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Pseudolinear Circuit Theory for Sinusoidal Oscillator Performance Maximization
Takashi OHIRA Tuya WUREN
Publication
IEICE TRANSACTIONS on Electronics
Vol.E91C
No.11
pp.17261737 Publication Date: 2008/11/01 Online ISSN: 17451353
DOI: 10.1093/ietele/e91c.11.1726 Print ISSN: 09168516 Type of Manuscript: INVITED PAPER (Special Section on Microwave and Millimeterwave Technologies) Category: Keyword: oscillator, NINO model, immittancedomain Barkhausen condition, equilibrium, active Q factor, circuit optimization criteria,
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Summary:
This paper introduces a theory for fast optimization of the circuit topology and parameters in sinusoidal oscillators. The theory starts from a system model composed of standard active and passive elements. We then include even the output load in the circuit, so that there is no longer any interaction with the outside of the system through the port. This model is thus called noinputnooutput (NINO) oscillator. The circuit is cut at an arbitrary branch, and is characterized in terms of the scalar impedance from the cut point. This is called active impedance because it is a function of not only the stimulating frequency but also the active device gain. The oscillation frequency and necessary device gain are estimated by solving impedancedomain Barkhausen equilibrium equations. This estimation works for the adjustment of circuit elements to meet the specified oscillation frequency. The estimation of necessary device gain enables us to maximize the oscillation amplitude, thanks to the inherent negativeslope nonlinearity of active devices. The active impedance is also used to derive the oscillation Q (quality) factor, which serves as a key criterion for sideband noise minimization i.e. frequency spectrum purification. As an alternative measure to active impedance, we also introduce branch admittance matrix determinant. This has the same numerical effect as the scalar impedance but can be used to formulate oscillator characteristics in a more elegant fashion, and provides a lucent picture of the physical behavior of each element in the circuit. Based on the proposed theory, we provide the tabled formulas of oscillation frequency, necessary device gain, active Q factor for a variety of typical Colpitts, Hartley, and crosscoupled twinFET (fieldeffect transistor) oscillators.

