Free-running Oscillator Research Articles

A $W$-Band Wide Locking Range and Low DC Power Injection-Locked Frequency Tripler Using Transformer Coupled Technique

A <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$W$</tex></formula> -band wide locking range injection-locked frequency tripler (ILFT) with low dc power consumption is presented in this paper. By using a transformer coupled (TC) topology, the proposed TC-ILFT features the following advantages: 1) the negative resistance of the cross-coupled pair is not degraded due to the proposed TC-ILFT without source degeneration, and the TC-ILFT can be operated in lower dc supply voltage as compared to the conventional ILFTs; 2) the dc bias of the injector can be properly designed for maximizing locking range; 3) the parasitic capacitance provided by the injector can be reduced due to the impedance transformation; and 4) the larger device size of the injector can be chosen enhancing the third harmonic. Moreover, the operation frequency and the locking range of this work are boosted using a multiorder resonator. A theoretical model of the proposed TC-ILFT is also established and it has been carefully verified with the experimental results. The free-running oscillation frequency of the proposed TC-ILFT is 94.51 GHz. As the input power is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${-}$</tex></formula> 1 dBm, the measured locking range is 5.9 GHz without varactor tunning. The dc supply voltage and the power consumption are 0.7 V and 1 mW, respectively.

Delayed Feedback Dynamics of Liénard-Type Resonant Tunneling-Photo-Detector Optoelectronic Oscillators

We use the nonlinear dynamics approach for studying delayed feedback optoelectronic oscillators (OEOs) formed by hybrid integration of resonant tunneling diode (RTD) photo-detectors with laser diodes, in both single and dual optical fiber feedback routes. In the single loop topology, the performance of the RTD-OEO free-running self-sustained oscillator is improved in terms of phase noise, with a compromise between the delay line and the strength of the optical re-injection. In the dual-loop configuration, superior performance is achieved due to the suppression of the side modes associated with the optical cavity length, resulting in a side mode suppression ratio of up to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 60}~{\rm dBc}$</tex></formula> of the carrier frequency. We compare experimental results with numerical simulations based on a system of delay differential equations comprising a Liénard oscillator model driven by white Gaussian noise and coupled with laser rate equations. The delayed feedback Liénard oscillator model gives considerable insight into the RTD-OEO dynamical regimes predicting its main features in both single- and dual-loop configurations.

Low-Power-Consumption Wide-Locking-Range Dual-Injection-Locked 1/2 Divider Through Simultaneous Optimization of VCO Loaded $Q$ and Current

A new 1/2 dual-injection-locked frequency divider (dual-ILFD) with wide locking range and low-power consumption is proposed, analyzed, and developed together with a divide-by-2 current-mode logic (CML) divider. The chip was fabricated using a 0.18-μm BiCMOS process. The 1/2 dual-ILFD enhances the locking range with low-power consumption through optimized load quality factor (QL) and output current amplitude (iOSC) simultaneously. The relationship between iOSC and QL, and hence the locking range, is explained analytically. The designed 1/2 dual-ILFD also works as a free-running oscillator between 3.592 and 4.102 GHz without injection signals. The 1/2 dual-ILFD achieves a locking range of 692 MHz between 7.512 and 8.204 GHz. The current consumption of the designed core 1/2 dual-ILFD is 2.93 mA with 1.5-V supply. The designed 1/2 dual-ILFD increases the locking range by 9.9 times over a single-injection counterpart. The new 1/2 dual-ILFD is especially attractive for microwave phase-locked loops and frequency synthesizers requiring low power and wide locking range.

Analysis of Oscillation Modes in Free-Running Ring Oscillators

An in-depth investigation of oscillation modes in ring oscillators is presented. The small-signal stability is initially considered, demonstrating that the poles associated with the dc regime are uniformly distributed on a circle on the complex plane, with increasing density for a higher number of stages. The existence of multiple pairs of poles on the right-hand side of the complex plane gives rise to different oscillation modes, related here to the eigenvectors of the circulant active-device immitance matrix. This paper shows that the stability properties of detected modes depend on both the order of appearance from dc regime, in a sequence of Hopf bifurcations, and the bifurcations undergone by each steady-state mode until reaching the final operation point, when changing a bias voltage, for instance. Thus, the stability analysis must combine a bifurcation analysis from dc regime and a bifurcation analysis of each individual oscillation mode in large-signal regime. The large-signal stability analysis presented shows the possible stabilization mechanisms, which lead to the common physical observation of some of these modes. The stabilization of the desired mode, using concepts from bifurcation theory, is also presented. All techniques have been successfully applied to a ring oscillator at 12.6 GHz.

Design of Wide-Band Frequency Shift Technology by Using Compact Brillouin Fiber Laser for Brillouin Optical Time Domain Reflectometry Sensing System

A novel wide-band optical frequency shift technology by using a compact single-frequency Brillouin fiber laser (BFL) configured with high-doped Er3+ fiber and high nonlinear fiber (HNLF) is proposed and investigated experimentally. By adjusting variable optical attenuator (VOA) to eliminate the free-running oscillation in the fiber ring cavity, a stable single-frequency BFL will be considered as local oscillator (LO) for coherent detection in Brillouin optical time domain reflectometry (BOTDR) sensing system. The BFL operates at 1549.06 nm red-shifted 0.084 nm (about 10.5 GHz) from the pump seed laser. The laser signal-to-noise ratio (SNR) is larger than 50 dB and the laser linewidth is about 3.1 kHz. Applying the BFL to the BOTDR system, the measured results show that the beat frequency between the spontaneous Brillouin scattering (SBS) and the LO is about 420 MHz and the frequency fluctuation is less than ± 2 MHz for 20-km sensing fiber.

The expression of NR2B subunit of NMDA receptor in the suprachiasmatic nucleus of Wistar rats and its role in glutamate-induced CREB and ERK1/2 phosphorylation

Most behavioral and physiological processes in living organisms exhibit periodic circadian rhythmicity. In mammals, these rhythms are coordinated by the circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. In order to precisely synchronize free-running circadian oscillations to the 24h solar cycle, signals from the external environment, primarily the light/dark cycle, must reach the circadian clock within the SCN. A light pulse elevates intracellular Ca2+ levels, and activates signaling cascades, leading to transcriptional activation of the clock genes mPer1 and mPer2 via phosphorylation of extracellular-signal-regulated kinases 1/2 (ERK1/2) and cyclic AMP-responsive element binding protein (CREB). Glutamate is the primary excitatory transmitter in retinal terminals in the SCN, and NMDA receptors (NMDAR) are the principal glutamate receptors that mediate the effect of light on resetting the circadian clock. Here we show the circadian rhythm in mRNA expression and protein level of the NMDAR 2B subunit (NR2B) in the SCN, with a peak at night. Also, we demonstrate ifenprodil inhibition of glutamate-induced phosphorylation of CREB (pCREB) and ERK1/2 (pERK1/2), and support thus the evidence for NR2B role in activation of signaling cascade involved in photic resetting of the circadian clock.

Noise suppression in injection-locked ring oscillators

Presented is a study of the optimal injection frequency using a time-domain model as a technique to improve the noise suppression in injection-locked ring oscillators. It is found that offsetting the injection signal frequency by roughly half of the one-sided lock range relative to the free-running oscillator frequency can lead to higher noise-suppression bandwidth and lower phase noise. Applied to a five-stage ring oscillator, the model shows good agreement with simulations, which indicate that the optimal injection frequency increases the noise-suppression bandwidth by up to 5×, and lowers the phase noise by 15dB.

Simultaneous narrow linewidth and broadband operation in the master oscillator power amplifier of a self-seeded Ti:sapphire laser

A narrow linewidth pulse and a broadband pulse were simultaneously operated in the master oscillator power amplifier (MOPA) of a self-seeded Ti:sapphire laser, and their intensity ratio was varied by increasing the incident pump energy. The broadband pulse from the independent free-running oscillation was preferentially amplified in the MOPA chain and replaced the narrow linewidth pulse. This explanation was confirmed by comparing the behavior with that of a bandpass filter inserted at the exit of the oscillator. The behaviors were well simulated by numerical calculations. From the results, a method to produce both narrow linewidth and broadband pulses was proposed with their ratio depending on the pump energy.

Multistability of twisted states in non-locally coupled Kuramoto-type models

A ring of N identical phase oscillators with interactions between L-nearest neighbors is considered, where L ranges from 1 (local coupling) to N/2 (global coupling). The coupling function is a simple sinusoid, as in the Kuramoto model, but with a minus sign which has a profound influence on its behavior. Without the limitation of the generality, the frequency of the free-running oscillators can be set to zero. The resulting system is of gradient type, and therefore, all its solutions converge to an equilibrium point. All so-called q-twisted states, where the phase difference between neighboring oscillators on the ring is 2πq/N, are equilibrium points, where q is an integer. Their stability in the limit N → ∞ is discussed along the line of Wiley et al. [Chaos 16, 015103 (2006)] In addition, we prove that when a twisted state is asymptotically stable for the infinite system, it is also asymptotically stable for sufficiently large N. Note that for smaller N, the same q-twisted states may become unstable and other q-twisted states may become stable. Finally, the existence of additional equilibrium states, called here multi-twisted states, is shown by numerical simulation. The phase difference between neighboring oscillators is approximately 2πq/N in one sector of the ring, -2πq/N in another sector, and it has intermediate values between the two sectors. Our numerical investigation suggests that the number of different stable multi-twisted states grows exponentially as N → ∞. It is possible to interpret the equilibrium points of the coupled phase oscillator network as trajectories of a discrete-time translational dynamical system where the space-variable (position on the ring) plays the role of time. The q-twisted states are then fixed points, and the multi-twisted states are periodic solutions of period N that are close to a heteroclinic cycle. Due to the apparently exponentially fast growing number of such stable periodic solutions, the system shows spatial chaos as N → ∞.

Non invasive radiofrequency diagnostics of cancer. The Bioscanner — Trimprob technology and clinical applications

A new paper by Pokorny, Vedruccio, Cifra, Kucera, titled Cancer physics: Diagnostics based on damped cellular elasto-electrical vibrations in microtubules, recently available on Eur. Biophys. J., discloses the mechanism of active grown cancer tissues interaction with a Non- Linear Resonance Interaction (NLRI) Bioscanner Trimprob diagnostic device that is certified and ready to be used to investigate suspected cases of disease and cancer. This technology spreads early capabilities of cancer detection by means of low level radiofrequency oscillations in UHF band. The system is based on an unique and extremely innovative non- linear radiofrequency oscillator working on 462-465 MHz plus the harmonics. The diseased tissues suspected of cancer, are irradiated by means of a handy probe near field emission, while a spectrum analyzer placed in the far field detects by means of a small antenna, the oscillator interaction within the tissues. The Bioscanner is characterized by a high dynamic range, in the order of 30 or more decibel, and is useful for detection of small cancer agglomerates, if used by a well trained operator. At the resonance, the free running oscillator locks-in on the specific interaction frequency, in a sharp frequency window centered on 462 MHz; the resulting effect is evidenced by a deep decrease of the 462 MHz spectral line propagation in the far field around the oscillator probe. The NLRI provides a selective characterization, like a sort of a electronic biopsy response of biologic tissues in support of modern imaging diagnostics. Further to existing literature describing methods for cancer detections by means of electromagnetic fields this paper shows this innovative in vivo medical diagnostic equipment and some clinical applications.

Performance Evaluation of Digital Coherent Receivers for Phase-Modulated Radio-Over-Fiber Links

The performance of optical phase-modulated (PM) radio-over-fiber (RoF) links assisted with coherent detection and digital signal processing (PM-Coh) is analyzed and experimentally demonstrated for next-generation wireless-over-fiber systems. PM-Coh offers high linearity for transparent transport of high-frequency microwave signals, and better receiver sensitivity than intensity modulated with direct detection systems. By including photonic downconversion in the PM-Coh link, in a form of a pulsed free-running local oscillator, it is possible to receive high-RF carrier frequencies, with low-bandwidth electronics. Analytical assessment and simulations are used to determine the ultimate performance with respect to laser linewidth, modulation index, and receiver sensitivity. Then, two different scenarios are studied and experimentally demonstrated as an application of PM-Coh links: a high-capacity multiantenna RoF system (12 subcarriers of 400 Mb/s and 6 subcarriers of 800 Mb/s) and photonic downconversion for the detection of high-RF carriers microwave signals (up to 3.2 Gb/s at 40 GHz).

Forced synchronization of a delayed-feedback oscillator

Dynamics of a delayed-feedback oscillator with cubic nonlinearity driven by an external harmonic signal is considered. Regimes of forced synchronization and their stability conditions are studied analytically and numerically for the cases of single-frequency and multiple-frequency (self-modulation) operation of the free-running oscillator. Special attention is paid to synchronization of the oscillator with bistability of steady states which arises near the boundary of generation zone. Results of numerical simulation of bifurcation transitions to synchronization regime for different driving frequencies are presented. Main differences from the classical picture of synchronization for a system with one degree of freedom are discussed.

Oscillation modes of direct current microdischarges with parallel-plate geometry

Two different oscillation modes in microdischarge with parallel-plate geometry have been observed: relaxation oscillations with frequency range between 1.23 and 2.1 kHz and free-running oscillations with 7 kHz frequency. The oscillation modes are induced by increasing power supply voltage or discharge current. For a given power supply voltage, there is a spontaneous transition from one to other oscillation mode and vice versa. Before the transition from relaxation to free-running oscillations, the spontaneous increase of oscillation frequency of relaxation oscillations form 1.3 kHz to 2.1 kHz is measured. Fourier transform spectra of relaxation oscillations reveal chaotic behavior of microdischarges. Volt-ampere (V-A) characteristics associated with relaxation oscillations describes periodical transition between low current, diffuse discharge, and normal glow. However, free-running oscillations appear in subnormal glow only.

Oscillator Noise: A Nonlinear Perturbative Theory Including Orbital Fluctuations and Phase-Orbital Correlation

We derive a full statistical characterization of the noise spectrum of a free running oscillator perturbed by white Gaussian noise sources, including the effect of orbital fluctuations and of their correlation with phase noise, thus extending the previous theory based on the Floquet decomposition of the linearized oscillator equations . This allows to derive explicit relationships for the relevant phase, amplitude and correlation spectra. The examples provide a validation of the theoretical results, and allow to assess the importance of the Floquet exponents and eigenvectors on the magnitude of the orbital noise contribution.

A Self-Synchronized Optoelectronic Oscillator Based on an RTD Photodetector and a Laser Diode

We propose and demonstrate a simple and stable low-phase noise optoelectronic oscillator (OEO) that uses a laser diode, an optical fiber delay line and a resonant tunneling diode (RTD) free-running oscillator that is monolithic integrated with a waveguide photo-detector. The RTD-OEO exhibits single-side band phase noise power below -100 dBc/Hz with more than 30 dB noise suppression at 10 kHz from the center free-running frequency for fiber loop lengths around 1.2 km. The oscillator power consumption is below 0.55 W, and can be controlled either by the injected optical power or the fiber delay line. The RTD-OEO stability is achieved without using other high-speed optical/optoelectronic components and amplification.

An ultra-low-power RF transceiver for WBANs in medical applications

A 2.4 GHz ultra-low-power RF transceiver with a 900 MHz auxiliary wake-up link for wireless body area networks (WBANs) in medical applications is presented. The RF transceiver with an asymmetric architecture is proposed to achieve high energy efficiency according to the asymmetric communication in WBANs. The transceiver consists of a main receiver (RX) with an ultra-low-power free-running ring oscillator and a high speed main transmitter (TX) with fast lock-in PLL. A passive wake-up receiver (WuRx) for wake-up function with a high power conversion efficiency (PCE) CMOS rectifier is designed to offer the sensor node the capability of work-on-demand with zero standby power. The chip is implemented in a 0.18 μm CMOS process. Its core area is 1.6 mm2. The main RX achieves a sensitivity of −55 dBm at a 100 kbps OOK data rate while consuming just 210 μA current from the 1 V power supply. The main TX achieves +3 dBm output power with a 4 Mbps/500 kbps/200 kbps data rate for OOK/4 FSK/2 FSK modulation and dissipates 3.25 mA/6.5 mA/6.5 mA current from a 1.8 V power supply. The minimum detectable RF input energy for the wake-up RX is −15 dBm and the PCE is more than 25%.

0.13-㎛ RFCMOS 공정 기반 54-GHz 주입 동기 주파수 분주기

본 논문에서는 54 GHz 대역의 위상 고정 루프에서 사용되기 위한 Ring 발진기를 이용한 3 분주 주입 동기 주파수 분주기(Injection-Locked Frequency Divider: ILFD)를 0.13-<TEX>${\mu}M$</TEX> Si RFCMOS 공정을 이용하여 설계, 제작한 결과를 보인다. 1.8 V의 공급 전압에 대해서 buffer단을 포함하여 70 mW의 전력을 소비하며, 입력 신호가 없을 때 0~1.8 V의 varactor 조정 전압 범위에 대하여 18.92~19.31 GHz에서 자유 발진(free-running oscillation)을 하였다. 0 dBm의 입력 전력에 대해서 1.02 GHz(54.82~55.84 GHz)의 동기 범위(locking range)를 가지며 varactor 조정(0~1.8 V)을 포함한 동작 범위(operating range)는 약 2.4 GHz(54.82~57.17 GHz)를 보였다. 제작된 회로의 크기는 측정 pad를 포함하여 0.42 mm<TEX>${\times}$</TEX>0.6 mm이며, pad를 제외한 실제 동작 영역의 크기는 0.099 mm<TEX>${\times}$</TEX>0.056 mm이다. In this work, a 54 GHz divide-by-3 injection-locked frequency divider(ILFD) based on ring oscillator has been developed in a 0.13-<TEX>${\mu}M$</TEX> Si RFCMOS technology for phase-locked loop(PLL) application. The free-running frequency is 18.92~19.31 GHz with tuning range of 0~1.8 V, consuming 70 mW with a 1.8 V supply voltage. At 0 dBm input power, the locking range is 1.02 GHz(54.82~55.84 GHz) and, with varactor tuning of 0~1.8 V, the total operating range is 2.4 GHz(54.82~57.17 GHz). The fabricated circuit size is 0.42 mm<TEX>${\times}$</TEX>0.6 mm including probing pads and 0.099 mm<TEX>${\times}$</TEX>0.056 mm for core area.

Photonic downconversion for coherent phase-modulated radio-over-fiber links using free-running local oscillator

A digital coherent receiver employing photonic downconversion is presented and experimentally demonstrated for phase-modulated radio-over-fiber optical links. Photonic downconversion adds additional advantages to optical phase modulated links by allowing demodulation of signals with RF carrier frequencies exceeding the bandwidth of electrical analog-to-digital converter. High spurious-free dynamic range is observed for RF carriers at 5 GHz photonically downconverted to 1 GHz.

Including orbital fluctuations in the noise spectrum of autonomous circuits

We discuss the impact of orbital fluctuations on the noise spectrum of a free-running oscillator, exploiting a rigorous nonlinear perturbative analysis based on the Floquet theory, and providing evidence of its relevance for high-Q oscillators.

Hearing Device Without Reference Clock Component

A hearing device, in particular a hearing aid, occupies a small volume and has high data transmission speeds for wireless transmission. In order to avoid using large volume frequency-stable components, for this purpose, an oscillator unit with a free-running oscillator is used instead. A receiver receives a synchronization signal cyclically. This is correlated to a reference signal in a correlator, such that the arrival time of the synchronization signal can be defined exactly. The free-running oscillator is then retuned correspondingly.