Or Devices Circuits

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Code No: NR10205

I B.Tech Supplementary Examinations, June 2005 SEMICONDUCTIOR DEVICES & CIRCUITS ( Common to Electrical & Electronic Engineering,Electronics & Communication Engineering,Computer Science & Engineering,Electronics & Instrumentation Engineering,Bio-Medical Engineering,Information Technology,Electronics & Control Engineering,Computer Science & Systems Engineering,Electronics & Telematics and Electronics & Computer Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Derive an expression for magnetic deflection sensitivity of a C.R.O. (b) An electron is injected with an initial velocity υox : 4 × 106 m/sec halfway between two large parallel plates 0.5cm apart. The XZ plane is parallel to the plates. There is a voltage of 200V impressed between the plates, and a magnetic field of 10mwb/m2 perpendicular to the plates, directed from the positive to the negative plate. Where does the electron strike the positive plate and with what velocity? 2. (a) Derive the expressions for diffusion and transition capacitances of pn. junction diode (b) An ideal Ge pn junction diode has a reverse saturation current of 30µA. At a temperature of 1250 C find the dynamic resistance for a 0.2V bias in i. the forward direction ii. the reverse directions. 3. (a) The reverse saturation current of the Ge transistor as shown in figure is 2µA at room temperature (250 C) and increases by a factor of 2 for each temperature increase of 100 C. Find the maximum allowable value for RB if the transistor is to remain cut off at a temperature of 750 C.

(b) Explain the working principle of MOSFET in enhancement and depletion modes. 1 of 2

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Code No: NR10205 4. (a) Explain various methods of bias stabilization.

(b) Design a self-bias circuit for V cc = 12V, Rc = 2kΩ, VCEQ = 9V andICQ = 3mA, S = 20, β=30. 5. (a) Derive the expressions for transconductance and input conductance of hybrid Q - P CE transistor model. Q (b) Compute the values of all the hybrid- parameters for the given values. IC=10mA, VCE=10V, at room temperature, hie=500Ω, hoe=10−5 A/V, hfe=100 hre=10− 4, ft =50 MHz, and cob=3PF. 6. (a) Mention the applications of feedback. (b) Prove that negative feedback decreases the distortion and decreases the o/p resistance of an amplifier. (c) In a collector-to-base bias feed back circuit RC=10k, Rb=100k, Rs=1k, Re=1kΩ. hfe=100, hie=1k, hre=hoe=0. Determine Avf, Rif. 7. (a) State and explain the conditions for sustaining oscillations. (b) Explain transistor wien-bridge oscillator working principle and derive an expression for frequency of oscillations. 8. (a) Mention the advantages and disadvantages of class B push-pull amplifier. (b) Derive the expression for collector power dissipation. (c) Explain the principle of complementary symmetry transformerless class B power amplifier. ?????

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