Abstract
The response of chirped oscillators under the injection of independent signals, for spectrum sensing in cognitive radio, and under self-injection, for radio frequency identification, is analyzed in detail. The investigation is performed by means of a semianalytical formulation, based on a realistic modeling of the free-running oscillator, extracted from harmonic-balance simulations or from experimental measurements, through a new characterization technique. In the new formulation, the oscillator is linearized about a free-running solution that varies with the control voltage. This enables its application to oscillators having a frequency characteristic that deviates from the linear one. In the case of injection by independent signals, the two-scale envelope-domain formulation will enable an efficient handling of the difference between the slow chirp frequency and the beat frequency. The input carriers can be detected from their dynamic synchronization intervals or, at lower input-power levels, from the dynamics of the beat frequency. Noise perturbations are introduced into the formulation, which enables an estimation of the minimum detectable signal. In the case of a self-injected oscillator for radio frequency identification, an insightful formulation is derived to predict the propagation and tag-resonance effects on the instantaneous oscillation frequency. The tag-resonance signature gives rise to a distinct modulation of the oscillation frequency during the chirp period, which can be detected from the variation of the oscillator bias current. The analysis methods are illustrated through their application to a chirped oscillator, operating in the band 2–3 GHz.
Highlights
RECENTLY two interesting applications of chirped oscillators under injection have been demonstrated
The new formulation considers a general dependence of the free-running oscillation frequency on the control voltage, which enables its application to oscillators with a tuning characteristic that deviates from a linear one
It relies on a realistic model of the standalone oscillator, which can be extracted through circuit-level harmonic-balance simulations or experimentally
Summary
RECENTLY two interesting applications of chirped oscillators under injection have been demonstrated. This gives rise to oscillation pulling effects [6], which can be described as the result of the oscillator self-injection locking [10] by the reflected signal In this operation mode, the tag bit pattern, implemented through a number of resonators [7], [11]-[12], gives rise to a particular modulation of the oscillator instantaneous frequency [6], which can be detected from the variation of the oscillator bias current, with no need for an expensive receiver front-end, as explained in [6]. The envelope-domain integration in the presence of noise perturbations will enable a prediction of the minimum detectable signal, depending on the noise power spectral density and the number of input carriers Another contribution with respect to [13] is the detailed investigation of the chirped-oscillator operation in selfinjection locked regime [6].
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