RF Electronics Chapter 6: Oscillators Page 202
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
the single resonator design of figures 6.38 and 6.44, the group delay is 13.6 ns at 1 GHz.
For the dual resonator design of figures 6.46 and 6.50, it is 16.17 ns at 1 GHz.
Figure 6.51. Measured output spectrum for the 1 GHz oscillator.
It is possible to improve the designs of figures 6.38-6.44 and 6.46-6.50, by reducing the
loading on the resonators. To achieve the best accuracy for the simulation, the EM based
MTEEX, MCROSSX and MLEFX elements are used and the Rogers recommended Er
=3.55 is used for the simulation of the RO4003 substrate.
For the single resonator oscillator, capacitor C1 in figure 6.39, significantly reduces the
loop gain as it is increased from 0 to 10 pF. Tuning without resonator gain variations can
however be achieved by having a very small capacitor coupled at the top of the resonator,
like the tuning screws in the interdigital filters as shown in figure 7.57 and 7.58. For the
PCB layout, this can simply be done by soldering a nut to the ground-plane at the top of
the resonator and using a screw parallel and above the top of the resonator to provide an
adjustable small capacitance. That significantly increases the Q of the resonator and
results in an OSCTEST loop-gain group delay of 23.09 ns.
For the dual resonator, resistors are included at the input and output of the resonator,
similar to those for the single resonator. For the dual resonator, the resonator cannot be
tuned effectively by tuning one of the resonators as can be done for the single resonator.
However, since the line lengths of the required tracks need to be much longer, as can be
seen by comparing figures 6.44 and 6.50, it is possible to obtain good tuning control by
RF Electronics: Design and Simulation
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