Download chapter 1 operational amplifier

Analogue Electronic 2
EMT 212
Chapter 1
Operational Amplifier
By
En. Rosemizi B. Abd Rahim
1
1.0 Operational Amplifier
 1.1 Introduction
 1.2 Ideal Op-Amp
 1.3 Op-amp input modes
 1.4 Op-amp Parameters
 1.5 Operation
Single-mode
 Differential-mode
 Common-mode operation
 1.6 Op-Amps basics

 1.7 Datasheet
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1.1 Introduction
Typical IC packages
IC packages placed on circuit board
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1.1 Introduction
Uses of Op-Amp
 To provide voltage amplitude changes




(amplitude and polarity)
Comparators
Oscillators
Filter circuits
Instrumentation circuits
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1.1 Introduction
Definition
 The operational amplifier or op-amp is a circuit of
components integrated into one chip.
 A typical op-amp is powered by two dc voltages and has
an inverting(-) and a non-inverting input (+) and an output.
 Op-amps were used to model the basic mathematical
operations ; addition, subtraction, integration,
differentiation etc in electronic analog computers.
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1.1 Introduction
 Two Power Supply


+V : Positive PS
-V : Negative PS
 One Output Terminal
Op-amp schematic symbol
 Two Input Terminal


Inverting input
Non-inverting input
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1.2 Ideal Op-Amp
Practical Op-Amp
Ideal Op-Amp
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1.2 Ideal Op-Amp
Properties
Practical Op-Amp
Ideal Op-Amp
 input impedance 500k-2M
 Infinite input impedance
 output impedance 20-100 
 Zero output impedance
 open-loop gain (20k to 200k)
 Infinite open-loop gain
 Bandwidth limited (a few kHz)
 Infinite bandwidth
 noise contribution
 Zero noise contribution
 Non-zero DC output offset
 Zero DC output offset
 Both differential inputs stick
together
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1.2 Ideal Op-Amp
 Infinite Input Impedance
 Input impedance is measured across the input
terminals
 It is the Thevenin resistance of the internal connection
between the two input terminals.
 Input impedance is the ratio of input voltage to input
current.
Zi=(Vi/Ii)
 When Zi is infinite, the input current is zero.
 the op amp will neither supply current to a circuit nor
will it accept current from any external circuit.
 In real, the resistance is 500k to 2M
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1.2 Ideal Op-Amp
 Zero Output Impedance

Looking back into the output terminal, we see voltage
source with an internal resistance.

The internal resistance of the op-amp is op-amp output
impedance


This internal resistance is in series with the load, reducing
the output voltage available to the load
Real op-amps have output impedance in the range 20100  .
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1.2 Ideal Op-Amp
Vout  AvVin
 Infinite Open-Loop Gain
 Open-Loop Gain, A is the gain of the op-amp
without feedback.
 In the ideal op-amp, A is infinite
 In real op-amp is (20k to 200k)
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1.2 Ideal Op-Amp
 Infinite Bandwidth

The ideal op-amp will amplify all signals from DC to the
highest AC frequencies

In real op-amps, the bandwidth is rather limited


This limitation is specified by the Gain-Bandwidth product,
which is equal to the frequency where the amplifier gain
becomes unity
Some op-amps, such as 741 family, have very limited
bandwidth up to a few kHz
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1.2 Ideal Op-Amp
 Zero Noise Contribution

in an ideal op amp, all noise voltages produced
are external to the op amp. Thus any noise in the
output signal must have been in the input signal as
well.

the ideal op amp contributes nothing extra to the
output noise.
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1.2 Ideal Op-Amp
 Zero Output Offset

The output offset voltage of any amplifier is the output
voltage that exists when it should be zero.

The voltage amplifier sees zero input voltage when both
inputs are grounded. This connection should produce a
zero output voltage.

If the output is not zero then there is said to be an
output voltage present.

In the ideal op amp this offset voltage is zero volts, but
in practical op amps the output offset voltage is nonzero.
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1.2 Ideal Op-Amp
 Both Differential Inputs Stick Together

this means that a voltage applied to one inverting
inputs also appears at the other non-inverting inputs.

If we apply a voltage to the inverting input and then
connect a voltmeter between the non-inverting input
and the power supply common, then the voltmeter will
read the same potential on non-inverting as on the
inverting input.
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1.3 Op-Amp input Modes
 Single-Ended input mode
input signal is connected to one input and the other input is
grounded.

input signal at +ve terminal
 output same polarity as
the applied input signal
 input signal at –ve terminal
 output opposite in phase
to the applied input signal
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1.3 Op-Amp input Modes
 Differential mode input
two out-of-phase signals are applied with the difference
of the two amplified and produced at the output.
Vout  AdVd
Vd  Vin1  Vin2
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1.3 Op-Amp input Modes
 Common mode input
two signals of same phase, frequency, and amplitude are applied
to the inputs which results in no output (signals cancel).
Practically, a small output signal will result.
 This is called common-mode rejection. This type of mode is
used for removal of unwanted noise signals.
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1.4 Op-Amp Parameters
 Common-Mode Rejection Ratio (CMRR)


The ability of amplifier to reject the common-mode signals
Ratio of open-loop gain to common-mode gain
CMRR 
Aol
Acm
A 
CMRR  20 log  ol 
 Acm 
 The higher the CMRR, the better

open-loop gain is high and common-mode gain is low.
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1.4 Op-Amp Parameters
 Common-Mode Input Voltage

The range of input voltages which, when applied to the both
inputs, will not cause clipping or other output distortion.
 Input Offset Voltage


The differential dc voltage required between the inputs to
force the output to zero volts.
Range between 2 mV
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1.4 Op-Amp Parameters
 Input Bias Current


The dc current required by the inputs of the amplifier to
properly operate the first stage.
Is the average of both input currents
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1.4 Op-Amp Parameters
 Input Impedance



Is the total resistance between the inverting and noninverting inputs.
Differential input impedance is measured by the changes of
differential input voltage over changes of bias current.
Common-mode input impedance is measured by the
changes of common-mode input voltage over changes of
bias current.
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1.4 Op-Amp Parameters
 Input Offset Current

Is the different of input bias currents
Input offset current
I os  I1  I 2
offset voltage
Vos  I1Rin  I 2 Rin  I1  I 2 Rin
Vos  I os Rin
error
Vout( error)  Av I os Rin
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1.4 Op-Amp Parameters
 Output Impedance

Is the resistance viewed from the output terminal of the opamp.
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1.4 Op-Amp Parameters
 Slew Rate

Is the maximum rate of change of the output voltage in
response to a step input voltage.
Vout
t
Vout  Vmax  (Vmax )
SlewRate 
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1.4 Op-Amp Parameters
 Example
Determine the slew rate
SlewRate 
Vout
t
SlewRate 
 9V  (9V )
 18V / s
1s
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1.5 Operation
Differential Amplifier Circuit
Basic amplifier circuit
 If an input signal is applied to either input with the other input is
connected to ground, the operation is referred to as ‘single-ended.’
 If two opposite-polarity input signals are applied, the operation is referred
to as ‘double-ended.’
 If the same input is applied to both inputs, the operation is called
‘common-mode.’
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1.5 Operation
Differential Amplifier Circuit
DC bias of differential amplifier circuit
DC Analysis
 VBE  I E RE  VEE  0
IE 
VEE  VBE
RE
I c1  I c2 
IE
2
IE
Vc1  Vc2  Vcc  I c Rc  Vcc  Rc
2
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1.5 Operation
Differential Amplifier Circuit
Example
Solution
IE 
VEE  VBE
RE
IE 
9V  0.7V
 2.5mA
3.3k
I c1  I c2 
• Calculate the dc voltages and
currents
I E 2.5m

 1.25mA
2
2
Vc  Vcc  I c Rc
Vc  9V  (1.25m)(3.9k )  4.1V
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1.5 Operation
Differential Amplifier Circuit
AC Analysis
 Single-Ended
AC connection of differential
amplifier
AC equivalent of differential amplifier
circuit
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1.5 Operation
Differential Amplifier Circuit
AC Analysis
 Single-Ended
connection to calculate
Av1 = Vo1 / Vi1
AC equivalent circuit
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1.5 Operation
Differential Amplifier Circuit
AC Analysis - Single ended
 KVL

Scan figure 10.11 & 10.15
Vi1  I b ri  I b ri  0
Vi1
Ib 
2ri
I c  I b  
Partial circuit for calculating Ib
1   2  
ri1  ri2  ri
I b1  I b2  I b
Vo  I c Rc  
Vi1
2ri
Vi1
2ri
Rc 
Rc
Vi
2re
1
Vo Rc
Av 

Vi1 2re
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1.5 Operation
Differential Amplifier Circuit
Example
Solution
V  0.7V 9V  0.7V
I E  EE

 193A
RE
43k
IC 
IE
 96.5A
2
Vc  Vcc  I c Rc
Vc  9  (96.5 )( 47k )  4.5V
 9V  (96.5A)( 47k)  4.5V
Calculate the single-ended output
voltage Vo1
ri1  ri2  20k
1  2  75
re 
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 269
0.0965
Av 
Rc
47 k

 87.4
2re 2(269)
Vo  AvVi  (87.4)(2m)  0.175
V
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1.5 Operation
Differential Amplifier Circuit
AC Analysis - Double ended
A similar analysis can be used to show that for the condition of
signals applied to both inputs, the differential voltage gain
magnitude is
Ad 
Vo Rc

Vd
2ri
Vd  Vi1  Vi 2
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1.5 Operation
Differential Amplifier Circuit
AC Analysis - Common-mode
Common-mode connection
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1.5 Operation
Differential Amplifier Circuit
AC Analysis - Common-mode
V  2(   1) I b RE
Ib  i
ri
Ib 
Vi
ri  2(   1) RE
Vi Rc
Vo  I c Rc  I b Rc 
ri  2(   1) RE
V
Rc
Av  o 
Vi ri  2(   1) RE
1
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1.6 Op-Amp Basics
 Basic Op-Amp
 Op-amp equivalent circuit
practical
ideal
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1.6 Op-Amp Basics
 Basic Op-Amp - Constant-gain multiplier
input voltage at minus
output voltage opposite in phase
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1.6 Op-Amp Basics
 Basic Op-Amp - Constant-gain multiplier
Op-amp ac equivalent circuit
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1.6 Op-Amp Basics
 Basic Op-Amp - Constant-gain multiplier
Ideal Op-amp equivalent circuit
Redrawn equivalent circuit
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1.6 Op-Amp Basics
 Basic Op-Amp - Constant-gain multiplier
Vi  Vi1  Vi 2 
Vi 
Vi 
Using Superposition theorem
i) V1 only (set –AvVi =0)
Rf
Vi1 
V1
R1  R f
ii) –AvVi only (set V1 =0)
Vi 2 
R1
 AvVi 
R1  R f
Rf
R1  R f
Rf
R f  (1  Av ) R1
Rf
V1 
R1
 AvVi 
R1  R f
V1
V1
Av R1
R f V1
Vo  AvVi  Av R f V1



Vi
Vi
Vi Av R1
R1 Vi
Rf
Vo

V1
R1
Shown that the ratio i/o depends only on
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the value of Rf and R1
1.6 Op-Amp Basics
 Basic Op-Amp - Unity Gain
Rf
Vo

V1
R1
If Rf = R1
Vo
 1
V1
Shown that the output voltage equal to input voltage
with 180º phase inversion.
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1.6 Op-Amp Basics
 Basic Op-Amp - Constant Magnitude Gain
Rf
Vo

V1
R1
If Rf = 10R1
Vo
 10
V1
Shown that the output voltage equal to 10x input
voltage with 180º phase inversion.
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1.7 Data Sheet
LM741
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1.7 Data Sheet
LM741
45
1.7 Data Sheet
LM741
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1.7 Data Sheet
LM741
47
1.7 Data Sheet
LM741
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1.7 Data Sheet
LM741
49