RF Electronics Chapter 6: Oscillators Page 204
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
corresponding to a higher effective Q and a lower expected phase noise. The group delay
of the single resonator oscillator is now 23.09 ns at 1 GHz and that of the dual resonator
is 40.69 ns, a ratio of 1.76. This should give a 4.9 dB better phase noise [8] for the dual
resonator oscillator compared with the single resonator oscillator.
Figures 6.53 and 6.54 show the corresponding layouts of the oscillators. Comparing
figure 6.43 with 6.53 shows only minor differences in the layout. The capacitor at the top
of the resonator in figure 6.53 is the 0-1 pF tuning capacitance used for setting the centre
frequency. Comparing figure 6.50 with figure 6.54 shows significant differences. The
spacing between the coupled resonators has increased significantly. To be able to produce
the correct length of the feedback path, the feedback track had to be run in-between the
resonators. It is not possible to obtain the correct length if the feedback was run outside
the resonator, as was done in figure 6.50. The frequency tuning capacitor is the capacitor
to ground at the top middle-right of the layout. Isolating that part of the ground-plane
allows a varactor diode to be used for electronic frequency tuning.
Figure 6.54. PCB layout for the improved 1GHz dual resonator oscillator.
The distance between the resonators is larger than the distance between a resonator and
the ground-plane. As a result, the ground-plane should have some effect on the oscillator
performance. That should be evaluated using an EM simulator like AXIEM prior to
construction of the circuit. The EM simulation process is described in the section "EM
RF Electronics: Design and Simulation
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