RIB. ELECTRICAL ENGINEERING Analog Electronics. 8 Electrical Engineering RIB-R T7. Detailed Explanations. Rank Improvement Batch ANSWERS.

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1 8 Electrical Engineering RIB-R T7 Session 08-9 S.No. : 9078_LS RIB Rank Improvement Batch ELECTRICL ENGINEERING nalog Electronics NSWERS. (d) 7. (a) 3. (c) 9. (a) 5. (d). (d) 8. (c) 4. (c) 0. (c) 6. (b) 3. (a) 9. (d) 5. (a). (a) 7. (c) 4. (c) 0. (b) 6. (b). (c) 8. (c) 5. (a). (c) 7. (a) 3. (d) 9. (c) 6. (b). (d) 8. (c) 4. (d) 30. (c) Detailed Explanations. (d) (6 m)(6 kω) 36 I 0 6 m 0 K I 0 6 m m 4 m I 0. (d) 00 k 0 k k 99 k

2 RIB-8 EE nalog Electronics 9 Set, 0 R then F R 99k where ( ) 99k k so, Now, set k 0 k k 99 k then hence , 0 3. (a) 5 9 I L(max) z(min) 0 k i m 4. (c) For M to operate in saturation; dsi gs tn i 0 i lso, I D kn( gs ) ( ) tn kn gs tn gs gs 5 i 5 i 5 i > i i 6 i 3 Thus, maximum input that can be applied is 3.

3 0 Electrical Engineering 5. (a) The feedback element (R F ) is directly connected to both input and output. So, voltage-shunt type of feedback. 6. (b) Since there is a D.C level shift in the output waveform, the circuit must be a clamper circuit and when the diode is conducting, the voltage at the output must be 5 as seen from the output waveform hence option (b) is correct. 7. (a) From the circuit it is clear that D will always be off. Thus kω 0 0 kω 0 kω (0 0.7) 0 kω 0 kω 8. (c) dt RC i t C 50 0 i t C.5 mf 9. (d) For the Hartly oscillator shown, L L 0. (b) For ve half cycle 0 ωt π L or 4 L 48 L L 48 µh L max 48 µh I B 0 sinωt 0k to produce sustained oscillations

4 RIB-8 EE nalog Electronics I B 0sinωt D 0 kω I B sinωt m For ve half cycle π ωt π I B 0 sinωt 0k I B 0sinωt 0 kω 0 kω I B sinωt m form here I B sinωt m for all ωt R B I B B 0sinωt 0 kω 3 sinω t 0. (c) 0 0 R kω R kω R 3 50 kω R kω v 0 R 3 50 kω R kω v 0 C 0.0 µ F 0.0 µ F C 0.0 µ F 0.0 µ F figure-i figure-ii alue of R corresponding to figure-i is kω and value of R B is 5 kω. alue of R corresponding to figure-ii is 5kΩ and value of R B is kω. So, kω R 5 kω kω R B 5 kω f max R R C ( ) B

5 Electrical Engineering f max ( ) f max.7 khz. (d) ssume that the gain is very large i.e. v >> thus v for unbypassed R E and for large values of R E R E >> thus, the voltage gain of above circuit will become βrc gmrc re βrc v gmr β R E r βr r 3. (c) now, since β is very large thus, RC v R v 0k Ω kω 5 E E e E e 4 k 50 Ω Ω 0.5 b i b 50 Ω 50 Ω 50 Ω 50 Ω b 3 i b 4.3k and i b 00 for b k b and for b 6

6 RIB-8 EE nalog Electronics Regulation Regulation 4.545% 00% 4. (c) Maximum power dissipation P Dmax Tjmax T 0 θ W (θ Thermal resistance) CE I C max P D max I C max (a) Base emitter loop.5 kω 500 kω I C I B IE kω R in 500 ki B 0.7 k (I B I C ) I C 00I B I E 0 I B from here I B 8.88 µ T T 6 β k Ω.38k Ω I I 8.8 C B R in ( β)r E.383k 0 k 0.38 kω 6. (b) Small signal circuit is i R G gs R D 7 kω gs 0 gs R D

7 4 Electrical Engineering gs i i R D W µ ncox I D m L v i R D (a) df f 0.% d 50, 000 d f f d β β 000 β 37.5 β Thus, f (c) Drawing the small signal model of the above circuit, we get R in in R r g π m π π Let R be the input resistance as seen in from point. Thus, to calculate R we can draw the diagram separately I π π R I r π gm

8 RIB-8 EE nalog Electronics 5 9. (a) Thus, the value of the output voltage o in (R R ) o g m R rπ in g m D γ R eq kω i 0 eq eq R eq 6 3 kω. 9 i 0; as i > eq, D is ON and the voltage across the diode will be γ. γ i volts. 0. (c) 9 50 kω B I B 0.7 I B R B 0.5 m EC 4.7 kω E C 9 I C I B β 49(0.5) ( I E) m 0.49 m β m 0 µ 50 E I B R B EB (0.0) (50) 0.7. C EC P Q I C R C 9 (0.49)(4.7) (6.697 ) I C EC (0.49)(7.897) mw 3.87 mw

9 6 Electrical Engineering. (a) kω 0 kω i kω kω kω i 0 k Ω 0 k Ω k k 0 Ω Ω i 0( ) 0 i kω k Ω i i so, 0 i 0 i (0sinωt 0cosωt) m i (sinωt) m and i (cosωt) m. (c) We know β 0 sin( ωt 45 ) m β kω 0 Drawing the small signal equivalent, we get Iin R S in R R π π R L R C R eq R E in R I in R S (R R R eq ) in now, to calculate R eq, we can use another model I (I π )R E now, π I I R E I R E I β ( (β )R E )I I R eq π R E π R eq rπ ( β ) RE I

10 RIB-8 EE nalog Electronics 7 R in R S [R R ( (β )R E ] putting the values R eq 0 kω kω R in kω 4.6 kω 5.6 kω 3. (d) Since the two port network is symmetric thus converting it into T network we get the circuit as shown below. 0 kω 0 kω I 3 i kω I I kω I 4 I i I k Ω 0 i and I 3 kω i and I 4 I I 3 kω 0 i or, i 0 4. (d) For S < 0 ; Diode is ON, and the positive terminal of op-amp is forced to O. 0 S For S > 0; Diode is off and the positive terminal of op-amp now follows S since no current flows in resistor, so must follow S. 0 S 5. (d) Let us assume M is in saturation I D W µ n Cox ( gs Th) 00 (0.36) µ L 0.8 I D 00 µ Now, D DD R D I D 0.8 DS ssumption is correct when g.0 s

11 8 Electrical Engineering 06.7 D Drain voltage changes by 34 m. I D 6. (b) Current through photodiode I (0.8) (0) m m I C β I E kω I I 0 I o kω ref I C I 8 m I E ( β ) IC 8.m β 80 β BE 0.7 so, I 0 kω 0.7 m I 0 I E I 8. ( 0.7) m 8.8 m 7. (c) knid m/ now, drawing the T equivalent model, we have R sig /g i m o sig i 0 R D R L i and out sig R gm sig ( R R ) D L R g m sig sig

12 RIB-8 EE nalog Electronics 9 8. (c) out gm( RD RL) out sig g R out m sig ( 0 0 ) 0 0 m R 4R i R i R 4 i 4 i 8 i gain i 8 9. (c) MOS T serve as drain resistance for T DD DD T R out out out in T in T Calculating R out of T I x gs gs x pplying KCL at node, I x gs gs x Thus x I x g m R out for transistor T in gs gs R out out out gs R out

13 0 Electrical Engineering gs out in v in R out gm ( R g out m ) 30. (c) CC 0.5 m I 0.5 m Using current mirror concept, For large β, I I ref so, I y ( ) m I x ( ) m I x I y (0.5) 5 m.5 m