EE2003 Circuit Theory - UNLVeebag/EE 220 Chap 4 draft.pdf · 2020. 3. 3. · For the op amp circuit...
Transcript of EE2003 Circuit Theory - UNLVeebag/EE 220 Chap 4 draft.pdf · 2020. 3. 3. · For the op amp circuit...
EE 220
Operational Amplifiers
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Operational Amplifiers (Op Amps)
1. Op Amp Characteristics
2. Ideal Op Amp
3. Inverting Amplifier
4. Non-Inverting Amplifier
5. Summing Amplifier
6. Difference Amplifier
7. Voltage Follower
8. Cascaded Op Amps
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What is an Op Amp?
It is an electronic circuit that behaves like a
voltage-controlled voltage source.
It is often used to perform mathematical
operations such as inversion, addition, subtraction,
multiplication, division, differentiation and integration.
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Inside The Op Amp
Operational Amplifier
Two input terminals, positive (non-
inverting) and negative (inverting)
One output
Power supply V+ , and
Op Amp showing power supply Op Amp with power supply not shown (which is how we usually display op amp circuits)
Op Amp Gain
Key important aspect of op amp: high voltage gain output,
◦ A is the op-amp gain (or open-loop gain)
◦ Linear response
Op Amp Equivalent Circuit
Circuit Analysis With Ideal Op-Amps
Use nodal analysis as before.
N
Do not apply KCL at op amp output
Inverting Amplifier
i
f
o vR
Rv
1
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An inverting amplifier reverses the polarity of the input signal while amplifying it.
Inverting Amplifier
Example 1:
Refer to the op amp circuit below. If vi = 0.5V, calculate the output voltage vo and the current in the 10 k resistor.
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Answer: (a) -1.25V; (b) 50μA
Non-Inverting Amplifier
in
f
o vR
Rv
1
1
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Non-inverting amplifier is designed to produce positive
voltage gain.
Vo = (1+R1/R2)vs
Example 2:
For the op amp circuit shown below, calculate the output voltage vo.
12 Answer: -1V
Non-Inverting Amplifier
Summing Amplifier
3
3
2
2
1
1
vR
Rv
R
Rv
R
Rv
fff
o
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Summing Amplifier is an op amp circuit that combines
several inputs and produces an output that is equal to the
weighted sum of the inputs.
Summing Amplifier
Example 3:
Calculate vo and io in the op amp circuit shown below.
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Answer: -3.8V, -1.425mA
Difference Amplifier
1 if , )/1(
)/1(
4
3
1
2121
1
22
431
212
R
R
R
Rvvvv
R
Rv
RRR
RRRv oo
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Difference amplifier is a device that amplifies the difference
between two weighted inputs.
Voltage Follower/Buffer
depends on load resistor.
is immune to load resistor.
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Cascaded Op Amps
It is a head-to-tail arrangement of two or more op amp
circuits such that the output to one is the input of the
next.
Cascaded Op Amps
Example 4:
Find vo and io in the circuit shown below.
18 Answer: 350mV, 25μA
Cascaded Op Amps
Example 5:
Find vo in terms of v1, v2 and v3.
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Practice Problems (Chap. 4)
Solve the following problems:
4, 8, 12, 16, 20, … 52.
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Another Transistor: the MOSFET
A MOSFET (metal-oxide semiconductor field-effect transistor) is
a voltage-controlled electronic switch.
A MOSFET has three terminals: the gate (G), the source (S),
and the drain (D).
Because the gate G is separated from the rest of the transistor
by the thin insulating layer, no dc current can flow from G to
either D or S.
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More to come on MOSFETs
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