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.

B.1 h-PARAMETER TWO-PORT MODEL

The h-parameter two-port model is defined as

(B.1)

Multiplying this gives

(B.2)

and

To solve these, we use the following

(B.3)

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

(B.4)

Given the definition for h ₁₁, we see immediately that

(B.5)