AMIETE – ET/CS/IT (NEW SCHEME) – Code: AE53/AC53/AT53

Subject: ELECTRONIC DEVICES AND CIRCUITS

Time: 3 Hours Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q.1 must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1 Choose the correct or the best alternative in the following: (210)

a. In practical current source, the source impedance is

(A) zero

(B) very low in comparison to load-resistance

(C) very high in comparison to load-resistance

(D) infinite

b. Avalanche breakdown primarily depends on the phenomenon of

(A) ionization (B) doping

(C) recombination (D) collision

c. For a given emitter-current, the collector current can be increased by

(A) reducing the recombination rate in the base region.

(B) doping the emitter region lightly.

(C) reducing the minority carrier mobility in the base region.

(D) making the base region more wider.

d. If and for a transistor then the value of will be

(A) 2.3 mA (B) 3.1 mA

(C) 4.6 mA (D) 5.2 mA

e. A FET

(A) incorporates a forward bias junction.

(B) uses a high concentration emitter junction.

(C) depends on variation of a magnetic field for its operation.

(D) depends on the variation of the depletion layer width with reverse voltage for its operation.

f. The h-parameters are called hybrid-parameters because

(A) they are obtained from different characteristics.

(B) they have mixed dimensions.

(C) they are mixed with other parameters.

(D) all of the above.

g. Multistage amplifiers are employed for having larger

(A) voltage gain (B) power gain

(C) frequency response (D) all the above

h. Transformer coupling is used in a class A power amplifier, so as to make it

(A) More efficient (B) less bulky

(C) less costly (D) distortion free

i. Feedback in an amplifier increases the input impedance from to because of

(A) positive feedback (B) shunt-current negative feedback

(C) series-current negative feedback (D) shunt-voltage negative feedback

j. In a RC-phase shift oscillator having three stages, which have equivalent resistors and capacitors, in order to satisfy Barkhausen criteria, should have a minimum gain of

(A) 6 (B) 29

(C) 31 (D) 49

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2 a. Obtain the response for a step input applied to RC low pass circuit. (4)

b. State and prove reciprocity theorem. (6)

c. For the resistive circuit shown in the Fig. 2c, find voltage V across the 40 resistance using mesh analysis. (6)

Fig. 2c

Q.3 a. Draw Volt-Ampere characteristics of silicon p-n junction (4)

b. Define Transition and Diffusion capacitance. (4)

c. (i) Draw the output waveform for the circuit shown in Fig.3c, considering Si practical diode, assuming negligible R_f and infinite reverse resistance (). (4)

(ii) Show that efficiency of the full-wave rectifier is

where R_s is Transformer secondary resistance.

R_f is forward diode drop

R_L is load resistance (4)

Q.4 a. Explain two-Transistor model of SCR. (5)

b. With neat diagram explain the Drain and Transfer characteristics of JFET. (6)

c. Define the current gain in Common Base and Common Emitter configuration. Obtain the relation between them. (5)

Q.5 a. Explain the working of CMOS digital Inverter. (4)

b. A transistor as a Common-Emitter amplifier is driving a load of 10 K. It is supplied by a source of 1 K internal resistance. The hybrid parameters of the transistor used are h_ie = 1.1 K, h_fe =50, h_re=2.5 10^-4, h_oe=.

Find (i) current gain (ii) Voltage gain (iii) Input impedance (iv) Output impedance.

(6)

c. Find the operating point for the circuit shown in Fig.5c, with =80 and V_BE=0.6 V. Plot the DC load line and mark Q-point. (6)

Q.6 a. Mention different types of distortion in Amplifiers. (3)

b. Obtain high frequency response of BJT RC-Coupled amplifier. (7)

c. A 1mH coil with Q=82 is used in tuned amplifier as shown in the Fig.6c. The transistor employed has =125 and r_o= 100 K and input resistance

R_i = . (i) Calculate the value of tuning capacitance such that the amplifier has a maximum gain at f_o=45 kHz. Also calculate the value of this gain (ii) Determine the bandwidth of the amplifier. (6)

Q.7 a. With neat circuit diagram explain class-B Transformer coupled Push-Pull power amplifier, show that maximum efficiency is 78.54%. (6)

b. What is Cross-Over distortion? How do you eliminate it? (4)

c. A transformer-coupled class-A power amplifier as shown in Fig. 7c, drives a 16 loud speaker through a 4:1 transformer with Vcc = 36 V, the circuit delivers 2W power to the load. Find (i) power across the transformer primary (ii) rms voltage across the load (iii) rms voltage across the transformer primary (iv) rms values of load current and primary current (v) Conversion efficiency if the dc collector current is 150 mA. (6)

Q.8 a. What are the properties of the negative feedback? (6)

b. Draw neat circuit diagram of Wein-bridge Oscillator and show that resonant frequency f_o=. (6)

c. Calculate the frequency of oscillations for the BJT Hartley Oscillator given L₁=750 H, mutual inductance M=180 H and capacitance C=160 pF. (4)

Q.9 a. Describe photolithographic process in IC fabrication. (7)

b. Draw the cross-sectional view of Monolithic n-p-n transistor and Discrete transistor. Compare the two types (6)

c. Calculate the chip area needed for a 220 pF MOS capacitor, if the thickness of SiO₂ layer is 480 Å and its relative dielectric constant is 3.8. (3)