The main objective of amplifier design is to achieve gain.
However, I am interested in the control of phase difference across amplifier for which I could not find any material.
Can we achieve a desired phase sift along with amplification using the same amplifier circuit (with no additional phase sifter)?
If anyone come across material regarding it. kindly share and any of your suggestions will be of immense help.
Srinaga,
welcome,
If you are given an amplifier with gain A which is assumed independent of frequency, then the phase shift between the output and input is equal to zero. In this case the relation between the the output voltage Vo and the input voltage Vi can be expressed by Vo= A Vi, A is real value, which means its phase is equal to zero.
If you want to use it to build an amplifier with a required gain Ad= IAdI e^j phi, where I ADI is the desired gain magnitude and phi is the desired phase,
Then you turn out to a negative feed amplifier by adding a feedback network called beta network. Beta is the transfer function of the feedback network which can be expressed by Beta= Vf/ Vo, with Vf is the feed back voltage and Vo is the output voltage. Beta network containing reactive circuit elements is a complex quantity has a magnitude= IbetaI and phase= phibeta. Then Beta= IbetaI e^ jphibeta,
From the theory of the feedback amplifier one can express the feed back amplifier gain Af as:
Af= Ad= A/ ( 1+ Beta A),
If Beta A is made much greater than one,
Then Ad= 1/ Beta = 1/( IbetaI e^j phibta) = IAdI e^j phi,
Fro this relation we can get
IAdI = 1/( IbetaI),
phi= - phibeta,
Which means that the desired gain can be controlled by the inverse value of beta while its phase is the negative value of the phase of beta.
We have to remember that one has only to satisfy the condition ABeta>>1.
which can be practically satisfied.
Best wishes
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