an understanding of the complex circuitry within the op amp is not necessary to use this amplifying...
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•An understanding of the complex circuitry within the op amp is not necessary to use this amplifying circuit in the construction of an amplifier.
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Ideal Op-Amp Characteristics
1. Internal differential gain Aod is infinite.
2. Differential input voltage (v2-v1) is
zero.3. Effective input resistance is infinite
(i1 and i2 are zero).
4. Output resistance is zero so output voltage is connected directly to dependent voltage source.
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i1 = i2
V0=V1-i2R2=0 - (VI/R1)R2
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Ex 9.1
For the circuit given in Fig., design an inverting op-amp such that Av = -15 and the input resistance Ri = 20 k. Assume an ideal voltage source.
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Op-Amp Integrator
t
ICodt)t(v
CRVv
021
1
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Noninverting Op-Amp
1
21R
R
v
vA
i
o
v Between (1) and (2) there is a
virtual short circuit (v1 = v2)
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Voltage Follower
1
1
1
1
2
v
i
o
v
ARIf
R
R
v
vA
Voltage follower is used as an impedance transformer or a buffer, where Zin ∞, Zout 0
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Voltage Follower
010.RR
R
v
v
SL
L
I
O
1I
O
v
v
Sever loading effect Almost zero loading effect
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Chapter Fifteen
Applications and Design of
Integrated Circuits
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Passive and active filters
• Filters are building blocks of communication and instrumentations.
• The oldest technology based on inductors and capacitors are called passive LC filters, which are incompatible with any of the modern techniques for assembling electronic systems.
• Active-RC filters utilize op amp together with resistors and capacitors.
• At present, the most viable approach for realizing fully integrated monolithic filters is the switch capacitance techniques.
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Active filters
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Uses of the filters• Some of the uses are listed below:
• in electronic power supply ripple smoothing
• as tuned circuits in RF stages
• for selection of particular sideband as in SSB transmitters
• for harmonic frequency suppression in transmitters
• As wave trap for eliminating undesirable signal from radio and TV receivers• for improving high and low frequency response in video amplifier
• for restricting audio frequency band pass in SSB transmitters
• For eliminating undesirable frequency from motors, generators and other electrical and electronic equipment.
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One pole active filters• Usually, passive filters suffers from loading effects, substantially
reducing the maximum gain from the unity.• Loading effect can be reduced by using active filters.
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(cont.)
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(cont.)
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(cont.)
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There are number of ways to solve this problem; perhapsthe easiest is using the principle of superposition and virtual short concept.
To apply superposition we first reduce VI2=0
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(cont.)
Next, we reduce the VI1=0 and evaluate the corresponding output voltageVO2
R3 and R4 form a voltage divider. Therefore,
or
The superposition principle tells us that the output voltage VO is equal to the sum ofVO1 and VO2.
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What is the condition under which this circuit will act as a difference amplifier?
Let VI1=VI2 VO=0
Which is clearly that of a difference amplifier with a gain of R2/R1
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Differential input resistanceWe know the condition for difference amplifier
R1=R3 and R2=R4
V2-V1=
Since two input of the op amp track each other in potential, we may write a loop equation
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EX 9.7
For the difference amplifier shown in Fig. if R1 = R3 = 10 kR2 = 20 kand R4 = 21 kdetermine vo when (a) vI1 = +1 V, vI2 = -1 V, (b) vI1 = vI2 = +1 V,
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