From Wideband Amplifier Design

It is useful to have two-port models available for the simplified transistor models introduced in Chapter 2. The model shown in Figure B-1 does not include any reference to C jc or R bb, but these items are easily added later, and there are times you would want to do an analysis without them. C jc is included in the equation for f t (and therefore T t) so the frequency response for the model has not been compromised. I have included R eb because it is an important factor, and it is not always easily added. From this model, we want to derive the two-port h-parameter and the two-port s-parameter model. We will begin with the h-parameter model.

Figure B-1: A simplified model of the type we used extensively throughout the book.

In this model, C ? = T tg m and . Combining these two equations, we get . We will use these relationships in the following analysis.


The h-parameter two-port model is defined as


Multiplying this gives



To solve these, we use the following


By inspection, we see immediately that for the circuit of Figure B-1, h 12 and h 22 are both zero. Using Mathematica to solve node and loop equations derived from Figure B-1, we find that


Given the definition for h 11, we see immediately that

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