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Mechatronics System Design
Lecture 03
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Instructor: Dr. Qari Khalid WaheedInstitute of Mechatronics
Engineering,
UET Peshawar.
By: Engr. Muhammad Usman Khan
(MtE-325)
Spring 2016
OPERATIONAL AMPLIFIERS
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An operational amplifier (op-amp) is a high-gain linear
amplifier.
Op-amps are usually packaged in IC form (one to four op-amps per
IC) and are relatively inexpensive.
Ideal Characteristics:
1. Very high open-loop gain: A = 100,000+, but unpredictable
2. Very high input resistance: Rin > 1 MΩ
3. Low output resistance: Rout = 50-75 ohm
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Fig 1: The op-amp symbol.
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Vout = A(V2 – V1)
where
Vout = output voltage
A = open-loop gain
V1 = inverting input
V2 = noninverting input
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Fig 2: Single-input, open-loop amplifiers.
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Fig 3: Equivalent circuit model of an op-amp.
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Voltage Follower
The voltage follower, which is very useful circuit, can boost
the current of a signal without increasing the voltage.
It can transform a high-impedance signal (easily loaded down)
into a robust low-impedance signal.
Fig 4: A voltage follower circuit.
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Voltage Follower (cont’d)
Vout = A(V2 – V1)
In the circuit, Vout is connected to V1; thus, Vout = V1.
Substituting in Vout and expanding;
Vout = (AV2) – (AVout)
Solving for Vout, we get
Vout = AV2 /(1+A) ≈ V2
But because A is much greater than 1,
Vout = AV2 /A ≈ V2
8Fig 5: Using a voltage follower to prevent load down.
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Inverting Amplifier
The input signal goes to the inverting input, which means the
output is outof phase with the input.
The inverting amplifier is probably the most common
op-ampconfiguration.
Fig 6: The inverting amplifier circuit.
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The voltage gain is determined by the resistor values.
Vout/Vin = - Rf/RiVout/Vin => voltage gain;
OR
AV = - Rf/Ri
where
oAV = voltage gain of the inverting amp
oRf= value of the feedback resistor
oRi= value of the input resistor
Inverting Amplifier (cont’d)
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Noninverting Amplifier
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Fig 7: The Non-inverting amplifier circuit.
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Noninverting Amplifier (cont’d)
Vout/Vin = ( Rf/Ri ) + 1
Vout/Vin => voltage gain;
AV = ( Rf/Ri ) + 1
where
oAV = voltage gain of the inverting amp
oRf= value of the feedback resistor
oRi= value of the input resistor
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Summing Amplifier
The summing amplifier has an output voltage that is the sum of
any number of input voltages.
Fig 7: The summing amplifier circuit.
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Summing Amplifier (cont’d)
If = Ia + Ib + Ic
If Ra = Rb = Rc = Ri, the output of the summing amp simplifies
to:
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Differential Amplifier
A differential amplifier amplifies the difference between two
input voltages.
common mode rejection
Fig 8: The differential amplifier circuit.
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Differential Amplifier (cont’d)
Vout = 𝑹𝒇
𝑹𝒂(Vb – Va)
𝑽𝒐𝒖𝒕(Vb – Va)
= 𝑹𝒇
𝑹𝒂𝑽𝒐𝒖𝒕
(Vb – Va), is
output
input, which is gain;
AV = 𝑹𝒇
𝑹𝒂
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Instrumentation Amplifier
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An instrumentation amplifier is a differential amp that has its
inputs buffered with voltage followers.
Fig 9: The instrumentation amplifier circuit.
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Integrators and Differentiators
Decibels (db)
Comparator
Examples 3.1 --- 3.10
Reading Assignment
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Active Filters
A filter using an op-amp is called an active filter.
1. Low pass filter
Fig 10: Low pass filter response.
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Fig 11: High-pass filter response
Active Filters (cont’d)
2. High-pass filter
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Active Filters (cont’d)
3. Band-pass filter
Fig 12: Band-pass filter response
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Active Filters (cont’d)
4. Notch filter
Fig 13: Notch filter response
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Questions ?
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