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Signal-Flow-Graph Analysis of Weakly Nonlinear Microwave Circuits around a Large-Signal Operating Point
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  • Shuhei Amakawa ,
  • Ryotaro Sugimoto ,
  • Korkut Kaan Tokgoz ,
  • Sangyeop Lee ,
  • Hiroyuki Ito ,
  • Ryotaro Sugimoto ,
  • Ryoko Kishikawa
Shuhei Amakawa
Hiroshima University, Hiroshima University

Corresponding Author:[email protected]

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Ryotaro Sugimoto
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Korkut Kaan Tokgoz
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Sangyeop Lee
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Hiroyuki Ito
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Ryotaro Sugimoto
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Ryoko Kishikawa
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Abstract

Signal flow graph (SFG) representation of small-signal responses of nonlinear microwave circuits around a large-signal operating point is developed using the X-parameters. It is shown that, unlike the SFGs for linear circuits, negative-frequency nodes need to be included explicitly. The development elucidates the circuit-operational meaning of the elusive T-type small-signal X-parameters, which represent interaction between positive- and negative-frequency components. As an example, such an SFG is used to derive a closed-form expression of the output power of an amplifier as a function of the load reflection coefficient. It is then used to plot approximate load-pull power contours. The result is consistent with the expressions of the optimum load reflection coefficient derived by Root et al. (EuMIC 2017) and of power contours derived by Peláez-Pérez et al. (TMTT 2013). SFGs provide an alternative systematic means to derive closed-form expressions in terms of X-parameters and to gain illuminating insights into the workings of weakly nonlinear circuits.
Sep 2023Published in IEEE Transactions on Microwave Theory and Techniques volume 71 issue 9 on pages 3722-3733. 10.1109/TMTT.2023.3248152