A loop-breaking method for the analysis and simulation of feedback amplifiers

Abstract

Two-circuit models for feedback subcircuits are developed from a modification to the two-port method of feedback amplifier analysis and are applied in a method to break the feedback loop. These models are terminally equivalent to linear and nonlinear subcircuits, have physically-disconnected topologies, and employ dependent sources to control lateral signal transfer with a switch-like on or off manner. With feedback subcircuits replaced by these models in a SPICE simulation, it is possible to keep the amplifier biased at its closed-loop dc operating point while it operates in an open-loop or a closed-loop ac configuration. Small-signal analysis of the amplifier's equivalent circuit yields exact expressions for open-loop and closed-loop response functions, and the loop-gain.

Novel comprehensive feedback theory—Part II: Unifying previous and new feedback models and further results

“…However, this arbitrary splitting does not mean that A f is undetermined. Indeed, the further development of Equation (25) gives again Equation (10) with T 0 ¼ 0, α ¼ α 0 , and γ ¼ γ 0 , without any arbitrariness deriving from the use of the TTC in Figure 4A; therefore, this does not limit the applicability of this TTC. In particular, the complete analysis leads to the overall amplification…”

“…Section 4 deals with other approaches that adopt "separable" TTCs. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] In particular, as a new result, we show two choices of TTCs which allow to split the flow through a network in an arbitrary way between a part "associated with" the feedback loop and a "direct" input-output flow (and an example of this is shown for a shunt-voltage MOS amplifier).…”

A Simplified Approach to Two-Port Analysis in Feedback

“…This is because neither the difference between the output and input voltages nor the difference between the input and output currents are measured and fed to the circuit in this case. Furthermore, the case of a differential pair will be reduced to the case of c (7) in Fig. 1, where the feedback signal is assumed to reach Q1 through its emitter or reduced to the case c(8) in Fig.…”

“…This technique, despite being probably the best method for advanced designers, is a bit too complex for beginning students. Perhaps the more intuitive method of feedback analysis presented in many circuit analysis textbooks, is based on the concept of Two-Port Networks [7]. This analysis scheme is basically based on derivation of the closed-loop parameters from the open-loop gain (a) and the feedback factor (f) [8] and is originated from twoport networks theory [2].…”

Understanding Loading In Feedback Amplifier Analysis

“…A more detailed description of the application of feedback theory to amplifier analysis can be found in textbooks 1,2,3,4 and articles 5,6,7 . While the advanced feedback theory was developed by Bode 8 in 1945, a book by Chen 9 provides a recent exposition.…”