# Electronic Devices and Circuits Dec-2011

Unit-I

1.  a) What do you understand by clamping circuit with neat diagram explain the action of

i) Positive clamming and

ii) Negative clamper

b) Describe the Hall effect? What properties of a semiconductor are determined From a Hall effect experiment?

OR

a) Find the output of a clipper as shown in Fig. (i). Assume that Vf = 0 and rf = 0 for both diode

b) Explain the significance of Fermi level in intrinsic and extrinsic semiconductor energy band distributions?

Unit-II

2. a) Find out the expression of S,S’ andS” for Potential divider biasing circuit (For C.E. configuration)

b) Draw and explain Ebers Molls representation of B JT? Also define the voltage

OR

a) Draw the circuit of transistor in common emitter configuration of BJT and sketch the output characteristics indicate the active, saturation and cutoff

region. Derive the relationship between a and /? for BJT?

b) h – parameter for CE amplifier has h.e =1100Q hfe = 50, hoe = 25* 10-6 Mho, hre = 2.5x 10-4 if Rl = iKH Determine the following parameters

i) current gain

ii) voltage gain in) power gain

Unit-III

3. a) Draw the R-C coupled amplifier circuit? Calculate the current gain for low, middle and high frequencies region?

b)  The amplifier of Fig. (2) Utilizes an N-channel FET for which Vp = -2V, gmo = 1.60 mA/V and IDSS = 1.65mA. It is desired to bias the circuit at ID = 0.8 mA using VDD = 24V assume rd >>Rd Determine such that the voltage gain is atleast 20 dB with Rs bypassed with a very large and current used in Ebers Molls Equation for PNP transition.

iv) input impedance

OR

a) Explain the working of n-channel MOSFET. What is the difference between

enhancement and depletion mode of operation.

b) Explain Miller’s theorem. Define Boot strapping with its electrical equivalent circuit?

Unit-IV

4. a) Explain the Brakhausen criterion for sustained oscillations, b) Prove that in a negative Feedback amplifier Where Af = gain with feedback, A – transfer gain, ft = feedback factor.

OR

a) Draw the circuit diagram of voltage shunt Feedback amplifier with its necessary effects? What are the difference between voltage shunt and voltage series Feedback amplifier?

b) Determine the operating frequency of a Hartley oscillator if L, = lOO^H l2 = lmH mutual inductance between coils M = 10/vH and C = 10 PF

Unit-V

5. a) Draw the circuit of the wein bridge oscillator. Derive the expression for frequency of oscillation for such as oscillator.

b) The parameter of a crystal oscillator equivalent circuit are Ls = 0.8 H, Cs = .08 PF Rs=5 RQ and Cp = l.9PF Determine the resonance frequencies Fsand Fp

OR

a) With the help of circuit diagram explain the working of “ Astable multivibrator” give its waveform what are the basic difference among the three types of multivibrator circuits

b) Draw the circuit of a Schmitt Trigger using BJT and explain its working with input voltage versus the output voltage curve.