Andhra University BE/B.Tech Electronics-II Previous Paper 2007
1. answer ALL questions.
(a) What is the effect of voitage series negative feed back on input and output
impedences of the amplifier.
(b) Why does non -linear distortion arises in amplifier?
(c) Justify why RC oscillators cannot be used at radio frequencies.
(d) Why an operational amplifier should have high CMRR?
(e) What is virtual grand in operational amplifier circuits?
(f) What is the role of the commutating capacitors in a binary circuit?
(g) Why it is prefered to trigger an ‘ON’ transistor to ‘OFF’ transistor to ‘ON’.
2. (a) proove the negative feedback in amplifiers improves the signal to Noise Ratio (SNR). State the assumptions made in your derivation. (6)
(b) An amplifier with an open loop voltage gain of 1000 delivers 10 watts of output power at 10% second harmonic distortion when the input signal is 10 mV. If 40 dB negative feedback in voltage series is applied and the output is to remain at 10 watts determine
(i) the required output signal
(ii) percentage of second harmonic distortion and
(iii) closed loop voltage gain. (8)
3. (a) Prove that the frequency stability of any LC oscillator is directly propotional to the ‘Q’ of the tank circuit employed.
(b) for the feedback amplified circuit shown in circuit shown in Figure 1.0, determine
(ii) Rif and
(iii) Rof assume that the transistors have hte=2K-0hm,hfe=120,hre=0;hoe=0 parameters.
4. (a) Copmpare RC ,LC and crystal controlled osciators with refference to frequency range of operationfrequency and amplitude stability and circuit complexity.
(b) Draw the circuit diagram of a RC phase shift oscillator and explain how Bark hausean conditions are satisfied. Derive an expression for its frequency of oscillations and for the minimum value of ‘hfe’ for the transistor for the system to oscillate. (10)
5. (a) Explain with neat circuit diagrams how the following parameters of the operational amplifier are measured
(i) input -offset voltage
(ii) unity -gain band width and
(iii) input impedence. (9)
(b) Design a circuit using an operational amplifier to generate the input voltage V0 =V1+2V2=3V3,where V1,V2,V3 are input voltages. Use minimum value of resistance as 10K-Ohm.
6. (a) Draw the circuit diagram of a stable differentiator using an operational amplifier and explain how it can provide stable operation with the help of its frequency response characteistics (8)
(b) design an inverting amplifier using an operational amplifier with a gain of -5 and an input resistance of 10K-Ohm. (6)
7. (a) Draw an astable multivibrator with collector coupled and explain its operation with wave forms . Derive an expression for the output pulse width. (6)
(b) Design an astable multivibrator using NPN transistors having Vbe(sat)=0.7 Volts,Vce(sat)=0V,Vbe(cutoff)=0Vand hfe(min)=80 to produce square at 10KHZ with 50% duty cycle. Show the circuit diagram and explain its operation with wave form. Use Vcc=10V,Ic(sat)=2mA.
8. (a) explain how a transistor can be used as a switch . Under what conditions a transistor is said to be ‘ON’and ‘OFF’. (5)
(b) A fixed bias binary circuit uses NPN transistor with Vbe(sat)=0.16V,Vce(sat)=0V, and Vbe(cutoff)=0V. The circuit parameters are Rc=1K-Ohm,R1=5K-Ohm,and R2=10K-Ohm. Supply voltages cof Vcc=+10V and Vbb=-6V are used .Determine the minimum value of ‘hfe”hfe’ for the circuit to function satisfactory . With this value of hff also verify when one transistor is ‘ON’ and the other is ‘OFF’http://www.stepinau.com/2013/10/31/andhra-university-beb-tech-electronics-ii-2007/CSE 2.2 Previous PapersCSE,CSE 2.2 Previous Papers,CSE Previous Papers,Discrete Electronics-II Previous Papers,IT,IT 2.2 Previous Papers,IT Previous Papers