Basic Concepts - Oakland University
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Transcript Basic Concepts - Oakland University
Operational Amplifiers (Op Amps)
Discussion D3.1
Operational Amplifiers (Op Amps)
•
•
•
•
•
•
•
Ideal Op Amp
Non-inverting Amplifier
Unity-Gain Buffer
Inverting Amplifier
Differential Amplifier
Current-to-Voltage Converter
Non-ideal Op Amp
Ideal Op Amp
i
i
1)
v
v
VDD
VSS v0 VDD
+
vo
-
VSS
v0 Av v v
The open-loop gain, Av, is very large, approaching infinity.
2)
i i 0
The current into the inputs are zero.
Ideal Op Amp with Negative Feedback
v
+
v
-
vo
Network
Golden Rules of Op Amps:
1. The output attempts to do whatever is necessary to
make the voltage difference between the inputs zero.
2. The inputs draw no current.
Operational Amplifiers (Op Amps)
•
•
•
•
•
•
•
Ideal Op Amp
Non-inverting Amplifier
Unity-Gain Buffer
Inverting Amplifier
Differential Amplifier
Current-to-Voltage Converter
Non-ideal Op Amp
Non-inverting Amplifier
v
vi
v
R1
+
vo
Closed-loop voltage gain
AF
-
vo
vi
R2
vi v v
R1
vo
R1 R2
vo
R2
AF 1
vi
R1
Operational Amplifiers (Op Amps)
•
•
•
•
•
•
•
Ideal Op Amp
Non-inverting Amplifier
Unity-Gain Buffer
Inverting Amplifier
Differential Amplifier
Current-to-Voltage Converter
Non-ideal Op Amp
Unity-Gain Buffer
vi
v
v
+
-
Closed-loop voltage gain
vo
AF
vo
vi
vi v v vo
AF
vo
1
vi
Used as a "line driver" that transforms a high input impedance
(resistance) to a low output impedance. Can provide substantial
current gain.
Operational Amplifiers (Op Amps)
•
•
•
•
•
•
•
Ideal Op Amp
Non-inverting Amplifier
Unity-Gain Buffer
Inverting Amplifier
Differential Amplifier
Current-to-Voltage Converter
Non-ideal Op Amp
Inverting Amplifier
R2
Current into op amp is zero
v v 0
v 0 vi
ii i
R1
R1
0 v0 v0
ii
R2
R2
vi
ii
ii
R1
v
v
+
vi v0
R1 R2
AF
vo
R
2
vi
R1
vo
Operational Amplifiers (Op Amps)
•
•
•
•
•
•
•
Ideal Op Amp
Non-inverting Amplifier
Unity-Gain Buffer
Inverting Amplifier
Differential Amplifier
Current-to-Voltage Converter
Non-ideal Op Amp
Differential Amplifier
R2
Current into op amp is zero
v1
v v
i1
v2
v1 v
R1
R1
v
v
+
R1
R2
v v0
i1
R2
R2
v
v2
R1 R2
i1
i1
v1 v v v0
R1
R2
v1
R2
R2
v2
v2 v0
R1 R2
R1 R2
R1
R2
vo
Differential Amplifier
R2
R2
R2
v1
v2
v2 v0
R1 R2
R R2
1
R1
R2
v1
v2
2
2
R2
R2
R
v0 v1
v2
v2
R1
R1 R2
R1 R1 R2
R2
R2 R2
v0 v1
1 v2
R1
R1 R2 R1
i1
R1
v
v
i1
+
R1
R2
R2
v0
v2 v1
R1
vo
Operational Amplifiers (Op Amps)
•
•
•
•
•
•
•
Ideal Op Amp
Non-inverting Amplifier
Unity-Gain Buffer
Inverting Amplifier
Differential Amplifier
Current-to-Voltage Converter
Non-ideal Op Amp
Current-to-Voltage Converter
v
v
ii
+
vo
-
RF
if
ii i f
v v 0
0 v0 i f RF
v0 ii RF
Transresistance v0 ii RF
Photodiode Circuit
ii 25A per milliwatt of incident radiation
v
v
h
ii
+
vo
-
At 50 mW
RF
if
ii 50 25 106 1.25mA
Assume RF 3.2k
v0 ii RF 1.25 103 3.2 103 4V
Operational Amplifiers (Op Amps)
•
•
•
•
•
•
•
Ideal Op Amp
Non-inverting Amplifier
Unity-Gain Buffer
Inverting Amplifier
Differential Amplifier
Current-to-Voltage Converter
Non-ideal Op Amp
Non-ideal Op Amp
•
•
•
•
•
•
•
•
•
•
Output voltage is limited by supply voltage(s)
Finite gain (~105)
Limited frequency response
Finite input resistance (not infinite)
Finite output resistance (not zero)
slew rate dv0 (t ) dtMAX
Finite slew rate
Input bias currents
Input bias current offset
Input offset voltage
Finite common mode rejection ratio (CMRR)