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Operational Amplifier
& aplikasinya
Elektronika(TKE 4012)
Eka Maulana
maulana.lecture.ub.ac.id
Op Amp
• Op Amp is short for operational amplifier
• Amplifiers provide gains in voltage or current
• Op amps can convert current to voltage
+
–
Non-inverting input
Inverting input
Ground
High Supply (+)
Low Supply (-)
Output
Simbol Op Amp
Applications of Op Amps
• Op amps can be configured in many different ways using resistors and other components
• Most configurations use feedback
• Op amps can provide a buffer between two circuits
• Op amps can be used to implement integrators and differentiators
• Lowpass and bandpass filters
Aplikasi Op-amp
• Komparator
• Penguat Non-inverting
• Penguat Inverting
• Penguat penjumlah
• Voltage follower
• Converter Tegangan ke Arus
• Integrator & Diferensiator
• Penguat diferensial
• Penguat instrumentasi
• Penguat histerisis
The Op Amp Model
+
–Inverting input
Non-inverting input
Rin
v+
v–
+
–
A(v+ – v– )
vo
• An operational amplifier is modeled as a
voltage-controlled voltage source.
Voltage controlled
voltage source
Typical vs. Ideal Op Amps
Typical Op Amp:
• The input resistance
(impedance) Rin is
very large (practically
infinite).
• The voltage gain A is
very large (practically
infinite).
Ideal Op Amp:
• The input resistance
is infinite.
• The gain is infinite.
• The op amp is in a
negative feedback
configuration.
Consequences of the Ideal
• Infinite input resistance means the current
into the inverting (–) input is zero:
i– = 0
• Infinite gain means the difference between
v+ and v– is zero:
v+ – v– = 0
Typical Op Amp Parameters
Parameter Variable Typical
Ranges
Ideal Values
Open-Loop
Voltage Gain
A 105 to 108
∞
Input
Resistance
Ri 105 to 1013 W ∞W
Output
Resistance
Ro 10 to 100 W 0 W
Supply
Voltage
Vcc/V+
-Vcc/V-
5 to 30 V
-30V to 0V
N/A
N/A
Symbols for Ideal and Real Op Amps
OpAmp uA741
LM324 LM111
Voltage Transfer Characteristic
Range where we
operate the op amp
as an amplifier.
vd
Vd = V1-V2
+
–
V1
V2
Vcc(+)
Vcc(-)
VO
+
–
V1
V2
Vcc(+)
Vcc(-)
When Vd is larger than 0V, Vo = Vcc(+).
When Vd is smaller than 0V, Vo = Vcc(-).
When Vd is equal to 0V, Vo = 0V.
Vo
Example #1: Voltage Comparator
Vd = V1-V2
Penguat Inverting Basic
–
+Vin
+
–
Vout
R1
R2
+
–
Solving the Amplifier Circuit
Apply KCL at the inverting (–) input:
i1 + i2 + i– =0
0i
111
R
V
R
VVi inin
222
R
V
R
VVi outout
–
R1
R2
i1 i–
i2
Vin
Vout
V–
Solve for Vout
• From KCL • Thus, the amplifier
gain is
21
21
21
00
0
R
V
R
V
R
V
R
V
iii
outin
outin
1
2
R
R
V
V
in
out
Lect8 EEE 202 15
Recap
• The ideal op-amp model leads to the
following conditions:
i– = 0 = i+
v+ = v–
• These conditions are used, along with KCL
and other analysis techniques (e.g.,
nodal), to solve for the output voltage in
terms of the input(s)
Penguat Non-inverting
+
–
vin
+
–
vout
R1
R2
+
–
KCL at the Inverting Input
+
–
vin
+
–
vout
R1
R2
i–
i1 i2
+
–
0i
11
1R
v
R
vi in
2
22
R
vv
R
vvi
inout
out
Solve for vout
1
2
21
21
1
0
0
R
Rvv
R
vv
R
v
iii
inout
inoutin
• Hence, the non-inverting amplifier has a gained output (> unity) relative to the resistance ratio
Rangkaian Penjumlah
–
+v2
+
–
vout
R2
RfR1
v1
+
–
+
–
KCL at the Inverting Input
1
1
1
11
R
v
R
vvi
2
2
2
22
R
v
R
vvi
0i
–
+v2
+
–
vout
R2
RfR1
v1
i1
i2
if
i–
+
–
+
–
f
out
f
out
fR
v
R
vvi
Solve for vout
• So, the mixer circuit output is a (negative)
combination of the input voltages
22
11
2
2
1
1
21
0
0
vR
Rv
R
Rv
R
v
R
v
R
v
iiii
ffout
f
out
f
ac coupled inverting amplifier
vout
vin
R1
R2
RL
C1
C2
AV =-R2
R1 R2
R1
+1
funityf2 =
fc1 = 2pR1C1
1fc2 = 2pRLC2
1
R2
Adjustable bandwidth
voutvin
R1
RA
f
-R2
R1
R1 R + R2
R1 RB =
f2 = Bfunity
R1
R2
ac coupled noninverting amplifier
C3
C2
C1
vout
R3
RL
vin
fc3 = 2pR1C3
1
Bdc = 1
R
JFET controlled inverter/noninverter
voutvinR
R
0 V
VGS(off)
R
Adjustable gain of ± 1
voutvin
R
R’
Phase shifter
vout
vin
R
R’
C
f
f = -2 arctan 2pRCf
t
R2
Differential amplifier
voutvin
R1’
R1
R2’
vin(CM)
vin(CM)
CMRR limiting factors
are the op amp itself and
the tolerance of the resistors.
AV =-R2
R1
±2 < ACM < ±4DR
RDR
R
Ideally:
R1 = R1’
R2 = R2’
R2
Wheatstone bridge
vout
R1
R4
R3
Transducer
+V
Wheatstone bridge
• The differential output signal is small.
• The common-mode output signal is large.
• Differential amplifiers are a good match.
• Transducers convert nonelectrical
quantities into an electrical quantity such
as resistance:
– examples: photoresistor, thermistor, strain
gage
Instrumentation amplifiers
• Differential amplifiers optimized for dc
performance
• Large differential voltage gain
• High CMRR
• Low input offsets
• Low temperature drift
• High input impedance
R
vout
vin
R
R
R
vin(CM)
vin(CM)
±2DR
RACM =AV =
-2R1
RG
+1
R1
R1
RG
Instrumentation amplifier
Monolithic instrumentation
amplifiers
• Use laser-trimmed resistors for high
performance.
• Resistor RG is external and is selected to
set the differential gain.
• Resistor RG can be split into two devices
for guard driving (bootstrapping the cable
shield to the common-mode potential).
RG
2
RG
2
vout
Guard driving
Guard voltage (common-mode voltage)
Instrumentation
amplifier
Summing amp with inverting
and noninverting inputs
vout
R1RF
R2
R3
R4
v1
v2
v3
v4
R5
D/A converter
vout
R R
2R
4R
8R
v3
v2
v1
v0
vout = -(v3 + 0.5v2 + 0.25v1 + 0.125v0)
Possible combinations = 2N = 24 = 16
N = 4
vin18
Unidirectional current booster
R2
R1 RL
vin
+VCC
vout
741
Imax = bdcISC = 100(25 mA) = 2.5 A
bdc = 100
Bidirectional current booster
R2
R1
RL
vin
+VCC
vout
-VEE
AGC circuit
vout
R1vin
R5
R6
R3
R4
R2
+VAGC
-VEE
As the signal level increases,
VAGC goes more positive.
As the JFET rds drops,
the input signal is attenuated.
Voltage-controlled
resistance
Single-supply inverting amplifier
vout
vin
R1
R2
RL
C1
C2
R
+VCC
RC3
+VCC
2