PULSE & DIGITAL SWITCHING CIRCUITS PAPER1

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PULSE & DIGITAL SWITCHING CIRCUITS (New) EC 309 5TH Sem May 2k5

Max marks 60

Note: Section A is compulsory. Attempt any Four questions from Section B and two questions from section C.

Section A Marks 2 each
1.
(a) (a)What are the disadvantages of RL linear waveshaping circuit compared to RC circuit?
(b) Draw V-I characteristics of an idea diode.
(c) Sketch diagram of a circuit that will clip all levels below -20V and above 30V.
(d) What are advantages and disadvantages of symmetrical and unsymmetrical triggering?
(e) Why step input amplifier response in not flat tapped?
(f) List uses of distributed amplifier.
(g) How Schottky diode reduces storage time in transistor?
(h) Describe clamping circuit theorem.
(i) Draw transistor based circuit diagram of Schmitt trigger.
(j) Design astable multivibrators using OP-AMP.

Section B Marks 5 each

2. Obtain the response of a low pass circuit to a ramp input. Discuss the effect of RC on the response.

3. Find the output response of the circuit:

(a) if input is 100 V peak to peak square wave having a period of 200 microsecond if L1=100 mh.
(b) 500 mh.

4. At low frequencies the short circuit CE current gain is related to short-circuit gain ? by :



Assuming this relationship remains valid at high frequencies and using b = -Ai, prove that:

where

Ai= current amplification under short circuit condition.

5. Find the value of minimum hfe required to saturate the transistor.

6. With the help of diagram, explain the operation of Bistable Multivibrator.

Section C Marks 10 each

7. Explain the working of a practical Boot strap time base generator. Sketch the output voltage waveshape and calculate the slope error.

8. (a) A fixed bias binary uses npn silicon transistors with hk=20, VCC=12 V, VBB= 3V, Rc= 1K, R1= 5K, R2= 10K.
Verify one transistor is cutoff and other transistor is saturation. Find stable currents and voltages if:
(i) VCE (sat) = 0.4 V, VBE(sat)= 0
(i) VCE (sat) = 0.4 V, VBE(sat)= 0.8V

(b) Find the input impedance of RC differentiating circuit. Is it same as that of rL differentiating circuit.

9. Design an Astable multivibrators using transistors and explain its action. Sketch waveform at various points. Design an Astable circuit using Ge transistors to generate a square waveform of amplitude 10 V at a frequency of 10 kHz with a duty cycle of 0.4. Choose C1=C2= 0.01 micro Farad.