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Ideal Op-Amp Equivalent Circuit

1. The document describes the ideal characteristics and equivalent circuit models of operational amplifiers (op-amps). 2. Key characteristics of ideal op-amps include infinite differential gain, zero differential input voltage, and zero output resistance. 3. The equivalent circuit shows the op-amp modeled as a dependent voltage source with zero output resistance connected to the inverting and non-inverting inputs.

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Piyush Dubey
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969 views20 pages

Ideal Op-Amp Equivalent Circuit

1. The document describes the ideal characteristics and equivalent circuit models of operational amplifiers (op-amps). 2. Key characteristics of ideal op-amps include infinite differential gain, zero differential input voltage, and zero output resistance. 3. The equivalent circuit shows the op-amp modeled as a dependent voltage source with zero output resistance connected to the inverting and non-inverting inputs.

Uploaded by

Piyush Dubey
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Ideal Op-Amp Equivalent Circuit

Ideal Op-Amp Characteristics


1. Internal differential gain Aod is infinite.
2. Differential input voltage (v2-v1) is zero.
3. Effective input resistance is infinite.
4. Output resistance is zero so output voltage is
connected directly to dependent voltage
source.

Equivalent Circuit of Op-Amp

Inverting Op-Amp

Input is applied
to the inverting input

Output is 180
out of phase
than the input

Advantage:
Can work as an amplifier or an attenuator.
Dis-advantage:
Low/medium input impedance (depends of resistor selection,
demands considerable current from input Vi).

Inverting Op-Amp with T-Network


R3 R3
R2
Av (1
)
R1
R4 R2

Advantage of T-network: Larger gain than a single resistor,


while achieving lower noise.

Inverting Op-Amp with Finite


Differential-Mode Gain

~1
Av

R2
R1

1
R2
1
[1
(1 )]
Aod
R1

Op-Amp based Summing Amplifier


(inverting summing amplifier)

vO (

RF
R
R
vI1 F vI 2 F vI 3 )
R1
R2
R3

Op-Amp based Summing Amplifier


(compound summing amplifier)

Gets inverted
at the output
Doesnt get
inverted
at the output

Noninverting Op-Amp
Output is in phase
with the input

Input is applied
to the non-inverting input

Equivalent circuit

Advantage:
High input impedance (doesnt demand large current from input Vi)
Dis-advantage:
Gain is always greater or equal to 1.

Unity gain amplifier (gain=1)/


Voltage Follower/ Voltage buffer
vO
RL

v I R L RS

Advantage:
Suitable if source is high impedance.
Purpose:
Isolates the input source from loading
(avoids drawing excessive current from the source).

Current-to-Voltage Converter
(Current input and voltage output)

Low output impedance


(suitable for driving alarge/
required/ on-demand load current,
while maintaining proportional
output voltage with an input current)

Voltage-to-Current Converter
(output I is proportional to input V)
Principle: Maintains a constant
voltage across R3

Applications:
LED driver.
Physiotherapy equipment.

Op-Amp Difference Amplifier

Generally,
we keep R1=R3 and R2=R4
for better common mode
Rejection performance.

Inverting amplifier

Non-inverting amplifier

Gain of Difference Amplifier

Common mode rejection ratio


(CMRR)

Common mode gain


Common mode voltage

Instrumentation Amplifier
High input impedance

Gain control
using one resistor

Low output
impedance

Op-Amp Integrator

Op-Amp Differentiator

Precision Half-Wave Rectifier

Log and Antilog Amplifiers

Antilog Amplifier
(exponential)

Log Amplifier

Signal Multiplier

v1

Log
Amplifier

v2

Log
Amplifier

ln v1

ln v1+ln v2
Summing
Amplifier

ln v2

Anti-Log
Amplifier

v1.v2

Op-Amp Voltage Reference Circuit

Applications:
Bias generation for amplifiers or sensors.
Range selection in analog-to-digital and digital-to-analog converters

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