Visualising the common-emitter transistor Hybrid-Pi model with QUCS-S and ngspice

Here I am reproducing the transistor hybrid-pi model in QUCS-S with ngspice. I wanted to view the behaviour of the Miller Effect of a transistor’s intrinsic capacitances - specifically the Collector-Base capacitance on the model at radio frequencies. This example uses a common-emitter configuration of amplifier.

This shows the basic hybrid-pi model with the collector-base capacitance disabled:-

Note the Y12 (reverse transfer admittance) parameters are all zero. The igain plot pretty much matches the expected “ideal” plot of hybrid-pi beta I show in Complex Beta of a Bipolar Transistor.

Here we enable the collector-base (Ccb) capacitance:-

further reducing gain at high frequencies (in this case above 1MHz).