1. Adder, Subtractor, Comparator by using IC 741 Op-Amp

Aim: To Study the operation of adder, subtractor and comparator using IC- 741.

Apparatus:

1) IC-741 Op-amp2) Resistors: 3.3KΩ(3), 1KΩ(5)3) Patch Chords4) CRO, Trainer Kit

Theory:

Adder:

Depending on the relationship between the feedback resistor Rf and the input resistors Ra,Rb and Rc the circuit can be used as either a summing amplifier or averaging amplifier.

The output voltage is given by

Vo=-Rf(Va/Ra+Vb/Rb+Vc/Rc)

If Ra=Rb=Rc then

Vo=-Rf(Va+Vb+Vc)

Subtractor:

A basic differential amplifier can be used as a subtractor input signals can be scaled to the desired values by selecting appropriate values for the external resistors

The output voltage of the differential amplifier with a gain of 1 is

Vo=Rf/R(Va-Vb)

Vo=Va-Vb

Hence the circuit is called as subtractor

Comparator: A fixed reference voltage Vref of 1V is applied to the input and the other time varying signal voltage Vin is applied to the input because of this arrangement the circuit is called as comparator when Vin>Vref, Vo is at +Vsat and when Vin<Vref the Vo is at –Vsat. Thus Vo changes from one saturation level to another saturation level when Vin=Vref. In short, comparator is a type of ADC. At any given time, the Vo the waveform shows whether Vin is greater than of lessthan than Vref.The comparator is sometimes also called a voltage level detector because, for a desired value of Vref the voltage level of voltage Vin can be detected.

Procedure:

Adder:

1) Connections are made as per the circuit diagram.2) V1, V2, V3 terminals are given to Ttl logic 0 to +5V3) Output is observed on CRO at pin no. 64) Output values are noted down for different input combinations(000, 001, 010, 011, …

111)5) Compare theoretical and practical values.

Subtractor:

1) Connections are made as per the circuit diagram.2) V1, V2 terminals are given to Ttl logic 0 to +5V3) Output is observed on CRO at pin no. 64) Output values are noted down for different input combinations(00, 01, 10, 11)5) Compare theoretical and practical values.

Comparator:

1) Connections are made as per the circuit diagram.2) Vref is given as +5V3) Vin is given as +20Vp-p.4) Output is observed on CRO at pin no. 65) Channel 1 is connected to output and channel 2 is connected to sine wave input.6) Note down the + Vsat value from the output.

Precautions:

1) Avoid loose connections2) Avoid unnecessary short connections.

Result:

For adder and subtractor theoretical and practical values are compared and found to be equal (appro.,).

For Comparator +Vsat= 22V

Circuit Diagram & Output Table

Input Output Theoritical Output Practical000001010011100101110111

Input Output theoretical Output practical00011011

2. INTEGRATOR AND DIFFERNTIATOR USING IC 741 OP-AMP

Aim:

To Design an Integrator and Differentiator using IC-741 Op amp and also Study the frequency response of both integrator and differentiator.

Apparatus:

1) IC 741 Op-amp (1).2) Resistors: 82Ω(1), 1KΩ(1), 5KΩ(1), 10KΩ (1)3) Capacitors: 0.005µF(1), 0.01µF(1), 0.1µF(1)4) Signal Generator5) CRO6) Connecting wires & Probes7) Trainer kit

Theory:

Integrator is normally operated in the inverting mode. If Vin is the input voltage applied at the inverting terminal of the Op-amp, Vo is the output, which is delivered by the relationship

Vo=-(1/R1Cf) ∫Vin dt

The output voltage is directly proportional to the negative integral of the input voltage and inversely proportional to the time constant R1Cf .The integrator converts the sinusoidal to cosine or a triangular to a square wave. For perfect integration the time period T of the signal is larger than or equal to R1Cf.

i.e. T> R1Cf where R1Cf = 1/2πfa

Where fa is gain timing frequency.

Integrator is in analog computers and Analog to digital converters and signal wave shaping circuits.

Differentiator:

It is normally operated in the inverting mode. If Vin is the input voltage applied at the inverting terminal of the Op-amp,vo is the output, which is derived by the relationship

Vo=-R1Cfd/dt(Vin)

The output voltage is directly proportional to the negative derivative of the input voltage and inversely proportional to the time constant R1Cf. the Differentiator converts square to a spikes.For perfect integration the time period T of the signal is larger than or equal to RFCF

i.e. T> RFCF, where RFCF = 1/2πfa

Where, fa is gain timing frequency.

Differentiator is used in wave shaping circuits, and FM modulators.

Design of Integrator:

Gain limiting frequency fa= 1/2πRfCf

Let fa=1 KHz, RF= 10KΩ

CF=1/2πfaRF µF

Design of differentiator:

fa=1/2πRFC1,

fb=1/2πRFc1

Let fa=1KHz,C1=0.1µF

fb=20fa, R1=1/2πfbC1

Procedure

1) Connections are made as per the circuit diagram.2) The input is applied from a signal generator to the inverting terminal and the

corresponding output waveforms are observed on the CRO.

Precautions:

1) Avoid loose connections2) Avoid unnecessary short connections

Result:

Thus the integrator and differentiator were designed and their frequency resposes were studied.

3. Active Low Pass and & High Pass Butterworth (Second Order) Filter

Aim:

To obtain the frequency responses of the second order LPF and second order HPF.

Apparatus:

1) IC-741 Op-amp(1)2) Resistors 10KΩ(3), 33KΩ(2), 27KΩ(1)3) Potentiometer-22kΩ(1)4) Capacitors-0.01µF(1),0.0047µF(2)5) CRO6) Probes & connecting wires7) Trainer kit

Theory:

The second order LPF uses an RC network for filtering and an Op-amp is in NI configuration hence it does not load down the RC network. The gain magnitude and phase angle equation of the LPF can be obtained by

Vo/Vin=Af/(1+(f/fh)2 )

Φ= -tan-1(f/fh)

fh =1/2πRC Af =1+(Rf/R1)

Second order HPF can be formed by simply inter changing the frequency determining resistors and capacitors in LPF. A 2nd order HPF is formed from a 2nd order LPF by inter changing components R &C. It has a lower cutoff frequency fh at which the magnitude of the gain 0.5 times the pass band value the highest frequency in passband is determined by closed loop bandwidth of the Op-amp.

Vo/Vin=Af (f/f1)/(1+(f/f1)2 )

Where f1=1/2πRC

Designs of II order LPF:

Let fh=1 KHz, R1= 1KΩ,C=0.01µF

fh =1/2πRCR=15.9KΩ

Af =1+ (Rf/R1)=2 Rf=R1=10KΩ

Design of II order HPF:

Let f1=1KHz, C=0.01µF

R=(1/2πf1C) =15.9KΩ

Af=1+(Rf/R1)=2Rf=R1=10K Ω

Procedure:

1) Connections are made as shown in the circuit diagrams fo both LPF and HPF.2) Switch on the power supply.3) Connect the output pin (pin 6) to CRO.4) By varying the frequencies of the input signals observe and note down the output values.5) Plot the frequency response of LPF and HPF on graph sheet with gain in db on Y-axis

and frequency in Hz on X-axis.

Precautions:

1) Avoid loose connections2) Avoid unnecessary short connections

Result:

The frequency responses for 2nd order LPF & HPF are observed and plotted on the graph sheet.

Frequency Response:

LPF:

Vin constant

Vin Frequency (in Hz) Vo(in V) Gain=20log(Vo/Vin) (in db)

HPF:

Vin Frequency (in Hz) Vo(in V) Gain=20log(Vo/Vin) (in db)

4. RC Phase Shift and Wien Bridge Oscillators using IC 741 Op-amp

Aim:

To construct a phase shift oscillator for fo =500Hz and study its operation

Apparatus:

1) IC-741 Op-amp.2) Resistors: 13KΩ(3), 10KΩ(1), 15KΩ(1), 470KΩ(1)3) Capacitors: 0.1µF(3)4) CRO5) Connecting Wires & Probes6) Trainer Kit

Theory:

This is the one type of audio frequency RC oscillator. The Op-amp provides a phase shift of 1800 as it is used in inverting mode. An additional phase shift of 1800 as it is provided by the feedback RC network. The gain Av should be greater than 29 to ensure that variations in circuit parameters will not make (Avβ)<1, otherwise oscillations will die out .

Design:

fo=1/2π RC and Rf=29R

Let C=0.1µF

fo =500Hz R=1.3KΩ

To prevent loading R1=10R

Therefore take R1=10R=15KΩ

Rf =29*15KΩ=435KΩ

Procedure:

1) Connections are made as per the circuit diagram2) See the output waveform on the oscilloscope and adjust rf to obtain a sine wave output.3) Measure the frequency of oscillation, voltage amplitude and plot the waveforms.

Precautions:

1) Avoid loose connections2) Avoid unnecessary short connections

Result:

The RC phase shift oscillator is constructed by using IC -741 Op-amp and the frequency of oscillations fo is obtained.

Wein Bridge Oscillator by using IC-741 Op-amp

Aim:

To construct the wein Bridge Oscillator by using IC-741 Op-amp for fo =1KHz and study its operation.

Apparatus:

1) IC-741 Op-amp2) Resistors: 3.3KΩ(2), 12KΩ(1)3) Potentiometer: 50KΩ(1)4) Capacitors:0.05µF(2)5) Probes & Connecting Wires6) CRO7) Trainer Kit

Theory:

This is one of the audio frequency oscillator, in which the feedback signal is given to the positive input terminal of the Op-amp. So it is called as a non inverting amplifier. Therefore the feedback network needs not to provide any phase shift. The condition of zero phase shift is achieved by balancing the bridge. As β=1/3 at fo. Therefore for sustained oscillation, the amplifier must have a gain of precisely 3.

Design:

fo= 1/2πRC and Rf=2R1

Let C=0.05µF, fo=1KHz

R=1/2πfoC

Procedure:

1) Connections are made as per the circuit diagram2) Observe the output wave form on the CRO3) Note down the amplitude and frequency of the waveform.4) Compare the practical and theoretical values.

Precautions:

1) Avoid loose connections2) Avoid unnecessary short connections

Result:

Wein bridge oscillator is constructed by using IC-741 Op-amp and frequency of oscillations fo is obtained.

5. IC 555 Timer in Monostable operation

Aim:

To study the 555 timer Monostable mode of operation.

Apparatus:

1) IC 555 2) Resistors:3) Capacitors4) CRO5) Connecting wires & Probes6) Trainer Kit

Theory:

Initially when the output is low, the circuit is in the stable state. The transistor Q1 is on and the capacitor C is shorted to the ground. However, upon application of a –Ve trigger pulse at pin 2, transistor Q1 is turned off, which releases the short circuit across the external capacitor C and drives the output high. The capacitor V now starts charging up toward V cc through Ra

However, when the voltage across the capacitors equals the 2/3 Vcc, Comparator 1’s output switches from low to high, which in turn drives the output to its low state via the output of the flip-flop At the same time, the output fo the flop-flop turns transistor Q1 on, and hence c rapidly discharges through the transistor. The output stay at low until a triggered pulse is applied and cycle repeats.

The time during the output is in HIGH state is given by

Tp=1.1RaC

Procedure:

1) Connect the circuit as per the circuit shown in the diagram2) Apply the square wave input to the input of trigger circuit and apply the output of trigger

circuit at the pin 2 of the 555 timer 3) Note downthe pulse width of the monostable multivibrator.4) Compare the theoretical and practical values

Precautions:

1) Avoid loose connections2) Avoid unnecessary short connections

Result:

The working of the 555 timer in the monosatble mode is studied.

6. Schmitt Trigger Circuits using IC 555 and IC 741

Aim:

To study the operation of Schmitt trigger using IC 741 Op-amp.

Apparatus:

1) IC 741(1).2) Resistors: 100Ω (2), 56KΩ(2)3) Function Generator4) Connecting wires & Probes5) CRO6) Trainer Kit

Theory:

An inverting comparator with +Ve feedback. This circuit converts a irregular-shaped waveform to a square or apulse. The circuit is known as Schmitt trigger or wquaring circuit. The input voltage Vin triggers the output Vo every time it exceeds a certain voltage levels called the upper threshold voltage VUT and lower threshold Voltage VLT. These threshold voltages are obtained by using voltage divider R1-R2, where the voltage across R1 is fed back to the +ve input. The voltage across R1 is variable reference threshold voltage that depends on the value

and polarity of the output voltage Vo. When Vo=+Vsat, The voltage\e across R1 is called the upper threshold voltage VUT. The input voltage Vin must be slightly more positive than VUT in order to cause the output Vo to switch from +Vsat to –Vsat. As long as Vin <Vsat, Vo is at + Vsat.

VUT=(R1/(R1+R2))(+Vsat).

On the other hand, when Vo is at –Vsat, the voltage across R1 is referred as lower threshold voltage, VLT.Vin must be slightly more negative than VLT inorder to cause Vo to switch from –Vsat to +Vsat, i.e. for Vin values greater than VLT is at –Vsat

VLT=(R1/(R1+R2))(-Vsat).

Thus if the threshold voltages VLT and VUT are made larger than the input noise voltages, the +Ve feedback will eliminate the false output transitions. Also the +Ve feedback, because of its regenerative action, will make Vo switch faster between +Vsat and –Vsat.

The output of the Schmitt trigger is a square wave when the input is a sine wave.

Procedure:

1) Connect the circuit as per the circuit diagram.2) Input of 1 Vp-p sinewave is given from function generator.3) Output is observed on CRO4) VUT and VLT are calculated and noted down by observing the output on CRO.5) The hysteresis voltage is found as Vhy=VUT-VLT.

Precautions:

1) Avoid loose connections2) Avoid unnecessary short connections

Result:

The Schmitt trigger operation is studied using IC 741 Op-amp.