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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 Page 1
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?
Department of ECE, VKCET Page 2
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 Page 3
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.
Department of ECE, VKCET Page 4
Electronic Circuit Lab ManualExpt. No. 2
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 Page 5
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
Department of ECE, VKCET Page 6
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 .
Department of ECE, VKCET Page 7
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
6. Turn off the power supply
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
Department of ECE, VKCET Page 8
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:
Department of ECE, VKCET Page 9
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
Design parameters and components used:
Department of ECE, VKCET Page 10
Electronic Circuit Lab ManualInput and Output waveforms:
Class B
Class AB
Department of ECE, VKCET Page 11
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.
Department of ECE, VKCET Page 12
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?
Department of ECE, VKCET Page 13
Electronic Circuit Lab ManualExpt. No. 3
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.
Components and equipments required:
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
Department of ECE, VKCET Page 14
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.
Department of ECE, VKCET Page 15
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.
Department of ECE, VKCET Page 16
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, ,
Department of ECE, VKCET Page 17
Electronic Circuit Lab Manual
From the above design: ,
Procedure:
Steps
1. Check the components
2. Connect the circuit diagram
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
Department of ECE, VKCET Page 18
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
Department of ECE, VKCET Page 19
Electronic Circuit Lab ManualDifferential Input and Unbalanced Output
Department of ECE, VKCET Page 20
Electronic Circuit Lab ManualCommon Mode Input Unbalanced Output
Department of ECE, VKCET Page 21
Electronic Circuit Lab ManualSimulated Results:
Differential Gain:
For balanced output:
For unbalanced output:
Common Mode Gain:
OBSERVATIONS
Design parameters and components used:
From data sheet of BC 107, ,
Differential Mode:
Input and output wave forms:
Department of ECE, VKCET Page 22
Electronic Circuit Lab Manuali) Balanced output:
ii) Unbalanced output:
Common Mode:
Input and output wave forms:
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 Page 23
Electronic Circuit Lab ManualExpt. No. 4
CASCADE AMPLIFIER
Objective: The aim of the experiment is to study the operation of cascade amplifier and obtain the frequency response and bandwidth
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 BJTs8. Connection Wires. 9. Oscilloscope Probes.
Circuit diagram:
Fig. 1
Department of ECE, VKCET Page 24
Electronic Circuit Lab ManualTheory:
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
Department of ECE, VKCET Page 25
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,
Department of ECE, VKCET Page 26
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
Department of ECE, VKCET Page 27
Electronic Circuit Lab Manual From the above design , where
For 1st stage amplifier:
For
From the above design , where
For capacitors:
Where
Department of ECE, VKCET Page 28
Electronic Circuit Lab Manual
Procedure:
Steps
1. Check the components
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.
9. Turn on the power supply, apply input signal of voltage 1mVpp (low voltage) to the input using function generator
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?
Department of ECE, VKCET Page 29
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):
Department of ECE, VKCET Page 30
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)
Output Voltage, vo (vpp)
Voltage Gain,
Av
Av in dB
Simulated Results:
Department of ECE, VKCET Page 31
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
Mid band gain = 46.3dB
Lower cutoff frequency fL = 257Hz
Upper cutoff frequency fH = 4.15MHz
Bandwidth = 4.15MHz
OBSERVATIONS
Design parameters and components used:
Input and output waveforms:
Single stage:
Department of ECE, VKCET Page 32
Electronic Circuit Lab ManualTwo stage:
Tabular column:
Single stage amplifier
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
Voltage Gain,
Av
Av in dB
Department of ECE, VKCET Page 33
Electronic Circuit Lab ManualTwo Stage Amplifier:
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
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?
Department of ECE, VKCET Page 34
Electronic Circuit Lab ManualExpt. No. 5
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.
Components and equipments required:
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
Department of ECE, VKCET Page 35
Electronic Circuit Lab ManualTheory:
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)
Department of ECE, VKCET Page 36
Electronic Circuit Lab Manual
Procedure:
Steps
1. Check the components
2. Connect the circuit diagram
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
Department of ECE, VKCET Page 37
Electronic Circuit Lab ManualPre-lab Assignments:
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
Department of ECE, VKCET Page 38
Electronic Circuit Lab ManualModel Waveforms:Input Wave form:
Output Waveform:
Tabular Column:
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
Voltage Gain,
Av
log10f Av in dB
Department of ECE, VKCET Page 39
Electronic Circuit Lab ManualSimulated Results:
Mid band gain =37.2dB
Lower cutoff frequency fL = 752 kHz
Higher cutoff frequency fH = 24MHz
Bandwidth = 25.8MHz
OBSERVATIONS
Design parameters and components used:
Given that
Input and output wave forms
Department of ECE, VKCET Page 40
Electronic Circuit Lab ManualTabular Column:
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
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?
Department of ECE, VKCET Page 41
Electronic Circuit Lab ManualExpt. No. 6
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
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 BJTs / BEL100N/BC1078. Connection Wires. 9. Oscilloscope Probes.
Circuit diagram:
a) Voltage series negative feedback amplifier
i) Without feed back
Fig.1
Department of ECE, VKCET Page 42
Electronic Circuit Lab Manualii) With feedback
Fig. 2
b) Current series negative feedback amplifier:
i) Without feedback
Fig. 3
Department of ECE, VKCET Page 43
Electronic Circuit Lab Manualii) With feedback
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.
Department of ECE, VKCET Page 44
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:
Department of ECE, VKCET Page 45
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
Department of ECE, VKCET Page 46
Electronic Circuit Lab Manual
From the above design , where
For 1st stage amplifier:
For
From the above design , where
For capacitors:
Where
Department of ECE, VKCET Page 47
Electronic Circuit Lab Manual
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
Department of ECE, VKCET Page 48
Electronic Circuit Lab ManualLower cutoff frequency without feedback
Lower cutoff frequency with feedback
b) Current series feedback amplifier:
Given that
Department of ECE, VKCET Page 49
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)
2. Check the components
3. Connect the circuit diagram without feedback
4. Turn on the power supply, apply input signal of voltage 2mVpp (low voltage) to the input using function generator
5. Connect CRO channel 1 probe to input and channel 2 to output.
6. Adjust the input signal frequency to mid band (10kHz)
7. Observe the input and output signal and measure the mid band gain
8. Vary input signal frequency from 10Hz to 3MHz (in decade roll-off rate), note down the corresponding output voltage for plotting frequency response
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
12. Connect CRO channel 1 probe to input and channel 2 to output.
13. Adjust the input signal frequency to mid band (10kHz) Department of ECE, VKCET Page 50
Electronic Circuit Lab Manual14. Observe the input and output signal and measure the mid band gain
15. Vary input signal frequency from 10Hz to 3MHz (in decade roll-off rate), note down the corresponding output voltage for plotting frequency response
Steps (Current series feedback)
1. Check the components
2. Connect the circuit diagram without feedback
3. Turn on the power supply, apply input signal of voltage 2mVpp (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.
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
11. Connect CRO channel 1 probe to input and channel 2 to output.
12. Adjust the input signal frequency to mid band (10kHz)
13. Observe the input and output signal and measure the mid band gain
14. Vary input signal frequency from 10Hz to 3MHz (in decade roll-off rate), note down the corresponding output voltage for plotting frequency response
Department of ECE, VKCET Page 51
Electronic Circuit Lab ManualPre-lab Assignments:
1. Consider the following circuit.
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.
Department of ECE, VKCET Page 52
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 Page 53
Electronic Circuit Lab ManualFrequency response:
Voltage Series Feedback Amplifier with feedback:
Input Wave form and Output Waveforms:
vin=20mVpp, vo = 28.8mVpp
Frequency response:
Department of ECE, VKCET Page 54
Electronic Circuit Lab ManualCurrent Series Feedback Amplifier without feedback:
Input Wave form and Output Waveforms:
vin=20mVpp vo = 5Vpp
Frequency response:
Department of ECE, VKCET Page 55
Electronic Circuit Lab ManualCurrent Series Feedback Amplifier with feedback:
Input Wave form and Output Waveforms:
vin=10mVpp, vo 25mVpp
Frequency response:
Department of ECE, VKCET Page 56
Electronic Circuit Lab ManualTabular Column:
Voltage Series Feedback Amplifier without feedback:
Input Signal Frequency, f
(Hz)
Output Voltage, vo (vpp)
Voltage Gain, Av
Av in dB
Voltage Series Feedback Amplifier with feedback:
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
Voltage Gain,
Av
Av in dB
Department of ECE, VKCET Page 57
Electronic Circuit Lab ManualCurrent Series Feedback Amplifier without feedback:
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
Voltage Gain,
Av
Av in dB
Voltage Series Feedback Amplifier with feedback:
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
Voltage Gain, Av
Av in dB
Department of ECE, VKCET Page 58
Electronic Circuit Lab ManualSimulated Results:
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 :
Mid band gain = 32.4dB
Lower cutoff frequency fL = 931Hz
Upper cutoff frequency fH = 5.48MHz
Bandwidth = 5.479MHz
c) Current Series feedback without feedback :
Mid band gain = 46.3dB
Lower cutoff frequency fL = 1.12kHz
Upper cutoff frequency fH =2.46MHz
Bandwidth = 2.458MHz
d) Currente Series feedback with feedback :
Mid band gain = 6.25dB
Lower cutoff frequency fL = 816Hz
Upper cutoff frequency fH = 12.2MHz
Bandwidth = 12.2MHz
OBSERVATIONS
Voltage Series Feedback:
Design parameters and components used:
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Electronic Circuit Lab Manual
For feedback network:
Input and output wave forms:
i) Without feedback
ii) With feedback
Tabular Column:
i) Without feedback
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
Voltage Gain,
Av
Av in dB
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Electronic Circuit Lab Manualii) With feedback
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
Voltage Gain,
Av
Av in dB
Current Series Feedback:
Design parameters and components used:
Input and output wave forms:
i) Without feedback
ii) With feedback
Department of ECE, VKCET Page 61
Electronic Circuit Lab ManualTabular Column:
i) Without feedback
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
Voltage Gain,
Av
Av in dB
ii) With feedback
Input Signal
Frequency, f (Hz)
Output Voltage, vo (vpp)
Voltage Gain,
Av
Av in dB
Department of ECE, VKCET Page 62
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?
Department of ECE, VKCET Page 63
Electronic Circuit Lab ManualExpt. No. 7
MULTIVIBRATORS
Objectives: a) To study the operation of astable, monostable and bistable multivibrators
b) To simulate multivibrator circuits using PSPICE
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 BJTs / BEL100N/BC1078. Connection Wires. 9. Oscilloscope Probes.
Circuit diagram:
a) Astable multivibrator:
Fig.1
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Electronic Circuit Lab Manualb) Monostable multivibrator:
Fig. 2
c) Bistable multivibrator
Fig. 3
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Electronic Circuit Lab ManualTheory:
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
Department of ECE, VKCET Page 66
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
Department of ECE, VKCET Page 67
Electronic Circuit Lab ManualBase current
Collector current
Condition for oscillation and
For that
ii) Asymmetry wave:
Given that
We have
Choose
Then
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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
Department of ECE, VKCET Page 69
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)
1. Check the components
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
Department of ECE, VKCET Page 70
Electronic Circuit Lab Manual7. Observe the wave forms
8. Turn off the power supply
9. Connect the circuit diagram for asymmetry waveform
10. Repeat the steps 3 to 7
Steps (Monostable multivibrator)
1. Check the components
2. Connect the circuit diagram
3. Turn on the power supply
4. Connect th trigger signal from function generator
5. Connect the CRO channel 1probe to the Q1 collector and channel 2 to trigger signal
6. Observe the wave forms
7. Connect the CRO channel 1probe to the Q1 base and channel 2 to trigger signal
8. Observe the wave forms
9. Connect the CRO channel 1probe to the Q2 collector and channel 2 to trigger signal
10. Observe the wave forms
11. Connect the CRO channel 1probe to the Q2 base and channel 2 to trigger signal
12. Observe the wave forms
Steps (Bistable multivibrator)
1. Check the components
2. Connect the circuit diagram
3. Turn on the power supply
4. Apply set (S) and reset (R) signal via switches, observe the states of outputs
Department of ECE, VKCET Page 71
Electronic Circuit Lab ManualPre-lab Assignments:
1. Consider the following circuit.
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.
3. Consider the following circuit.
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.
Department of ECE, VKCET Page 72
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
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Electronic Circuit Lab Manual
Asymmetry waves
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Electronic Circuit Lab Manual
Monostable multivibrator:
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Electronic Circuit Lab Manual
Department of ECE, VKCET Page 76
Electronic Circuit Lab Manual
Bistable multivibrator:
OBSERVATIONS:
Astable Multivibrator
Design parameter and components used:
i) Symmetry wave:
Given that
ii)Asymmetry wave:
Given that
Choose
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Electronic Circuit Lab Manual
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)
Department of ECE, VKCET Page 78
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?
Department of ECE, VKCET Page 79
Electronic Circuit Lab ManualExpt. No. 8
OSCILLATORS
Objectives: a) To study the operation of Phase shift, Wien bridge, Hartley and Colpitts Oscillators.
b) To simulate oscillator circuits using PSPICE
Components and equipments required:
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
Department of ECE, VKCET Page 80
Electronic Circuit Lab Manual2. Wien Bridge Oscillator:
Fig. 2(a)
Fig. 2(b)
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Electronic Circuit Lab Manual3. Hartley Oscillator:
Fig. 3
4. Colpitts Oscillator:
Fig. 4Department of ECE, VKCET Page 82
Electronic Circuit Lab ManualTheory:
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.
Department of ECE, VKCET Page 83
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 )
Department of ECE, VKCET Page 84
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)
Department of ECE, VKCET Page 85
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:
Department of ECE, VKCET Page 86
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
.
Department of ECE, VKCET Page 87
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)
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Electronic Circuit Lab Manual
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)
1. Check the components
1. Connect the circuit diagram
2. Turn on the power supply
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
Department of ECE, VKCET Page 89
Electronic Circuit Lab Manual8. Connect CRO probes to the nodes of RC network and observe the 60o phase
shift signals
Steps (Wien Bridge oscillator)
1. Check the components
2. Connect the circuit diagram
3. Turn on the power supply
4. Connect the CRO probe to the output
5. Vary the potentiometer to get a proper wave form
6. Observe the amplitude and frequency of output wave form
7. Change C and observe the variation in frequency of the output wave
Steps (Hartley oscillator)
1. Check the components
2. Connect the circuit diagram
3. Turn on the power supply
4. Connect the CRO probe to the output
5. Vary the inductance decade box to the desired value
6. Observe the amplitude and frequency of output wave form
7. Change C and observe the variation in frequency of the output wave
Steps (Colpitts oscillator)
1. Check the components
2. Connect the circuit diagram
3. Turn on the power supply
4. Connect the CRO probe to the output
5. Vary the inductance decade box to the desired value
6. Observe the amplitude and frequency of output wave form
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Electronic Circuit Lab Manual7. Change L and observe the variation in frequency of the output wave
Pre-lab Assignments:
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
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Electronic Circuit Lab ManualTuned Oscillators
Simulated Results:
a) RC Phase Shift Oscillator
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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.)
Department of ECE, VKCET Page 93
Electronic Circuit Lab ManualOBSERVATIONS:
1. RC Phase Shift Oscillator:
Design parameters and components used:
Given that
For amplifier
(Use 1kΩ potentiometer to get accurate value)
Wave form:
2. Wien Bridge Oscillator :
Design parameters and components used:
Given that
For amplifier
Department of ECE, VKCET Page 94
Electronic Circuit Lab Manual (Use 10k pot)
Wave form:
3. Hartley Oscillator :
Design parameters and components used:
Given that
For amplifier
L1= 10µF L2 = 470µF
Wave form:
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Electronic Circuit Lab Manual4. Colpitts Oscillator:
Design parameters and components used:
Given that
For amplifier
C1= 0.1µF C2 = 0.001µF
(Use Inductance Decade box)
Wave form:
Department of ECE, VKCET Page 96
Electronic Circuit Lab ManualExpt. No. 9
SCHMITT TRIGGER
Objective: To study the operation of Schmitt trigger circuit using BJT.
Components and equipments required:
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
Department of ECE, VKCET Page 97
Electronic Circuit Lab ManualTheory:
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
Department of ECE, VKCET Page 98
Electronic Circuit Lab ManualProcedure:
Steps
1. Check the components
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
Pre-lab Assignments:
• 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
Department of ECE, VKCET Page 99
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
Department of ECE, VKCET Page 100
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
Input and output wave forms:
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