Operational Amplifiers - Agricultural engineering
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Transcript Operational Amplifiers - Agricultural engineering
Operational Amplifiers
A brief introduction
2/1/2005
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Op-Amp Introduction
• Need exists for a circuit element that can perform:
– Add, subtract, multiply, divide, differentiate, integrate
• Evolved from Analog Computers
• Op-Amp properties
– Single building block which can be assembled into above
functions by adding passive components (R,L,C)
– Inexpensive (used in high volume)
– Compact
• Op-Amp analysis
• Use assumptions of “Ideal Op-Amp” to allow low frequency
performance to be approximated
• Typically have near ideal characteristics but frequency
response of an integrator (G(s) = 1/ts). (Otherwise, the
high bandwidth would be impossibly difficult to manage.)
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Ideal Op-Amp Assumptions
+Vsupply
+
• Differential function
• Vout = A•DV
• Infinite
DV
• Intrinsic gain: A =
• Input impedance: Zin =
• Bandwidth: Vout f(w)
Zin
A Zout
Vout
-
• Zero
-Vsupply
• Input offset voltage: Vio = 0 for Vout+ Vio= A•DV
• Input impedance: Zout = 0
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Rf
Inverting Amplifier
• Consider the circuit
configuration to the right
Vin VRin DV VRb
+Vsupply
Rin
iin_op-amp
DV
Vin
ib
+
Vout
Rb
Vout VR f DV VRb
-Vsupply
iRin iR f iin _ opamp
• Assuming intrinsic gain of the op-amp is very large
for the frequency of interest: DVA Vout
– Vout is finite and typically within +15 to -15 V implying DV is
very small
• Assuming ib is very small given the intrinsic input
impedance is very large, Vb must be very small
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Inverting Amplifier
Vin VRin
Vout VR f
VRin
VR f
Rf
Vout
Vin
Rin
Rin
Rf
Vin
Vout
iRin iR f
Rin
Rf
• Amplifier performance is a function of external
components only for ideal assumptions
• Input and output impedances of the amplifier can be
calculated as approximately:
Zin Rin
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Z out
Z out _ intrinsic
1 A Rin
Rin R f
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Non-Inverting Amplifier
Rin
Vin VRin DV VRb
Vout VR f VRb
iR f ib iRb
+
DV
Vin
ib
Vout VR f Vin
Vout
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-Vsupply
Vin VRb
iR f iRb
+Vsupply
VR f
Rf
Rb
VRb
Rb
VR f Vin
Rf
Vin
Vin Vin 1
Rb
Rb
Rf
Vout
Rf
Rf
Rb
BAE 5413
Vout R f
1
Vin Rb
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Non-Inverting Amplifier
• Input and output impedances can be calculated as
approximately:
Rin
Z in Z in _ intrinsic1 A
R R
f
in
Z out
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Z out _ intrinsic
Rin
1 A
R R
f
in
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