ELEC207 Linear Integrated Circuits

ELEC207 Linear Integrated Circuits

Week 1 &2

Atef Abu Salim

Fall 2014/2015

University of Nizwa

Faculty of Engineering and Architecture

Electrical and Computer Engineering

TEXTBOOK Ramakant A, Gayakward, “Op-Amps and Linear Integrated Circuits”,

Prentice

Hall of India, New Delhi, 4th Edition

REFERENCES • Behzad Razavi, “Design of Analog CMOS Integrated

Circuits”, McGraw Hill,

• 2001

• D. Roy Choudhry, Shail Jain, “Linear Integrated Circuits”, New Age

• International Pvt. Ltd., 2000

INTRODUCTION

• We are living in an electronics age. We can say that the evolution of electronic

• components started from Vaccum tube Diodes through Transistors to Integrator

• Circuits.

• Integrated Circuit (IC)

• It is a miniature, low cost electronic circuit consisting of active (can amplify)

and

• passive components (can’t amplify, but attenuate) fabricated together on a

single

• crystal of semiconductor (silicon)

• Linear integrated circuit (Linear IC)

• It is a solid-state analog device characterized by a theoretically infinite number

of

• possible operating states. It operates over a continuous range of input levels.

• Note Digital IC has a finite number of discrete input and output states

Linear Amplifier

• When the output of the amplifier is a proportional change of the input, the

• amplifier is referred as a Linear amplifier

• For linear amplifier the input and output relationship can be given as

• Vout(t) = A Vin(t)

• where, A is a constant known as the amplifier gain.

Linear amplifier Non-Linear amplifier

Note When the output of the amplifier is not a proportional change of the

input, the amplifier is referred as Non-Linear amplifier

Operational Amplifier

• Op-amp is a Linear Integrated Circuit used to amplify DC as well as AC

signals

• and also in signal conditioning, filtering or to perform mathematical

• operations such as addition, subtraction, integration and differentiation.

741 OP-AMP Pin Diagram

Operational Amplifier

• An AC or DC voltage applied to the non-inverting terminal produces an

• in-phase (or same polarity) signal at the output

• An AC or DC voltage applied to the inverting terminal produces an 180°

• out-of-phase (or opposite polarity) signal at the output

• The input-output relationship of the op-amp is Vout = A (Vn – Vi)

• where, A is a constant known as the amplifier gain

OP-AMP Schematic Symbol

CHARACTERISTICS OF AN OP-AMP

• Input Resistance (Ri): Equivalent resistance that can be measured at either

• the inverting or non-inverting input terminal with the other terminal

• connected to the ground

• Output Resistance (Ro): Equivalent resistance that can be measured

• between the output terminal of the op-amp and the ground

• Voltage Gain: Ratio of the output voltage and the differential input voltage

i.e

CHARACTERISTICS OF AN OP-AMP

• Common-Mode Rejection Ratio (CMRR): Measure of rejection of unwanted

signals common to both the inputs. Ratio of differential gain (Ad) and the common

mode gain (Acm). Ad is very large so CMRR is also large

• Slew Rate (SR): Maximum rate of change of output voltage per unit of time. It

indicates how rapidly the output of an op-amp can change in response to changes in

the input frequency

• Gain-Bandwidth Product (GBP)/Closed-loop bandwidth/Unity gain

bandwidth: Bandwidth of the op-amp when the voltage gain is 1

CHARACTERISTICS OF AN IDEAL OP-AMP

• Infinite voltage gain A

• Infinite input resistance, so that any signal source can drive it and there is no loading of the preceding stage

• Zero output resistance, so that the output can drive an infinite number of other devices and so that it can supply as much current as necessary to the load

• Zero output voltage when input voltage is zero

• Infinite bandwidth so that any frequency signal from 0 to ∞ Hz can be amplified without attenuation. This ensures that the gain of the op-amp will be constant over the frequency range from DC (zero frequency) to infinite frequency. So op-amp can amplify DC as well as AC signals

Cont.

• Infinite common-mode rejection ratio (CMRR) so that the

output common mode noise voltage is zero

• Infinite Slew Rate so that output voltage changes occur

simultaneously with input voltage changes

COMPARISON: CHARACTERISTICS OF AN IDEAL OP-

AMP AND A REAL OP-AMP

OP-AMP Equivalent Circuit

Vo = A Vid = A(V+

– V-)

A = Vo/ Vid

• The output voltage is directly

proportional to the algebraic

difference between the two input

voltages.

• The op-amp amplifies the

difference between the two input

voltages and not the input voltage

itself.

• The polarity of the output voltage

depends on the polarity of the

difference voltage.

• Equivalent circuit is useful in

analyzing the basic operating

principles of Op-Amps

Vo =A Vid

IDEAL VOLTAGE TRANSFER CURVE

• Graphical representation of the equation Vo = A Vid is given by the Ideal

voltage transfer curve. Output Voltage is directly proportional to the input

difference voltage only until it reaches the saturation voltages and there after

output remains constant . In other words the output voltage never excess the

DC voltage supply of the Op-Amp

Representation of Op- Amp output

wave form

Voltage Transfer

Curve

Open loop Frequency Response of an

Operational Amplifier • From the frequency response curve we can see that the product of the gain against frequency is

constant at any point along the curve. Gain Bandwidth Product = Gain x Bandwidth or A x BW

A dB = 20 log10A From the graph gain of the amplifier at 100 KHz, is A = 20 dB 20 dB = 20 log10 A log10 A = 1; A = 101 = 10 GBP = 100KHz x 10 = 1 MHz Similarly, at 1KHz, A = 60 dB 60 dB = 20 log10A log10A = 3; A = 103 = 1000 GBP = 1KHz x 1000 = 1 MHz At 0 dB, it has Unity Gain 20 log10A = 0; A = 100 = 1 GBP = 1 MHz x 1 = 1 MHz

For feedback amplifiers constructed with op-amps, the two op-amp terminals

will always be approximately equal (V+ = V-)

This condition in op-amp feedback amplifiers is known as the “virtual short”.

This is to avoid saturation as gain of the amplifier is ideally infinitely large.

It appears that the two input terminals are shorted together ( Not shorted in

real. It is the feedback that enforces short). If a true short were present, then

current could flow from one terminal to the other. However, we know that the

input resistance of an op-amp is ideally Infinite and thus we know that the

input current into an op-amp is zero.

Conclusion from Virtual short Concept

The voltage difference between Non-inverting and Inverting terminal is zero

V+ = V-

The current into both Non-inverting and Inverting terminal is zero.

I+ = 0 and I- = 0

Concept of VIRTUAL SHORT

Concept of VIRTUAL SHORT

0)( 21

outout V

A

VVV

Applying the concept of a virtual short we can simplify the analysis of an op-amp feedback amplifiers

)( 21 VVAVout

0)( 21 VV

21 VV

Inverting Amplifier

Input is applied to the inverting terminal of Op-amp

Non-inverting terminal is grounded

Output voltage is out of phase with the input voltage by 180 degree or is of opposite

polarity

V0= - A Vin

Non-Inverting Amplifier

Input is applied to the non-inverting terminal of Op-amp

Inverting terminal is grounded

Output voltage is in phase with the input voltage or is of same polarity

V0= A Vin

A practical op-amp alone cannot be used as an amplifier with controlled gain and is limited to comparator applications. External resistors are therefore connected to the op-amp in a feedback arrangement to set the gain of the amplifier.

Analysis of INVERTING AMPLIFIER using the concept of VIRTUAL SHORT

in

F

in

out

F

out

in

in

F

out

in

in

Fin

Fin

R

R

V

VGain

R

V

R

V

VV

R

VV

R

VV

II

I

III

0

0

12

22

We know,

We know,

If RF= Rin,then Vout= -Vin

Analysis of NON-INVERTING AMPLIFIER using the concept of VIRTUAL

SHORT

22

2

2

21

1R

R

R

RR

V

VAGainVoltage

VRR

RVV

FF

in

out

out

F

in

Using Potential divider Rule:

EXAMPLES:

1. Find the closed loop gain of the following circuit.

2. If Rin is 10kΩ, what value of Rf is required to produce a non-inverting amplifier

with voltage gain of 25?

SOLUTION:

1. Find the closed loop gain of the following circuit.

2. If Rin is 10kΩ, what value of Rf is required to produce a non-inverting amplifier

with voltage gain of 25?

in

f

in

out

R

R

V

VGain

1010

100

k

k

R

RGain

in

f

kR

k

R

R

RGain

f

f

in

f

240

10125

1