GATE EC 1994 Electronics Question Paper
GATE 1994
· Added December 2009
GATE EC - 1994 Electronics and Communication Engineering Question Paper
Read the following instructions carefully: (i) This question paper consists of two sections: A & B. (ii) Section A has NINE questions, Answer all questions in this section. (iii) Section B has TWENTY questions. Answer any TEN questions in this section. (iv) Begin answer for this section on a fresh page. (v) Answer to questions in each section should appear together in the same sequence in which they appear in the question paper. (vi) There will be no negative marking. SECTION - A 1. For each of the following (1.1 œ 1.19) questions, four possible alternatives (A,B, C and D) are given. Indicate the correct or the best answer by writing the corresponding letter (A,B,C,or D) in each question num ber. 1.1 The Laplace transform of a unit ramp function starting at t = a, is 1.2 The Fourier Series of a odd periodic function, contains only (a) odd harmonics (b) even harmonics (c) cosine terms (d) sine terms X X = = 20 and 20 , is connected 1.3 A series LCR circuit consisting of R = 10 , L C across an a.c. supply of 200V rms. The rms voltage across the capacitor is: (a) 200 90 V - ° (b) 200 90 V + ° (c) 400 90 V - ° (d) 400 90 V + ° ( ) 1.4 A ramp voltage, t = 100 volts, is applied to an RC differentiating circuit with R = 5k and C = 4 F. The maximum output voltage is: (a) 0.2 volts (b) 2.0 volts (c) 10.0 volts (d) 50.0 volts 1.5 The 3-dB bandwidth of a typical second-order system with the transfer function 1.6 If the open loop transfer function is a ratio of a numerator polynomial of degree "m' and a denominator polynomial of degree "n', then the integer (n-m) represents the number of (a) breakaway points (b) unstable poles (c) separate root loci (d) asymtotes 1.7 A small concentration of minority carries is injected into a homogeneous semiconductor crystal at one point. An electric field of 10 V.cm is applied across the crystal and this moves the minority carriers a distance of 1 cm is 20 sec. The mobility (in cm /volt.sec) will be 2 (a) 1,000 (b) 2,000 (c) 5,000 (d) 500,000 1.8 The threshold voltage of an n channel MOSFET can be increased by (a) increasing the channel dopant concentration (b) reducing the channel dopant concentration (c) reducing the gate-oxide thickness (d) reducing the channel length 1.9 A class œ A transformer coupled, transistor power amplifier is required to deliver a power output of 10 watts. The maximum power rating of the transistor should not be less than (a) 5 W (b) 10 W (c) 20 W (d) 40 W 1.10 Data can be changed from spatial code to temporal code and vice-versa by using (a) ADCs and DACs (b) shift registers (c) synchronous counters (d) timers 1.11 The output of a logic gate is "1' when all its inputs are at logic "0'. Then gate is either (a) a NAND or an EX-OR gate (b) a NOR or an EX-NOR gate (c) an OR or an EX-NOR gate (d) an AND or an EX-OR gate 1.12 A PLA can be used (a) as a microprocessor (b) as a dynamic memory (c) to realize a sequential logic (d) to realize a combinational logic 1.13 A dynamic RAM consists of (a) 6 transistors (b) 2 transistors and 2 capacitors (c) 1 transistor and 1 capacitor (d) 2 capacitors only 1.14 t t t t = - × 5 cos10 sin 10 sin 10 6 3 6 / represents (a) DSB suppressed carrier signal (b) AM signal (c) SSB upper sideband signal (d) Narrow band FM signal 1.15 Increased pulse-width in the flat-top sampling leads to (a) attenuation of high frequencies in reproduction (b) attenuation of low frequencies in reproduction (c) greater aliasing errors in reproduction (d) no harmful effects in reproduction 1.16 Medium wave radio signals may be received at far off distances at night because (a) radio waves travel faster at night (b) ground wave attenuation is low at night (c) the sky wave is stronger at night (d) there is no fading at night 1.17 For a short wave radio link between two stations via the ionosphere, the ratio of the maximum usable frequency to the critical frequency (a) is always less than 1 (b) is always greater than 1 (c) may be less than or more than 1 depending on the distance between the two stations (d) does not depend on the distance between the two stations 1.18 A plane electromagnetic wave traveling along +z œ direction, has its electric filed given by E t E t = = + ° 2 cos* and 2 cos * 90 . The wave is (a) linearly polarized (b) right circularly polarized (c) left circularly polarized (d) elliptically polarized 1.19. For a dipole antenna (a) the radiation intensity is maximum along the normal to the dipole axis (b) the current distribution along its length is uniform irrespective of the length (c) the effective length equals its physical length (d) the input impedance is independent of the location of the feed-point 2. In each of the following questions (2.1 œ 2.20) fill in the blanks appropriately. 2.2. The rank of an m n × matrix m n
Read the following instructions carefully: (i) This question paper consists of two sections: A & B. (ii) Section A has NINE questions, Answer all questions in this section. (iii) Section B has TWENTY questions. Answer any TEN questions in this section. (iv) Begin answer for this section on a fresh page. (v) Answer to questions in each section should appear together in the same sequence in which they appear in the question paper. (vi) There will be no negative marking. SECTION - A 1. For each of the following (1.1 œ 1.19) questions, four possible alternatives (A,B, C and D) are given. Indicate the correct or the best answer by writing the corresponding letter (A,B,C,or D) in each question num ber. 1.1 The Laplace transform of a unit ramp function starting at t = a, is 1.2 The Fourier Series of a odd periodic function, contains only (a) odd harmonics (b) even harmonics (c) cosine terms (d) sine terms X X = = 20 and 20 , is connected 1.3 A series LCR circuit consisting of R = 10 , L C across an a.c. supply of 200V rms. The rms voltage across the capacitor is: (a) 200 90 V - ° (b) 200 90 V + ° (c) 400 90 V - ° (d) 400 90 V + ° ( ) 1.4 A ramp voltage, t = 100 volts, is applied to an RC differentiating circuit with R = 5k and C = 4 F. The maximum output voltage is: (a) 0.2 volts (b) 2.0 volts (c) 10.0 volts (d) 50.0 volts 1.5 The 3-dB bandwidth of a typical second-order system with the transfer function 1.6 If the open loop transfer function is a ratio of a numerator polynomial of degree "m' and a denominator polynomial of degree "n', then the integer (n-m) represents the number of (a) breakaway points (b) unstable poles (c) separate root loci (d) asymtotes 1.7 A small concentration of minority carries is injected into a homogeneous semiconductor crystal at one point. An electric field of 10 V.cm is applied across the crystal and this moves the minority carriers a distance of 1 cm is 20 sec. The mobility (in cm /volt.sec) will be 2 (a) 1,000 (b) 2,000 (c) 5,000 (d) 500,000 1.8 The threshold voltage of an n channel MOSFET can be increased by (a) increasing the channel dopant concentration (b) reducing the channel dopant concentration (c) reducing the gate-oxide thickness (d) reducing the channel length 1.9 A class œ A transformer coupled, transistor power amplifier is required to deliver a power output of 10 watts. The maximum power rating of the transistor should not be less than (a) 5 W (b) 10 W (c) 20 W (d) 40 W 1.10 Data can be changed from spatial code to temporal code and vice-versa by using (a) ADCs and DACs (b) shift registers (c) synchronous counters (d) timers 1.11 The output of a logic gate is "1' when all its inputs are at logic "0'. Then gate is either (a) a NAND or an EX-OR gate (b) a NOR or an EX-NOR gate (c) an OR or an EX-NOR gate (d) an AND or an EX-OR gate 1.12 A PLA can be used (a) as a microprocessor (b) as a dynamic memory (c) to realize a sequential logic (d) to realize a combinational logic 1.13 A dynamic RAM consists of (a) 6 transistors (b) 2 transistors and 2 capacitors (c) 1 transistor and 1 capacitor (d) 2 capacitors only 1.14 t t t t = - × 5 cos10 sin 10 sin 10 6 3 6 / represents (a) DSB suppressed carrier signal (b) AM signal (c) SSB upper sideband signal (d) Narrow band FM signal 1.15 Increased pulse-width in the flat-top sampling leads to (a) attenuation of high frequencies in reproduction (b) attenuation of low frequencies in reproduction (c) greater aliasing errors in reproduction (d) no harmful effects in reproduction 1.16 Medium wave radio signals may be received at far off distances at night because (a) radio waves travel faster at night (b) ground wave attenuation is low at night (c) the sky wave is stronger at night (d) there is no fading at night 1.17 For a short wave radio link between two stations via the ionosphere, the ratio of the maximum usable frequency to the critical frequency (a) is always less than 1 (b) is always greater than 1 (c) may be less than or more than 1 depending on the distance between the two stations (d) does not depend on the distance between the two stations 1.18 A plane electromagnetic wave traveling along +z œ direction, has its electric filed given by E t E t = = + ° 2 cos* and 2 cos * 90 . The wave is (a) linearly polarized (b) right circularly polarized (c) left circularly polarized (d) elliptically polarized 1.19. For a dipole antenna (a) the radiation intensity is maximum along the normal to the dipole axis (b) the current distribution along its length is uniform irrespective of the length (c) the effective length equals its physical length (d) the input impedance is independent of the location of the feed-point 2. In each of the following questions (2.1 œ 2.20) fill in the blanks appropriately. 2.2. The rank of an m n × matrix m n