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ECE 4991 Electrical and Electronic
Circuits
Chapter 8
Where are we?
• Chapter 2 - The basic concepts and practice at
analyzing simple electric circuits with sources
and resistors
• Chapter 3 – More harder networks to analyze and
the notion of equivalent circuits
• Chapter 4 – Capacitors and inductors added to
the mix
• Chapter 5 – Analyzing transient situations in
complex passive networks
• Chapter 8 – New subject – the wonders of
operational amplifiers as system elements
• Chapter 9 – Introduction to semiconductors – the
basics and diodes – more network analysis
• Chapter 10 – Bipolar junction transistors and how
they work – now you can build your own op amp
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What’s Important in
Chapter 8
1.
2.
3.
4.
5.
6.
7.
8.
9.
Definitions
Op Amp Basics
Inverting Amplifiers
Summing Amplifiers
Non-inverting Amplifiers
Voltage Followers
Diff Amps
Integrators
Differentiators
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1. Definitions
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Operational Amplifier
Open-loop
Feedback
Inverting (input)
Non-inverting (input)
Open-loop voltage gain
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2. Op Amp Basics
• An operational amplifier is an IC
“engine” that can support many
applications
• Defining characteristics
– Amplifies difference between two input
voltage
– Extremely high gain
– Extremely high input resistance
– Extremely low output resistance
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Diagramming an Op Amp
+
Pwr
Inverting
Input
Non-inverting
Input
_
+
Output
_
Pwr
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Design Assumptions
Two main design assumptions for op
amp applications using negative
feedback
1. Zero input current
2. Input voltages forced to be equal
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3. Inverting Amplifier
•
•
•
•
+ input grounded
Input signal to (–) input through RS
Output fed back to (–) input through RF
Gain = - RF/RS
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Inverting Amplifier
Practice
• Design an inverting amplifier with a
gain of - 250
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Inverting Amplifier
Practice
• Given the following resistors to work
with – 1KΩ, 1KΩ, 3KΩ, 20KΩ, 30KΩ –
design an inverting amp with gain -40
_
+
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4. Summing Amplifier
•
•
•
•
+ input grounded
Several input signals to (–) input through RS’s
Output fed back to (–) input through RF
Vout = -  (RF / RSi) vsi
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Summing Amplifier
Practice
• Design an amplifier with
Vout = - 50 (v1 + v2 + v3)
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Summing Amplifier
Practice
• Design an amplifier with
Vout = - (20v1 +30v2 + 40v3)
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5. Non-Inverting Amplifiers
•
•
•
•
Ground the (-) input through RS
Signal input to + input through any R
Output fed back to (-) input through RF
Gain is 1 + RF / RS
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Non-Inverting Amplifier
Practice
• Design a non-inverting amp with gain =
10
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+
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Non-Inverting Amplifier
Practice
• Resistor collection is 20Ω, 50Ω, 100Ω,
100Ω, 300Ω, 300Ω, 500Ω
• Design a non-inverting amplifier with a
gain of 5
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6. Voltage Follower
• Output fed back directly to (-) input
• Signal input directly to + input
• Vout = vS
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What’s a Voltage Follower
For?
• Op amp input impedance very high
• Op amp output impedance very low
• Voltage followers buffer sensitive
circuits or circuit elements
• Also used for driving speakers, long
cables, etc
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7. Differential Amplifiers
• V1 input fed to (-) input through R1
• V2 input fed to + input through a different
R1
• Output tied back to (-) input through R2
• + input tied to ground through R2
• Vout = (R2/R1) (V2 – V1)
_
+
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Differential Amplifier
Practice
• Design a diff amp with Vout = 50 (V2 – V1)
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Differential Amplifier
Practice
• Design a diff amp with Vout = 200 sin t –
600 cos 3t
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Differential Amplifier
Practice
• Design a diff amp with Vout = 40 sin t –
10 V1
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8. Integrating Amplifiers
• Signal input fed to (-) input through RS
• Output tied back to (-) input through CF
• + input tied to ground
• Vout = - (1/RSCF)
 V dt
S
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Integrating Amplifier Practice
• VS = 4 sin t, RS = 100 , CF = 50 F
• Vout = ?
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Integrating Amplifier Practice
• Vout = - 200 t4 Volts
• VS = ?, RS = 1K, CF = ?
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9. Differentiating Amplifiers
•
•
•
•
Signal input fed to (-) input through CS
Output tied back to (-) input through RF
+ input tied to ground
Vout = - RFCS dVS/dt
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Differentiating Amplifier
Practice
• Vout = - RFCS dVS/dt
• Design a differentiating amplifier with
Vout = 30 sin t
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+
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Differentiating Amplifier
Practice
• Vout = - RFCS dVS/dt
• VS = 25 sin 2t, RF = 100, CS = 10 F
• Vout = ?
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Op Amp Practice
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Op Amp Practice
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Op Amp Practice
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Op Amp Practice
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Op Amp Practice
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Op Amp Practice
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