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RF Electronics Chapter 6: Oscillators Page 201 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Figure 6.49 shows a comparison of the oscillator open loop gain for the single and dual resonator oscillator open loop gain. The rate of change of phase for the dual resonator is greater and since the same amplifier is used, the phase noise of the dual resonator oscillator should be less. The open loop gain has been adjusted to be the same for both circuits. Both circuits were also designed to have a 0 phase shift at 1 GHz. Both circuits should thus have the same oscillating frequency. Figure 6.50 shows the resulting hardware and figure 6.51 shows the corresponding measured output spectrum. The oscillators of figures 6.44 and 6.50 use the same PCB material, the same amplifier and supply voltage and the same measurement technique. The only difference is the type of resonator used. Comparing figures 6.45 and 6.51 clearly shows the improved phase noise of the dual resonator design. Since the non-linear models of the MAR amplifier are not available, it was not possible to do a phase noise measurement using NI AWR DE as was done for in figures 6.13, 6.22, 6.26 and 6.36. A paper by the author [8] includes the design of a transistor amplifier, which is used with both the single resonator of figure 6.39 and the dual resonator of figure 6.47, and thus allows the phase noise for single and dual resonator designs to be compared. For those designs, the dual resonator oscillator gives a 3 dB phase noise improvement. It is possible to extend this technique to more resonators, however an N resonator design can produce N x 180 degree phase shift, making it progressively more difficult to ensure that only one oscillating frequency is possible. Figure 6.50. Photograph of the 1GHz dual resonator oscillator. Design Improvements The group delay of the open loop circuit gain as obtained from OSCTEST is directly related to the Q of a single resonator network. For a dual resonator, Q is not defined, so that the group delay is a good measure of the expected phase noise of the oscillator. For RF Electronics: Design and Simulation 201 www.cadence.com/go/awr