Analog Circuits Cookbook

RF circuits and techniques 261

The tuned circuit

In the tuned circuit shown in Figure 8.31 the drive is inductively coupled

via a single closely coupled turn. This effectively generates a small voltage

from a (near) zero source impedance generator in series with the inductor.

Thus the arrangement is actually a series resonant circuit, but the perfor-

mance is virtually the same as the current-fed parallel circuit of Figure 8.24

for values of QJiigh enough to be useful, say 20 or greater, and it is perhaps

a little easier to see what is going on. This is illustrated in the figure, which

shows the situation at a frequency slightly above F, wher ...