INTRODUCTION TO ANALOG DISCOVERY KIT

1

INTRODUCTION TO ANALOG DISCOVERY KIT

Overview The Digilent Analog Discovery , developed in conjunction with Analog Devices Inc., is a multi- function instrument that can measure, record and generate analog and digital signals.

Figure: Analog Discovery used in a circuit design experiment

The small, portable and low-cost Analog Discovery (above Figure) was created so that engineering

students could work with analog and digital circuits anytime, anywhere - right from their PC. The

Analog Discovery’s analog and digital inputs and outputs connect to a circuit using simple wire

probes. Inputs and outputs are controlled using the free PC- based Waveforms software that can

configure the Discovery to work as any one of several traditional instruments. Instruments include:

• Two channel oscilloscope (1MΩ, ±25V, differential, 14 bit, 100Msample/sec, 5MHz

bandwidth);

• Two channel arbitrary function generator (22Ω, ±5V, 14 bit, 100Msample/sec, 5MHz

bandwidth);

• Stereo audio amplifier to drive external headphones or speakers with replicated AWG

signals;

• 16-channel digital logic analyzer (3.3V CMOS, 100Msample/sec)*;

• 16-channel pattern generator (3.3V CMOS, 100Msample/sec)*;

• 16-channel virtual digital I/O including buttons, switches and LEDs –good for logic

trainer applications*;

• Two input/output digital trigger signals for linking multiple instruments (3.3V CMOS);

• Two power supplies (+5V at 50mA, -5V at 50mA).

• Single channel voltmeter (AC, DC, ±25V);

• Network analyzer – Bode, Nyquist, Nichols transfer diagrams of a circuit. Range: 1Hz to

10MHz;

• Spectrum Analyzer - power spectrum and spectral measurements (noise floor, SFDR,

SNR, THD, etc.);

• Digital Bus Analyzers (SPI, I2C, UART, Parallel);

2

The Analog Discovery was designed for students in typical university-based circuits and electronics

classes. Its features and specifications, including operating from USB power, a small and portable

form factor, and the ability to be used by students in a variety of environments at low cost, are

based directly on inputs from many professors at many universities. Meeting all the requirements

proved challenging, and resulted in some new and innovative circuits. This document is a reference

for the Analog Discovery’s electrical functions and operations. This reference also provides a

description of the hardware’s features and limitations. It is not intended to provide enough

information to enable complete duplication of the Analog Discovery, or to allow users to design

custom configurations for programmable parts in the design.

The pin-out terminals of Analog Discovery Kit (AD Kit) is shown below

3

STEPS TO RUN WAVEFORM SOFTWARE

Step1: Open the “Waveform” software from the start menu of the windows desktop

Figure: Showing the selection of Waveform software from the start menu

Step2: Each block representation of Waveform software

“in” -To check waveforms at the output terminals of the hardware connections done on Bread

board “in” is selected

“out”- To give different input signals to the circuit done on the Bread board “out” is selected

“voltage”-This option is selected to apply +Vcc and –Vcc to the circuit connections done on Bread

board

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Figure: showing the Window of Waveform software

Step 3: The window shown below is obtained when “in” is selected from the “Waveform” software.

Two waveforms can be seen at one time (one is “orange” and the other is “Blue”). The right side

window shows the settings of different waveforms who’s Y and X axis can be set. After selecting the

required options, click the “Run” button on Top left side of the Window to see the obtained output of

the circuit connected on the Bread board.

Figure: Shows the “in” window of “Waveform” software

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Step4: “Out” tab of Waveform software is used for selecting the types of waveforms like-sinusoidal,

square, triangular, trapezoidal, random signal of different frequencies from this window. The signal

selected from this window is given as input signal to the circuit connected on the Bread board. After

making the required settings click on the “Run AWG1” option from the window.

Figure: The “Out” window of Waveform in which different waveforms can be given as input

Step5: “Voltage” is selected for giving the input voltage of either +Vcc (Constant +5V) or –Vcc

(Constant -5V) or both. When the “Power is ON/OFF” is selected the respective voltages are applied

to the circuit connected.

Figure: The “Voltage” window of Waveform helps to run the ADE kit

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EXPERIMENT-1

LINEAR WAVE SHAPING CIRCUITS

AIM: To design linear wave shaping circuits: high pass filter and low pass filter circuits.

APPARATUS: Resistors

Capacitors

Analog Discovery Kit

Connecting wires and Bread board

CIRCUIT:

THEORY:

High Pass RC circuit:

The reactance of the capacitor depends upon the frequency of operation. At very high frequencies, the

reactance of the capacitor is very low. Hence the capacitor in fig.1.1 acts as short circuit for high

frequencies. As a result the almost entire input appears at the output across the resistor.

At low frequencies, the reactance of the capacitor is very high. So the capacitor acts as almost open

circuit. Hence the output is very low. Since the circuit allows only high frequencies, it is called as

high pass RC circuit.

High - pass RC circuit as a differentiator:

In high pass RC circuit, if the time constant is very small in comparison with the time required for the

input signal to make an appreciable change, the circuit is called a “Differentiator”. Under

these circumstances the voltage drop across R will be very small in comparison with the drop across

C. Hence we may consider that the total input Vi appears across C. So that the current is determined

entirely by the capacitor.

i = C dVi/dt.

The output voltage across R is,

Fig 1.1 High Pass RC circuit Fig 1.2 Low Pass RC circuit

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Vo = RC (dVi/dt).

i.e., The output voltage is proportional to the differential of the input. Hence the high pass RC circuit

acts as a differentiator when RC << T.

Low Pass RC circuit:

The reactance of the capacitor depends upon the frequency of operation. At very high frequencies, the

reactance of the capacitor is almost zero. Hence the capacitor in fig.1.2 acts as short circuit. As a

result, the output will fall to zero.

At low frequencies, the reactance of the capacitor is infinite. So the capacitor acts as open

circuit. As a result the entire input appears at the output. Since the circuit allows only low

frequencies, it is called as low pass RC circuit.

Low - Pass RC circuit as an integrator:

In low pass circuit, if the time constant is very large in comparison with the time required for the

input signal to make an appreciable change, the circuit is called an “integrator”. Under these

circumstances the voltage drop across C will be very small in comparison to the drop across R

and almost the total input Vi appears across R. i.e., i = Vi/R.

Therefore the output signal across C is

i.e., The output is proportional to the integral of the input. Hence the low pass RC circuit acts as a

integrator for RC >> T.

Input wave Form

a. RC = T

b. RC << T (RC = 0.1T)

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Expected output wave forms of Low pass RC circuit for square wave input:

Consider the input at V1 during T1 and V11 during T2 then the voltages V01, VO2 during T1 and T2 is given by following equations.

For a symmetrical square wave V2= V/2(tanhx) and V1= -V2 where x = T/(4RC)

a. RC = T

b. RC << T

Procedure:

1. Connect the circuit as shown in figure (fig.1.1 and fig 1.2).

2. Apply the Square wave input to this circuit (Vi = 2 VP-P, f = 1KHz)

3. Observe the output waveform for

a. RC = T

b. RC >> T

4. Verify the values with theoretical calculations.

9

S.no

Time

Constant Voltage levels

1 RC = T V1

V11

V2

V21

2 RC >> T

(RC = 10T)

V1

V11

V2

V21

3 RC << T

(RC = 0.1T)

V1

V11

V2

V21

S.No

Time

Constant Voltage levels

1 RC = T V1

V2

2 RC >> T

(RC = 10T)

V1

V2

3 RC << T

(RC = 0.1T)

V1

V2

Time

Constant

Voltage levels

(Theoretical)

Voltage levels

(Practical)

% Tilt

(Theoretical)

% Tilt (use

equation 1.1)

(Practical)

V1 V11 V V1 V1

1 V

RC << T

RC = T

Result:

Exercise: Obtain the graphs for RC >> T condition and solve the values.

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EXPERIMENT-2

NON-LINEAR WAVE SHAPING CIRCUITS

CLIPPING CIRCUITS

AIM: To design Non- linear wave shaping circuits: Clipping Circuits.

APPARATUS:

Resistors (2.2 K ) – 2 No’s

Diode (1N4007) – 2 No’s

Analog Discovery Kit

Connecting wires

Bread board

THEORY:

The process whereby the form of sinusoidal signals is going to be altered by transmitting through a

non-linear network is called non-linear wave shaping. Non-linear elements (like diodes, transistors) in

combination with resistors can function as clipper circuit.

Clipping circuits are used to select transmission of that part of an arbitrary wave form which lies

above or below some particular reference voltage level. Clipping circuits are also referred to as

Limiters, Amplitude selectors or Slicers.

Clipping circuits are constructed using a combination of resistors, diodes or transistor and reference

voltage. Clipping circuits are classified based on the position of diode as

i. Series diode clipper

ii. Shunt diode clipper

and further they are classified as, with ‘0’ reference, with +ve reference, with –ve reference; also, as

positive clipper, negative clipper.

PROCEDURE:

1. Connect the circuit as shown in the figures given below.

2. In each case, apply 10 VP-P, 1 KHz Sine wave.

3. Observe the Output waveform (VO in the circuit) and compare it with Input waveform.

4. Sketch the Input as well as Output waveforms and mark the voltage levels.

5. Note the changes in the Output due to variations in the reference voltage VR = 0V, 2V, etc.

6. Repeat the above steps for all the clipping circuits.

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CIRCUIT DIAGRAMS:

Fig 2.1 Negative clipper with zero reference (Series clipper)

Fig 2.2 Positive clipper with zero reference (Series clipper)

Input Signal

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Fig 2.3 Negative clipper with zero reference (Shunt clipper)

Fig 2.4 Positive clipper with zero reference (Shunt clipper)

Fig. 2.5 Positive clipper with positive reference (Series clipper)

Fig. 2.6 Positive clipper with positive reference (Shunt clipper)

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Fig. 2.7 Negative clipper with positive reference (Series clipper)

Fig.2.8 Negative clipper with positive reference (Shunt clipper)

Fig.2.9 Clipping at two independent levels

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OBSERVATIONS:

S.No. Type of Clipper Reference Voltage Practical Clipping Voltage levels

1 Series Positive Clipper 0V V1

V2

2V V1

V2

2 Series Negative Clipper 0V V1

V2

2V V1

V2

3 Shunt Positive Clipper 0V V1

V2

2V V1

V2

4 Shunt Negative Clipper 0V V1

V2

2V V1

V2

5 Two level clipper V1

V2

RESULT:

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EXPERIMENT-2

NON-LINEAR WAVE SHAPING CIRCUITS

CLAMPING CIRCUITS

AIM: To design Non- linear wave shaping circuits: Clamping circuits.

APPARATUS:

Resistors (100K ) – 1 No

Diode (1N4007) – 1 No

Capacitor (0.lpF) – 1 No

Analog Discovery Kit

Connecting wires

Bread board

Theory:

The process where sinusoidal signals are going to be altered by transmitting through a non-linear

network is called non-linear wave shaping. Non-linear elements (like diodes) in combination with

resistors and capacitors can function as clamping circuit.

Clamping circuits add a DC level to an AC signal. A clamper is also referred to as DC restorer or DC

re-inserter. The Clampers clamp the given waveform either above or below the reference level, which

are known as positive or negative clampers respectively.

Clamping circuits are classified as two types.

i. Negative Clampers

ii. Positive Clampers

Procedure:

1. Connect the circuit as shown in the figure 3.1 below.

2. Apply a Sine wave of 10V P-P, 1KHz at the input terminals.

3. Observe the I/P & O/P waveforms on CRO and plot the waveforms and mark the values

with VR = 0V, 3V, etc.

4. Output is taken across the load RL.

5. Repeat the above steps for all clamping circuits ( fig 3.2 to fig 3.6) as shown.

6. Draw the waveforms, assuming the diode is practical.

Circuit diagrams:

Input Signal

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Fig.3.1 Negative clamping with zero reference voltage

Fig.3.2 positive clamping with zero reference voltage

Fig.3.3 Negative clamping with Negative reference voltage

Fig.3.4 positive clamping positive reference voltage

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Fig.3.5 Negative clamping with Positive reference voltage

Fig.3.6 Positive clamping with Negative reference voltage

Observations:

S.No. Type of Clamper Ref. Voltage Practicle clamping ref.voltage levels

1. Positive Clamper 0V V1

V2

2V V1

V2

-2V V1

V2

2. Negative Clamper 0V V1

V2

2V V1

V2

-2V V1

V2

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EXPERIMENT-3

VOLTAGE FOLLOWER

AIM: To design a Voltage Follower Circuit using Op-Amp.

APPARATUS: LM324AD/741/OP27 IC or its equivalent

Analog Discovery Kit (AD Kit)

Breadboard, Connecting Wires

CIRCUIT DIAGRAM:

Figure: Voltage Follower

PROCEDURE:

1. Connect the components as per the circuit diagram on the Bread board

2. The color terminals represent the connections made with respect to the Analog Discovery kit

at the respective terminals on the Bread board

3. Adjust the input voltage starting with 500mv and find the output voltage.

4. Repeat the above steps for different voltages complete the table.

5. Draw the graph between input and output voltages for the values obtained from the two tables.

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TABULAR COLUMN:

S. No Vin V out Vout/Vin

MODEL GRAPH:

20

GRAPH SHEET:

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RESULT:

EXERCISE:

1. List the applications of Voltage Follower circuit.

2. What is meant by unity gain amplifier?

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EXPERIMENT-3

INVERTING AMPLIFIER

AIM: To design an Inverting Amplifier Circuit using Op-Amp. APPARATUS: LM324AD/741/OP27 IC or its equivalent

Rf, R1 resistors (select Rf and R1 such that Rf >> R1

Analog Discovery Kit (AD Kit),

Connecting wires

Breadboard

CIRCUIT DIAGRAM:

Figure: Inverting Amplifier

THEORY:

As the open loop DC gain of an Operational Amplifiers is extremely high we can therefore

afford to lose some of this high gain by connecting a suitable resistor across the amplifier from the

output terminal back to the inverting input terminal to both reduce and control the overall gain of the

amplifier. This then produces and effect known commonly as Negative Feedback, and thus produces

a very stable Operational Amplifier based system.

Negative Feedback is the process of “feeding back” a fraction of the output signal back to the

input, but to make the feedback negative, we must feed it back to the negative or “inverting input”

terminal of the op-amp using an external Feedback Resistor called Rƒ. This feedback connection

between the output and the inverting input terminal forces the differential input voltage towards zero.

This effect produces a closed loop circuit to the amplifier resulting in the gain of the amplifier

now being called its Closed-loop Gain. Then a closed-loop inverting amplifier uses negative feedback

to accurately control the overall gain of the amplifier, but at a cost in the reduction of the amplifiers

gain. This negative feedback results in the inverting input terminal having a different signal on it than

the actual input voltage as it will be the sum of the input voltage plus the negative feedback voltage

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giving it the label or term of a Summing Point. We must therefore separate the real input signal from

the inverting input by using an Input Resistor, Rin.

In this Inverting Amplifier circuit the operational amplifier is connected with feedback to produce a

closed loop operation. When dealing with operational amplifiers there are two very important rules to

remember about inverting amplifiers, these are: “No current flows into the input terminal”and

that “V1 always equals V2”. However, in real world op-amp circuits both of these rules are slightly

broken.

This is because the junction of the input and feedback signal (X ) is at the same potential as the

positive ( + ) input which is at zero volts or ground then, the junction is a “Virtual Earth”. Because of

this virtual earth node the input resistance of the amplifier is equal to the value of the input

resistor, Rin and the closed loop gain of the inverting amplifier can be set by the ratio of the two

external resistors.

We said above that there are two very important rules to remember about Inverting Amplifiers or any

operational amplifier for that matter and these are.

1. No Current Flows into the Input Terminals

2. The Differential Input Voltage is Zero as V1 = V2 = 0 (Virtual Earth)

PROCEDURE: 1. Connect the components as per the circuit diagram on the Bread board

2. The color terminals represent the connections made with respect to the Analog Discovery kit at

the respective terminals on the Bread board

3. Adjust the input voltage starting with 500mv and find the output voltage.

4. Repeat the above steps for different voltages by taking different input signals

5. Draw the graph between input and output voltages for the values obtained from the table.

TABULAR COLUMN:

S. No Vin V out Vout/Vin

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THEORETICAL CALCULATIONS:

MODEL GRAPH:

25

GRAPH SHEET:

26

RESULT:

EXERCISE:

1. Execute the following “Non-inverting Amplifier” circuit with different values of Rf

resistances.

2. List the applications of Inverting and Non-Inverting Amplifier.

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EXPERIMENT-4

SUMMING AMPLIFIER

AIM: To design a Summing Amplifier Circuit using Op-Amp. APPARATUS: LM324AD/741/OP27 IC or its equivalent

10 KΩ, 1.5KΩ Resistors

Analog Discovery Kit (AD Kit)

Connecting wires, Breadboard

THEORY:

Summing amplifier is a circuit whose output is the sum of several input signals. For

example: An inverting summing amplifier with two input voltages V1 and V2 two input resistors

R1 and R2 and a feedback resistor (consider all are of equal values).

CIRCUIT DIAGRAM:

Figure: Summing Amplifier Circuit

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PROCEDURE:

1. Connect the relevant circuit for the summing configuration as shown in the

circuit diagram.

2. Measure the output voltage Vo from AD Kit.

3. Observe the waveforms at V1, V2, and Vo.

4. Note the phase of the output voltage Vo with respect to the input voltage.

5. Set different values of two input voltages, and find the output voltage

6. Repeat the steps 3, 4, and 5.

7. The waveforms are to be plotted.

TABULAR COLUMN:

S.No Vin1 V in2 Vout

THEORETICAL CALCULATIONS:

29

GRAPH SHEET:

RESULT:

Exercise: 1. List the applications of Summing amplifier. 2. What is the gain of Summing

Amplifier?

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EXPERIMENT-5

SUBTRACTOR CIRCUIT

AIM: To design a Subtractor Circuit using Op-Amp.

APPARATUS: LM324AD/741/OP27 IC or its equivalent

Resistors 2.2KΩ, 10KΩ

Analog Discovery Kit (AD Kit)

Connecting Wires, Breadboard

CIRCUIT DIAGRAM:

Figure: Subtractor/Difference Circuit

THEORY:

The differential amplifiers amplify the difference between two voltages making this type of

operational amplifier circuit a Subtractor unlike a summing amplifier which adds or sums together

the input voltages. This type of operational amplifier circuit is commonly known as a Differential

Amplifier configuration.

By connecting each input in turn to 0v ground we can use superposition to solve for the output

voltage Vout. Then the transfer function for a Differential Amplifier circuit is given as:

When resistors, R1 = R2 and R3 = R4 the above transfer function for the differential amplifier can be

simplified to the following expression:

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If all the resistors are all of the same ohmic value, that is: R1 = R2 = R3 = R4=R then the circuit will

become a Unity Gain Differential Amplifier and the voltage gain of the amplifier will be exactly

one or unity. Then the output expression would simply be V out = V2 - V1. Also note that if input V1

is higher than input V2 the output voltage sum will be negative, and if V2 is higher than V1, the

output voltage sum will be positive.

The Differential Amplifier circuit is a very useful op-amp circuit and by adding more resistors in

parallel with the input resistors R1 and R3, the resultant circuit can be made to either “Add” or

“Subtract” the voltages applied to their respective inputs. One of the most common ways of doing

this is to connect a “Resistive Bridge” commonly called a Wheatstone Bridge.

PROCEDURE:

1. Connect the relevant circuit for the difference configuration as shown in the circuit

diagram.

2. Measure the output voltage Vo from AD Kit.

3. Observe the waveforms at V1, V2, and Vo.

4. Note the phase of the output voltage Vo with respect to the input voltage.

5. Set different values of two input voltages, and find the output voltage

6. Repeat the steps 3, 4, and 5.

7. The waveforms are to be plotted.

TABULAR COLUMN:

S.No Vin1 V in2 Vout

32

THEORITICAL CALCULATIONS:

33

GRAPH SHEET:

RESULT:

Exercise: Derive the expression for the Difference Amplifier. List the applications of Differential

amplifier.

34

35

EXPERIMENT-6

INTEGRATOR CIRCUIT

AIM: To design an Integrator Circuit using Op-Amp

APPARATUS: LM324AD/741/OP27 IC or its equivalent

10 KΩ, 1KΩ Resistor

100nF Capacitor

Analog Discovery Kit (AD Kit)

Breadboard

CIRCUIT DIAGRAM:

Figure: shows the Integrator

THEORY:

It is a low pass RC filter circuit. It can work as an integrator when time constant is very

large. This requires very large values of R and C by Miller’s theorem the effective input

capacitance becomes C!(1-Av)where Av is the gain of the op-amp. The gain Av is infinite for an

ideal op-amp.so, the effective time constant of the op-amp becomes large which results in perfect

integration. The output voltage of an integrator is shown below

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PROCEDURE:

1. Connect the circuit as shown in the circuit diagram.

2. Suitable Rf and C1 are chosen such that the output of the circuit is the integral of the input

voltage.

3. Apply square wave or sine wave input voltage (V) or any other type of signal at the input

terminal.

4. Observe the output voltage waveform on the CRO and note down the corresponding values.

5. The time constant RfC1 is changed by changing the values of Rf or C1 and the corresponding

output waveforms are noted.

6. The connection of RL is optional.

MODEL GRAPH:

Figure: showing the output waveforms for different input waveforms

37

THEORETICAL CALCULATIONS:

38

GRAPH SHEET:

RESULT:

Exercise: List the applications of integrating amplifier and derive the expression of Integrating

Amplifier

39

EXPERIMENT-7

DIFFERENTIATOR CIRCUIT

AIM: To design a Differentiator Amplifier Circuit using Op-Amp. APPARATUS: LM324AD/741/OP27 IC or its equivalent

100 KΩ, 1 KΩ Resistors

10nF, 100pF Capacitor

Analog Discovery Kit (AD Kit), Connecting Wires

Breadboard

CIRCUIT DIAGRAM:

Figure: Differentiator

THEORY:

It consists of a high pass RC filter .It acts as a differentiator for low values of time constant. Here the

output is the derivative of the input signal.

Thus output is not only the derivative of the input but also out of phase by 180o with respect to the input.

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PROCEDURE:

1. Connect the circuit as shown in the circuit diagram.

2. Suitable values of R1, R2, C1, C2 are chosen such that the output of the circuit is the integral of

the input voltage.

3. A square wave input voltage (V) is applied at the input terminal.

4. Observe the output voltage waveform on the CRO and note down the corresponding values.

5. The time constant R2C1 is changed by changing the values of R2 or C1 and the corresponding

output waveforms are noted.

MODEL GRAPHS:

Figure: Model output waveforms for different input signals

41

THEORETICAL CALCULATIONS:

42

GRAPH SHEET:

RESULT:

Exercise: List the applications of integrating amplifier and derive the expression of

Differentiating Amplifier

43

EXPERIMENT-8

ASTABLE MULTIVIBRATOR

AIM: To design an Astable Multivibrator using a 555 timer

APPARATUS:

Operational Amplifier – 555 Timer

Capacitors – 10µF, 0.01µF

Resistors – 4.7kΩ, 100kΩ (variable), 1kΩ, 330Ω

LED (Optional)

Analog Discovery Kit (AD Kit)

Bread Board.

CIRCUIT DIAGRAM:

Figure: Astable Multivibrator using 555 timer

THEORY:

An astable multivibrator, also known as “free running multivibrator” is nothing but an

oscillator that generates square waves. These waves are required to control the timing circuits.

These multivibrator circuits can be designed using an op-amp.

An astable multivibrator designed using a 555-Timer op-amp is shown. To explain the

principle operation, the internal circuit diagram of 555 Timer is also shown beside.

44

PROCEDURE:

1. Calculate the values of R, R, and C for different duty cycles using the formulae given.

2. Connect the circuit as per the diagram.

3. Calculate the frequency of the astable multivibrator by noting the waveform and compare

it with the theoretical values.

4. Change the value of R and C to change the frequency of oscillation and verify the

theoretical values.

5. Note the output voltages at pin no. 3 and capacitor voltage at pin no.6 and plot it on a

graph sheet.

MODEL GRAPH:

Figure: Model graphs of Astable Multivibrator

THEORETICAL CALCULATIONS:

GRAPH SHEET:

45

RESULT:

Exercise:

1. Derive the expression of Frequency for the Astable Multivibrator

46

EXPERIMENT-9

Monostable Multivibrator Circuit

AIM: To design a Monostable Multivibrator circuit using LM324AD/LM741

Operational Amplifier.

APPARATUS:

LM324AD/LM741/OP27 or its equivalent

Resistors – 10kΩ (2), 22kΩ, 47kΩ

Capacitor – 0.1µF , Diodes

Analog discovery Kit (AD Kit)

Connecting wires, Bread Board

CIRCUIT DIAGRAM:

Figure 1

DESCRIPTION:

At initial power on (that is t = 0), the output (VOUT) will saturate towards either the positive rail

(+Vcc), or to the negative rail (-Vcc), since these are the only two stable states allowed by the op-

amp. Lets assume for now that the output has swung towards the positive supply rail, +Vcc. Then

the voltage at the non-inverting input, VB will be equal to +Vcc*β where β is the feedback fraction.

47

The inverting input is held at 0.7 volts, the forward volt drop of diode, D1 and clamped to 0v

(ground) by the diode, preventing it from going any more positive. Thus the potential at VA is

much less than that at VB and the output remains stable at +Vcc. At the same time, the capacitor,

(C) charges up to the same 0.7 volts potential and is held there by the forward-biased voltage drop

of the diode.

If we were to apply a negative pulse to the non-inverting input, the 0.7v voltage at VA now

becomes greater than the voltage at VB since VB is now negative. Thus the output of the Schmitt

configured op-amp switches state and saturates towards the negative supply rail, -Vcc. The result is

that the potential at VB is now equal to -Vcc*β.

This temporary meta-stable state causes the capacitor to charge up exponentially in the opposite

direction through the feedback resistor, R from +0.7 volts down to the saturated output which it has

just switched too, -Vcc. Diode, D1 becomes reverse-biased so has no effect. The capacitor, C will

discharge at a time constant τ = RC.

As soon as the capacitor voltage at VA reaches the same potential as VB, that is -Vcc*β, the op-amp

switches back to its original permanent stable state with the output saturated once again at +Vcc.

Note that once the timing period is complete and the op-amps output changes back to its stable

state and saturates towards the positive supply rail, the capacitor tries to charge up in reverse

to +Vcc but can only charge to a maximum value of 0.7v given by the diodes forward voltage drop.

Op-amp Monostable Model Waveforms

48

The time delay period (T) of the rectangular pulse at the output, the unstable state time, is given as:

If the two operational amplifiers feedback resistors are of the same value, that is: R1 = R2, then the

above equation simplifies down too:

T = 0.693RC

Then in order to ensure the correct operation of the op-amp monostable circuit upon the application

of the next trigger pulse, the time period between trigger pulses, (Ttotal) must be greater than the

timing period, T plus the time required for the capacitor to recharge, (Tcharging).

In order to ensure that the op-amp monostable circuit has a good negative trigger signal which

starts the timing period on the leading edge of the negative going pulse, and also to stop any false

triggering of the circuit when it is in its stable state, we can add a RC differentiating circuit to the

input.

A differentiator circuit is useful in producing a negative output spike from a square or rectangular

input waveform. The sharp and abrupt reduction of the comparators threshold voltage below its

feedback fraction, β value drives the op-amp monostable into its timing period. A differentiator

circuit is formed using a resistor-capacitor (RC network as shown.

RC Differentiator Circuit

The basic differentiator circuit above uses another resistor-capacitor (RC) network whose output

voltage is the derivative of the input voltage, with respect to time. When the input voltage changes

from 0 to -Vcc, the capacitor begins to charge exponentially. Since the capacitor voltage, Vc is

initially zero, the differentiator output voltage suddenly jumps from 0 to -Vcc producing a negative

spike and then decays exponentially as the capacitor charges up.

Generally for a RC differentiator circuit, the peak value of the negative spike is approximately

equal to the magnitude of the trigger waveform.The advantage of using a differentiator circuit is

that any constant DC voltage or slowly varying signal will be blocked allowing only rapidly

varying trigger pulses to initiate the monostable timing period.

Adding the RC differential circuit to the basic op-amp monostable gives the circuit diagram shown

in Figure 1

49

EXPERIMENT-10

TRIANGULAR WAVE GENERATOR

AIM: To design and demonstrate Triangular wave generator Circuit.

APPARATUS:

LM324AD/LM741/OP27 or its equivalent

Resistors – 10kΩ (2), 22kΩ, 47kΩ

Capacitor – 0.1µF

Analog discovery Kit (AD Kit)

Connecting wires, Bread Board

THEORY:

This experiment is about a triangular wave generator using opamp IC. Triangular wave is a

periodic, non-sinusoidal waveform with a triangular shape. People often get confused between

triangle and sawtooth waves. The most important feature of a triangular wave is that it has equal

rise and fall times while a sawtooth wave has un-equal rise and fall times. The applications of

triangular wave include sampling circuits, thyristor firing circuits, frequency generator circuits,

tone generator circuits etc. There are many methods for generating triangular waves but here we

focus on method using opamps. This circuit is based on the fact that a square wave on integration

gives a triangular wave.

The circuit uses an opamp based square wave generator for producing the square wave and an

opamp based integrator for integrating the square wave. The circuit diagram is shown in the figure.

The square wave generator section and the integrator section of the circuit is explained in detail.

Square wave generator:

The square wave generator is based on a uA741 opamp (IC1). Resistor R1 and capacitor C1

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Figure: Shows the circuit diagram of Triangular wave (Square wave generator and

Integrator Amplifier Combination) generator

determines the frequency of the square wave. Resistor R2 and R3 forms a voltage divider setup

which feedbacks a fixed fraction of the output to the non-inverting input of the IC.

Initially, when power is not applied the voltage across the capacitor C1 is 0V. When the power

supply is switched ON, the C1 starts charging through the resistor R1 and the output of the opamp

will be high (+Vcc). A fraction of this high voltage is fed back to the non- inverting pin by the

resistor network R2, R3. When the voltage across the charging capacitor is increased to a point the

the voltage at the inverting pin is higher than the non-inverting pin, the output of the opamp swings

to negative saturation (-Vcc). The capacitor quickly discharges through R1 and starts charging in

the negative direction again through R1. Now a fraction of the negative high output (-Vcc) is fed

back to the non-inverting pin by the feedback network R2, R3. When the voltage across the

capacitor has become so negative that the voltage at the inverting pin is less than the voltage at the

non-inverting pin, the output of the opamp swings back to the positive saturation. Now the

capacitor discharges trough R1 and starts charging in positive direction. This cycle is repeated over

time and the result is a square wave swinging between +Vcc and -Vcc at the output of the opamp.

If the values of R2 and R3 are made equal, then the frequency of the square wave can be expressed

using the following equation:

F=1 / (2.1976 R1C1)

Integrator:

Next part of the triangular wave generator is the opamp integrator. Instead of using a simple

passive RC integrator, an active integrator based on opamp is used here. The opamp IC used in this

stage is also uA741 (IC2). Resistor R5 in conjunction with R4 sets the gain of the integrator and

resistor R5 in conjunction with C2 sets the bandwidth. The square wave signal is applied to the

inverting input of the opamp through the input resistor R4. The opamp integrator part of the circuit

is shown in the figure below.

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Figure: Integrator Circuit

Let’s assume the positive side of the square wave is first applied to the integrator. By virtue

capacitor C2 offers very low resistance to this sudden shoot in the input and C2 behaves something

like a short circuit. The feedback resistor R5 connected in parallel to C2 can be put aside because

R5 has almost zero resistance at the moment. A serious amount of current flows through the input

resistor R4 and the capacitor C2 bypasses all these current. As a result the inverting input terminal

(tagged A) of the opamp behaves like a virtual ground because all the current flowing into it is

drained by the capacitor C2. The gain of the entire circuit (Xc2/R4) will be very low and the entire

voltage gain of the circuit will be close the zero.

After this initial “kick” the capacitor starts charging and it creates an opposition to the input current

flowing through the input resistor R4. The negative feedback compels the opamp to produce a

voltage at its out so that it maintains the virual ground at the inverting input. Since the capacitor is

charging its impedance Xc keeps increasing and the gain Xc2/R4 also keeps increasing. This results

in a ramp at the output of the opamp that increases in a rate proportional to the RC time constant

(T=R4C2) and this ramp increases in amplitude until the capacitor is fully charged.

When the input signal (square wave) falls to the negative peak at integrator, the capacitor quickly

discharges through the input resistor R4, and starts charging in the opposite polarity. Now the

conditions are reversed and the output of the opamp will be a ramp that is going to the negative

side at a rate proportional to the R4R2 time constant. This cycle is repeated and the result will be a

triangular waveform at the output of the opamp integrator.

CIRCUIT DIAGRAM:

52

PROCEDURE:

1. Connect the components on the bread board as shown in the Circuit diagram

2. Connect the AD kit and find the output voltage and its frequency of the circuit connected on

the Bread board

3. Calculate the frequency by changing the value of R1.

4. Tabulate the values taken and write the frequency obtained

5. Plot the graph of output voltage considering both square and triangular waves.

TABULAR COLUMN:

S.No R2(kΩ)

F (Theoretical

Value)

Square

Amplitude

Triangular

Amplitude Positive

Pulse Negative

Pulse

F

(Practical

Value)

MODEL GRAPH:

53

GRAPH SHEET:

RESULT:

Exercise: List the advantages of using Triangular wave generator. Write the formula for the

frequency of Triangular wave generator

54

EXPERIMENT-11

SQUAREWAVE GENERATOR

AIM: To design and demonstrate square wave generator using op-amp.

APPARATUS:

LM324AD/LM 741/OP27 or its equivalent

Capacitor – 0.1µF

Resistors – 10KΩ (2), 1KΩ (2)

AD Kit, Connecting Wires

Bread Board.

THEORY:

The non-sinusoidal waveform generators are also called relaxation oscillators. The op-amp

relaxation oscillator shown in figure is a square wave generator. In general, square waves are

relatively easy to produce.

The comparator uses positive feedback that increases the gain of the amplifier. In a

comparator circuit this offer two advantages. First, the high gain causes the op-amp’s output to

switch very quickly from one state to another and vice-versa. Second, the use of positive feedback

gives the circuit hysteresis. In the op-amp square-wave generator circuit given in figure, the output

voltage vout is shunted to ground by two Zener diodes Z1 and Z2 connected back-to-back and is

limited to either VZ 2 or –VZ 1. A fraction of the output is fedback to the non-inverting (+) input

terminal. Combination of IL and C acting as a low-pass R-C circuit is used to integrate the output

voltage vout and the capacitor voltage vc is applied to the inverting input terminal in place of

external signal. The differential input voltage is given as vin = vc - β vout

When vin is positive, vout = – Vz1 and when vin is negative vout = + Vz 2. Consider an instant

of time when vin < 0. At this instant vout = + Vz 2 , and the voltage at the non-inverting (+) input

terminal is β Vz 2 , the capacitor C charges exponentially towards Vz 2, with a time constant Rf C.

The output voltage remains constant at Vz 2 until vc equal β Vz 2.

When it happens, comparator output reverses to – Vz 1. Now vc changes exponentially

towards -Vz1 with the same time constant and again the output makes a transition from -Vz1

to + Vz 2. when vc equals -βVz 1

Let Vz1 = Vz 2

The time period, T, of the output square wave is determined using the charging and

discharging phenomena of the capacitor C. The voltage across the capacitor, vc when it is charging

from – β Vz to + Vz is given by

Vc = [1-(1+β)]e-T/2τ

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Where τ = RfC

The waveforms of the capacitor voltage vc and output voltage vout (or vz) are shown in figure.

When t = t/2

Vc = +β Vz or + β Vout

Therefore β Vz = Vz [1-(1+β)e-T/2τ]

Or e-T/2τ = 1- β/1+ β

Or T = 2τ loge 1+β/1- β = 2Rf C loge [1+ (2R3/R2)]

The frequency, f = 1/T , of the square-wave is independent of output voltage Vout. This

circuit is also known as free-running or astable multivibrator because it has two quasi-stable

states. The output remains in one state for time T1 and then makes an abrupt transition to the

second state and remains in that state for time T2. The cycle repeats itself after time T = (T1 + T2)

where T is the time period of the square-wave.

The op-amp square-wave generator is useful in the frequency range of about 10 Hz -10

kHz. At higher frequencies, the op-amp’s slew rate limits the slope of the output square wave. The

symmetry of the output waveform depends on the matching of two Zener diodes Z1 and Z2. The

unsymmetrical square-wave (T1 not equal to t2) can be had by using different constants for

charging the capacitor C to +Vout and -Vout

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CIRCUIT DIAGRAM:

Figure: Circuit diagram for square wave generator

PROCEDURE:

1. Expression for the frequency of oscillation,

f = 1/ (2RCloge (1+ β/1-β)), where β = (R3/R3+R2).

2. Choose any frequency between 1 kHz and 5 kHz and select the values of R1, R2, R, and C.

3. Connect the circuit as per the circuit diagram and give the supply volt age.

4. Observe the frequency of operation of the circuit and compare with the theoretical values.

5. Change the R and C values to change the frequency and oscillation and verify with the

theoretical values.

6. Trace the output waveform for inverting and non-inverting inputs.

7. Connection of Zener diodes are optional. They are used to limit the output voltages

MODEL GRAPHS:

57

GRAPH SHEET:

RESULT:

Exercise:

1. Write a short notes on types of oscillators and their applications and list application of the

above circuit.

58

EXPERIMENT- 12

BISTABLE MULTIVIBRATOR

AIM: To design a fixed bias Bistable Multivibrator using BJT and to measure the stable state

voltages and after triggering.

APPARATUS:

Capacitor (0.001 F, 0.33 F) - 2 Nos each.

Resistors (1 k , 10k , 100K ) - 2 Nos each.

Transistor (BC 107) - 2 No. each.

Diode (IN4007) - 4 No. each.

Analog Discovery Kit(AD Kit)

Bread Board

Connecting Wires

CIRCUIT DIAGRAM:

THEORY:

A Bistable circuit is one which can exist indefinitely in either of two stable states and which

can be induced to make an abrupt transition from one state to the other by means of external

excitation. The Bistable circuit is also called as Bistable multivibrator, Eccles Jordon circuit,

Trigger circuit, Scale-of-2 toggle circuit, Flip-Flop & Binary.

A Bistable multivibratior is used in a many digital operations such as counting and the storing of

binary information. It is also used in the generation and processing of pulse-type waveform. They

can be used to control digital circuits and as frequency dividers.

There are two outputs available which are complements of one another. i.e. when one output is

high the other is low and vice versa .

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OPERATION:

When VCC is applied, one transistor will start conducting slightly more than that of the other,

because of some differences in the characteristics of a transistor. Let Q2 be ON and Q1 be OFF.

When Q2 is ON, The potential at the collector of Q2 decreases, which in turn will decrease the

potential at the base of Q1 due to potential divider action of R1 and R2. The potential at the

collector of Q1 increases which in turn further increases the base to emitter voltage at the base of

Q2. The voltage at the collector of Q2 further decreases, which in turn further reduces the voltage at

the base of Q1. This action will continue till Q2 becomes fully saturated and Q1 becomes fully

cutoff.

Thus the stable state of binary is such that one device remains in cut-off and other device

remains at saturation. It will be in that state until the triggering pulse is applied to it. It has two

stable states. For every transition of states triggering is required. At a time only one device will be

conducting.

NEED OF COMMUTATING CAPACITORS (SPEED UP CAPACITORS):

It is desired that the transition should take place as soon as the trigger pulse is applied but such is

not the case.

When transistor is in active region it stores charge in its base and when it is in the saturation region

it stores even more charge. Hence transistor cannot come out of saturation to cut- off. Until all such

charges are removed. The interval during which conduction transfer one transistor to other is

called as the transition

DESIGN PROCEDURE:

-1.2 = (-15R1 + 0.2R2) /(R1 + R2) ; given R1=10K

R2 = 100K

Fmax = (R1 + R2)/2C R1 R2 R1 = 10K , R2 = 100K and C = 0.1µF

= (10 + 100) X 103 / (2 X 0.3 X 10-6 X 10 X 100 X 106) = 55KHz

PROCEDURE:

1. Make the connections as per the circuit diagram.

2. Apply trigger pulse of 1 KHz 5v (p-p) from function generator.

3. Obtain waveforms at different points such as VB1, VB2, VC1 & VC2.

4. Trace the waveform at collector and base of each transistor with the help of dual trace CRO.

Note the Time relation of waveforms.

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MODEL GRAPH:

RESUT: Bistable Multivibrator is designed; and the waveforms are observed.

61

Annexure 1. LM741 IC

Operational Amplifiers often known as Op-Amps are used in a range of circuits. They are

generally used to amplify weak electrical current in a circuit. It is one of the most versatile

devices in all of electronics. Op-amps are integrated circuits that cram the equivalent of many

transistors, resistors and capacitor into a small silicon chip. The most popular type of Op Amp is the 741 as shown below as 8 pin dual layout IC's. They are

represented in circuit diagrams as follows:

V + : non-

inverting input

V − : inverting

input

Vout: output

VS + : positive

power supply

VS − : negative

power supply

The op-amp is basically a differential amplifier having a large voltage gain, very high input

impedance and low output impedance. The op-amp has a "inverting" or (-) input and "non-

inverting" or (+) input and a single output. The op-amp is usually powered by a dual polarity

power supply in the range of +/- 5 volts to

+/- 15 volts.

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The chip can be used in a circuit in two ways. If the voltage goes into pin 2 then it is

known as an INVERTING AMPLIFIER.

If the voltage goes into pin 3 then the circuit becomes a NON-INVERTING AMPLIFIER.

2. 555 TIMER

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse

generation, and oscillator applications. The 555 can be used to provide time delays, as an

oscillator, and as a flip-flop

element.

The connection of the pins for a DIP package is as follows: Pin

Name

Purpose

1

GND

Ground, low level (0 V)

2

TRIG

OUT rises, and interval starts, when this input falls below 1/3 VCC.

3

OUT

This output is driven to approximately 1.7V below +VCC or GND.

A timing interval may be reset by driving this input to GND, but the timing does

not begin again until RESET rises above approximately 0.7 volts. Overrides

TRIG which overrides THR.

4

RESET

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5

CTRL

"Control" access to the internal voltage divider (by default, 2/3 VCC).

6

THR

The interval ends when the voltage at THR is greater than at CTRL.

7

DIS

Open collector

output; may discharge a capacitor between intervals. In phase with

output. 8

VCC

Positive supply voltage is usually between 3 and 15 V.

Modes

The 555 has three operating modes:

1. Monostable mode: in this mode, the 555 functions as a "one-shot" pulse generator.

Applications include timers, missing pulse detection, bounce free switches, touch

switches, frequency divider, capacitance measurement, pulse-width modulation (PWM)

and so on.

2. Astable: free running mode: the 555 can operate as an oscillator. Uses include LED

and lamp flashers, pulse generation, logic clocks, tone generation, security

alarms, pulse position modulation and so on. The 555 can be used as a simple ADC,

converting an analog value to a pulse length. E.g. selecting a thermistor as timing

resistor allows the use of the 555 in a temperature sensor: the period of the output

pulse is determined by the temperature. The use of a microprocessor based circuit can

then convert the pulse period to temperature, linearize it and even provide

calibration means.

3. Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is not

connected and no capacitor is used. Uses include bounce-free latched switches.

64