Short Notes: Operational & Differential Amplifiers

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Op erational & Differen tial Amplifiers
Op e rational amplifiers (op-amps) and differen tial amplifiers are fundamen tal building blo c ks in analog
circuits, widely used for signal amplification, filtering, and pro cessing. This section co v ers their k ey
concepts, configurations, and p erformance parameters.
Key Concepts
• Op erational Amplifier : A high-gain, direct-coupled amplifier with differen tial inputs and a
single-ended output, t ypically used with external feedbac k.
• Differen tial Amplifier : Amplifies the difference b et w een t w o input signals, forming the core of
most op-amps.
• Ideal Op-Amp Characteristics : Infinite op en-lo op gain, infinite input imp edance, zero output
imp edance, infinite bandwidth, and zero offset v oltage.
Differen tial Amplifier
• Op eration : Amplifies the difference b et w een t w o input v oltages ( V
1
and V
2
).
• Differen tial Gain :
A
d
=
V
out
V
1
-V
2
• Common-Mo de Rejection Ratio (CMRR) :
CMRR=20log
10
(
A
d
A
c
)
dB
where A
c
is the common-mo de gain (ideally zero).
• Input/Output Characteristics :
– Input: High imp edance, t ypically differen tial.
– Output: Single-ended or differen tial, dep ending on the configuration.
Op erational Amplifier Configurations
1. In v erting Amplifier
• Op eration : Input applied to the in v erting input (- ), non-in v erting input (+ ) grounded via
resistor.
• V oltage Gain :
A
v
=-
R
f
R
1
where R
f
is the feedbac k resistor, R
1
is the input resistor.
• Input Imp edance : Appro ximately R
1
.
• Output Imp edance : Lo w (close to zero for ideal op-amp).
2. Non-In v erting Amplifier
• Op eration : Input applied to the non-in v erting input (+ ), feedbac k to the in v erting input
(- ).
• V oltage Gain :
A
v
=1+
R
f
R
1
• Input Imp edance : V ery high (approac hing infinit y for ideal op-amp).
• Output Imp edance : Lo w.
3. V oltage F ollo w er (Buffer)
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Op erational & Differen tial Amplifiers
Op e rational amplifiers (op-amps) and differen tial amplifiers are fundamen tal building blo c ks in analog
circuits, widely used for signal amplification, filtering, and pro cessing. This section co v ers their k ey
concepts, configurations, and p erformance parameters.
Key Concepts
• Op erational Amplifier : A high-gain, direct-coupled amplifier with differen tial inputs and a
single-ended output, t ypically used with external feedbac k.
• Differen tial Amplifier : Amplifies the difference b et w een t w o input signals, forming the core of
most op-amps.
• Ideal Op-Amp Characteristics : Infinite op en-lo op gain, infinite input imp edance, zero output
imp edance, infinite bandwidth, and zero offset v oltage.
Differen tial Amplifier
• Op eration : Amplifies the difference b et w een t w o input v oltages ( V
1
and V
2
).
• Differen tial Gain :
A
d
=
V
out
V
1
-V
2
• Common-Mo de Rejection Ratio (CMRR) :
CMRR=20log
10
(
A
d
A
c
)
dB
where A
c
is the common-mo de gain (ideally zero).
• Input/Output Characteristics :
– Input: High imp edance, t ypically differen tial.
– Output: Single-ended or differen tial, dep ending on the configuration.
Op erational Amplifier Configurations
1. In v erting Amplifier
• Op eration : Input applied to the in v erting input (- ), non-in v erting input (+ ) grounded via
resistor.
• V oltage Gain :
A
v
=-
R
f
R
1
where R
f
is the feedbac k resistor, R
1
is the input resistor.
• Input Imp edance : Appro ximately R
1
.
• Output Imp edance : Lo w (close to zero for ideal op-amp).
2. Non-In v erting Amplifier
• Op eration : Input applied to the non-in v erting input (+ ), feedbac k to the in v erting input
(- ).
• V oltage Gain :
A
v
=1+
R
f
R
1
• Input Imp edance : V ery high (approac hing infinit y for ideal op-amp).
• Output Imp edance : Lo w.
3. V oltage F ollo w er (Buffer)
1
• Op eration : Output connected directly to the in v erting input, input to the non-in v erting
input.
• V oltage Gain :
A
v
=1
• Use : Imp edance matc hing, high input imp edance, lo w output imp e dance.
Small-Signal Mo del of Op-Amp
• Op en-Lo op Gain : A
OL
, t ypically v ery high (10
5
to 10
6
).
• Input Resistance : R
in
, t ypically v ery high (10
6
to 10
12
? ).
• Output Resistance : R
out
, t ypically lo w (10 to 100? ).
Key P erformance P arameters
• Slew Rate : Maxim um rate of c hange of output v oltage:
Slew Rate=
dV
out
dt
(V/µ s)
• Bandwidth : F requency range o v er whic h the op-amp op erates effectiv ely , limited b y the gain-
bandwidth pro duct.
• Offset V oltage : Small v oltage difference b et w een inputs required to pro duce zero outpu t (ideally
zero).
• CMRR : Abilit y to reject common-mo de signals, ideally infinite.
Applications
• Differen tial Amplifier : Instrume n tation amplifiers, sensor signal pro cessing.
• Op-Amp : A ctiv e filters, oscillators, comparators, analog computations, signal conditioning.
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