Radio Frequency Integrated Circuit Design - Webs

The Use and Design of Passive Circuit Elements in IC Technologies
Figure 5.24 Comparison of the basic � model for (a) regular inductor, and (b) shielded inductor.
baluns consist of two interwound spirals that are magnetically coupled. A sample
layout of a basic structure is shown in Figure 5.25. In this figure, two spirals
are interwound in a 3:3 turns ratio structure. The structure can be characterized
by a primary and secondary inductance and a mutual inductance or coupling
factor, which describes how efficiently energy can be transferred from one spiral
to the other. A symmetric structure with a turns ratio of 2:1 is shown in Figure
5.26.
A simplified transformer model is shown in Figure 5.27. This is modeled
as two inductors, but with the addition of coupling coefficient k between them,
and interwinding capacitance C IW from input to output.
Example 5.8 Placing the Dots
Place the dots on the transformer shown in Figure 5.26.
Solution
We will start by assuming that a current is flowing in the primary winding, as
shown in Figure 5.28(a). This will cause a flux to flow into the page at the
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