Op-Amp

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Universal Collage Of Engineering And Technology
Subject Analog Electronics
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Topic BASICS OF OP-AMP
ELECTRICAL 3RD SEM
DIVC GROUP7

• EN.NO

• NAME

• 130460109006
• 130460109013
• 130460109034
• 130460109043

• Jay Bhavsar
• Yagnik Dudharejiya
• JAY Pandya
• Darshan Patel

Guidance by Prof. Kapil Dave
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FLOW OF PRESENTATION

• Symbol of op-amp
• Analyze of op-amp circuit
• Packages of op-amp
• Pin configuration of op-amp
• Applications of op-amp
• Frequency response of op-amp
• Design of op-amp
• Power supplies of op-amp

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SYMBOL OF OP-AMP
Circuit symbol of an op-amp

• Widely used
• Often requires 2 power supplies V
• Responds to difference between two signals

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IDEAL OP-AMP

• Characteristics of an ideal op-amp
• Rin infinity
• Rout 0
• Avo infinity (Avo is the open-loop gain,
  sometimes A or Av of the op-amp)
• Bandwidth infinity (amplifies all frequencies
  equally)

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MODEL OF AN IDEAL OP-AMP
I
V

Vout A(V - V-)
I-
V-
-

• Usually used with feedback
• Open-loop configuration not used much

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SUMMARY OF OP-AMP BEHAVIOR
Vout A(V - V-) Vout/A V - V- Let A
infinity then, V -V- 0
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SUMMARY OF OP-AMP BEHAVIOR
V V- I I- 0
Seems strange, but the input terminals to an
op-amp act as a short and open at the same time
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TO ANALYZE AN OP-AMP CIRCUIT

• Write node equations at and - terminals (I
  I- 0)
• Set V V-
• Solve for Vout

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PACKAGES OF OP-AMP

• Types of Packages
• Small scale integration(SSI)lt10 components
• Medium Scale integration of op-amp(MSI)lt100
  components
• Large scale integration (LSI)gt100 components
• Very large scale integration (VLSI)gt1000
  components

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ANALYSIS OF INVERTING CONFIGURATION
I2
I1 (Vi - V- )/R1 I2 (V- - Vo)/R2 set I1 I2,
(Vi - V-)/R1 (V- - Vo)/R2 but V- V 0 Vi /
R1 -Vo / R2 Solve for Vo Vo / Vi -R2 / R1
I1
Gain of circuit determined by external components
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INTEGRATED CIRCUIT PACKAGE

• TYPES
• The flat pack
• Metal can or Transistor Pack
• The duel-in-line packages(DIP)

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INVERTING CONFIGURATION
Very popular circuit
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APPLICATIONS OF THE INVERTING CONFIGURATION
Current in R1, R2, and R3 add to current in
Rf (V1 - V-)/R1 (V2 - V-)/R2 (V3 - V-)/R3
(V- - Vo)/Rf Set V- V 0, V1/R1 V2/R2
V3/R3 - Vo/Rf solve for Vo, Vo -Rf(V1/R1
V2/R2 V3/R3) This circuit is called a weighted
summer
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PIN CONFIGURATION OF OP-AMP
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APPLICATIONS

• As a integrator
• As a differentiator

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INTEGRATOR( Applications of the inverting
configuration)
I2
I1 (Vi - V-)/R1 I2 C d(V- - Vo)/dt set I1
I2, (Vi - V-)/R1 C d(V- - Vo)/dt but V- V
0 Vi/R1 -C d(Vo)/dt Solve for Vo Vo -(1/CR1)(
? Vi dt)
I1
Output is the integral of input signal. CR1 is
the time constant
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TRANSIENT RESPONSE OF AN INTEGRATOR
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NON-INVERTING CONFIGURATION
(0 - V-)/R1 (V- - Vo)/R2 But, Vi V V-, ( -
Vi)/R1 (Vi - Vo)/R2 Solve for Vo, Vo
Vi(1R2/R1)
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BUFFER AMPLIFIER
Vi V V- Vo Vo Vi
Isolates input from output
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ANALYZING OP-AMP CIRCUITS
Write node equations using V V- I I-
0 Solve for Vout Usually easier, can solve
most problems this way.
Write node equations using model, let A
infinity Solve for Vout Works for every
op-amp circuit.
OR
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INPUT RESISTANCE OF NONINVERTING AMPLIFIER
Rin Vin / I, from definition Rin Vin /
0 Rin infinity
V-
I
V
V
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INPUT RESISTANCE OF INVERTING AMPLIFIER
Rin Vin / I, from definition I (Vin -
Vout)/R I Vin - A (V - V-) / R But V
0 I Vin - A( -Vin) / R Rin VinR / Vin
(1A) As A approaches infinity, Rin 0
I
V-
V
Vout A(V - V-)
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SUMMARY OF OP-AMP BEHAVIOR
Non-inverting configuration
Inverting configuration
Rin 0 at this point
Vo/Vi 1R2/R1 Rin infinity
Vo /Vi - R2/R1 Rin R1
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DIFFERENCE AMPLIFIER
Use superposition, set V1 0, solve for Vo
(non-inverting amp) set V2 0, solve for Vo
(inverting amp)
Fig. A difference amplifier.
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DIFFERENCE AMPLIFIER
Vo1 -(R2/R1)V1
Vo2 (1 R2/R1) R4/(R3R4) V2
Add the two results Vo -(R2/R1)V1 (1
R2/R1) R4/(R3R4) V2
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DESIGN OF DIFFERENCE AMPLIFIERS
Vo -(R2/R1)V1 (1 R2/R1) R4/(R3R4)V2
For Vo V2 - V1 Set R2 R1 R, and set R3 R4
R For Vo 3V2 - 2V1 Set R1 R, R2 2R,
then 3R4/(R3R4) 3 Set R3 0
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INPUT RESISTANCE OF DIFFERENCE AMPLIFIERS
When measuring Rin at one input, ground all
other inputs. Rin at V1 R1, same as inverting
amp Rin at V2 R3 R4
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IMPROVING THE INPUT RESISTANCE OF AMPLIFIERS
Add buffer amplifiers to the inputs Rin
infinity at both V1 and V2
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MAGNITUDE RESPONSE OF SINGLE CAPACITOR CIRCUIT
where w0 1/RC
(a) Magnitude response of (single time constant)
STC networks of the low-pass type.
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OPEN-LOOP FREQUENCY RESPONSE OF OP-AMP
Open-loop gain at low frequencies
Break frequency(bandwidth), occurs where Ao
drops 3dB below maximum
Unity gain frequency, occurs where Ao 1 (A
0dB)
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FREQUENCY RESPONSE OF OP-AMP CIRCUITS

• Open-loop op-amp
• Inverting and non-inverting amplifiers
• Low-pass filter
• High-pass filter

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FREQUENCY RESPONSE OF OPEN-LOOP OP-AMP
Open-loop op-amp ft Ao fb where Ao is gain
of op-amp
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FREQUENCY RESPONSE OF INVERTING AND NON-INVERTING
AMPLIFIERS
Inverting or noninverting amplifier ft A fb,
where A gain of circuit
- 20 dB/dec
A - R2 / R1, inverting A 1 R2/R1,
non-inverting
A
ft
fb
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FREQUENCY RESPONSE OF LOW-PASS FILTER
A - Z2 / Z1
Z2
Z1

• At large frequencies A becomes zero.
• Passes only low frequencies.

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FREQUENCY RESPONSE OF LOW-PASS FILTER
Low-pass filter C acts as a short at
high frequencies, gain drops to zero at high
frequencies, ft A fb. fb 1/2pR2C
Due to external Due to
- 20
fb
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FREQUENCY RESPONSE OF HIGH-PASS FILTER
A - Z2 / Z1
Z2
Z1

• At large frequencies A becomes - R2 / R1.
• Passes only high frequencies.

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FREQUENCY RESPONSE OF HIGH-PASS FILTER
High-pass filter C acts as an open at
low frequencies, gain is zero at low
frequencies,
Due to external capacitor Due to op-amp
fL 1/2pR1C
bandwidth
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DESIGN OF A HIGH-PASS FILTER
Design the circuit to obtain High-frequency Rin
1KW High-frequency gain 40dB lower 3 dB
frequency 100Hz

• Rin R1 1/sC. At high frequencies, s becomes
  large, Rin ? R1. Let R1 1KW
• A - R2 / (R1 1/sC). At high frequencies, s
  becomes large, A ? - R2 / R1 .
• A 40dB 100, 100 R2 / 1KW, R2
  100KW.
• fL 1/2pR1C C 1/2p R1 fL, C 1/2p(1KW)100
  1.59mF

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DESIGN OF A HIGH-PASS FILTER
20 DB/DECADE (DUE TO CAPACITOR)
-20 DB/DECADE (DUE TO OP-AMP)
FL 100HZ
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OUTPUT OF HIGH-PASS FILTER IN EXAMPLE
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BANDPASS FILTER

• Both C2 and C1 act as shorts at high
  frequencies.
• C2 limits high-frequency gain
• C1 limits low-frequency gain
• The gain at midrange frequencies - R2 / R1
• fL 1/2pR1 C1
• fH 1/2pR2 C2

-20 dB/decade (due to C2)
bandwidth
fL
fH
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LARGE-SIGNAL OPERATION OF OP-AMPS

• Saturation
• Input must be small enough so the output remains
  less than the
• supply voltage.
• Slew rate
• Maximum slope of output voltage. Response time of
  op-amps are
• described by a slew rate rather than a delay.

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TYPES OF POWER SUPPLY

• PSRR(Power supply rejection ratio)
• CMRR(Common mode rejection ratio)

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PSRR

• Definition
• The change in an op-amp input
  offset voltage (Vios) caused by variation in the
  supply voltage and it is called as power supply
  rejection ratio.
• It is also called a SVRR, AND PSS.
• Equation
• PSRRVios/v
  

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CMRR

• Definition
• It is the ratio of common mode gain
  and differential gain.
• Equation Vcm(V1V2)/2
• VoAdVdAcmVcm
• Where AdDifferential gain and
• Vcm Common mode gain
• CMRR(Acm/Ad)
• Final equation
• VoV1-V2Vcm/CMRRAd

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REFERENCE

• www.google.com
• 1. Op-Amp and Linear integrated Circuit
  technology- Ramakant A Gayakwad, PHI Publication
• 2. Digital Fundamentals by Morris and Mano, PHI
  Publication
• 3. Micro Electronics Circuits by
  SEDAR/SMITH.Oxford Pub F.COUGHLIN, FREDERICK F.
  DRISCOLL
• 4. Operational Amplifier and Linear integrated
  Circuits By K.LAL kishore.
• 5. Fundamentals of Logic Design by Charles H.
  Roth Thomson

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• Thank you ?