Operational Amplifier II & III

8/8/2019 Operational Amplifier II & III

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JORDAN UNIVERSITY OF SCIENCE AND TECHNOLOGY

Operational Amplifier II & III

Measurements and Dynamics Lab

Hasan Sami Toubasi 20070025074

Due to Nov 1st/2010

This paper reports the experiment taken on Oct 25th/2010

Fall Semester 2010/2011 Section of Monday


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Objectives1. To introduce the most important types ofoperational amplifier (op-amp for

short), inverting and non-inverting amplifiers.

2. To find applications as buffers (load isolators) (follower), subtractors,integrators, anddifferential amplifiers.

3. To construct buffers (load isolators) (follower), subtractors, integrators, anddifferential amplifiers, andsee theoutput ofthem on an oscilloscope.

4. To befamiliarwith theoutput resultsofa different typesofOP-AMP.

TheoryAn amplifier has an input port and an output port. (A port consists of two

terminals, one of which is usually connected to the ground node.) In a linear

amplifier, theoutput signal = Av input signal, where A is the amplification factoror "gain". Depending on the natureof the input andoutput signals, wecan havefourtypesof amplifier gain: voltage gain (voltageout / voltage in), current gain (current

out / current in), transresistance (voltage out / current in) and transconductance(current out / voltage in). Since most op-amps are used as voltage-to-voltage

amplifiers, wewill limit thediscussion here to this typeofamplifier.

The amplifier model shown in - Fig (1) - showing the standard op-amp

notation. An op-amp is a differential-to-single-ended amplifier, i.e., it amplifies thevoltage differenceVp Vn = Vi at the input port and produces a voltageVo at the

output port that is referenced to the ground nodeofthecircuit in which theop-amp isused.

Vi

Ri

AVi

Ro

Vo

+

_

+

_

+

_

Vp

Vn

ip

in

+

_

Vi

AViV

+

_

+

_

+

_

Vp

Vn

+

_

a) Standardo p-amp b) Ideal op-amp

Fig (1): amplifier model.

The ideal o p-amp model was derived to simplify circuit analysis and it is

commonly used by engineers for first-order approximate calculations. The idealmodel makes threesimplifying assumptions:

Gain is infinite:A = gInput resistance is infinite:Ri = gOutput resistance is zero:Ro= 0


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VinR2

R1

Vout+

_

Vp

Vn

I

i

Vout

+

_

Vp

Vn Vi

R2R1

Vout+_

VnVp

I

Vin

Vout

A=1

Vi

Vout

A>=1

Vin

Vout

A


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Vin

Vout

A=1

-

r

+Vpower

Vin

Vout

A=1

-Vpower

+Vpower


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Vin

R2R1

Vout+_

VnVp

C

amplifier by letting R1= g and R2 = 0 in in ut R

R

1

21 . The voltagetransfercurve

is shown in Fig (3-b). A frequently as ed question is why the voltage follower is

useful, since it just copies input signal to the output. The reason is that it isolates the

signal source and the load. We know that a signal source usually has an internal

series resistance. When it is directly connected to a load, especially a heavy (highconductance) load, the output voltage across the load will degrade (according to the

voltage-divider formula). With a voltage-follower circuit placed between the sourceand the load, the signal source sees a light (low conductance) load -the input

resistance of the o p-amp. At the same time, the load is driven by a powerful drivingsource- theoutputoftheop-amp.

I a By adding a capacitorin parallelwith thefeedback resistorR2in an inverting

amplifier asshown in Fig (5), theop-amp can beused to perform integration. An ideal

or lossless integrator (R2= g) performs the computation

dtCR

inout

1

1

. Thus, a

square-wave input would cause a triangle-wave output. However, in a real circuit

(R2 < g) there is some decay in the system state at a rate proportional to the stateitself. Thisleadstoexponential decay with a timeconstantofX= R2C.

Fi 5 integrator Amplifier.

Di iaBy adding a capacitor in series with the input resistor R1 in an inverting

amplifier as shown in Fig (6) below, the op-amp can be used to perform

differentiation. An ideal differentiator (R1

= 0) has no memory and performs thecomputation

dt

d

CRin

!

ut 2! . Thus a triangle-wave input would cause a square-

wave output. However, a real circuit (R1 > 0) will have some memory of the system

statewith exponential decay oftimeconstantX= R1C.


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Fig (6): Differentiator Amplifier.

Experiment l setup & Procedure1. OP-AMP

2. AC powersupply (variablefrequency )

3. Variablecapacitor

4. Variable resistor

5. Oscilloscope.

Now, Procedure

Integr tor circuit OP-AMP

1) Assemble the integrator circuit as shown in the data sheet using 9990nfcapacitorshunt with 100K resistors; (the resistors isused here tostabilize

the integrator). For the input resistanceuses 10K resistor.

2) Apply a sinusoidal wave (170Hz freq.) to the input. Display both input and

output on theoscilloscope. (Usescale 1V/D for input, 10mV/D foroutput,

and 2mS/D for the timescale).

3) Sketch the input andoutput waveform .observe the phaseshift.

4) Repeat step 2 and 3 above forsquare and triangularwaves as input to the

integrator.

Differenti tor mplifier1) Assemble thedifferentiatorcircuit using 9990nfcapacitorwith 1K resistor.

2) Apply a 100Hz sinusoidal signal to the input and measure the gain of the circuit

(use 1V/D for input and 5V/D foroutput, and 2 mS/D for time).

3) Record the gain of the circuit. For frequency in the range (50 Hz ~ 400Hz) and

for three valuesofthe resistances 0.5, 1.5 K, andobserve theclipping.4) Check the processofdifferentiation for both triangle andsquarewaves.

5) Set up thedifferentiatorfor (R2 =100), input scale andoutput scale in (mv/D).

Volt ge follower circuit1) Construct the Voltage Followercircuit as in Fig (2-b).


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2) Measure and record theinput and outputimpedanceofthis amplifier

3) Measurethe gain and record it

4) Plotthe gain vs.theinputfrequency

Da a, Cal la i R l

I a i i P P

In this partweobservetheoutput resultsfrom theoscilloscopefor:

1) Sinusoidalwaveinput, Vin=5 V, Vout=35 V.

2) Triangularwaveinput, Vin=5 V, Vout=30 V.

3) Squarewave, Vin=5 V, Vout=40V.

output

input


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Differenti tor mplifier1)Vin= 5 V, C= 9990nf; thesedata forsinusoidal input wave.

Table(1):

Freq. Hz Vout

50 15

100 30

200 50

300 65

400 80

Output: red

Input: blue.

2) Triangularwave input


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3) Squarewave

Volt ge follower circuit

Table(2):Data for voltagefollower amplifier:

Freq. KHz Vout Gain

10 5.0 1

100 5.0 1

200 5.0 1

200 5.0 1

400 5.0 1

500 5.0 1

600 5.2 1.04

700 5.4 1.08

800 5.5 1.1

900 5.6 1.12

1000 5.6 1.12

1200 5.8 1.16

1300 5.8 1.16

1400 5.8 1.16

1600 5.8 1.16

2000 6.0 1.2

Samplecalculation:

Gain= ( Vout/Vin)= (5/5) = 1.

TheGain must = 1.


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1.95

2

2.05

2.1

2.15

2.2

2.25

0 500 1000 1500 2000 2500

Freq. (KHz)

G

Chart (1): Gain vs. input frequency.

Discussion of esults:In integrator amplifier the capacitor in feedbackworks as the opposite of differential

amplifier, when the input shape for the signal was triangular the output was square withphase shift of 90 degree, but when the input is a sinusoidal signal the output is a

sinusoidal with some phase shift all of this can be observed in the chartsunder integrator

amplifier title.

The differential amplifier circuit contains capacitor and resistance and we can see

that when the input signal was triangular the output was square shape with no phase

change. Andwhen the input wassinusoidal theoutput lags the input by 90 degrees.

The voltagefollower is a devicewhich matching the impedance.

Thecapacity of the capacitor and the resistance has a large effect on theoutput signal

asweseen in thisexperiment.

In the Differentiator amplifierwee see that theclipping occur at freq. = 400KHz, and

R= 1100 .In the follower amplifier we see from chart (1) that the frequency flat at a range

from(10 ~ 500 KHz) with the gain then it will be increased with the gain increased this

means that thedesired range is between (10 ~ 500 KHz) this indication ofclipping.


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Conclusion:1) At high input frequency (in the rangeofMHz) theoutput will experiencesome

clipping (in both voltagefollower anddifferentiator)

2) Wecan use the voltagefollower as an impedance matching between high inputimpedance and low output impedance. (weutilize from the fact that the input

andoutput is thesamewith the needed impedance)3) There are phase shift angle between input andoutput in the integratorop-ampbut there is no in the voltagefollower.

4) from thedata we noticed that the gain for thedifferentiator is highly effected bythe input frequency

5) From theexperiment weobserve that theoutput is related to the magnitudeofRin greatersensitivity morefor thechange in C.

6) There are some bias error (equipment errors) and Precision error (personalerrors).

7) Thedifferentiator amplifier isused todifferentiate the input signal.8) In thedifferentiator amplifier ifC increasing the gain will be increasing too.

9) In the integrator amplifier ifC increasing the gain will bedeceasing.


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Operational Amplifier II & III