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TECHNICAL MEMORANDUM Page 5 of 12 now be observed over various coupling values. Under very light loading conditions, the common-collector oscillator behaves in a similar manner to that encountered when connected in the push-push configuration. The 'prevailing' wisdom with respect to oscillator operation in the steady-state may be succinctly represented with the graphic of Figure 4, where a negative resistance – whether created via feedback or transfer electron device, e.g. Gunn or Impatt diode – is connected to a resonant circuit and then to a load. Figure 4: Oscillator operation in the steady-state. All oscillators may be distilled to this circuit embodiment. Typically, both device and load are coupled to the resonator using either distributed or lumped element circuit components. In the steady-state, the total loop resistance is equal to zero, otherwise, the oscillator signal would continue to increase until the device saturates and the negative resistance decreases to the value of the positive resistance of the coupled load. It is for this reason, that the large signal impedance is examined at the negative resistance port of the common-collector oscillator and the coupling value is adjusted to ensure that the conditions for sustained oscillation are achieved. If the load coupling is adjusted to the point where the net loop resistance becomes positive, the system will cease to oscillate. In fact, this condition was examined and found to validate the intuitive oscillator operation. The fact that this result was validated by the large signal simulation of the common-collector oscillator and correlation with earlier experimental results of load coupling was quite satisfying and validated the simulation algorithm and model; although specific transistor model parametric values are still in question. III. PUSH-PUSH OSCILLATOR The push-push oscillator circuit topology joins two, common-collector oscillators at the grounded end of the resonator as disclosed in Figure 5, where the voltage null of each section of the oscillator becomes the common junction of the push-push configuration and the coupled transmission line has been removed in favor of a simple coupling capacitor. Figure 5: Push-Push Oscillator Circuit Topology. The Push-Push oscillator is structured from the connection of two common-collector oscillators such that the null point of the circuit is maintained. X-Band Push-Push Oscillator Simulation and Measurement 5 www.cadence.com/go/awr

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