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UANDISTAR Code No: V0421/R07 II B.Tech II Semester, Regular Examinations, Apr – 2011 PULSE AND DIGITAL CIRCUITS (Com. to ECE, BME, ECC) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. a) Verify that one of the levels of the voltage across Capacitor V 2 = (V/2) (e 2x -1) / (e 2x +1) = (V/2) tan hx when a symmetrical square wave with time period of ‘T’ is applied to a low pass RC circuit. Here x = T/(4RC). b) A 1 kHz symmetrical square wave of ±10 V is applied to an RC circuit having 1 ms time constant. Calculate and plot the output for the RC configuration as i) high-pass circuit ii) Low pass circuit. 2. a) Explain transfer characteristics of the emitter coupled clipper and derive the necessary equations. b) Draw the basic circuit diagram of positive peak clamper circuit and explain its operation. 3. Write the following in detail: a) Diode switching times, b) Switching characteristics of a transistor and c) FET as a switch. 4. a) With the aid of circuit diagram, obtain the mathematical relation that a collector coupled astable multivibrator can function as a voltage to frequency converter. b) Consider a symmetrical collector coupled astable multivibrator using n-p-n Si transistors. The circuit and device parameters are: V CC = 6 V, R C = 560 g525 , R = 5.6 k g525 , C = 50 pF, h FE = 40 and r bb = 100 g525 . Calculate i) the waveforms at the base and collector of one transistor and plot to the scale. Also find the recovery time and frequency of oscillations. 5. a) Draw and explain the typical waveform of a time-base voltage generator. Explain various types of errors encountered in time base generators. b) Explain the principle of working of exponential sweep circuit with neat circuit diagram and also derive the equations for slope, transmission and displacement error. 6. a) How an astable multivibrator can be synchronized? Illustrate with waveforms. b) A symmetrical astable multivibrator using Germanium transistors and operating from a 10 V collector supply voltage has a free period of 1ms. Triggering pulses whose spacing is 750 μs are applied to one base through a small capacitor from a high impedance source. Find the minimum triggering pulse amplitude required to achieve 1:1 synchronization. Assume that the timing portion of the base waveform is linear. 7. a) Sketch circuit of a simple diode bidirectional sampling gate and describe its functioning with neat waveforms. Obtain the expressions for gain A, and the two minimum control voltage levels. b) Describe the operation of chopper amplifier. Give the operation of the transistor as a chopper switch in ON state and in OFF state.
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