# RTU Previous Exam Papers BE EC 3rd Semester

# 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 V_{f} = 0 and r_{f} = 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 h_{fe} = 50, h_{oe} = 25* 10^{-6} Mho, h_{re} = 2.5x 10^{-4} if R_{l} = 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 V_{p} = -2V, g_{mo} = 1.60 mA/V and I_{DSS} = 1.65mA. It is desired to bias the circuit at I_{D} = 0.8 mA using V_{DD} = 24V assume r_{d} ^{>>}R_{d} Determine such that the voltage gain is atleast 20 dB with R_{s} 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 A_{f} = 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 l_{2} = 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 L_{s} = 0.8 H, C_{s} = .08 PF R_{s}=5 RQ and C_{p} = l.9PF Determine the resonance frequencies F_{s}and F_{p}

**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.