Lab Report-2 - Implementation

7/28/2019 Lab Report-2 - Implementation

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EL202L - ELECTRONIC CIRCUITS II LAB

LAB SESSION

LAB #2 FUNCTION GENERATOR - IMPLEMENTATION

Name: Serhat Can

Student ID:

Due to: 18.03.2011


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1)INTODUCTION

This lab session is a two-part lab, in which students are expected to design and then

build their own function generator circuits. In the first part, designs will be done with a

circuit simulation program (Orcad v9.2) through necessary calculations to meet the givenconditions for circuit such as the frequency and amplitude range. In second part designed

circuits will be implemented. Function generator is desired to be designed with four main

parts; Schmitt Trigger, Integrator, Wave Shaping Circuit, and a Sine Wave Amplifier. Designs

can be done freely, depending on the creativity of the student; however given structure is

enough for a general function generator. This lab report is only about the design part of this

two-part lab session.

2)EXPERIMENT DESCRIPTION

Goal of the Experiment: Main objective of this design lab is to be able to obtainsquare wave, triangular wave and a sine wave, from one function generator circuit.

As well as the design, the implemented circuit will have adjustable frequency(for all

wave shapes) and amplitude(only for sine wave). Circuit is composed of certain

components, and students are expected to use only them. All steps are done by

calculations, such as models and values of the components, how to range the

frequency and the amplitude, and so on. All steps will be tried to be built carefully

according to design.

Setup of the Experiment: This circuit has four main stages in it, nevertheless, two ofthem are handled together. These stages are as this in the order; Schmitt Trigger,

Integrator, Wave Shaping Circuit, and a Sine Wave Amplifier. All stages are

connected from the input to the next output. Only the output of the Integrator is

also connecting to input of the Schmitt Trigger. Figure below can explain the

structure better:

In general, this circuit is powered with 15 Volts. Its frequency range is varying from

0.5 kHz to 20 kHz. Peak voltages of square wave and triangular wave is 5V, however

sine wave has a peak voltage adjustable from 5V to 10V.


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Schmitt Trigger: The design of the Schmitt Trigger is like this:

This design has three resistances and two diodes, as it can be seen. In the designpart, I have taken the values of and equal (680), since I want to pass the

coming wave with no change. To do this these values have the ratio of 1.

Resistance has the value of 68 . This value is obtained by trials, to give the best

wave shape, since it was affecting the shape of the wave. As it can be seen, there are

two Zener diodes at the output node of the trigger. These two zener diodes has

forward-bias voltage for 0.7V and reverse-bias voltage for 4.3V. This calculation leads

us to total , which is exactly the desired voltage limit for square wave. They are

put there in order to prevent any current to go through to that node. Also there is

the concept of the positive feedback, which is crucial for the wave shape of the

square wave. Positive feedback calculations are done with the following formula:

Integrator: The design of the integrator is like this:


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Schmitt Trigger is an important stage for this circuit. This part is about

adjusting the range of the frequency. There is a fixed value capacitor and an

adjustable resistor, which is responsible of the frequency. As you can see, the

amplifier has a negative feedback. This is so because positive feedback has an

clipping effect on the wave-shape (the output wave becomes a square wave

in positive feedback, this is why we used it in Schmitt Trigger). However

negative feedback does not have such a property. Value of the capacitor is

10nF. To be able to get frequency range between 0,5 kHz and 20 kHz, resistor

value should be adjustable from 1,25k to 50k. And the necessary

calculations are made with the following formula:

Wave Shaping Circuit: The design of the wave shaping circuit is like this:

Wave-shaping circuit can also be named as triangular to sine wave converter.

This circuit does this by clipping the triangular wave from some certain levels

of the voltage. Normal slope of the wave is changed during the clipping stage.In each clip till the voltage reaches to its negative peak value, slope is

lowered. From this point to the next positive peak value slope is enhanced.

As it can be seen, there are lots of different resistors. The ones in the most

right are crucial for the certain clipping level voltages. They determine these

voltages. And other remaining resistor values are obtained by trials to be able

to get the best wave-form. In the figure above, the value levels for voltage are

determined by resistor values. In this stage, I have used these resistor values:

220k for , 100k , 47k for , 1k for , 12k for . and

values are done by trials as Ive said. All the other values are calculated

trough the voltage divider principle.


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Sine-Wave Amplifier: The design of the sine-wave amplifier circuit is like this:

As it can be seen, this amplifier has negative feedback as well, because of thesame reason earlier. There are two important resistor values for the

amplification process; and. value is not important since it is there

only to create a voltage in the output. We want the sine wave voltage

adjustable from 5V to 10 volts. To do this I have given to the value of 1k

and the value changing between 1.8k and 430. With these values I get

exactly 10V-5V range.

And finally there is my complete circuit:


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Measured Values, Graphs: There are six main measurements in this lab session. Allof them are listed below with their explanations. In addition, they are compared with

the previously measured simulation results, and the fact that why are they different

from them will be explained. However, in the implementation part of the lab session,

DC Sweep Analysis and AC Sweep Analysis are not done.

Sweep analysis for Schmitt Trigger. Dc sweep analysis is done with operating the trigger separately from remaining

cuit. I have connected a DC source to the input and then measured the output in the range of -10V and 20V with 0.01

olts of increment. This graph represents the upper trigger point. And the graph below represents the lower trigger

point.


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his graph represents the AC Sweep analysis of the Integrator circuit. Ac sweep options are adjusted to starting value

of 0.5 kHz and ending value of 20 kHz.

From this part, there will be shown the real-time measured values for implemented function generator:

1)5V peak and 0.5 kHz frequency

is photo represents the square wave and triangular wave shapes for 5V peak and 0.5 kHz. All photos are taken from

the oscilloscope measuring the implemented circuit. First node measures square wave, and second one measures

triangular wave.


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his photo represents the triangular and sine-wave shapes, again for 5V peak and 0.5 kHz. Again first node measures

triangular wave and other one measures the sine-wave.

This graph represents the all wave shapes in one for designed circuit in Orcad. The measurement is done with

mplete circuit. For 0.5 kHz, adjustable resistor is adjusted to 50 k ohms. Sine wave amplifier is adjusted to 430 ohms.

As you can see, real-time measured values and simulation values are very close.


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2)10V peak for sine-wave with 0.5 kHz

This photo represents the sine-wave and triangular wave for 0.5 kHz, however sine-wave has 10V peak.

3)5V Square wave and 5V Triangular wave on 20kHz


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The photo above represents square wave and triangular wave for 20 kHz. Peak voltages are around 5

volts for both shapes.

The photo above shows the triangular and sine-wave shapes for 5V peak voltages and 20 kHz.

his graph represents the all wave shapes in one. As it can be seen, the frequency is 20 kHz. This graph clearly shows

e difference between the simulated design and the real circuit, since we could not obtain exactly desired frequencyor voltages for all parts.


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4)5V Triangular wave and 10V sine wave on 20 kHz

hoto above represents the triangular and sine-wave shapes for 20 kHz. Triangular wave has 5 volts peak, however

sine-wave has 10 volts peak.

s graph represents the all wave shapes in one. As it can be seen, the frequency is 20 kHz. However the amplitude for

ne-wave is 10V. The measurement is done with complete circuit. This graph also shows the difference between real

circuit and simulated design


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Analysis and Discussion: Implementation lab was all about building a before headdesigned circuit. In the first part, it seems to be easy to build such a circuit, since we

already have the design of it. However it was clearly not like what we have assumed.

Building part was very challenging, because firstly, building the design was not that

easy on the breadboard, since it requires much more planning than the thinking in

connecting the wires in simulation. Secondly, it was not possible for us to obtain

exact desired values like 5V peak and 20 kHz, since most of the components (almost

all of them) cannot behave as they are in ideal. These differences are the major

factors for obtaining those graphs in Measured Values and Graphs section. As they

can be seen, some wave-shapes have ringing behaviour around their peak voltages.

This is caused mostly by not being able to connect the cables or components each

other(there were conductivity and connection problems sometimes). We observed

this case, because each time we made the connection of a component a little weaker,

say a resistor, the waves started to have ringing. Secondly, the measured voltage

values were not equal to what have desired. And this is due mostly to the non-ideal

characteristics of the components, such as zener diodes or op-amps. These factorsprevented us from getting exact voltage or frequency values. Nevertheless, this lab

session was certainly very educational for us to how one can generate Ac signals with

basic circuit components, and to realize the main differences between designs and

their implementations, and how to fix the small problems(like decreasing the ringing,

or adjusting the frequency level). If we again met problems like these, we would have

more comprehensive aspects on problem.

4)OVERALL DISCUSSION, CONCLUSION

This lab session gave me three very helpful aspects for a complete process of a

circuit project: how to design a desired working circuit only with your current circuit

knowledge and how to make it real by implementing it and finally how to make that circuit

better and more useful in terms of desired results. After all, this session might be a very

good repetition and application of all the labs I have been in.

Lab Report-2 - Implementation

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