eca1212 introduction to electrical & electronics engineering chapter 7: operational amplifier by...
TRANSCRIPT
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ECA1212Introduction to Electrical &
Electronics EngineeringChapter 7: Operational Amplifier
by Muhazam Mustapha, November 2011
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Learning Outcome
• Be able to explain and solve some problems involving operational amplifier
By the end of this chapter students are expected to:
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Chapter Content
• Reason for Op Amp
• Regular Op Amp Circuits
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Why Operational Amplifier
CO1 Text Book page 410
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Need for Semi-Finished Amplifier
CO1 Text Book page 412
• The kind of amplifier that we can build from BJT as we learnt in Chapter 5 was constructed using raw components
• We need something more robust, flexible and easier to install
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Need for Semi-Finished Amplifier
CO1 Text Book page 413
• Operational Amplifier (Op-Amp) is a semi-finished amplifier fabricated on IC
• Its gain and operation is easily adjustable using some combination of resistors
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Fundamentals
CO1 Text Book page 413
• Input current iin is assumed to be zero because the input resistance is very high
• Virtual ground: inverting (v−) and noninverting (v+) inputs are assumed to be at the same voltage but no current going to ground (close loop mode)
Inverting input
Noninverting input
OutputVin
v+
v−
Vout
iin
• Symbol:• Gain (A, open loop gain):
vout = Avin
– Value is high ranging 105 ~ 107
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Op-Amp Circuits
CO1 Text Book page 414
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Close Loop Mode
• Most of the time op-amp is used in close loop mode
• This is done by putting a resistor from the output to the input (mostly the inverted one)
• The resistor is the called feedback resistor
• This feedback resistor pulls down the voltage gain to a more manageable value– But we won’t discuss the detail
CO1
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Close Loop Mode
• In close loop mode the previous assumptions are always applied:
CO1
iin = 0
v− = v+
Text Book Eq. 8.19, 8.37, etc
• For all circuits that we are going to cover, we won’t go through into the derivation details, but references will be made to the respective pages in the text book
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Inverting Amplifier
• Circuit:
CO1 Text Book page 413-417, Example 8.1 partly
• Voltage Gain:
S
F
S
out
R
R
v
v
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Summing Amplifier
• Circuit:
CO1 Text Book page 418
• Voltage Gain:
N
nS
S
Fout n
n
vR
Rv
1
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Noninverting Amplifier
• Circuit:
CO1 Text Book page 419
• Voltage Gain:
S
F
S
out
R
R
v
v1
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Voltage Follower
• Circuit:
CO1 Text Book Example 8.2
• Voltage Gain:
outS vv
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Differential Amplifier
• Circuit:
CO1 Text Book page 421-422
• Voltage Gain:
)( 121
2 vvR
Rvout
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Integrator
• Circuit:
CO1 Text Book page 433, Example 8.7
• Output Voltage:
dtvCR
v SFS
out
1
vout and vS are functions of time
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Differentiator
• Circuit:
CO1 Text Book page 449
• Output Voltage:
dt
dvCRv s
SFout
vout and vS are functions of time