ch3-2

Feed Back
Feedback has been exploited in the design of amplifiers since the early days of vacuum-tube electronics. Feedback theory was developed by electronic engineers to satisfy the demand for amplifiers and repeaters exhibiting stable performance for telephone applications.
Since then, feedback has become a key design issue both in analog and digital electronic circuits and systems.
Feedback applied around an analog network allows gain to be stabilized (desensitised) with respect to variations in circuit elements, and active device model parameters. This desensitisation property is crucial in view of parametric uncertainties caused by device parameters spreads, power supply variations, temperature changes, aging phenomena, and so on. Feedback allows the input and output resistances of a given circuit to be suitably modified in any fashion desired. It improves the linearity of the output signal by reducing dependence on the parameters of inherently nonlinear active devices used to implement the open loop circuit. Finally, it can lead to an increase in the closed-loop bandwidth.