Hybrid-pi model

The hybrid-pi model is a popular circuit model used for analyzing the small signal behavior of bipolar junction and field effect transistors. Sometimes it is also called Giacoletto model because it was introduced by L.J. Giacoletto in 1969. The model can be quite accurate for low-frequency circuits and can easily be adapted for higher frequency circuits with the addition of appropriate inter-electrode capacitances and other parasitic elements.

The hybrid-pi model is a linearized two-port network approximation to the BJT using the small-signal base-emitter voltage, ${\displaystyle \scriptstyle v_{\text{be}}}$, and collector-emitter voltage, ${\displaystyle \scriptstyle v_{\text{ce}}}$, as independent variables, and the small-signal base current, ${\displaystyle \scriptstyle i_{\text{b}}}$, and collector current, ${\displaystyle \scriptstyle i_{\text{c}}}$, as dependent variables.

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