Free-running Oscillator Research Articles

Direct optical injection locking of InP/InGaAs HPT oscillator ICs for microwave photonics and 40-Gbit/s-class, optoelectronic clock recovery

Presents fully monolithically integrated 10- and 39-GHz-band InP/InGaAs heterojunction phototransistor (HPT) oscillators that can be optically injection locked by directly illuminating the HPT. When optical signals are modulated by fundamental frequencies around free-running oscillations, the 10-GHz-band HPT oscillator integrated circuit (IC) achieves an ultra-wide locking range of 1401 MHz (relative bandwidth of 13.6%), and the 39-GHz-band HPT oscillator IC achieves a wide locking range of 768 MHz, which are records among the indirect and/or direct optical injection-locked oscillators reported to date. The 10-GHz-band HPT oscillator IC also achieves very wide locking ranges of 618 and 160 MHz for third and fifth subharmonic modulated optical signal injection, respectively, which is very useful for microwave photonics applications. Optoelectronic clock recovery for optical transmission systems was tested by using the 39-GHz-band HPT oscillator IC and a planar lightwave circuit Mach-Zehnder interferometer. A 38.8-GHz electrical clock signal was successfully extracted from 38.8-Gbit/s nonreturn-to-zero optical data streams.

Analysis of jitter in phase-locked loops

Jitter in clock signals is analyzed, linking noise in free-running oscillators to short-term and long-term time-domain behavior of phase-locked loops. Particular attention is given to comparing the impact of 1/f noise and white noise in oscillators and frequency dividers on jitter in phase-locked loops of first- and second-order. Theoretical analysis is supported by results obtained using mixed-signal behavior simulation.

Analytical comparison between time- and frequency-domain techniques for phase-noise analysis

In the literature, different techniques have been presented for the phase-noise analysis of free-running oscillator circuits. In order to give some insight into the relationships existing between them, an analytical comparison is carried out in this paper between three different approaches. Two of them are time-domain approaches, based on Floquet's theory and the impulse sensitivity function, respectively, and the third one is the carrier modulation approach, in frequency domain. The application of Floquet's theory enables the calculation of periodic sensitivity functions to the noise perturbations. Here, the possibility to determine these functions through harmonic balance is demonstrated. This allows applying the whole stochastic characterization of phase noise, obtained from time-domain analysis, to circuits simulated through harmonic balance. For illustration, calculations in a cubic-nonlinearity oscillator are presented.

A 7.5-GHz super regenerative detector

In this paper, simulated and measured results are presented for a microwave-integrated-circuit super regenerative detector operating at 7.5 GHz and brief comparisons made to a monolithic-microwave integrated-circuit super regenerative detector operating at 34 GHz. The sensitivity of the 7.5-GHz detector was measured at -83-dBm (AM, 1 kHz, 100 % mod) RF signal for 12 dB (signal + noise + distortion)/(noise + distortion). Simulation results show that, to produce a sensitive super regenerative detector, a high rate of change in loop gain of the oscillator circuit with respect to the gate bias (quenching) voltage and a high maximum loop gain at the point of detection is required. It has also been shown, by simulation and measurement, that the detection frequency of the super regenerative detector is lower than the normal free-running oscillation frequency.

Electrical Silencing of Drosophila Pacemaker Neurons Stops the Free-Running Circadian Clock

Electrical silencing of Drosophila circadian pacemaker neurons through targeted expression of K + channels causes severe deficits in free-running circadian locomotor rhythmicity in complete darkness. Pacemaker electrical silencing also stops the free-running oscillation of PERIOD (PER) and TIMELESS (TIM) proteins that constitutes the core of the cell-autonomous molecular clock. In contrast, electrical silencing fails to abolish PER and TIM oscillation in light-dark cycles, although it does impair rhythmic behavior. On the basis of these findings, we propose that electrical activity is an essential element of the free-running molecular clock of pacemaker neurons along with the transcription factors and regulatory enzymes that have been previously identified as required for clock function.

An accelerated Poincaré-map method for autonomous oscillators

A novel time-domain method for finding the periodic steady state of a free-running electrical oscillator is introduced. The method is based on the extrapolation technique MPE. The new method is applied to a family of artificial benchmark problems and to a real circuit (Colpitt’s oscillator). It turns out to have super-linearly convergence properties in both cases. Full implementational details are provided.

Responses of a Plant Circadian Rhythm to Thermoperiodic Perturbations with Asymmetric Temporal Patterns and the Rate of Temperature Change

The circadian CO2 exchange rhythm of the CAM plant Kalanchoë daigremontiana Hamet et Perrier de la Bâthie in continuous light has been exposed to various thermoperiodic perturbation patterns. Under a fixed thermocycle period of 16–h the time of temperature exposure has been varied, yielding asymmetric temporal patterns of the perturbation. The data are analyzed considering frequency spectra and a correlation analyses of temperature and gas exchange time series. It is shown that short high-temperature patterns give rise to a significant contribution of the plant's circadian rhythm in the response of the CAM plant to the thermoperiodic perturbation. Comparison with numerical simulations using a theoretical model of CAM dynamics suggests that the experimental data can be understood as emerging from a continuous transition between free running oscillations and full synchronisation to the external driver. Furthermore, evidence for an acute response of the plant to the rate of temperature change is provided. It is proposed that the absolute value and the rate of change of temperature, respectively, should be considered as independent experimental variables.

A novel technique for automatic frequency control of microwave IMPATT oscillators

A new technique for automatic frequency control (a.f.c.) of the IMPATT oscillator has been developed in the X-band (8–12GHz), using a cavity-type frequency discriminator. The error correction for the frequency of the oscillator is realized through a microprocessor delivering control signals to a current compensating circuit which automatically adjusts the required bias supply to the IMPATT diode. The stability characteristics of the a.f.c. controlled oscillator, studied in terms of the values of the Allan variance, shows that the frequency deviation of the locked oscillator may be reduced by a factor of 100 as compared to the freerunning oscillator. The system is found to be fast acting and capable of operation over a broad range of frequency changes, and is thus expected to be of great practical use.

A low-power-consuming SOM for wireless communications

This paper presents theoretical and experimental results of a low-power-consuming hybrid push-pull self-oscillating mixer (SOM) circuit at the UHF frequency band. The frequency-stable SOM circuit is designed and fabricated using matched-pair Si bipolar junction transistors and high-Q resonators, where measured phase noise of this free-running voltage-controlled oscillator is -101.2 dBc/Hz at 100-kHz offset. A 20-dB up-conversion gain, a compression dynamic range (CDR) of 65 dB/spl middot/MHz, and a spurious-free dynamic range of 50 dB/spl middot/MHz/sup 2/3/ are also measured for the mixer portion of this SOM. Moreover, a down-conversion gain of /spl ap/-2 dB with a CDR of 100 dB/spl middot/MHz is also measured.

A low-power low-noise ultrawide-dynamic-range CMOS imager with pixel-parallel A/D conversion

A CMOS image sensor with pixel-parallel analog-to-digital (A/D) conversion fabricated with different array sizes and photodiode types in a three-metal 0.5-/spl mu/m process is presented. Nominal power dissipation is 40 nW per pixel at V/sub DD/=3.3 V. A/D conversion results from sampling a free-running photocurrent-controlled oscillator to give a first-order /spl Sigma/-/spl Delta/ sequence. The sensor displays dynamic range capability of greater than 150000:1 and exhibits fixed pattern noise correctable to within 0.1% of signal.

Quasilinear theory of mode interaction in gyrotrons with azimuthally inhomogeneous electron emission

A theory is developed which describes the effect of the azimuthal inhomogeneity of the electron current on the gyrotron operation. The theory is simplified by using a quasilinear approach, which allows one to study analytically the stability of oscillations in free-running and phase-locked gyrotron oscillators with inhomogeneous current emission. Also the numerical analysis of nonstationary processes in a three-mode gyrotron oscillator is carried out. The results show that, at low currents, the inhomogeneity may cause excitation of additional modes at the frequency of the operating one. At higher currents, one can observe the onset of phase-locked triplets with equidistant frequency spectrum. As the inhomogeneity increases, this enhances the beating effects in such triplets, e.g., the mode amplitudes exhibit some oscillations whose period is inversely proportional to their frequency separation and whose modulation increases with the inhomogeneity in the beam current.

Use of induced noise to calibrate injection-locked phase noise measurements

A new calibration approach is described for phase noise measurements of free-running voltage controlled oscillators using the injection locking technique. The injection locking technique allows the locking of free running oscillators to a reference over a wide bandwidth during a phase noise measurement. Compared to conventional phase noise measurement techniques, the injection locking technique involves a calibration procedure, which may be tedious and time consuming. The new approach may be used to perform an automated calibration procedure of the system commonly used for these measurements.

Estimation of the Fulfillment of the Local Thermodynamic Equilibrium Criterion for the Plasma Generated by Laser Pulses of Various Shapes at the Surface of a Solid Target

The results of experimental estimation of the fulfillment of the local thermodynamic equilibrium (LTE) criterion for the plasma generated by laser pulses of various duration at the surface of a solid target placed in a gaseous atmosphere at standard pressure are given in the present paper. The fulfillment of all the LTE criteria is demonstrated for an ensemble of neutral atoms contained in the plasma generated by a giant laser pulse or by a laser pulse whose complex shape represents several giant pulses against the background of free-running laser oscillations. The plasma excited by the radiation of a Nd : YAG laser with energy ≤ 0.4 J per pulse is examined. We have recorded a resonance broadening of atomic Al and Mg lines. This has allowed us to estimate the density of neutral atoms contained in a plasma plume.

An Increase in the Energy Yield and Giant-Pulse Generation Efficiency in a Laser with Self-injection of the Initiating Radiation

Optical laser systems that ensure generation of giant pulses from a narrow-band initiating free-running oscillation upon change in the Qfactor of the laser cavity and (or) in the amplification factor in it are described. The result of experimental studies of the parameters of a giant-pulse radiation generated by this type of ruby lasers with electrooptical switching of a branched combined cavity are presented.

Free-running emerald laser

The spectral and energy characteristics of an emerald laser are studied experimentally. Its performance is compared with that of an alexandrite laser. For free-running oscillation under normal conditions, undamped pulsating behavior of output intensity is observed, as is the case with other lasing media containing Cr ions.

A micromachined cavity resonator for millimeter-wave oscillator applications

High stability and low phase noise oscillators are key components in millimeter-wave (MMW) systems. Using microelectromechanical system (MEMS) technology, the silicon cavity resonator has been developed for MMW oscillator applications. Thanks to the superior Q-factor of the cavity over planar resonators, low phase noise and high stability is expected. The fabricated, micromachined cavity showed an unloaded Q-factor of 120 and Ka-band voltage controlled oscillator (VCO) coupled with the cavity resonators showed a phase noise improvement of more than 15 dB over free-running oscillators (FROs). To the best of our knowledge, this is the first experimental demonstration of a high electron mobility transistor (HEMT) microwave monolithic integrated circuit (MMIC) oscillator combined with a micromachined cavity resonator.

Low phase noise operation of microwave oscillator circuits

In this paper, we describe a theoretical basis, leading to new results, on the general conditions to be fulfilled by oscillator circuits to achieve a very low phase noise. Three main conditions must be fulfilled by a transistor oscillator circuit to reach the minimum phase noise. The energy stored in the resonator must be maximum. Its transfer to the controlling voltage port of the transistor current source must be first maximized. A possible conversion noise at the transistor output port will be also minimized by maximizing the energy transferred to that port. The proposed method has been applied to an experimental oscillator set up with a PHEMT transistor. A state-of-the-art phase noise of -80 dBc/Hz at 100 Hz offset from carrier with a 1/f(3) slope has been measured at room temperature with a 9.2 GHz, oscillator. The application of these new results to free-running oscillator circuits with one-stage then multistage transistor amplifiers demonstrate clearly the validity of the design method. The efficiency of this design method and its ease of use represent a real breakthrough in the field of low noise transistor oscillator circuit design.

Efficiency enhancement of free electron Maser oscillator by mode selection with a prebunched electron beam

We present a method for enhancing the efficiency of a Free Electron Laser Maser oscillator by locking it to a preferred resonator mode. This is done by prebunching of the e beam before injection into the wiggler. In a free running oscillator, the longitudinal mode that dominates the mode competition process during the oscillation buildup period is usually the highest gain mode. However, this mode does not extract the highest energy from the e beam. Lower eigenfrequency modes would provide a higher efficiency if they could dominate the mode competition process. By prebunching the e beam at a frequency near any one of the longitudinal eigenfrequencies of the resonator (having a gain>1), we can make that mode dominant at saturation. The eigenfrequency for which the maximum efficiency is obtained is the lowest eigenfrequency of the resonator for which the net small signal gain is greater than 1. Employing an experimental setup of a prebunched beam Free Electron Maser, we demonstrated efficiency enhancement of 30% for this lowest eigenfrequency mode (as compared to the highest gain mode). Simulation results predict an efficiency enhancement of up to 50%.

Combination dielectric resonator, power combiner, and antenna

A rectangular dielectric resonator housed in a cutoff parallel-plate waveguide is used both as a radiating element and microwave power combiner. The resonator is excited by using tuned electrically short monopole antennas to induce a longitudinal electric operating mode. The resonator is then used in conjunction with free-running oscillators in order to provide, via mutual injection locking, stable in-phase power combining. Furthermore, the resonator is arranged such that one of its faces radiates a portion of the power-combined signal. Since the resonator is housed in a cutoff waveguide, the cross-polarization radiation from the antenna is suppressed. It was found that, for a single element, a gain in the azimuthal plane of 5 dB could be achieved and, for a two-element array, a gain of 7 dB was obtained with better than -25-dB cross polarization for each case. The oscillator power-combining efficiency for a single-element antenna (two oscillators) was 91%, and the spatial power-combining efficiency for a two-element antenna array, (four oscillators) was found to be 90%. In addition, it is shown that the presence of the dielectric inserts in conjunction with coupled oscillator dynamics provides moderate overall oscillator phase noise improvement.

Multiloop optoelectronic oscillator

We describe and demonstrate a multiloop technique for single-mode selection in an optoelectronic oscillator (OEO). We present experimental results of a dual loop OEO, free running at 10 GHz, that has the lowest phase noise (-140 dBc/Hz at 10 kHz from carrier) of all free-running room-temperature oscillators to date. Finally, we demonstrate the first fiber-optic implementation of the carrier suppression technique to further reduce the close-to-carrier phase noise of the oscillator by at least 20 dB.