Hybrid-pi model

Hybrid-pi is a popular circuit model used for analyzing the small signal behavior of bipolar junction and field effect transistors.

The hybrid-pi model is a linearized two-port network approximation to the BJT using the small-signal base-emitter voltage,

[2] A basic, low-frequency hybrid-pi model for the bipolar transistor is shown in figure 1.

Ce is the diffusion capacitance representing minority carrier storage in the base.

[4] A basic, low-frequency hybrid-pi model for the MOSFET is shown in figure 2.

is the transconductance, evaluated in the Shichman–Hodges model in terms of the Q-point drain current,

Figure 1: Simplified, low-frequency hybrid-pi BJT model.
Full hybrid-pi model
Figure 2: Simplified, low-frequency hybrid-pi MOSFET model.