Explanation: The given circuit is used in inverting mode and produce a phase shift of 180o. For two corner frequency, the maximum phase shift associated with gain AoL is -180o which makes total phase shift = 0 and for some value of ß, the magnitude of Aß becomes unity. In this case the amplifier begins to oscillate as both magnitude and phase conditions are satisfied. Thus, the circuit enter into verge of instability. 15. Find out the system stability when a system has three RC poles pairs
A. Attain stability at low frequency
B. Attain stability at high frequency
C. Attain instability at high frequency
D. Attain instability at low frequency
Answer:A
Explanation: The given circuit is used in inverting mode and produce a phase shift of 180o. For two corner frequency, the maximum phase shift associated with gain AoL is -180o which makes total phase shift = 0 and for some value of ß, the magnitude of Aß becomes unity. In this case the amplifier begins to oscillate as both magnitude and phase conditions are satisfied. Thus, the circuit enter into verge of instability. 15. Find out the system stability when a system has three RC poles pairs
A. Attain stability at low frequency B. Attain stability at high frequency C. Attain instability at high frequency D. Attain instability at low frequency
Explanation: For a system with three pole pairs, AoL have three corner frequencies and contribute to maximum of 270o phase shift, at this condition AoL×ß is negative and instability occurs at high frequencies.