Electronic Devices - May 2015
Electronics Engineering (Semester 3)
TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) What are non-ideal effects in BJT? Explain any one non-ideal effect in BJT.(5 marks) 1 (b) Determine the ideal reverse saturation current density in silicon p_N diode at 300°k Given Na=Nd=1016 cm-3, ni=1.5×1010cm-3(5 marks) 1 (c) With neat diagram explain the operation of UJT relaxation oscillator.(5 marks) 1 (d) Compare photo diode with phototransistor.(5 marks) 2 (a) Draw energy band diagram of P-N Junction for zero, forward, reverse bias clearly showing junction diagram, depletion width, fermi energy level and barrier potential.(10 marks) 2 (b) calculate the theoretical barrier height, built in potential barrier and maximum electric field in a metal semiconductor diode for zero applied bias consider a contact between tungsten and a type silicon doped to Nd=1016cm-3 at T=300k.
The metal work function for tungsten is ϕm=4.55V and electron a affinity for silicon is x=4.01V.
Nc=2.8×1019 cm-3, K=1.38×10-23J/K, εs=11.7×8.85×10-14, e=1.6×1019c.(10 marks) 3 (a) Calculate the threshold voltage VTO at VSB for a polysilicon gate n channel MOS transistor with the following parameters-
substrate doping density NA=1016 cm-3 polysilicon gate doping density ND=2×1020 cm-3 gate oxide thickness tox=500A° oxide Interface fixed charge density NOX= 4×1010 cm-2.(10 marks) 3 (b) Derive the drain current equation ID for MOSFET in ohmic and saturation regions.(10 marks) 4 (a) Draw and explain construction, working characteristics of JFET. Explain frequency limitation factors.(10 marks) 4 (b) Explain schottky effect. Derive the position of maximum barrier Xm.(10 marks)
Draw and explain, Construction and working of:
5 (a) (i) HEMT (MODFET)(5 marks) 5 (a) (ii) MESFET(5 marks)
Explain basic structure and characteristics of:
5 (b) (i) SCR(5 marks) 5 (b) (ii) DIAC(5 marks)
Solve any four of the following:
6 (a) Draw and explain Ebers-moll model of transistor.(5 marks) 6 (b) With the help of circuit diagram and characteristics explain application of zener diode as a voltage regulator.(5 marks) 6 (c) What are optocouplers? Explain any one application of optocoupler.(5 marks) 6 (d) Sketch and explain V-I and C-V characteristics of MOSFET.(5 marks) 6 (e) Explain channel length modulation with cross section of MOSFET. Write equation associated with this effect.(5 marks)