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Analog Electronics

Section 2Prof. Dr. Murat Aşkar

D-211E-mail: askar@eee.metu.edu.tr

Web: www.eee.metu.edu.tr/~askar

Analog and Digital Signals

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Analog Signals are links to the real world

Transreceiver

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Bio-eng: Neuronal implants

Linear Amplifiers (1)Multiply amplitude of a signal by a constant scalar quantity

xo(t) = A xi(t)

Non-scalar or non-uniform amplification is called distortion

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Linear Amplifiers (2)• Symbol for a single-ended

input linear voltage amplifier.

• Ideally provides linear voltage gain regardless of the amplitude of the input signal

• Real amplifiers have powersupplies that limit theamplitude of the output

• If input is too large, outputclamps

Transfer Characteristics (1)Plot of amplifier output versus amplifier input

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Transfer Characteristics (2)

• Gain = Slope• To operate amplifier in its linear region, the input

must be kept small enough

Real Transfer Characteristics

• Each circle represents a different DC component for the input and output signals – called an operating point

• Location of operating point has an effect on• input signal range• amplifier gain magnitude• amount of distortion

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Operating Point (1)Voltage gain, output DC voltage, allowable input magnitude range are affected

Operating Point (2)

Derivative of transfer characteristic gives measure of amplifier gain linearity (and distortion)

Input and output signal amplitude ranges are maximized when operating point is near middle of linear region

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Signal Convention (1)• DC magnitudes in uppercase symbol and

subscript– Example: ID, VD

• Ac signal quantities in lowercase symbol & subscript

– Example: id(t), vd(t)• Total DC + ac signal quantities in lowercase

symbol, uppercase subscript– Example: iD(t), vD (t)

Signal Convention (2)In general

vD(t) = VD + vd(t)

iC(t) = IC + ic(t)

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Superposition• If the amplifier is linear, superposition can be

applied. Each component can be determined seperately.

• Determine the DC magnitude of the output using DC model (i.e capacitors are open circuited, inductors are short circuited)

– Example: IO, VO

• Determine the ac signal component of the output using the ac model (i.e., DC sources are killed and capacitors are short circuited, inductors are open circuited) as

– Example: vo(t) = Av vi(t)

Amplifier Classification

CurrentCurrentCurrent

TransresistanceVoltageCurrent

TransconductanceCurrentVoltage

VoltageVoltageVoltage

TypeOutputInput

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+vi

-

+vo

-

Ideal Voltage Amplifier

Avi

+

RoAvi

+vi-

+vo-

Ri

+

Real Voltage Amplifier

Loaded Ideal Voltage Amplifier

Avi

+vi-

+vo-

+RL

Rsvs

+

Avv

s

o =

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Loaded Voltage Amplifier

RoAvi

+vi-

+vo-

Ri

+RL

Rsvs

+

Lo

L

is

i

s

oRR

RRR

RAv

v++=

Ideal Current Amplifier

Real Current Amplifier

Aii

ii io

Aii

ii ioRi Ro

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Loaded Ideal Current Amplifier

Aii

s

o =

Aii RL

iiRsis

io

Loaded Current Amplifier

Aii RL

iiRSis

ioRi Ro

Lo

o

is

s

s

oRR

RRR

RAi

i++=

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To determine Input Resistance Ri

RoAvi

+vi-

+vo-

Ri

+• Apply input voltage vi

(or input current ii) • Determine the input

current ii (or input voltage vi)

ThenRi = vi / iiAii

ii ioRi Ro

ii

+vi-

Voltage Amplifier

Current Amplifier

To determine Output Resistance Ro

RoAvi

+vi-

+vx-

Ri

+• Kill the input signal

(set vi or ii to zero)• Apply a test voltage

vx to the output node• Determine the current

ix that the source delivers to the circuit

ThenRo = vx / ix

Aii

ii ixRi Ro

ii

+vi-

Voltage Amplifier

Current Amplifier

+vx-

ix