Synthesis-oriented double-loop feedback model

Abstract

This paper presents a new feedback model that focuses on the synthesis rather than the analysis of feedback amplifiers. First, a single-loop synthesis-oriented feedback model is developed that enables the full synthesis of such amplifiers in a hierarchical and systematicway. This model is subsequently extended to a double-loop synthesismodel, so that also feedback amplifierswith a characteristic input or output impedance-employing two feedback loops-can be synthesized through the same systematic approach. That these new models are suitable for synthesis lies in the fact that they map directly to the circuit level, such that the intended, asymptotic behavior as well as the various individual contributors to the deviation from this intended behavior, like finite loop gain, non-ideal input and output impedances of the forward gain block, direct feed-through and attenuations outside the feedback loop(s), are clearly distinguished and can be assigned to the responsible sections of the network. For this purpose, the double-loop synthesis model makes the transfers of the two feedback networks explicitly visible, so that it gives immediate insight in how to design these networks to get the required signal transfer and characteristic impedance.