CO2037 – Electrical Electronic Circuits
Operational Amplifier (Op-Amp)
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CO2037 – Operational Amplifier (Op-Amp)
Contents
§ Operation
§ Feedback Circuit
§ Characteristics
§ Practical Applications
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CO2037 – Operational Amplifier (Op-Amp)
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Basic Op-Amp
§ Op-Amp = Operational Amplifier
§ An Op-Amp consists of …
▫ Inverting input
▫ Noninverting input
▫ Output
https://www.youtube.com/watch?v=kiiA6WTCQn0
CO2037 – Operational Amplifier (Op-Amp)
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Op-Amp Gain
§ Op-Amps have a very high gain. They can be connected open-loop or
close-loop.
▫ Open-loop refers a configuration where there is no feedback from
output back to the input. In the open-loop configuration, the gain can
exceed 105.
▫ Closed-loop configuration reduces the gain. In order to control the
gain of an op-amp it must have feedback. This feedback is a negative
feedback. A negative feedback reduces the gain and improves many
characteristics of the op-amp.
CO2037 – Operational Amplifier (Op-Amp)
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Op-Amp Models
§ Practical Model
▫ Zin is very large
▫ Zout is small
"
▫ The gain 𝐴! = !"# in open-loop configuration is very high.
"$%
§ Ideal Model (used for analysis)
▫ Zin = ∞ ® Iin+ = Iin- = 0; Vin+ = Vin▫ Zout = 0
▫ The open-loop gain: 𝐴! =
"!"#
"$%
=∞
CO2037 – Operational Amplifier (Op-Amp)
Op-Amp Operation
§ The amplitude of Vout is higer than amplitude of Vin.
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CO2037 – Operational Amplifier (Op-Amp)
Op-Amp Operation
§ The differential signal of 2 inputs is amplified.
§ When 2 inputs use common signal, the output is zero.
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CO2037 – Operational Amplifier (Op-Amp)
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Feedback Circuits
§ For the circuits without feedback (i.e. no connection between output
and input), the open-loop gain is very large (>105).
§ The output voltage will easily reach the saturation and the amplitude will
be trimmed.
CO2037 – Operational Amplifier (Op-Amp)
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Feedback Circuits
§ In order to control the gain of an op-amp it must have feedback. This
feedback is a negative feedback. A negative feedback reduces the
gain and improves many characteristics of the op-amp.
CO2037 – Operational Amplifier (Op-Amp)
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Inverting Op-Amp Gain
https://www.youtube.com/watch?v=AuZ00cQ0UrE
CO2037 – Operational Amplifier (Op-Amp)
Non-Inverting Op-Amp
§ https://www.youtube.com/watch?v=uyOfonR_rEw
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CO2037 – Operational Amplifier (Op-Amp)
Op-Amp Datasheet
§ IC LM358
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CO2037 – Operational Amplifier (Op-Amp)
Op-Amp Datasheet (IC LM358)
§ Maximum power supply: ±22V
§ Maximum input voltage: ±15V
§ Maximum differential input voltage: ±30V
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CO2037 – Operational Amplifier (Op-Amp)
Op-Amp Datasheet
§ IC 741
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CO2037 – Operational Amplifier (Op-Amp)
Op-Amp Datasheet (µA741)
§ Điện thế hoạt động 3 đến 30 à nếu nguồn đôi là
±15V
§ Điện thế ngõ vào từ (Vcc-) – 0.3 đến (Vcc+) – 1.5
• AVD – Large-signal differential voltage amplification
– 200V/mV = 200.000
• ri – input resistance: 2MW
• ro – output resistance: 75W
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CO2037 – Operational Amplifier (Op-Amp)
Output Voltage Threshold
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CO2037 – Operational Amplifier (Op-Amp)
Practical Op-Amp Circuits
§ Unity Follower
§ Summing Amplifier
§ Integrator
§ Differentiator
§ Comparator
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CO2037 – Operational Amplifier (Op-Amp)
Unity Follower
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CO2037 – Operational Amplifier (Op-Amp)
Summing Amplifier
https://www.youtube.com/watch?v=jsKSfaFQ4d4
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CO2037 – Operational Amplifier (Op-Amp)
Integrator
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CO2037 – Operational Amplifier (Op-Amp)
Differentiator
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CO2037 – Operational Amplifier (Op-Amp)
Comparator
§ Vout = +Vout(max) when V+ > V▫ Vin > VREF
§ Vout = -Vout(max) when V+ < V▫ Vin < VREF
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CO2037 – Operational Amplifier (Op-Amp)
Noisy Comparator
§ Unexpected pulses
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CO2037 – Operational Amplifier (Op-Amp)
Noiseless Comparator
§ Hysteresis
▫ 0 ®1 if Vin is greater than β threshold
▫ 1 ® 0 if Vin is smaller than α threshold
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CO2037 – Operational Amplifier (Op-Amp)
Application (1)
§ Protection Circuit using Op-Amp Comparator
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CO2037 – Operational Amplifier (Op-Amp)
Application (2)
§ Analog to Digital Conversion
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CO2037 – Operational Amplifier (Op-Amp)
IC 555
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CO2037 – Operational Amplifier (Op-Amp)
IC555 – Clock Pulse Generator
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CO2037 – Operational Amplifier (Op-Amp)
IC555 – Delay Circuit
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CO2037 – Operational Amplifier (Op-Amp)
Exercise 1
§ Compute the output voltage in the following circuits using ideal op-amp
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CO2037 – Operational Amplifier (Op-Amp)
Exercise 1 – Solution
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CO2037 – Operational Amplifier (Op-Amp)
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Exercise 2
§ Characteristics of an Op-Amp is given in the following table. The power supply is
±15V.
Parameter
Minimum
Typical
Output Voltage
±12V
±13.5V
Input Voltage
±11V
±12.5V
Output current of
shorted-circuit
±12mA
±20mA
§ Determine VX
Maximum
CO2037 – Operational Amplifier (Op-Amp)
Exercise 2 – Solution
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CO2037 – Operational Amplifier (Op-Amp)
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Exercise 3
§ Characteristics of an Op-Amp is given in the following table. The power supply is
±15V.
Parameter
Minimum
Typical
Output Voltage
±12V
±13.5V
Input Voltage
±11V
±12.5V
Output current of
shorted-circuit
±12mA
±20mA
§ Determine Vo when Vin=±6V
Maximum
CO2037 – Operational Amplifier (Op-Amp)
Exercise 3 - Solution
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CO2037 – Operational Amplifier (Op-Amp)
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Exercise 4
§ Characteristics of an Op-Amp is given in the following table. The power supply is
±15V.
§ Determine Vo
Parameter
Minimum
Typical
Output Voltage
±12V
±13.5V
Input Voltage
±11V
±12.5V
Output current of
shorted-circuit
±12mA
±20mA
Maximum
CO2037 – Operational Amplifier (Op-Amp)
Exercise 4 - Solution
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