ch3-3

F.B method
However, all the features are paid for in terms of a proportional reduction in gain. This is usually a small price to pay, particularly in applications using operational amplifiers whose dc open-loop voltage gain is very large. Besides, as already mentioned, (negative) feedback can determine oscillation; hence, frequency compensation is usually mandatory.
There are several approaches for analysing feedback circuits. The most straightforward one is to directly analyse the circuit by writing the Kirchhoff equations on the small-signal circuit and deriving the circuit characteristics. However, this approach is computationally tedious, it does not allow one to disclose the general properties of feedback circuits which can greatly simplify the analysis and, perhaps more importantly, it gives no insight into circuit behavior and hardly provides useful design equations. Thus, alternative approaches have been developed.
These are four types which realise voltage, current, transresistance and transconductance closed-loop amplifiers, respectively, and are capable of significantly reducing the dependence of forward transfer characteristics on the ill-controlled parameters implicit to the open-loop gain. Particularly, this chapter analyses first the low-frequency performance of these architectures, which are normally realised by multi-stage topologies, and subsequently gives frequency compensation guidelines.