Phase-locked Oscillator Research Articles

Sampling phase detector using a resonant tunneling high electron mobility transistor for microwave phase-locked oscillators

A novel sampling phase detector (SPD) using a resonant-tunneling high electron mobility transistor (RTHEMT), which features strong nonlinear characteristics, is proposed and demonstrated as a means of achieving a simple, low-power-consumption SPD. We confirmed promising performance for an RTHEMT as a simple pulse generator in an SPD with low power consumption, even for a low reference-signal input level. An 11-GHz phase-locked oscillator is constructed along with the present SPD, and successfully phase-locked signals are obtained with it. These results clearly show the potential of constructing high-performance analog RF circuits based on RTHEMTs.

Single-sweep analysis of the theta frequency band during an auditory oddball task

The P300 component and the oscillatory 4–7 Hz electroencephalographic activity of auditory event-related brain potentials (ERPs) were assessed to study differences between passive and oddball task conditions. Theta responses from 15 adults were analyzed for single-sweep amplitude, phase locking, and enhancement against prestimulus activity. ERPs were characterized by enhanced and strongly phase-locked theta oscillations in the early (0–300 ms) poststimulus epoch, with only the late (300–600 ms) theta responses at Fz and Pz affected by the oddball condition. P300 was strongly associated not only with the concurrent theta oscillations but also with the evoked theta activity preceding P300 (0–300 ms). It was concluded that single theta response parameters can reveal specific functional differences between passive and oddball conditions and that a strong relationship exists between the theta frequency component and the time domain P300 ERP component.

Single‐sweep analysis of the theta frequency band during an auditory oddball task

The P300 component and the oscillatory 4-7 Hz electroencephalographic activity of auditory event-related brain potentials (ERPs) were assessed to study differences between passive and oddball task conditions. Theta responses from 15 adults were analyzed for single-sweep amplitude, phase locking, and enhancement against prestimulus activity. ERPs were characterized by enhanced and strongly phase-locked theta oscillations in the early (0-300 ms) poststimulus epoch, with only the late (300-600 ms) theta responses at Fz and Pz affected by the oddball condition. P300 was strongly associated not only with the concurrent theta oscillations but also with the evoked theta activity preceding P300 (0-300 ms). It was concluded that single theta response parameters can reveal specific functional differences between passive and oddball conditions and that a strong relationship exists between the theta frequency component and the time domain P300 ERP component.

Comparison of Single-Carrier and Multi-Carrier QAMSystem Performance in the Presence of Carrier Phase Jitter

In this contribution, we investigate how the carrier phase jitter of a phase-locked oscillator for IF-to-baseband conversion affects the performance of single-carrier QAM (SC-QAM) and multi-carrier QAM (MC-QAM); the considered multi-carrier system is of the OFDM (orthogonal frequency-division multiplexed) type. This phase jitter reduces the signal-to-noise ratio (SNR) at the input of the decision device, and therefore gives rise to an increase of the bit error rate. We show that, for a given jitter variance, SC-QAM and MC-QAM yield the same SNR degradation. However, when the synchronization for MC-QAM is derived from a pilot tone, we point out that the resulting jitter variance is considerably larger than for SC-QAM, in which case MC-QAM is degraded much more than SC-QAM.

Phase-locked one- and two-dimensional Josephson-junction arrays as millimeter and submillimeter wave generators

The results of numerical simulations of phase-locked 1D and 2D Josephson-junction arrays are reported. It is shown that the multi-junction structures with non-local junction interaction provide phase-locked oscillation state within wide critical current margins /spl Delta/I/sub c/ up to 40...50%. The effective non-local interaction in 2D structure based on 4-junction interferometer cell can be provided by the regular single flux quantum array flow across it. The wide tolerable spread in /spl Delta/I/sub c/ allows one to realize both (i) phase-locked 2D high-T/sub c/ Josephson-junction array with the oscillation frequency F close to characteristic value F/sub c/ and (ii) based on Nb tunnel Josephson-junction technology 1D array with the voltage-controlled phase-locked oscillation frequency within wide frequency band from 0.4 F/sub c/ to 1.2 F/sub c/.

Technical noise in gyroklystrons and phase-locked gyrotron oscillators

The formalism describing the effect of fluctuations in the technical parameters and in the driving signal on the radiation linewidth in gyroklystrons and phase locked gyrotron oscillators is developed. The phase locking by direct injection of the input signal into the resonator and by prebunching of electrons in the input cavity followed by the drift section is considered. In the first case the results of analysis of the free running gyrotron oscillator given in a companion paper [Phys. Plasmas 4, 1413 (1997)] can be used in a straightforward manner. For gyroklystrons and phase-locked gyrotron oscillators with prebunched electron beams, the numerical study is carried out. In particular, the effect of the detuning of the signal frequency from the eigenfrequency of the resonator on the linewidth of radiation in a gyrodevice with a given level of technical noise is analyzed.

An MMIC V-band phase-locked oscillator using a GaAs MMIC sampling phase detector

A V-band full-monolithic phase-locked oscillator (PLO) has been developed. All the circuits are integrated into three monolithic microwave integrated circuit (MMIC) chips. One is a highly integrated multifunction MMIC for 15-GHz voltage-controlled oscillation and 15-30-GHz frequency doubling. The second is for 30-60-GHz frequency doubling. The third is a sampling phase detector (SPD) chip, which operates up to 20 GHz and can be driven at 0-dBm power. Each circuit is greatly reduced in size by using a uniplanar structure; the oscillator area is only 5.5 mm/sup 2/ and the SPD area is 3.0 mm/sup 2/. The PLO exhibits output power of 3.5 dBm with single-sideband (SSB) phase noise in the phase-locked state of -64 dBc/Hz at 10 kHz offset from 60.0 GHz in spite of the low Q full-monolithic oscillator circuitry.

A 3 mm waveband Gunn oscillator phase-locked with a high- Josephson harmonic mixer and its applications to the quantum voltage standard

Using a high- superconducting harmonic mixer at 77 K and a phase-locking loop, a signal source (a Gunn oscillator in the 3 mm waveband) was directly phase-locked to a local oscillator for frequencies less than 1 GHz and harmonic numbers up to 120. The phase-locked Gunn oscillator achieved a frequency instability of less than Hz, with the counting time of 1 s, while the phase noise at intermediate frequency 40 MHz was ( kHz) for 120th harmonic mixing and ( kHz) for 42nd harmonic mixing. The output of this phase-locked signal source was applied to a Josephson junction array used in a voltage-standard system against which a solid-state voltage source (a Zener voltage reference) was measured. The experimental results showed that the quality of this phase-locked microwave source was good enough to justify its use in the quantum voltage standard.

Oscillatory γ-Band (30–70 Hz) Activity Induced by a Visual Search Task in Humans

The coherent representation of an object in the visual system has been suggested to be achieved by the synchronization in the gamma-band (30-70 Hz) of a distributed neuronal assembly. Here we measure variations of high-frequency activity on the human scalp. The experiment is designed to allow the comparison of two different perceptions of the same picture. In the first condition, an apparently meaningless picture that contained a hidden Dalmatian, a neutral stimulus, and a target stimulus (twirled blobs) are presented. After the subject has been trained to perceive the hidden dog and its mirror image, the second part of the recordings is performed (condition 2). The same neutral stimulus is presented, intermixed with the picture of the dog and its mirror image (target stimulus). Early (95 msec) phase-locked (or stimulus-locked) gamma-band oscillations do not vary with stimulus type but can be subdivided into an anterior component (38 Hz) and a posterior component (35 Hz). Nonphase-locked gamma-band oscillations appear with a latency jitter around 280 msec after stimulus onset and disappear in averaged data. They increase in amplitude in response to both target stimuli. They also globally increase in the second condition compared with the first one. It is suggested that this gamma-band energy increase reflects both bottom-up (binding of elementary features) and top-down (search for the hidden dog) activation of the same neural assembly coding for the Dalmatian. The relationships between high- and low-frequency components of the response are discussed, and a possible functional role of each component is suggested.

An in vitro preparation of frog nose and brain for the study of odour-evoked oscillatory activity

An in vitro preparation is described that consists of frog brain rostral to the brainstem connected to the nasal epithelium by the olfactory nerves. Field potential and intracellular recordings from various brain structures can be obtained while stimulating the nasal epithelium with air-borne odours for at least 12 h after removal of the brain. Power spectra, amplitude and duration of odour-evoked and spontaneous field potentials in vitro are similar to those obtained from paralyzed, spinal cord pithed frogs. A brief puff of odourant applied to the olfactory epithelium produces a 1–2 s bout of 7–13 Hz oscillations in the field potential recorded from the ipsilateral bulb and various ventral, lateral and medial telencephalic structures. Odour evoked bulbar oscillations are maintained after removal of the telencephalon. Electrical stimulation of the olfactory nerves will not elicit oscillations like those evoked by odour stimulation. High-pressure puffs of non-odourised, moist air, elicit olfactory bulb oscillations similar to those evoked by lower pressure puffs of odourised air. Intracellular recordings from most mitral cells reveal oscillations in membrane potential that are phase-locked to the field potential. The extent to which these phase-locked oscillations produce action potentials varies, apparently as a function of the strength and duration of a long-lasting inhibitory potential that is superimposed upon the 7–13 Hz oscillations. This preparation is well-suited for the study of the cellular basis of oscillatory activity in vertebrate brain, and the function of sensory-evoked oscillatory responses in processing of sensory information.

An in vitro preparation of frog nose and brain for the study of odour-evoked oscillatory activity

An in vitro preparation is described that consists of frog brain rostral to the brainstem connected to the nasal epithelium by the olfactory nerves. Field potential and intracellular recordings from various brain structures can be obtained while stimulating the nasal epithelium with air-borne odours for at least 12 h after removal of the brain. Power spectra, amplitude and duration of odour-evoked and spontaneous field potentials in vitro are similar to those obtained from paralyzed, spinal cord pithed frogs. A brief puff of odourant applied to the olfactory epithelium produces a 1–2 s bout of 7–13 Hz oscillations in the field potential recorded from the ipsilateral bulb and various ventral, lateral and medial telencephalic structures. Odour evoked bulbar oscillations are maintained after removal of the telencephalon. Electrical stimulation of the olfactory nerves will not elicit oscillations like those evoked by odour stimulation. High-pressure puffs of non-odourised, moist air, elicit olfactory bulb oscillations similar to those evoked by lower pressure puffs of odourised air. Intracellular recordings from most mitral cells reveal oscillations in membrane potential that are phase-locked to the field potential. The extent to which these phase-locked oscillations produce action potentials varies, apparently as a function of the strength and duration of a long-lasting inhibitory potential that is superimposed upon the 7–13 Hz oscillations. This preparation is well-suited for the study of the cellular basis of oscillatory activity in vertebrate brain, and the function of sensory-evoked oscillatory responses in processing of sensory information.

Picosecond pump-probe using an FEL and a synchrotron source

Abstract We performed a two color pump-probe experiment using the Duke Storage Ring as a synchrotron light source for visible light and the Mark III FEL as a tunable, high peak power IR source. The purpose of this experiment was to measure the timing jitter between these two separately driven electron beam light sources. The visible synchrotron source was used as a probe of vibrational excitation from the IR FEL in an experiment using vibrationally-assisted fluorescence as an indicator of overlap of the IR and the visible pulses. An optical delay line in the FEL beam allowed adjustment of the arrival time of the IR pulse relative to the visible probe. The Duke Storage Ring and the Mark III IR FEL RF sources were driven by phase locked master oscillators. This two color experiment establishes an upper bound on the timing jitter between these sources of 45 ps. With these two synchronous sources, other experiments exploring coupling between electron excitation and lifetimes of vibrational excitation of fluorescence compounds in solution can be performed.

Array of coupled phase-locked oscillators at 160 GHz

A ten-channel millimeter-wave heterodyne phase measurement system is currently under construction. This system will be used for electron density measurement at the plasma experiment W7-AS. The main features are: (1) twofold usage of each 160-GHz oscillator to excite both the transmitting signal to the plasma and the local oscillator (LO) signal for downconversion and (2) the phase-locked loops (PLL's) of each oscillator are coupled in a chain. The authors describe the millimeter-wave part and the digital PLL circuits of that system. Test results of the first three channels, which are already running in the laboratory, are presented.

Fluxon motion in the stacked intrinsic Josephson junctions in Bi 2Sr 2CaCu 2O y single crystals

The fluxon motion excited by external microwaves has been investigated in naturally stacked, intrinsic Josephson junctions of Bi 2Sr 2CaCu 2O y single crystals. For mesa-shaped single-crystals in cavity resonant modes, either odd or even order subharmonic steps, in addition to fundamental steps, caused by the phase-locked oscillation of a coupled multifluxon have been successfully observed in the current-voltage characteristics, depending on the frequency of the microwaves. For mesa-shaped and as-grown single-crystals in off-resonant modes, only fundamental steps caused by the one-way flow of such a multifluxon have been observed.

Novel microwave-induced steps of intrinsic Josephson junctions in mesa-shaped BSCCO single crystals

We have been investigated the current - voltage characteristics of naturally stacked intrinsic Josephson junctions in mesa-shaped single crystals, having dimensions in the ab plane larger than the Josephson penetration depth, without and with microwave irradiations. In the absence of microwave irradiation, a gaplike feature and multiple resistive branches that imply SIS series junctions were observed in the current - voltage characteristic. Under appropriate conditions of microwave irradiation, we successfully observed striking microwave-induced subharmonic steps, caused by the phase-locked oscillation of a coupled multifluxon, with nearly equal voltage separations on the I - V characteristics of a mesa in the cavity resonant mode.

Spatially heterogeneous discrete waves in predator-prey communities over a patchy environment

A model motivated by the earlier work of J. D. Murray and D. Stirzaker is proposed to describe the dynamics of predator-prey communities over a patchy environment. The model is a system of delay differential equations. It is shown that if only one time lag is incorporated into the model, then a branch of spatially homogeneous periodic solutions occur as a primary Hopf bifurcation. However, if two time lags are used to measure different delayed factors in the process of growth, decay, and predator consumption of the prey population, then stable spatially heterogeneous periodic solutions (discrete waves or phase-locked oscillations) may exist. The utilized method is based on center manifold, normal form, and equivariant Hopf bifurcation theory.

Neurons in the globus pallidus do not show correlated activity in the normal monkey, but phase-locked oscillations appear in the MPTP model of parkinsonism.

1. To test the mode of functional connectivity in the basal ganglia circuitry, we studied the activity of simultaneously recorded neurons in the globus pallidus (GP) of a behaving rhesus monkey. The cross-correlograms of pairs of neurons in the GP were compared with those of neurons in the thalamus and frontal cortex and to the cross-correlograms of pallidal pairs after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. 2. In contrast with cortical and thalamic neuronal activity, almost all pairs (n = 76/81 pairs; 93.8%, 1,629/1,651 histograms; 98.7%) of GP neurons in the normal monkey were not driven by a common input. 3. The monkey was systemically treated with MPTP until the appearance of parkinsonian signs and an intermittent 7- to 11-Hz action/postural tremor. After the MPTP treatment, many pallidal neurons (49/140; 35%) became oscillatory, and 19% (n = 31/162) of pallidal pairs had oscillatory cross-correlograms. 4. These results support the model of parallel processing in the basal ganglia of normal monkeys and suggest a breakdown of the independent activity in the parkinsonian state.

Multi-branch entrainment and multi-peaked order-functions in a phase model of limit-cycle oscillators with uniform all-to-all coupling

A peculiar type of mutual entrainment is found numerically in a phase model of a large population of limit-cycle oscillators with uniform all-to-all coupling strongly modulated by higher harmonics, in which more than one branch of mutually phase-locked oscillators exists, accompanied by a multi-peaked order function. For system size N, at least eN different entrained states are likely to coexist with almost identical order functions. Also discussed is how to extend the order-function theory for dealing with such a phenomenon.

Basic cells for phase-locked 1- and 2-D Josephson-junction arrays

The results of a numerical simulation of a few Josephson-junction unit cells and phase-locked 1- and 2-D arrays based on the cells are presented. The numerical simulation was performed by means of the PSCAN program in the framework of both RSJ and Werthamer models of Josephson junctions with finite intrinsic capacitance. It is shown that 1-D arrays, as well as 2-D arrays, can keep a phase-locked oscillation state within wide critical current margins |/spl Delta/I/sub c/| up to 40%. The possible fabrication and use of the phase-locked structures are discussed.

Vulnerability to noise of a phase-locked oscillator array

The effect of noise on the in-phase attractor of a set of N globally coupled oscillators is studied; these discrete-time maps are associated with the continuous-time equations of motion for a series array of Josephson junction oscillators. We investigate both geometrical properties of the basin of attraction in the large N limit, and the implications of this geometry on the average time for the system to escape from the phase-locked mode. Our main results are that the attractor basin maintains a box-shaped “core” of finite radius even as N → ∞, and that the in-phase attractor of a large N array is much less vulnerable to noise than are the out-of-phase attractors.