GOVERNMENT OF KARNATAKA KARNATAKA STATE PRE-UNIVERSITY EDUCATION EXAMINATION BOARD II YEAR PUC EXAMINATION MARCH-03 SCHEME OF VALUATION Subject Code: 0 Subject: PART - A 0. What does the arrow mark indicate in the symbolic representation of a transistor? Conventional current flow. 0. Name the transistor amplifier which has very high input impedance. CC amplifier. 03. What happens to the distortion of the amplifier when negative feedback is given to it? Decreases or reduces. 0. What is the value of output voltage if both the input voltages are equal in the case of ideal differential amplifier? Zero OR non-zero OR two times input 05. Between LC and RC oscillators, which is preferred for generating low frequency? RC Oscillator 06. Define skip zone Skip zone: The region where there is no reception of any signal, i.e., silent zone. 07. Write the expression for modulation index in terms of V max and V min. 08. Write the output of XOR gate, when the inputs are A = 0 and B = or high 09. Write the excess-3 code for (0) 0. 00 00 000 0. What is voice mail? Voice mail is an electronic telecommunication system that records, stores and delivers voice messages. OR Voice mail is a device (answering machine) that records and retrieves audio messages and play announcements to callers. PART - B. A transistor has α = 0.98. If I c = 5 ma, find I B. = I E /I C, hence I E = 5 ma/0.98 = 5. ma I B = I E I C = (5.0 5)m = 0. ma Page
β = α/( - α) = 0.98 / ( - 0.98) = 9 OR β = I C /I B, hence I B = 5 ma / 9 = 0.0 ma = 0 µa. Draw the frequency response curve of a CE amplifier. Mention its bandwidth. Band Width = f H - f L 3. Draw the circuit diagram of CC amplifier. Draw the input and output waveforms. Input Output. Distinguish between positive feedback and negative feedback. Positive feedback Negative feedback. Feedback voltage in phase with Feedback voltage out of phase with the input the input. A f = A / ( - Aβ) A f = A / ( + Aβ) 3. Noise and distortion increases Noise and distortion decreases. Gain increases Gain decreases Any two, mark each. 5. Mention any two applications of a comparator. Zero crossing detector. Schmitt trigger 3. Phase detector. Voltage level detector 5. Oscillator Any two applications, mark each. 6. Draw the circuit symbol and electrical equivalent circuit of a crystal. Page
Circuit symbol of crystal Electrical equivalent circuit of crystal 7. What are sky waves and space waves? EM waves sent towards the sky which get reflected by the ionosphere and return back to the earth surface is called sky wave. Line of sight waves are called space waves. OR The radio waves that are transmitted in the troposphere are called space waves. OR The radio waves which penetrate the ionosphere, get reflected by satellite and reach the earth surface is called as space waves. 8. Draw the block diagram of AM transmitter 9. Distinguish between latch and flip-flop Latch Flip-Flop. Store data temporarily Store data permanently. Clock is not required Clock is required 0. Draw the logic diagram of full adder using 3-input XOR gate and basic gates Page 3
. The truth table of a gate is given below. Identify the gate and write its logic symbol. Inputs Output A B Y 0 0 0 0 0 0. X-NOR gate. Name the two techniques that increases channel capacity in mobile communication Frequency reuse Cell splitting PART C 3. Using the following data, calculate the experimental and theoretical values of voltage gain for an Op-Amp non-inverting amplifier. Input V i = 0.5 V 3. Sl. R i in kω R f in kω V 0 in volts Voltage gain Theoretical Practical. 8..36. 5.6.83 A VT = A VP = V o / V i A VT = + (8. k /. k) =.7, A VP =.36 / 0.5 =.7 A VT = + (5.6 k /. k) = 5.66, A VP =.83 / 0.5 = 5.66 OR 3. The output waveform of Wien-bridge oscillator is shown below. Calculate the value of resistance when C = 0.0µF (Consider R = R = R and C = C = C) 3 = = khz OR Page
R = 5.93 kω. Find the input base resistance and voltage gain of the CE transistor amplifier for the data given below: R = 7 kω, R = kω, R C = 3.3 kω, R E = kω, R L = 0 kω, V cc = 8 V, β = 00, V BE = 0.7 V and r e = (5mV / I E ). V = = ( ) = 3.66 V V E I E = 3.66 0.7 =.96 V = V E / R E =.96 / k =.96 ma r e = 5 ma /.96 ma = 7.56 Ω Z in base = β r e = 00 x 7.56 = 756Ω A v = - (R c R L ) / r e = - (3.3k 0k) / 7.56 = -.9 5. Draw the circuit diagram of RC coupled amplifier. Mention its two advantages 5. Any two advantages, mark each.. It is less costly. It has wide frequency response 3. It provides less frequency distortion. It has no coils or transformers 5. Overall gain is high Page 5
6. An amplifier has an open gain of 50 and bandwidth of 00 khz. Calculate its gain and bandwidth after % negative feedback. A f = A / ( + Aβ) = 50 / ( + (50 x 0.0)) =. BW f = ( + Aβ) BW = ( + (50 x 0.0)) 00k =. MHz OR BW f = A BW / A f = (50 x 00k) /. =. MHz 7. With a circuit diagram, derive an expression for the output voltage of an Op-Amp subtractor Let V o be the output, with input V acting alone, assuming V = 0 ------------------- () Let V o be the output, with input V acting alone, assuming V = 0 ( ) -------------------- () Vo = Vo + V0 If R = R and R 3 = R f, then, = + If R f = R = R, then Vo = V V Page 6
8. A Hartley oscillator oscillates at 5 khz. If the capacitor in tank circuit has a value of 0.0 µf and one of the inductors is mh, calculate the value of the other inductor. ( ) ( ) ( ) = 0.06 H Hence L = 0.06 H 0.00 H = 0.006 mh = 0 mh 9. Draw the amplitude modulated waveform. Derive an expression for the instantaneous voltage of an AM wave. 9. Instantaneous voltage of modulating signal, v m = V m Sin m t Instantaneous voltage of carrier signal, v c = V c Sin c t V m and V c are maximum amplitudes of modulating and carrier signals respectively. Instantaneous voltage of amplitude modulated wave v AM = (V c + v m ) Sin c t = (V c + V m Sin m t) Sin c t = V c ( + m a Sin m t) Sin c t because, (V m / V c ) = m a Where m a is the modulation index. ( ) ( ) Page 7
30. With a circuit diagram, explain the working of linear diode detector. Circuit Diagram: Working: Diode D rectifies AM wave. Capacitor C 3 provides low reactance to carrier and high reactance to signal. Resistor R provides discharging path to C. Capacitor C adds zero level to detected signal. 3. Simplify the following Boolean expression by using K-map, Y = f(a, B, C, D) = m(0,,,, 5, 8, 9, 0,, 3). Draw the logic circuit for the simplified expression using only NAND gates. Y = f(a, B, C, D) = m(0,,,, 5, 8, 9, 0,, 3) PART D 3. Draw the PIN diagram of IC-7. Describe an experiment to study Op-Amp adder. 6 Page 8
3. PIN Diagram: Aim: To construct an op-amp adder and to compare theoretical and practical values of the output voltages (for DC inputs). Equipments and Components: Dual power supply ± V, variable RPS, resistors, IC 7, voltmeter Circuit Diagram: Procedure:. Rig up the circuit as shown in figure. Set the different values of V and V and record the output voltages Tabular column or observation: Input voltage (in volts) Theoretical o/p voltage (in volts) V V V o = - ( V + V ) Practical o/p voltage (in volts) Result: The theoretical and practical values are agreeing with each other. Page 9
3. OR 3. Draw the pin configuration of IC 700. Describe an experiment to realize halfadder using NAND gates. PIN diagram of IC 700: 6 Aim: To construct half adder using IC700 and to verify its truth table. Equipments and components: Digital trainer kit, IC700, LED, RPS 5V Logic Diagram: Procedure:. Rig up the circuit as shown in figure.. For various combinations of inputs A and B, as given in the truth table, the logic levels at the output are verified, by on and off of LEDs. Inputs Outputs LED response A B Sum Carry Sum Carry 0 0 0 0 Off Off 0 0 On Off 0 0 On Off 0 Off On Result: Truth table of the half adder is verified. Page 0
33. With the circuit diagram, describe the procedure to draw input and output characteristic curves of a transistor in CB configuration. 6 CB Amplifier Input characteristics:. Set V CB constant.. Set different values of V EB and find the corresponding values of I E. 3. Plot the graph of I E versus V EB Output Characteristics:. Set I E constant. Set different values of V CB and find the corresponding values of I C. 3. Plot the graph of I C versus V CB. Page
3a. What is dark current? Draw the circuit diagram of opto-coupler. Mention its one application. 3a. When there is no incident light a small, thermally generated collector to emitter leakage current, I CEO flows. This is called dark current. Circuit diagram: Applications (any one).. For telephone line coupling. In audio applications 3. In peripheral equipment isolation 3b. A single stage CE amplifier has a gain of 60 db. If the input signal is 0 mv, 3b. calculate the output voltage. 60 db = 0 log A v A v = 000 A v = V o / V i Hence V o = 0 x 0-3 x 000 = 0 V 35a. What is an integrator? Draw the circuit diagram and obtain an expression for its output voltage. The circuit whose output is proportional to the integral of the input is referred to as an integrator. Circuit Diagram: Page
From the figure i f = i i....() i f = dq/dt = Cd(V 0 - V G )/dt = Cd(V 0 )/dt.() i i = (V G -V i )/R = -V i /R (3) Therefore, Cd(V 0 )/dt = -V i /R V0 - Vi dt RC (Proper steps must be considered) 35b. Calculate the output voltage in the circuit shown below: 35b. Note: If the quastion number (35b) is written by the student, full () marks must be awarded because signs of inverting and non inverting terminals of the first op-amp is printed wrongly in question paper. 36a. With a circuit diagram, explain the working of phase shift oscillator. Write the expression for frequency of oscillations. Circuit diagram: 3 RC sections produce a phase shift of 60 o each and the total phase shift is 80 o in the RC network. The op-amp inverting amplifier introduces a phase shift of 80 o between its input and output. Total phase shift is 360 o and loop gain Aβ =, which are required for the sustained oscillations. Page 3
36b. Calculate the feedback factor in the tank circuit shown below. C = µf, C = 0 µf, L = mh 36.b β = C / C = µ / 0µ = 0. 37a. Draw the block diagram of FM receiver. Mention two advantages of FM. 37a. Block diagram: Any two advantages: ( mark each). All transmitted power is useful.. Noise supression is better than AM 3. Signal interference from adjacent channel is very less. Signal to noise ratio is high 37b. A 50 MHz carrier is modulated by a 0 Hz audio signal. If the carrier voltage is 37b. V, and the maximum deviation is 0 khz, calculate the bandwidth. BW = ( + f m ) = (0 k + 00) = 0.8 khz 38a. Draw the block diagram of digital computer. Explain the function of ALU and memory unit. 38a. Block diagram: \ Page
ALU: Arithmetic Logic Unit is designed to perform basic arithmetic operations (add, subtract), logical operations (AND, OR, etc) Memory unit: The function of the memory unit is to store programs and data. 38b. Express the expression into canonical SOP form.. ( ) ( ) 39a. With a block diagram, explain the working of RS flip-flop 39a. Block diagram: The output of an RS flip-flop remains in the same state as long as the clock pulse is zero, regardless of the R&S inputs.. When clock=, R=0, S=0, the output remains in the previous state.. When clock=, R=, S=0, the output is reset 3. When clock=, R=0, S=, the output is set. When clock=, R=, S=, the output is in forbidden state Truth table: Inputs Output Clock State S R Q X X NC NC 0 Remains in the previous state 0 0 NC NC Remains in the previous state 0 0 SET 0 0 RESET?? Forbidden or invalid condition 39b. Construct OR and AND gates using NOR gates OR Gate using NOR gate Page 5
AND Gate using NOR gate 0a. Draw the block diagram of monochrome TV receiver. Block diagram of monochrome TV receiver 0b. What are uplink and downlink signals? The signal transmitted from the earth to satellite is called uplink signal. The signal transmitted from the satellite to earth is called downlink signal. ******* s * s ******** Page 6