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TECHNICAL MEMORANDUM Page 3 of 12 ABSTRACT – This article explores the push-push oscillator configuration via harmonic balance computer simulation 1 and test measurement. Basic oscillator theory of generated negative resistance via feedback is presented and the common-collector, single-stage oscillator is analyzed and subsequently utilized as a basic building block of the push-push oscillator configuration. Unique aspects of resonator loading and oscillation conditions are explored. Conventional oscillator theory is reinforced via computer simulation of large signal loading analysis using the single-stage, common-collector oscillator. The unique operation of the push-push oscillator configuration is investigated using harmonic balance simulation of spectral content and time-domain voltage waveforms. Dynamic load lines are investigated and utilized to explore peak signal excursion and degree of non-linearity. Predictions of power output, phase noise, voltage control and harmonic content are compared with measured data. I. INTRODUCTION The push-push oscillator configuration has been used to extend the frequency of operation of bipolar transistors well into the microwave and millimeter wave regions and has sustained service and attractiveness via performance not achievable by other signal generation methods and recently has been implemented within SiGe and InGaP HBT technologies. Several authors have attempted to explain the frequency multiplication and noise cancellation properties with limited success [1, 2, 3]. A common-collector oscillator is demonstrated to be a fundamental element of the push-push oscillator architecture, when implemented with bipolar transistors. The investigation begins with exploration of negative resistance generation, resonator coupling and loading of the basic oscillator element. The coupling of oscillator output power is found to profoundly impact power output, load-line, harmonic content and noise. The push-push oscillator is formed from the back-to-back combination of two common collector oscillators that are operated in phase opposition, thereby creating a null at the harmonic output node. Specific aspects of large signal simulation, device models and simulation algorithm are discussed with respect to parameter prediction accuracy. Measurement data is presented that discloses satisfactory correlation with the parameters of power output, harmonic content and phase noise and reduced accuracy with respect to operational frequency prediction. II. BASIC OSCILLATOR CONCEPTS There are several types of oscillators: blocking, relaxation, mono-stable and bi-stable – typical of lower frequency operation; higher frequency oscillators are generally segmented within two classes: negative resistance oscillators and feedback oscillators. Gunn and Impatt diode oscillators are examples of negative resistance oscillators, while feedback oscillators are characterized as reflection or reaction types. Feedback oscillators create a negative resistance, i.e., > 1.0 as a result of circuit topology. This presentation will focus on feedback type oscillators. The modified Colpitts oscillator is fundamental to sinusoidal signal generation in RF, microwave and millimeter wave frequency bands. Various configurations of the modified Colpitts oscillator are illustrated in Figure 1, where alternate terminals of the transistor are grounded and the feedback and resonator networks are represented. 1 The harmonic balance simulation software for this task is offered by Microwave Office circuit design software. The harmonic balance method is a powerful technique for the analysis of high-frequency, nonlinear circuits such as mixers, power amplifiers, and oscillators. Additional information at www.awr.com. Figure 1: Modified Colpitts Oscillator Configurations. Three electrically equivalent circuit topologies. X-Band Push-Push Oscillator Simulation and Measurement 3 www.cadence.com/go/awr

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