L.F. Transistor Feedback Amplifier

ABSTRACT

1.	If the feedback amplifier's circuit configuration allows its return ratio—Aβ to be expressed in factored form, the inherent poles and zeros contributing to its transmission characteristics are easily seen and could be employed for constructing a pole zero diagram. Such a diagram would indicate at once though not precisely, the locations of additional poles and zeros required to correct the Aβ characteristics in a desired manner. Further, if the correcting network's performance is also expressed in terms of their poles and zeros, then all that is required is to introduce the correcting networks having poles and zeros corresponding to the desired ones.
2.	The above method has been adopted for the design of a low frequency feedback amplifier with 27db. feedback and 45 db. of closed loop gain. Transfer ratios (current/voltage, etc.) of simple compensating networks have also been derived in terms of poles and zeros and network element values. These could readily be employed for the design of correcting networks possessing the specified values of poles and zeros.
3.	The above design method based on pole zero diagram could further be extended to embrace the plotting of the locus of the roots of return difference 1 + Aβ and used for locating the poles and zeros to yield maximally flat or any desired closed loop response with the required amount of feedback.