REV NO EXPERIMENT NO 1 AIM: To study the PN junction diode characteristics under Forward & Reverse bias conditions. APPARATUS REQUIRED:

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1 KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: REV NO EXPERIMENT NO 1 AIM: To study the PN junction diode characteristics under Forward & Reverse bias conditions. APPARATUS REQUIRED: THEORY: A PN junction diode is a two terminal junction device. It conducts only in one direction (only on forward biasing). FORWARD BIAS: On forward biasing, initially no current flows due to barrier potential. As the applied potential exceeds the barrier potential the charge carriers gain sufficient energy to cross the potential barrier and hence enter the other region. The holes, which are majority carriers in the P-region, become minority carriers on entering the N-regions, and electrons, which are the majority carriers in the N-region, become minority carriers on entering the P-region. This injection of Minority carriers results in the current flow, opposite to the direction of electron movement. REVERSE BIAS: On reverse biasing, the majority charge carriers are attracted towards the terminals due to the applied potential resulting in the widening of the depletion region. Since the charge carriers are pushed towards the terminals no current flows in the device due to majority charge carriers. There will be some current in the device due to the thermally generated minority carriers. The generation of such carriers is independent of the applied potential and hence the current is constant for all increasing reverse potential. This current is referred to as Reverse Saturation Current (IO) and it increases with temperature. When the applied reverse voltage is increased beyond the certain limit, it results in breakdown. During breakdown, the diode current increases tremendously. PROCEDURE: FORWARD BIAS: 1. Connect the circuit as per the diagram. 2. Vary the applied voltage V in steps of 0.1V. 3. Note down the corresponding Ammeter readings If. 4. Plot a graph between Vf & If OBSERVATIONS 1. Find the d.c (static) resistance = Vf / If.= 2. Find the a.c (dynamic) resistance r = δv / δi (r = ΔV/ΔI) =V2-V1/I2-I1 3. Find the forward voltage drop = [Hint: it is equal to 0.7 for Si and 0.3 for Ge]=

2 REVERSE BIAS: 1. Connect the circuit as per the diagram. 2. Vary the applied voltage Vr in steps of 0.5V. 3. Note down the corresponding Ammeter readings Ir. 4. Plot a graph between Vr & Ir 5. Find the dynamic resistance r = δv / δi. FORMULA FOR REVERSE SATURATION CURRENT (IO): Io = I/[exp( V/ηVT)]-1= Where VT is the voltage equivalent of Temperature = kt/q k is Boltzmann s constant, q is the charge of the electron and T is the temperature in degrees Kelvin. η =1 for Silicon and 2 for Germanium Specification for 1N4001: Silicon Diode Peak Inverse Voltage: 50V Maximum forward voltage drop at 1 Amp is 1.1 volts Maximum reverse current at 50 volts is 5μA CIRCUIT DIAGRAM: FORWARD BIAS: REVERSE BIAS:

3 MODEL GRAPH: TABULAR COLUMN:

4 RESULT: Forward and Reverse bias characteristics of the PN junction diode was Studied and the dynamic resistance under Forward bias = Reverse bias = Reverse Saturation Current = PREPARED BY: APPROVED BY: CHECKED BY:

5 KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: REV NO EXPERIMENT NO 2 AIM: To Plot and study the characteristics of UJT APPARATUS REQUIRED: THEORY: UJT(Double base diode) consists of a bar of lightly doped n-type silicon with a small piece of heavily doped P type material joined to one side. It has got three terminals. They are Emitter(E), Base1(B1),Base2(B2).Since the silicon bar is lightly doped, it has a high resistance & can be represented as two resistors, rb1 & rb2. When VB1B2 = 0, a small increase in VE forward biases the emitter junction. The resultant plot of VE & I E is simply the characteristics of forward biased diode with resistance. Increasing VEB1 reduces the emitter junction reverse bias. When VEB1 = VrB1 there is no forward or reverse bias. & IE = 0. Increasing VEB1 beyond this point begins to forward bias the emitter junction. At the peak point, a small forward emitter current is flowing. This current is termed as peak current( IP ). Until this point UJT is said to be operating in cutoff region. When IE increases beyond peak current the device enters the negative resistance region. In which the resistance rb1 falls rapidly & VE falls to the valley voltage.vv. At this point IE = Iv. A further increase of IE causes the device to enter the saturation region. PROCEDURE: 1. Connect the circuit as per the circuit diagram. 2. Set VB1B2 = 0V, vary VEB1, & note down the readings of IE & VEB1 3. Set VB1B2 = 10V, vary VEB1, & note down the readings of IE & VEB1 4. Plot the graph : IE Versus VEB1 for constant VB1B2. 5. Find the intrinsic standoff ratio. FORMULA FOR INTRINSIC STANDOFF RATIO: η = VP - VD/ VB1B2., where VD = 0.7V. PROCEDURE: 1. Give the circuit connections as per the circuit diagram. 2. The dc input voltage is set to 20 V in RPS. 3. The output sweep waveform is measured using CRO. 4. The graph of output sweep waveform is plotted.

6 CIRCUIT DIAGRAM: SPECIFICATION FOR 2N2646: * Inter base resistance RBB = 4.7 to 9.1 KΩ * Minimum Valley current = 4 ma * Maximun Peak point emitter current 5 μa *Maximum emitter reverse current 12 μa. MODEL GRAPH:

7 TABULAR COLUMN: RESULT: Thus the characteristics of given UJT was Plotted PREPARED BY: APPROVED BY: CHECKED BY:

8 REV NO KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: EXPERIMENT NO 3 Aim: To generate the pulse width modulated and demodulated signals Apparatus required: Theory: Pulse Time Modulation is also known as Pulse Width Modulation or Pulse Length Modulation. In PWM, the samples of the message signal are used to vary the duration of the individual pulses. Width may be varied by varying the time of occurrence of leading edge, the trailing edge or both edges of the pulse in accordance with modulating wave. It is also called Pulse Duration Modulation.

9 Circuit Diagram: Fig: 1 Pulse Width Modulation Circuit Fig: 2 Demodulation Circuit Procedure: 1. Connect the circuit as per circuit diagram shown in fig Apply a trigger signal (Pulse wave) of frequency 2 KHz with amplitude of 5v (p-p). 3. Observe the sample signal at the pin3. 4. Apply the ac signal at the pin 5 and vary the amplitude. 5. Note that as the control voltage is varied output pulse width is also varied. 6. Observe that the pulse width increases during positive slope condition & decreases under negative slope condition. Pulse width will be maximum at the +ve peak and minimum at the ve peak of sinusoidal waveform. Record the observations. 7. Feed PWM waveform to the circuit of Fig.2 and observe the resulting demodulated waveform.

10 Observations: Waveform: Result: We have studied Pulse Width Modulation/Demodulation

11 PREPARED BY: APPROVED BY: CHECKED BY:

12 REV NO KARNAL INSTITUTE OF TECHNOLOGY & MANAGEMENT KUNJPURA, KARNAL LAB MANUAL OF SUBJECT CODE DATE OF ISSUE: SEMESTER: BRANCH: EXPERIMENT NO 1 Aim: To generate pulse position modulation and demodulation signals and to study the effect of amplitude of the modulating signal on output. Apparatus required: Theory: In Pulse Position Modulation, both the pulse amplitude and pulse duration are held constant but the position of the pulse is varied in proportional to the sampled values of the message signal. Pulse time modulation is a class of signaling techniques that encodes the sample values of an analog signal on to the time axis of a digital signal and it is analogous to angle modulation techniques. The two main types of PTM are PWM and PPM. In PPM the analog sample value determines the position of a narrow pulse

13 relative to the clocking time. In PPM rise time of pulse decides the channel bandwidth. It has low noise interference. Circuit Diagram: Fig: 1 Pulse Position Modulation Circuit Fig: 2 Demodulation Circuit Procedure: 1. Connect the circuit as per circuit diagram as shown in the fig Observe the sample output at pin 3 and observe the position of the pulses on CRO and adjust the amplitude by slightly increasing the power supply. Also observe the frequency of pulse output. 3. Apply the modulating signal, sinusoidal signal of 2V (p-p) (ac signal) 2v (p-p) to the control pin 5 using function generator. 4. Now by varying the amplitude of the modulating signal, note down the position of the pulses. 5. During the demodulation process, give the PPM signal as input to the demodulated circuit as shown in Fig Observe the o/p on CRO. 7. Plot the waveform.

14 Observations: Waveform: Result: We have studied Pulse Position Modulation/Demodulation PREPARED BY: APPROVED BY: CHECKED BY:

Objective: To study and verify the functionality of a) PN junction diode in forward bias. Sl.No. Name Quantity Name Quantity 1 Diode

Experiment No: 1 Diode Characteristics Objective: To study and verify the functionality of a) PN junction diode in forward bias Components/ Equipments Required: b) Point-Contact diode in reverse bias Components