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TECHNICAL MEMORANDUM Page 4 of 12 In each case, the feedback network is the result of a capacitive voltage divider while the resonator is formed using the feedback network augmented by an inductor-capacitor resonator. The inductor-capacitor resonator is selected to increase the slope of the reactance at the resonant frequency, and thereby, also the 'Q' or quality factor. As will be demonstrated, the inductor-capacitor resonator may also represent a distributed resonator as the operation of the oscillator is extended to higher frequency bands. All the illustrated configurations are designed to generate negative two-terminal resistance at a desired frequency band from which power may be extracted. An old adage states that 'positive resistance dissipates power while negative resistance generates power'. The common-collector oscillator configuration is popular in the microwave frequency band because the collector may be directly attached to ground which facilitates heat removal and because the collector is normally the substructure of the bipolar junction transistor. A feedback voltage divider is formed using the intrinsic base-emitter capacitance and a discrete capacitor attached from the emitter to ground. In this configuration, a negative resistance is generated at the collector-base junction to which a resonator may be coupled, and from which power at the resonator frequency may be extracted. Figure 2 illustrates the complete schematic of the grounded-collector oscillator with the discrete inductance replaced with a distributed, coupled transmission line. Figure 2: Common-Collector, Coupled Transmission Line Resonator Oscillator. The common-collector oscillator circuit topology with capacitor-coupled, grounded resonator is fundamental to the Push-Push oscillator topology. The series capacitor serves as an effective coupling mechanism to the coupled transmission line resonator. 2 See Hittite data sheet HMC398QS for example. In addition, the feedback capacitor is illustrated as an adjustable element to highlight the profound influence on oscillator parameters, specifically, power output, phase noise and start voltage. The common-collector oscillator using coupled transmission line resonator is specifically selected for study because the structure forms an element of the push-push oscillator architecture, as will be demonstrated. The coupled transmission line resonator facilitates examination of the output power coupling via the odd and even mode impedance while observing the dynamic load line and determination of the oscillator frequency and power output. Loading is introduced to the oscillator system by means of the coupled transmission line resonator and the series capacitor. This is important to all aspects of oscillator design because high quality signal generation has – in many cases – been a matter of accepting the output signal quality from a given configuration. Greater spectral signal quality was attainable only through the use of high-quality resonators. Recently, this adage has been proven false by MMIC oscillator performance that exhibits phase noise comparable to good quality cavity oscillators at X-Band. 2 The ability to accurately simulate the loading effects on power output, phase noise and harmonics suggests the use of lower cost oscillator circuit implementation. The coupled transmission line facilitates both output loading and control of the total resistance reflected across the collector-base port of the oscillator at the resonant frequency. This effect may be readily understood by observation of the equivalent circuit of the coupled transmission line as illustrated in Figure 3. Figure 3: Equivalent Circuit of Coupled Transmission Line. This configuration is selected due to the ease with which the effects of load coupling may be observed. The coupled transmission line implements an impedance transformer where the impedance transformation ratio is controlled by the odd and even mode admittance. This is a powerful analysis tool because the load line and the reflected impedance may X-Band Push-Push Oscillator Simulation and Measurement 4 www.cadence.com/go/awr

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