Bias T

An ideal bias t is a combination of a DC block and a DC feed (fig. 9.1). During DC simulation the MNA matrix of an ideal bias t writes as follows:

$$\begin{bmatrix}. & . & . & 0\\ . & . & . & 1\\ . & . & . & -1\\ 0... ...\\ I_{2}\\ I_{3}\\ 0 \end{bmatrix} = \begin{bmatrix}0\\ 0\\ 0\\ 0 \end{bmatrix}$$ (9.21)

Figure 9.1: bias t

The MNA entries of the bias t during AC analysis write as follows.

$$\begin{bmatrix}. & . & . & -1\\ . & . & . & 1\\ . & . & . & 0\\ -... ...\\ I_{2}\\ I_{3}\\ 0 \end{bmatrix} = \begin{bmatrix}0\\ 0\\ 0\\ 0 \end{bmatrix}$$ (9.22)

The scattering parameters writes as follows.

$$(S) = \begin{pmatrix}0 & 1 & 0\\ 1 & 0 & 0\\ 0 & 0 & 1\\ \end{pmatrix}$$ (9.23)

A bias t is noise free. A model for transient simulation does not exist. It is common practice to model it as an inductor and a capacitance with finite values which are entered by the user.