Monday, April 11, 2011

Analog Communiaction Viva-Voce Question With Answers for 5th Semester Students


Q1. What are flip flops ?

Ans: It is an electronic circuit (a bistable multivibrator) that has two stable states and thereby is capable of serving as one bit of memory.

Q2. What is a multivibrator ?

Ans: A multivibrator is an electronic circuit used to implement a variety of sample two state systems such as oscillators, timers and flip-flops. It is characterized by two amplifying devices (transistors, electron tubes or other devices) cross coupled by resistors and capacitors. The most common form is the stable or oscillating type, which generates a square wave- the high level of harmonics in its output is what gives the multivibrator its common name.

Q3. What is the purpose of multivibrator ?

Ans: The multivibrator is one form of relaxation oscillator, the frequency of which may be controlled by external synchronizing pulses.

Q4. What is an astable multivibrator called so ?

Ans: There is no stable state where the circuit can come to rest, so this circuit is known as an astable multivibrator.

Q5. Why is an monostable multivibrator called so ?

Ans: The monostable circuit has only one stable state (output low) hence the name monostable.

Q6. What is an astable multivibrator ?

Ans: Astable multivibrator is a two stage switching circuit in which the output of the first stage is fed to the input of the first stage and vice versa. The output of both the stages are complementry. It has two stable states and switches back and forth from one state to another, remaining in state for a time depending upon the discharging of the capacitive circuit.

Q7. What is a monostable multivibrator ?

Ans: Monostable multivibrator often called a one shot multivibrator is a pulse generating circuit in which the duration of this pulse is determined by the RC network connected externally to the 555 timer.

Q8. What is the purpose of monostable multivibrator ?

Ans: A monostable device, on the other hand, is only able to hold in one particular state indefinitely. Its other state can only be held momentarily when triggered by an external input.

Q9. Give some examples of multivibrator.

Ans: The flip-flop is a free running multivibrator.

Q10. Mention the applications of multivibrator.

Ans: It finds applications in a variety of systems where square waves or timed intervals are required. Simple circuits tend to be inaccurate since many factors affect their timing, so they are rarely used where very high precision is required.

Q11. What is the principle of monostable multivibrator ?

Ans: All monostable multivibrators are timed devices. That is, their unstable output state will hold only for a certain minimum amount of time before returning ti its stable state.

Q12. How does a monostable multivibrator work in terms of the astable multivibrator ?

Ans: Like the astable multivibrator, one transistor conducts and the others cut-off when the circuit is energized.

Q13. What is the disadvantage of an astable multivibrator ?

Ans: When the astable m/v was first energized, it was impossible to predict which transistor would initially go to cut-off because of circuit symmetry.

Q14. What are the different types of multivibrator circuits?

Ans: There are three types of m/v circuits: Astable, Monostable, Bistable.

Q15. What is Schmitt trigger ?

Ans: The schmitt trigger is a comparator application which switches the output negative when the input passes upward through a positive reference voltage. It then uses negative feedback to prevent switching back to the other state until the input passes through a lower threshold voltage, thus stabilizing the switching against rapid triggering by noise as it passes the trigger point. In electronics, a schmitt trigger is a comparator circuit that incorporates positive feedback.


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