ec lab manual (08.407)

Electronic Circuit Lab ManualExpt. No. 1

SERIES VOLTAGE REGULATOR

Objective:

Aim of the experiment is to understand the operation of simple series voltage regulator

Equipments and Components Required:

1. Digital Multimeters (DMM).2. DC power supply.3. Project Breadboard. 4. Resistors.5. BC107 BJT6. Zener diode.7. Connection Wires.

Circuit Diagram:

Design:

Given thatVo = 15V, ILmin = 1mA, ILmax = 100mA, Vin min = 16V, Vin max = 30V, IZ max = 100mA and β = 100

Optimum value of and

Optimum value of and

Department of ECE, VKCET

Electronic Circuit Lab ManualProcedure:

1. Test all components

2. Connect the circuit diagram

3. Connect the variable dc power supply as input and turn on.

4. Vary the input voltage from 0 to 30V and note down the corresponding output voltage using voltmeter for line regulation

5. Turn off the power supply

6. Replace RL with 100k pot in series with RLmin

7. Turn on power supply and set it to 20V

8. Vary the pot from higher position to lower position, note down the output voltage using voltmeter and load current using ammeter for load regulation

Pre-Lab Assignments:

1. If 15Vpp sinusoidal input voltage is applied to the circuit shown above, sketch the output waveform.

2. If the input Vin = 10V and R1 = 10kΩ , calculate I1 and IZ, where VZ = 5.2V and β = 50.

3. If R1 reduces what is the improvement of the circuit?

4. Derive the expression for Vo of the circuit shown in fig.1

5. Find optimum value of R1.

6. How does changing RL affect Vo?


Electronic Circuit Lab ManualModel Characteri stics:

Line Regulation: Load Regulation

OBSERVATIONS

Design parameters and components used:

Vo = 15V, ILmin = 1mA, ILmax = 100mA, Vin min = 16V , Vin max = 30V, IZ max = 100mA and β = 100

(For maximum current) (For minimum current) 10Ω to 1.5k Ω

Tabular Column

Line regulation

RLmax=15kΩ, R1max=1.5kΩ

Vin(V) Vo(V)0 01 1.32 1.23 2.24 3.25 4.16 5.17 5.98 6.99 7.910 8.811 9.812 10.514 12.215 13.216 1417 14.418 14.620 14.630 14.6Department of ECE, VKCET

Electronic Circuit Lab ManualLoad regulation

Vin = 30V, RLmin = 150Ω

IL(mA) Vo(V)0 151 14.82 14.74 14.77 14.78 14.79 14.710 14.750 14.7

Viva Questions::

1. Define regulation. List out different types of regulators.

2. Define line and load regulation.

3. What is percentage of voltage regulation?

4. Compare different types of regulators.

5. Draw the basic block diagram of series voltage regulator.



POWER AMPLIFIERS

Objective: The aim of the experiment is to study the operation and efficiency of Class B and Class AB power amplifiers

Components and equipments required:

1. Oscilloscope (Scope/CRO).2. Function Generators (FG).3. DC power supply.4. Project Breadboard. 5. Resistors.6. Capacitors. 7. SL100, SK100 BJTs8. 1N4007 Diodes 9. Connection Wires. 10. Oscilloscope Probes.

Circuit diagram:

Class B Power Amplifier:

Fig. 1Department of ECE, VKCET

Electronic Circuit Lab ManualTheory:

Class B circuit provides an output signal varying over one-half the input signal cycle, or for 180° of signal. The dc bias point for class B is therefore at 0 V, with the output then varying from this bias point for a half cycle. Obviously, the output is not a faithful reproduction of the input if only one half-cycle is present. Two class B operations—one to provide output on the positive output half-cycle and another to provide operation on the negative-output half-cycle are necessary. The combined half-cycles then provide an output for a full 360° of operation. This type of connection is referred to as push-pull operation.

An amplifier may be biased at a dc level above the zero base current level of class B and above one-half the supply voltage level of class A; this bias condition is class AB. Class AB operation still requires a push-pull connection to achieve a full output cycle, but the dc bias level is usually closer to the zero base current level for better power efficiency. For class AB operation, the output signal swing occurs between 180° and 360° and is neither class A nor class B operation.

Following figure shows a diagram for push-pull operation.

An ac input signal is applied to the push-pull circuit, with each half operating on alternate half-cycles, the load then receiving a signal for the full ac cycle. The power transistors used in the push-pull circuit are capable of delivering the desired power to the load, and the class B operation of these transistors provides greater efficiency than was possible using a single transistor in class A operation.

DC Analysis: The dc power supplied to the load by an amplifier is given by

AC Analysis: Output power is given by

The efficiency of Class B amplifier can be calculated by Maximum η of Class B operation is given by 78.5%The power dissipated by the individual output transistor is given by


Electronic Circuit Lab ManualDesign:

Given that

The transistors are as emitter follower.

Output power,

Input power,

Efficiency,

Power dissipation by each transistor,

For R1:

Under dc conditions,

and

To keep transistor at cut-off region under dc biased condition I1 should be low.

And .

For R2:

Class B operation R2 should be negligible. Use the equation .


Electronic Circuit Lab ManualChoose

For Class AB operation or replace the resistors with diodes

Choose

Note: Try to observe the output for different R2

For coupling capacitors:

Choose and

Procedure:

Steps:

1. Check the components

2. Connect the circuit (use R1 for class B operation)

3. Turn on the power supply and apply input signal vin (1Vpp) from function generator

4. Connect CRO probes channel 1 to input and channel 2 to output

5. Observe the input and output wave forms and measure Idc by setting vin =0V and Io

vin=1Vpp, also measure corresponding Vo


7. Replace R1 for Class AB operation

8. Turn on power supply

9. Observe the input and output wave forms and measure Idc by setting vin =0V and Io

vin=1Vpp, also measure corresponding Vo


Electronic Circuit Lab Manual Pre-lab Assignments:

1. What is the ideal DC value of the output signal of Class B and Class AB amplifier if there is no input? Compare this with Class A amplifier.

2. Plot one of the collector current (IC) vs. time, is it full-wave of half-wave?3. Derive expressions for of Class B power amplifier.4. List out the advantages and disadvantages of Class A, Class B, Class AB power,

Class C and Class D amplifiers.

5. Design the circuits shown in fig.1 for , β =100,

and draw the output wave form for sinusoidal input.

Model Waveforms:Class B power amplifier:

Class AB power amplifier:


Electronic Circuit Lab ManualSimulated Results:

Efficiency:

Class B Power Amplifier:

R1=24kΩ (If it is very high, η can be increased to ideal value), R2=100Ω

, RMS current delivered from source during the operation

Class AB Power Amplifier (R2=10k ) :

, RMS current delivered from source during the operation

OBSERVATIONS



Electronic Circuit Lab ManualInput and Output waveforms:

Class B

Class AB


Electronic Circuit Lab Manual

Efficiency

Class B

(?) Not satisfied. This is due to the lack of true RMS meter

Class AB

(?) Not satisfied. This is due to the lack of true rms meter

Viva Questions:

1. Differentiate Voltage Amplifiers and Power Amplifiers.

2. Classify Power amplifiers.


Electronic Circuit Lab Manual3. Define efficiency of Power Amplifiers.

4. Suggest a way (with a diagram) how you might be able to improve the biasing to eliminate the crossover distortion.

5. How you might reduce distortion by using a negative feedback?6. What is the practical application of power amplifiers?



DIFFERENTIAL AMPLIFIER USING BJT

Objective: The aim of the experiment is to study the operation of differential amplifiers using BJT and obtain CMRR and input resistance.


1. Oscilloscope (Scope/CRO).2. Function Generators (FG).3. DC power supply.4. Project Breadboard. 5. Resistors.6. Capacitors7. Diodes 1N40078. BC 107 or SL100 BJTs9. Connection Wires. 10. Oscilloscope Probes.

Circuit diagram:

a) Differential Amplifier using BJT:

i) Differential Mode, Balanced Output (for differential gain)

Fig. 1


Electronic Circuit Lab Manualii) Common mode, balanced output (for common mode gain)

Fig. 2

Different Modes:

a) Dual input balanced output

The circuit is same as shown in Fig. 1

b) Dual input unbalanced output

The input is same as above, but output is taking across any of the transistor’s collector and ground.

c) Single input balanced output.

One of the inputs set to ground and output is same as first mode.

d) Single input unbalanced output.

One of the inputs set to ground and output is same as second mode.


Electronic Circuit Lab ManualPower Supply Arrangement for Dual Voltage Source:

Fig. 3

Note: For unbalanced output use coupling capacitor at the output

Theory:

The differential amplifier, or differential pair, is an essential building block in all integrated amplifiers. In general, the input stage of any analog integrated circuit with more than one input consists of a differential pair or differential amplifier. The basic differential pair circuit consists of two-matched transistors Q1and Q2 , whose emitters are joined together and biased by the constant current source circuit. Q1, D1, D2, R2 and RE acts as current source, which introduce constant current IEE to the differential amplifier with high ac source resistance, since ac equivalent of this dc current source is ideally open circuit.

The important characteristics of the differential amplifier are: the common-mode rejection ratio CMRR, the input differential resistance R id, and the differential-mode gain Ad.

Differential gain:, where Vid is differential input voltage, and Vod is differential

output. For a perfectly matched pair transistor differential gain should be infinite.

CMRR: Common Mode Rejection Ratio, , where Ac is common mode gain

and it is , where Vcm is common mode input voltage, and Voc is common mode output. For perfectly matched pair transistor common mode gain should be zero, and then CMRR should be infinite.

Differential input resistance: The resistance between the differential input and ideally it should be infinite.


Electronic Circuit Lab ManualDC Analysis:

For constant current source circuit:

AC Analysis: Balanced output Mode:

Differential gain

Common mode gain

CMRR Differential mode input resistance Output resistance

Unbalanced output Mode:Differential gain

Common mode gain

CMRR Differential mode input resistance Output resistance

Resistance of current source circuit:

Design:Given that

From data sheet of BC 107, ,



From the above design: ,

Procedure:

Steps



3. Turn on the power supply and apply differential input signals v1 and v2 using function generator

4. Connect CRO probe of channel 1 to one input and channel 2 to unbalanced output vo1 via a coupling capacitor, observe the differential input and output for differential gain

5. Repeat the above step for other vo2

6. Connect channel 2 probe across the collector of transistors without coupling capacitors

7. Observe the balanced output voltage for differential gain

8. Apply same signal to the two inputs as common mode input

9. Repeat step 6 and observe input and output for common mode gain


Electronic Circuit Lab ManualPre-lab Assignments:

1. Define CMRR.

2. Draw the basic circuit of differential amplifier using BJT. Give the significance of RC and REE

3. Design differential amplifier with current source circuit using BJT using the following specifications

4.

5. Give the use of current mirror circuit in differential amplifier.

6. Give the advantages of MOSFET differential amplifier.

7. Design differential amplifier with current source circuit using MOSFET using the following specifications

8. Draw the differential amplifier circuit using BJT with active load.

Model Waveforms:

Differential Input and Balanced Output


Electronic Circuit Lab ManualDifferential Input and Unbalanced Output


Electronic Circuit Lab ManualCommon Mode Input Unbalanced Output



Differential Gain:

For balanced output:

For unbalanced output:

Common Mode Gain:

OBSERVATIONS


From data sheet of BC 107, ,

Differential Mode:

Input and output wave forms:


Electronic Circuit Lab Manuali) Balanced output:

ii) Unbalanced output:

Common Mode:


i) Balanced output:

Viva Questions:

1) Define differential amplifier and give its application

2) Draw a current mirror circuit. Differentiate it with constant current source.

3) In a differential amplifier |VCC| ≠ |VEE|, list out the problems

4) Differentiate different configurations of differential amplifiers. Which one is commonly used?

5) Give the main advantage of constant current bias over emitter bias.Department of ECE, VKCET


CASCADE AMPLIFIER

Objective: The aim of the experiment is to study the operation of cascade amplifier and obtain the frequency response and bandwidth


1. Oscilloscope (Scope/CRO).2. Function Generators (FG).3. DC power supply.4. Project Breadboard. 5. Resistors.6. Capacitors. 7. SL100 BJTs8. Connection Wires. 9. Oscilloscope Probes.

Circuit diagram:

Fig. 1



A single stage of amplification is not enough for a particular application. The overall gain

can be increased by using more than one stage, so when two amplifiers are connected in such a

way that the output signal of the first serves as the input signal to the second, the amplifiers are

said to be connected in cascade. The most common cascade arrangement is the common-emitter

RC coupled cascade amplifier. Common-emitter amplifier exhibit high voltage, high current, and

high power gains, so they are very familiar than other configurations.

Multistage amplifiers can be used either to increase the overall small signal voltage gain,

or to provide an overall voltage gain greater than 1, with a very low output resistance. Figure 1

shows an RC-coupled cascaded amplifier. Capacitors C1 and C2 couple the signal into Q1 and Q2,

respectively. C3 is used for coupling the signal from Q2 to its load. If the operation of coupled

amplifiers is considered, a complicating factor appears. The addition of a second stage may alter

the characteristics of the first stage and thus affect the level of signal fed to the second stage.

To compute the overall gain of the amplifier, it is easier to calculate unloaded voltage

gain for each stage, then including the loading effect by computing voltage dividers for the

output resistance and input resistance of the following stage. This idea is illustrated in figure 2.

Each transistor is drawn as an amplifier consisting of an input resistance Rin , an output

resistance, Rout along with its unloaded gain, AV(NL).

Fig. 2


Electronic Circuit Lab ManualThen, the overall loaded gain VA , of this amplifier can be found by:

For the RC Coupled (CE - CE) multistage amplifier with CE:

and

Note that if a load resistor was added across the output, an additional voltage divider consisting

of the output resistance of the second stage and the added load resistor is used to compute the

new gain.

If and

DC Analysis: For 1st stage amplifier:

Where, and

Stability factor

For 2nd stage amplifier the analysis is same.

AC Analysis: For 1st stage amplifier:

Voltage gain,


Electronic Circuit Lab ManualInput resistance,

Output resistance, For 2nd stage amplifier:

Voltage gain,

Input resistance,

Output resistance,

Design:

Given that

For 2nd stage amplifier:

For


Electronic Circuit Lab Manual From the above design , where

For 1st stage amplifier:

For

From the above design , where

For capacitors:

Where



Procedure:

Steps


2. Connect the circuit diagram for second stage amplifier

3. Turn on the power supply, apply input signal of voltage 10mVpp (low voltage) to the input using function generator

4. Connect CRO channel 1 probe to input and channel 2 to output.

5. Adjust the input signal frequency to mid band (10kHz)

6. Observe the input and output signal and measure the mid band gain

7. Vary input signal frequency from 10Hz to 3MHz (in decade roll-off rate), note down the corresponding output voltage for plotting frequency response

8. Turn off the power supply and construct first stage of amplifier and coupled its output to second stage.


10. Repeat the steps 4 to 7

Pre-lab Assignments:

1. Find the Q-point of each stage of the circuit shown in fig.1, where R1 = R3 = 20kΩ, R2 = R4 = 10kΩ, RE1=RE2= 1kΩ, RC1=4kΩ, RC2=1kΩ VCC = 15V, VCE1= VCE2=0.2V, VBE1= VBE2=0.6V

2. Re-design the components of the circuit shown in fig. 1 for fL=1kHz

3. Define Power gain, Voltage gain and Current gain. How it represent in dB?


Electronic Circuit Lab Manual4. What is transition frequency of transistor? Give the typical value for the given transistor.

5. Simulate the circuit given in experiment using SPICE. Compare designed and simulated dc biasing conditions, show input and its corresponding output wave forms, plot frequency response and compare it with designed values.

Model Waveforms:Input Wave form:

Output Waveforms (1st stage and 2nd stage):


Electronic Circuit Lab ManualTabular Column:

For Single Stage Amplifier:

Input Signal

Frequency, f (Hz)

Output Voltage, vo (vpp)

Voltage Gain,

Av

Av in dB

For Two Stage Amplifier:

Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB

Simulated Results:


Electronic Circuit Lab ManualFirst Stage

Mid band gain = 21.9dB

Lower cutoff frequency fL = 192Hz

Upper cutoff frequency fH = 4.3MHz

Bandwidth = 4.3MHz

Multi stage




Bandwidth = 4.15MHz

OBSERVATIONS


Input and output waveforms:

Single stage:


Electronic Circuit Lab ManualTwo stage:

Tabular column:

Single stage amplifier

Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB


Electronic Circuit Lab ManualTwo Stage Amplifier:

Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB

Viva Questions:

7. What are the requirements of biasing and coupling circuits in BJT amplifiers?8. What is the use of CE in RC coupled amplifier and give its influence in frequency

response?9. Give the advantages and disadvantages of cascade amplifier.10. What is half-power frequency?11. In amplifiers, why mid frequency gain is independent to frequency?12. What is bode-plot?13. What is the method to increase the output voltage swing of an amplifier?14. How load resistances influence the gain of BJT amplifiers?15. What is SPICE?



CASCODE AMPLIFIER

Objectives: a) To study the operation of cascode amplifier using BJT and obtain the frequency response and bandwidth.

b) To simulate cascode amplifier circuit using SPICE.


1. Oscilloscope (Scope/CRO).2. Function Generators (FG).3. DC power supply.4. Project Breadboard. 5. Resistors.6. Capacitors. 7. BEL100N BJTs8. Connection Wires. 9. Oscilloscope Probes.

Circuit diagram:

a) Cascode amplifier using BJT

Fig. 1



The bandwidth of CE amplifier is limited due to the Miller capacitance effect at high frequency operation. This can be overcome by using adding a second stage CB amplifier (direct coupling with CE stage). This arrangement is called cascode amplifier. This amplifier has high bandwidth due to the reduction in Miller capacitance effect. The gain of the amplifier is high due the overall gain of CE and CB stage. The circuit has an input characteristics of CE amplifier and output characteristics of CB amplifier.

In fig.1 R1, R2, and R3 form biasing network for Q1 and Q2; C1 and C3 for coupling ac signals; C2 and CE for bypassing resistors R2 and RE, respectively at ac signals. Transistors Q1 and Q2 should be identical

DC Analysis:

AC Analysis: Voltage gain,

Current gain, , where

Input resistance,

Output resistance,

Design:

Given that

Find typical value of β from the data sheet of BEL100N.

(To get maximum output swing keeps Q1 collector voltage low)

(To get maximum output swing keeps Q2 collector voltage 50% of VCC)



Procedure:

Steps










1. Consider the following circuit.

Where

.

Find Voltage gain, Current gain Input impedance and Output impedance of the circuit

2. Simulate the above circuit (use using SPICE and submit: a) Circuit diagram with dc bias voltages, b) Input and output wave forms and c) Frequency response curve


Electronic Circuit Lab ManualModel Waveforms:Input Wave form:

Output Waveform:

Tabular Column:

Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

log10f Av in dB



Mid band gain =37.2dB

Lower cutoff frequency fL = 752 kHz

Higher cutoff frequency fH = 24MHz

Bandwidth = 25.8MHz

OBSERVATIONS


Given that

Input and output wave forms



Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB

Viva Questions:

9. Define miller effect.

10. Say the advantages and disadvantages of CE, CC and CB configuration of BJT.

11. How the bandwidth improved in cascode amplifier?

12. Which multistage amplifier has maximum bandwidth?

13. Give the expression for current gain of cascode amplifier using BJT.

14. What are the applications of cascode amplifier?

15. In an amplifier which factors limits gain at low and high frequencies?



FEED BACK AMPLIFIERS

Objectives: a) To study the operation of voltage series negative feedback amplifier and obtain the frequency response and bandwidth

b) To study the operation of current series negative feedback amplifier and obtain the frequency response and bandwidth


1. Oscilloscope (Scope/CRO).2. Function Generators (FG).3. DC power supply.4. Project Breadboard. 5. Resistors.6. Capacitors. 7. SL100 BJTs / BEL100N/BC1078. Connection Wires. 9. Oscilloscope Probes.

Circuit diagram:

a) Voltage series negative feedback amplifier

i) Without feed back

Fig.1


Electronic Circuit Lab Manualii) With feedback

Fig. 2

b) Current series negative feedback amplifier:

i) Without feedback

Fig. 3



Fig. 4

Theory:

A feedback amplifier is one in which the output signal is sampled and fed back to the input to form an error signal that drives the amplifier. The basic block diagram of feedback amplifier is shown below.


Electronic Circuit Lab ManualThe input signal, Vs, is applied to a mixer network, where it is combined with a feedback

signal, Vf. The difference of these signals, Vi, is then the input voltage to the amplifier. A portion of the amplifier output, Vo, is connected to the feedback network of gain k, which provides a reduced portion of the output as feedback signal to the input mixer network. If the feedback signal is of opposite polarity to the input signal, negative feedback results otherwise positive feedback.

The advantages of negative feedback are:1. Higher input impedance.2. Better stabilized voltage gain.3. Improved frequency response.4. Lower output impedance.5. Reduced noise.6. More linear operation.

Four basic types of feedback connections along with the properties are given below:

Series-Shunt (Voltage-Series)Shunt-Shunt (Voltage-Shunt)Series-Series (Current-Series)Shunt-Series (Current-Shunt)

In the list above, voltage refers to connecting the output voltage as input to the feedback network; current refers to tapping off some output current through the feedback network. Series refers to connecting the feedback signal in series with the input signal voltage; shunt refers to connecting the feedback signal in shunt (parallel) with an input current source. Series feedback connections tend to increase the input resistance, while shunt feedback connections tend to decrease the input resistance. Voltage feedback tends to decrease the output impedance, while current feedback tends to increase the output impedance.

The gain and feedback factor of four feedback configurations are given below:


Electronic Circuit Lab Manuala) Voltage Series Feedback

Figure 2 show two-stage RC coupled amplifier cascaded with voltage series feedback. The cascade amplifier gain , feedback gain and gain

with feedback . The part of output voltage ( is feedback to the

input loop and it opposes and results voltage series negative feedback. If ,

the amplifier gain is

b) Current Series FeedbackFigure 4 show single stage RC coupled amplifier with current series feedback.

The gain of the amplifier without feedback (with CE) . The feedback

element is RE . The gain of the amplifier with feedback . Here the output

current is fed back to the input ( ) is fed back to the input and it

opposes the input voltage . The feedback gain of the circuit is

Design:

a) Voltage series feedback amplifier:

Given that

For 2nd stage amplifier:

For




For 1st stage amplifier:

For


For capacitors:

Where



For obtaining higher cutoff frequency:

where and (considering first stage)

From datasheet

For feedback network:

Let

From the above design theoretical values of:

Voltage gain with feedback


Electronic Circuit Lab ManualLower cutoff frequency without feedback

Lower cutoff frequency with feedback

b) Current series feedback amplifier:

Given that


Electronic Circuit Lab ManualFrom the above design theoretical values of:

Voltage gain with feedback,

Conductance Gain without feedback

Conductance Gain with feedback

Lower cutoff frequency without feedback

Lower cutoff frequency with feedback

Procedure:

Steps (Voltage series feedback)


3. Connect the circuit diagram without feedback






9. Turn off the power supply.

10. Connect the feedback circuit

11. Turn on the power supply, apply input signal of voltage 10mVpp to the input using function generator


13. Adjust the input signal frequency to mid band (10kHz) Department of ECE, VKCET

Electronic Circuit Lab Manual14. Observe the input and output signal and measure the mid band gain


Steps (Current series feedback)


2. Connect the circuit diagram without feedback






8. Turn off the power supply.

9. Connect the feedback circuit (Remove CE )

10. Turn on the power supply, apply input signal of voltage 10mVpp to the input using function generator








If

Find a) Feedback factor b) Voltage gain without and with feedback c) Input impedance without and with feedback d) Output impedance without and with feedback

2. Simulate the circuits shown in fig.1 to fig.2. Submit the following: a) Input and output waveforms b) Frequency response.


Electronic Circuit Lab Manual3. Consider the following circuit.

Find bandwidth of the circuit where

Model Waveforms and Frequency Response:

Voltage Series Feedback Amplifier without feedback:

Input Wave form and Output Waveforms:

vin=2mVpp vo = 356mVppDepartment of ECE, VKCET

Electronic Circuit Lab ManualFrequency response:

Voltage Series Feedback Amplifier with feedback:


vin=20mVpp, vo = 28.8mVpp

Frequency response:


Electronic Circuit Lab ManualCurrent Series Feedback Amplifier without feedback:


vin=20mVpp vo = 5Vpp

Frequency response:


Electronic Circuit Lab ManualCurrent Series Feedback Amplifier with feedback:


vin=10mVpp, vo 25mVpp

Frequency response:



Voltage Series Feedback Amplifier without feedback:

Input Signal Frequency, f

(Hz)


Voltage Gain, Av

Av in dB


Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB


Electronic Circuit Lab ManualCurrent Series Feedback Amplifier without feedback:

Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB


Input Signal

Frequency, f (Hz)


Voltage Gain, Av

Av in dB



a) Voltage Series feedback without feedback :

Mid band gain = 45dB

Lower cutoff frequency fL = 1.21kHz

Upper cutoff frequency fH =4.33MHz

Bandwidth = 4.32MHz

b) Voltage Series feedback with feedback :




Bandwidth = 5.479MHz

c) Current Series feedback without feedback :


Lower cutoff frequency fL = 1.12kHz

Upper cutoff frequency fH =2.46MHz

Bandwidth = 2.458MHz

d) Currente Series feedback with feedback :




Bandwidth = 12.2MHz

OBSERVATIONS

Voltage Series Feedback:




For feedback network:


i) Without feedback

ii) With feedback

Tabular Column:

i) Without feedback

Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB



Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB

Current Series Feedback:



i) Without feedback

ii) With feedback



i) Without feedback

Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB

ii) With feedback

Input Signal

Frequency, f (Hz)


Voltage Gain,

Av

Av in dB


Electronic Circuit Lab ManualViva Questions:

1. What are the types of mixing and sampling used in voltage series and current series feedback?

2. What is the effect of feedback on the input and output resistances in various feedback?

3. What is the effect of negative feedback?

4. Show that the gain with feedback is independent of amplifier parameters.

5. What is meant by gain de-sensitivity?



MULTIVIBRATORS

Objectives: a) To study the operation of astable, monostable and bistable multivibrators

b) To simulate multivibrator circuits using PSPICE


1. Oscilloscope (Scope/CRO).2. Function Generators (FG).3. DC power supply.4. Project Breadboard. 5. Resistors.6. Capacitors. 7. SL100 BJTs / BEL100N/BC1078. Connection Wires. 9. Oscilloscope Probes.

Circuit diagram:

a) Astable multivibrator:

Fig.1


Electronic Circuit Lab Manualb) Monostable multivibrator:

Fig. 2

c) Bistable multivibrator

Fig. 3



Multivibrators are switching circuits and switches between a "HIGH" state and a "LOW"

state producing a continuous output. They can be used as oscillators, timers and flip-flops. The

circuit can be characterized by two amplifying devices (transistors) cross-coupled by resistors or

capacitors. There are basically three types of multivibrator circuits:

Astable - A free-running multivibrator that has NO stable states but switches continuously

between two states this action produces a train of square wave pulses at a fixed frequency.

Monostable - A one-shot multivibrator that has only ONE stable state and is triggered externally

with it returning back to its first stable state.

Bistable - A flip-flop that has TWO stable states that produces a single pulse either positive or

negative in value.

Fig. 1 shows the circuit diagram of astable multivibrator. The circuit has two stable states

that change alternatively with maximum transition rate because of the "accelerating" positive

feedback. It is implemented by the coupling capacitors C1 and C2 that instantly transfer voltage

changes because the voltage across a capacitor cannot suddenly change. In each state, one

transistor is switched on and the other is switched off. Accordingly, one fully charged capacitor

discharges (reverse charges) slowly thus converting the time into an exponentially changing

voltage. At the same time, the other empty capacitor quickly charges thus restoring its charge

(the first capacitor acts as a time-setting capacitor and the second prepares to play this role in the

next state). The circuit operation is based on the fact that the forward-biased base-emitter

junction of the switched-on bipolar transistor can provide a path for the capacitor restoration.

The switching periods of each transistor are . Thus

time period and frequency of square output at collector of transistor is

where

Figure 2 shows the circuit diagram of monostable multivibrator with trigger circuit. In

this one resistive-capacitive network is replaced by a resistive network (just a resistor). The


http://en.wikipedia.org/wiki/Flip-flop_(electronics)

http://en.wikipedia.org/wiki/Timer

http://en.wikipedia.org/wiki/Oscillators

Electronic Circuit Lab Manualcircuit can be thought as a half astable multivibrator. When triggered by an input pulse, a

monostable multivibrator will switch to its unstable position for a period of time, and then return

to its stable state. The time period monostable multivibrator remains in unstable state is given by

(at collector output of Q2 or at collector of Q1). If repeated

application of the input pulse maintains the circuit in the unstable state, it is called a retriggerable

monostable. If further trigger pulses do not affect the period, the circuit is a non-retriggerable

multivibrator.

In the bistable multivibrator (shown in Figure 3), both the resistive-capacitive network

are replaced by resistive networks (just resistors or direct coupling).This latch circuit is similar to

an astable multivibrator, except that there is no charge or discharge time, due to the absence of

capacitors. Hence, when the circuit is switched on, if Q1 is on, its collector is at 0 V. As a result,

Q2 gets switched off. This results in more than half +V volts being applied to R4 causing current

into the base of Q1, thus keeping it on. Thus, the circuit remains stable in a single state

continuously. Similarly, Q2 remains on continuously, if it happens to get switched on first.

Switching of state can be done via Set (S) and Reset (R) terminals connected to the bases. For

example, if Q1 is on and Set is grounded momentarily, this switches Q1 off, and makes Q2 on.

Thus, Set is used to "set" Q2 on, and Reset is used to "reset" it to off state.

Design:

1. Astable multivibrator:

i) Symmetry wave:

Given that

For symmetrical wave

We have

Choose

Then


Electronic Circuit Lab ManualBase current

Collector current

Condition for oscillation and

For that

ii) Asymmetry wave:

Given that

We have

Choose

Then


Electronic Circuit Lab Manual2. Monostable multivibrator:

Given that and time period of trigger signal Ti=2ms

Choose

Then

Under stable state

To keep Q1 ON in quasi-stable state

For low current to bias Q1 , R1>>RC2

Let


Electronic Circuit Lab ManualDesign for trigger circuit:

Time period Ti of trigger signal vT must be more than TON.

Given that Ti=2ms.

Then

Choose

3. Bistable Multivibrator

Given that

Operation is always symmetry: then

R1>>RC1 and R2 > R1

Let

Procedure:

Steps (Astable multivibrator)


2. Connect the circuit diagram for symmetry waveform

3. Turn on the power supply

4. Connect the CRO channel 1probe to the Q1 collector and channel 2 to Q2

collector

5. Observe the wave forms

6. Connect the CRO channel 1probe to the Q1 base and channel 2 to Q2 base


Electronic Circuit Lab Manual7. Observe the wave forms


9. Connect the circuit diagram for asymmetry waveform

10. Repeat the steps 3 to 7

Steps (Monostable multivibrator)




4. Connect th trigger signal from function generator

5. Connect the CRO channel 1probe to the Q1 collector and channel 2 to trigger signal


7. Connect the CRO channel 1probe to the Q1 base and channel 2 to trigger signal


9. Connect the CRO channel 1probe to the Q2 collector and channel 2 to trigger signal


11. Connect the CRO channel 1probe to the Q2 base and channel 2 to trigger signal


Steps (Bistable multivibrator)




4. Apply set (S) and reset (R) signal via switches, observe the states of outputs




If Vcc =5V, VBB=10V, RC1=RC2=RC=1kΩ, R1=R2=R=50kΩ, C1=C2=.01µF. Draw the signals at vC1,vC2, vB1 and vB2. Find the frequency of oscillation. If VBB is a sinusoidal wave what is the output?

2. Design a circuit to turn ON an LED for 2 seconds and OFF for 4 seconds continuously.


Design the components for VCC =5V, βmin = 25, TON = 4seconds

4. Draw a circuit to generate a square wave. Design it for VCC =5V, βmin = 25, f=4kHz

5. Simulate the above circuits.


Electronic Circuit Lab Manual6. Consider the following truth table and construct a circuit using BJT to generate the logic.

Inputs OutputS R Qn+1

0 0 Qn

0 1 0 11 0 1 01 1 1 1

7. Construct a circuit to generate the following wave.

Model Waveforms

Astable multivibrator

Symmetry waves



Asymmetry waves



Monostable multivibrator:



Bistable multivibrator:

OBSERVATIONS:

Astable Multivibrator

Design parameter and components used:

i) Symmetry wave:

Given that

ii)Asymmetry wave:

Given that

Choose



Monostable Multivibrator

Design parameter and components used:

Given that and time period of trigger signal Ti=2ms

Bistable Multivibrator

Given that

Wave forms:

i) Astable multivibrator (Symmetry)

ii) Astable multivbrator (Asymmetry)


Electronic Circuit Lab Manualiii) Monostable multivibrator

Viva Questions:

1. Maximum frequency of oscillation of astable multivibrator is limited due to which property?

2. Give the applications of multivibrators.

3. Give the expression for the delay in trailing edge of square wave generated by astable multivibrator.

4. Define duty cycle.

5. Compare three multivibrator circuits.

6. Which circuit is referred as one-shot circuit and why?

7. Which multivibrator operates as SR flip-flop and why?

8. Which multivibrator is called free running multivibrator and why?

9. Triggering a monostable multivibrator during TON , what will happen to the output?



OSCILLATORS

Objectives: a) To study the operation of Phase shift, Wien bridge, Hartley and Colpitts Oscillators.

b) To simulate oscillator circuits using PSPICE


1. Oscilloscope (Scope/CRO).2. Function Generators (FG).3. DC power supply.4. Project Breadboard. 5. Resistors.6. Capacitors. 7. Inductors.8. Inductance decade box9. Capacitance decade box10. SL100 BJTs / BEL100N/BC10711. Connection Wires. 12. Oscilloscope Probes.

Circuit diagram:

1. RC phase shift oscillator:

Fig.1


Electronic Circuit Lab Manual2. Wien Bridge Oscillator:

Fig. 2(a)

Fig. 2(b)


Electronic Circuit Lab Manual3. Hartley Oscillator:

Fig. 3

4. Colpitts Oscillator:

Fig. 4Department of ECE, VKCET


Oscillators are circuits that produce a repetitive waveform with only a DC voltage at the output. The output waveform can be sinusoidal, rectangular, triangular, etc. At the base of almost any oscillator there is an amplification stage with a positive feedback (regenerative feedback) circuit that will produce a phase shift and attenuation. Positive feedback consists in the redirecting of the output signal to the input stage of the amplifier without a phase shift. This feedback signal is then amplified again generating the output signal, which produces the feedback signal. This phenomenon, in which the output signal “takes care” of itself in order to generate continuum signal is called oscillation. Two conditions then should be fulfilled to have a stable oscillator:

1. The phase shift of the feedback loop should be 02. The overall gain of the feedback loop should be 1

In order to arrive to the stable operation of the oscillator, during the starting period the gain of the feedback loop should be greater than one, to allow the amplitude of the output signal to achieve the desired level. These conditions are called Barkhausen criteria. Sinusoidal oscillators are classified into two types:

i) RC oscillatorsii) LC oscillators

RC oscillators use RC elements in the feedback branch. They are useful to frequencies upto 200kHz. Two types of RC oscillators are:

i) RC phase shift oscillatorii) Wien Bridge oscillator

Figure 1 shows RC phase shift oscillator, which uses RC coupled amplifier as inverting amplifier and three RC networks as feedback circuit with voltage shunt feedback. Each RC circuit provide at least 60o phase shift, so total 180o phase shit. The

gain of the feedback network is The frequency of oscillation is

and the current gain of the amplifier to satisfies the Barkhausen criteria is .

Figure 2 shows Wien Bridge oscillator. It consists two stage RC coupled amplifier as non-inverting amplifier (360o phase shift) with voltage series negative feedback and voltage shunt positive feedback. Wien Bridge contains series RC and parallel RC network, while feedback resistor element act as resistance arms of the bridge. Resistor arms provide voltage series feedback and RC resonance arms provide voltage shunt feedback. The bridge offer 360o phase shift at resonance frequency and the gain introduced by the network is . So the gain of the amplifier , to satisfy

Barkhausen criteria. The frequency of oscillation is . The main advantage of this oscillator over Phase shift oscillator is its amplitude stability due to the negative feedback.


Electronic Circuit Lab ManualLC oscillator uses amplifier with 180o phase shift and LC tuned circuit as

feedback network. These oscillators are suitable for high frequency oscillation because of it phase stability, frequency stability and less harmonics.

The two familiar LC oscillators are:i) Hartley Oscillatorii) Colpitts Oscillator

Figure 3 shows Hartley Oscillator circuit and it consists of a parallel LC resonator tank circuit and RC coupled amplifier. It uses a pair of tapped coils and a capacitor to produce regenerative feedback. The output voltage is developed across and the feedback voltage is developed across . The attenuation caused by the feedback

network . So the gain of the amplifier, . The tank circuit determines the

operating frequency of the Hartley oscillator and is ,

where .

Figure 4 shows Colpitts Oscillator circuit and it consists of a parallel LC resonator tank circuit and RC coupled amplifier. It uses a pair of tapped capacitors and an inductor to produce regenerative feedback . The output voltage is developed across and the feedback voltage is developed across . The attenuation caused by the feedback

network . So the gain of the amplifier, . The tank circuit determines the

operating frequency of the oscillator and is , where . This oscillator has better frequency stability than Hartley oscillator.

Design:

1. RC Phase Shift Oscillator:

Given that

For amplifier

We have

(Given >> required )


Electronic Circuit Lab ManualDesign for amplifier:

(or for better stability )

(Typical value of β =100)

Design for feedback network:

Let

(Designed Av > hfe)

(Use 1kΩ potentiometer to get accurate value)


Electronic Circuit Lab Manual2. Wien Bridge Oscillator :

Given that

For amplifier

We have

Where is the gain of cascade amplifier with feedback. Then feedback factor k ≤ 0.5

Design of amplifier:

(We are using negative feedback, so ignore the

loading effect and use same design for each stage)

(Typical value of β =100)

Design of RC network for Wien Bridge:


Electronic Circuit Lab ManualDesign for feedback network:

Let

(Use 10k pot)

3. Hartley Oscillator:

Given that

We have where

And loop gain

According to Barkhausen criteria

Then

Design for amplifier:

Choose

(Designing is similar to amplifier used for RC phase shift oscillator. Use low value for IC, to avoid loading effect at the input and output of the amplifier with feedback LC tuned circuit. Low IC value provide medium matched impedances with the available L1 and L2)

Design of LC circuit:

Choose L1 and L2 according to the availability and the conditions

.


Electronic Circuit Lab Manual and

Let L1= 10µF (Use Inductance Decade box) and L2 = 470µF (Available)

Then and is less than the gain of the amplifier

Check the conditions at resonant frequency fo. (Where

)

(If standard capacitor is not available, use Capacitance Decade box)

4. Colpitts Oscillator:

Given that

We have where

And loop gain

According to Barkhausen criteria

Then

Design for amplifier:

Choose

(Designing is similar to amplifier used for RC phase shift oscillator. Use low value for IC, to avoid loading effect at the input and output of the amplifier with feedback LC tuned circuit. Low IC value provide medium matched impedances with the available C1 and C2)



Design of LC circuit:

Choose C1 and C2 according to the availability and the conditions

.

and

Let C1= 0.1µF and C2 = 0.001µF (Both are available)

Check the conditions at resonant frequency fo. (Where

)

(Use Inductance Decade box)

Procedure:

Steps (RC phase shift oscillator)




3. Connect the CRO probe to the output

4. Vary the potentiometer to get a proper wave form

5. Observe the amplitude and frequency of output wave form

6. Change C and observe the variation in frequency of the output wave

7. Change RC and observe the variation in amplitude of the output signal


Electronic Circuit Lab Manual8. Connect CRO probes to the nodes of RC network and observe the 60o phase

shift signals

Steps (Wien Bridge oscillator)





5. Vary the potentiometer to get a proper wave form



Steps (Hartley oscillator)





5. Vary the inductance decade box to the desired value



Steps (Colpitts oscillator)





5. Vary the inductance decade box to the desired value



Electronic Circuit Lab Manual7. Change L and observe the variation in frequency of the output wave


1. Design RC network of RC phase shift oscillator for frequency 20kHz.

2. Design RC network of Wien bridge oscillator for frequency 15kHz.

3. Design tuned circuit of Hartley oscillator for frequency 500kHz.

4. Design tuned circuit of Colpitts oscillator for frequency 750kHz.

5. Compare phase shift oscillators and tuned oscillators.

6. Define frequency and amplitude stabilization used in oscillators.

Model Waveforms Phase Shift Oscillators


Electronic Circuit Lab ManualTuned Oscillators

Simulated Results:

a) RC Phase Shift Oscillator


Electronic Circuit Lab Manualb) Wien Bridge Oscillator

(Only real time simulation using virtual oscilloscope is possible. SPICE simulation is not possible !)

c) Hartley Oscillator

d) Colpitts oscillator

(To simulate inductors using SPICE, connect a low resistance of value 10mΩ in series with it.)


Electronic Circuit Lab ManualOBSERVATIONS:

1. RC Phase Shift Oscillator:


Given that

For amplifier

(Use 1kΩ potentiometer to get accurate value)

Wave form:

2. Wien Bridge Oscillator :


Given that

For amplifier


Electronic Circuit Lab Manual (Use 10k pot)

Wave form:

3. Hartley Oscillator :


Given that

For amplifier

L1= 10µF L2 = 470µF

Wave form:


Electronic Circuit Lab Manual4. Colpitts Oscillator:


Given that

For amplifier

C1= 0.1µF C2 = 0.001µF

(Use Inductance Decade box)

Wave form:



SCHMITT TRIGGER

Objective: To study the operation of Schmitt trigger circuit using BJT.


1. Oscilloscope (Scope/CRO).2. Function Generators (FG).3. DC power supply.4. Project Breadboard. 5. Resistors.6. SL100 BJTs / BEL100N/BC1077. Connection Wires. 8. Oscilloscope Probes.

Circuit diagram:

Fig. 1



Schmitt trigger is a threshold circuits with positive feedback having a loop gain > 1. The circuit is named "trigger" because the output retains its value until the input changes sufficiently to trigger a change: in the non-inverting configuration, when the input is higher than a certain chosen threshold (UTP), the output is high; when the input is below a different (lower) chosen threshold (LTP), the output is low; when the input is between the two, the output retains its value. This dual threshold action is called hysteresis and implies that the Schmitt trigger possesses memory and can act as a bistable circuit (latch). There is a close relation between the two kinds of circuits that actually are the same: a Schmitt trigger can be converted into a latch and v.v., a latch can be converted into a Schmitt trigger.

Design:

Given that

Upper threshold point voltage

Choose (Determines voltage drop at output when Q2 is ON, so keep a low value)

Lower threshold point voltage

Choose


http://medlibrary.org/medwiki/Latch

http://medlibrary.org/medwiki/Latch_(electronics)#Basic_bistable_circuit

http://medlibrary.org/medwiki/Memory

http://medlibrary.org/medwiki/Hysteresis

http://medlibrary.org/medwiki/Loop_gain

http://medlibrary.org/medwiki/Positive_feedback#In_electronics

Electronic Circuit Lab ManualProcedure:

Steps


2. Connect the circuit

3. Turn on power supply, apply input signal (10Vpp, 1kHz).

4. Connect CRO channel 1 (Y) probe to output and channel 2 (X) probe to input

5. Observe input and output wave

6. Put the CRO in XY mode and observe the hysteresis

7. Observe output for different input signal by changing signal mode of function generator.

8. Turn off power supply

9. Connect variable dc source to the input

10. Turn on power supply.

11. Vary input dc voltage from 0V to 4V, note down the change in output for VUT

12. Vary input dc voltage from 4V to 0V, note down the change in output for VLT


• Consider the circuit shown in fig.1. Find the Hysteresis voltage of the circuit, if

• For the input wave shown below, plot the output wave for the circuit in fig.1.

Where Vm=10V


Electronic Circuit Lab ManualModel Waveforms

Input and Output waveforms:

Hysteresis Curve

Hysteresis Voltage VH = VUT - VLT = 2V

Tabular Column

a) For UTP

Vin (V) Vo (V)0

0.40.81.21.62

2.42.83.23.64


Electronic Circuit Lab Manualb) For LTP

Vin (V) Vo (V)4

3.63.22.82.42

1.61.2.80.40

(Observe the hysteresis curve on oscilloscope by applying Vin as X-axis signal and Vo as Y-axis signal. Put oscilloscope in XY mode)

OBSERVATIONS:

Given parameters and components used:

Given that



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