Unit 1 Amplifiers

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Unit 1:

Amplifiers


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Differential Amplifier

is a type of electronic amplifier that multiplies the difference between twoinputs by some constant factor (the differential gain).

is the basic building block of operational amplifiers.

A Schematic Symbol of aDifferential Amplifier

where:Vs+ and Vs_= supply voltagesA= amplifier gainV

+= non-inverting input

V_ = inverting input


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Basic Differential Amplifier Circuit

DC Bias


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Example page 651

Calculate the dc voltages and currents in the circuit below.


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Single-Ended AC Voltage Gain

AC Equivalent


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Double-Ended AC Voltage Gain

AC Equivalent

21

2

iidid

od

VVV

r

Rc

V

VA

where:Ad= Differential Mode Gain


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Common-Mode Operation

Common-Mode ConnectionAC Circuit in Common-Mode Connection

Ei

C

i

oC

Rr

R

V

VA

12


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Example page 656

Calculate the common-mode gain for the amplifier circuit shown below.

1= 2=75ri1

= ri2= ri

=20k


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Use of ConstantCurrent Source

Differential Amplifier with constant-current source AC Equivalent

EiC

i

oC

Rr

R

V

VA

12


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Example page 657

Calculate the common-mode gain for the differential amplifier in the circuit below.

1= 2= =75ri1

= ri2= ri

=11k

Q3

ro=200k3=75


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Infinite input impedance

Infinite open-loop gain

High Common Mode Rejection Ratio (CMMR)

Differential input voltage is zero

Zero output impedance

Infinite Bandwidth

Characteristics of an Ideal op-amp


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Inverting Amplifier-is a constant gain amplifier circuit.

Example Page 685

If the circuit above has R1=100k and Rf=500k, what output voltage resultsfor an input of V1=2V?

VV

k

kV

R

RVo

f10)2(

100

5001

1


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Noninverting Amplifier-is a constant gain amplifier circuit.

Example Page 686

If the circuit above has R1=100k and Rf=500k, what output voltage resultsfor an input of V1=2V?


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Example page 716

Calculate the output voltage from the circuit below for an input of 120V.

240k

2.4k +16V

-16V


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Example page 717

Show the connection of an LM124 quad op-amp as a three-stageamplifier with gains of +10, -18 and -27. Use 270-k feedback resistor for

all three circuits. What output voltage will result for an input of 150V?


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Example page 718

Show the connection of three op-amp stages using an LM348 IC toprovide outputs that are 10, 20 and 50 times larger than the input. Use a

feedback resistor of Rf=500k

in all stages.


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Example

5V

10

3mA

1M

100k

20k

1k+ v

x-

100

1M

100


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Voltage Summing Amplifier

33

f2

2

f1

1

fo V

R

RV

R

RV

R

RV

The output is the sum of individual signals times the gain:

The summing amplifier is used to add the voltages.Since the input resistance is very large V1=V2=0, therefore


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Example Page 720

Calculate the output voltage for the circuit of the figure below. The inputsare V1= 50mV sin(1000t) and V2=10mV sin(3000t).

330k

33k

10k

+9V

-9V

741

4

56

11

10


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Subtractor Amplifier

21

22

41

2

42

31

3

VVVo

RRandRRif

VR

RV

R

RR

RR

RVo

4231

-is used to subtract two voltages.

Vo

V2

V1

113

22

22

113

VRR

RfRV

R

RVo

VR

RV

R

R

R

RVo

ff

fff


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Example page 721Determine the output for the circuit below with the components Rf=1 M, R1=100k,R2=50k and R3=500k.


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Example page 721Determine the output voltage for the circuit shown below.

Vo

100k100k

20k

20k Vo741


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Example 7-15 page 279

In the circuit of Figure 1, R1CF= 1 second and the input is a step (dc) voltageas shown in Figure 2. Determine the output voltage and sketch it. Assume thatthe op-amp is initially nulled.

Figure 1

Figure 2


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Differentiator Amplifier

frequencylimitinggainCRCR

f

0dBisgainthewhichatfrequencyCR

f

dt

tdvRCtv

FFb

Fa

o

,2

1

2

1

,2

1

)()(

11

1

1

-is used to produce a voltage output proportional to the input voltage's rate of change-is used in waveshaping circuits to detect high frequency components in an input signaland also as a rate-of-change detector in FM modulators.

Input-output waveforms


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Precision Rectifier

Why?

Signals of few millivolts (peak)

High open loop gain Rectifier output same as input


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Precision Rectifier

Precision Half-wave rectifier


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Precision Rectifier

Precision Full-wave rectifier

Vi


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Example page 728


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Example page 728

Calculate the output voltage expression for the instrumentation amplifier circuitgiven below. Assume that all resistors are 5k.


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Log AmplifierA logarithmic amplifier has an output voltage that is proportional to the logarithmof the input.

Logarithmic Amplifier circuit

ampopofcurrentbiasinput

VR

I

VR

i

c

i

_____

ma x

ma x

ma x

1

1

The capacitor across the npn transistor is used to reduce the ac gain.

The diode protects the transistor against excessive reverse base-to-emitter voltage.

Resistor R1 is determined by the inequality pair

VBE = A log (Ic)


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Multiplication of two input signals using log and antilog amplifier

log (AB) = log A + log B

log (A/B) =log A - log B

B i M lti li Ci it


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Basic Multiplier Circuitry

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Unit 1 Amplifiers