laparoscopes.
 Fibers can be used under sea communication.
 Fibers are used in military applications such as aircrafts, ships, tanks etc.
 Nuclear testing applications use optical fiber phase sensors and transducers
 Fibers are used in public utility organizations like railways, TV transmission etc.
 Fibers are used in LAN systems of offices, industrial plants and colleges etc.
 Fibers are used in telecommunication such as voice telephones, video phones,
telegraph services, message services and data networks

CONVERSION DEVICES
 Converts electrical into
photo ionic energy.
 Eg. LED, Laser diode,
photoemissive cell etc.
 Converts photo ionic
energy into electrical
energy
 Eg. LDR, Solar cell,
photo diodeetc.
Electro optic Opto electric

ASSIGNMENT 2
 Explain about 3 op-amp instrumentation Amplifier with their
features.
 What is communication of data in instrumentation system?
 How data are transferred in Optical fiber communication
system?
 Discuss about advantage and disadvantage of optical fiber
over conventional data transmission system.

Electrical signal processing and transmission

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