Amplitude Tuning Research Articles

An Accurate Automatic Quality-Factor Tuning Scheme for Second-Order <emphasis emphasistype="italic">LC</emphasis> Filters

This paper presents a scheme to accurately tune the quality factor of second-order LC bandpass filters. The information of the magnitude response at the center and one of the cutoff frequencies is used to tune both the amplitude and the quality factor of the filter using two independent yet interacting loops. Furthermore, the synergic interaction between the loops makes the proposed scheme stable and insensitive to the mismatch between the input amplitudes. A chip prototype was implemented in a 0.35-mum CMOS process and consumes 4.3 mA from a single 1.3-V supply. Measurement results show that at 1.97 GHz the quality factor is tunable from 60 to 220 while the amplitude is tunable between -15 and 0 dBm with worst case quality factor and amplitude tuning accuracies of 10% and 7%, respectively

Tunable Pulse Amplitude and Position Modulation Technique for Reliable Optical Wireless Communication Channels

Modulation techniques have attracted increasing attention in optical wireless communications. Basic schemes such as on off keying (OOK), pulse amplitude modulation (PAM) and pulse position modulation (PPM) have been validated as suitable for the optical wireless channel. This paper starts from the analysis of these three modulation schemes in terms of their power and bandwidth requirements. As a result, a new tunable hybrid modulation technique is proposed. The proposed modulation scheme takes the real time channel conditions into account, which is different from other schemes. By employing amplitude and position modulation selectively, a guaranteed system performance can be secured, without compromising power and bandwidth efficiency. This is also a new approach to realize reliable optical wireless links.

Stimulus Dependence of Barrel Cortex Directional Selectivity

Neurons throughout the rat vibrissa somatosensory pathway are sensitive to the angular direction of whisker movement. Could this sensitivity help rats discriminate stimuli? Here we use a simple computational model of cortical neurons to analyze the robustness of directional selectivity. In the model, directional preference emerges from tuning of synaptic conductance amplitude and latency, as in recent experimental findings. We find that directional selectivity during stimulation with random deflection sequences is strongly dependent on the mean deflection frequency: Selectivity is weakened at high frequencies even when each individual deflection evokes strong directional tuning. This variability of directional selectivity is due to generic properties of synaptic integration by the neuronal membrane, and is therefore likely to hold under very general physiological conditions. Our results suggest that directional selectivity depends on stimulus context. It may participate in tasks involving brief whisker contact, such as detection of object position, but is likely to be weakened in tasks involving sustained whisker exploration (e.g., texture discrimination).

A Stable Loss Control Feedback Loop for VCO Amplitude Tuning

In practical implementations of LC oscillators in which the quality factor of the tank is dominated by the quality factor of the inductor, due to dependence of the oscillation amplitude on the square of the oscillation frequency and the bias current of the LC tank, a stable amplitude control loop is essential to maintain a constant oscillation amplitude over the tuning range of the voltage-controlled oscillator (VCO) and to optimally bias the VCO over different conditions. In this paper, an enhanced loss control scheme incorporating an integral feedback to automatically tune the oscillation amplitude of LC oscillators is proposed. The proposed loss control feedback (LCF) loop is conditionally stable with an easy stability requirement to meet and its stability is examined: 1) by linearizing the system around the stable point using a perturbation method; and 2) by numerically solving the nonlinear differential equation of the LCF loop describing the transient behavior of the step response of the loop. A prototype including the LC VCO and the proposed LCF loop has been implemented in TSMC 0.35-mum CMOS process and occupies an area of 0.057 mm2 and consumes 8.1 mA from a 2.8-V power supply. The LCF loop, with respect to the VCO, has an overhead of 25% on the area and consumes only 1.3% of the total power. Measurement results of the proposed LCF loop show an 11 dBm amplitude tuning range from -16 dBm to -5 dBm at any frequency over the 2-2.5-GHz tuning range of the VCO. The step response of the loop has a settling time less than 0.5 ns

Nonlinear acoustic experiments involving landmine detection: Status and future

In past experiments [J. Acoust. Soc. Am. 116, 3354–3369 (2004)], airborne sound at two primary tones, f1 and f2 (closely spaced near resonance), undergo acoustic-to-seismic coupling. Due to interactions with the buried plastic landmine, a scattered surface profile can be measured. Particle velocity profiles at f1, f2, and f1−(f2−f1) exhibit single peaks; those at 2f1−(f2−f1), f1+f2, and 2f2+(f2−f1) involve higher-order mode shapes. For some combination frequencies the ‘‘on target’’ to ‘‘off target’’ contrast ratio can improve by over 20 dB. Near resonance, the bending (softening) of a family of increasing amplitude tuning curves, involving the vibration over the landmine, exhibits a linear relationship between the peak particle velocity and corresponding frequency. Hysteresis effects and slow dynamic behavior have also been observed. The interaction between the top-plate interface of a buried landmine and the soil above it appears to exhibit many characteristics of the mesoscopic/nanoscale nonlinear effects that are observed in geomaterials like rocks (sandstone). In linear detection schemes the natural inhomogeneous soil layering can generate some false alarms. Recent ‘‘off target’’ versus. ‘‘on target’’ tuning curve measurements show a substantial increase in nonlinearity, suggesting this to be a good false alarm discriminator. [Work supported by ONR.]

8 GHz 1V, CMOS quadrature downconverter for wireless applications

The design and implementation of an 8 GHz CMOS quadrature downconverter, achieving simultaneously low voltage supply operation and good linearity is presented in this paper. This is achieved by relaxing the inherent tradeoff between power conversion gain and linearity governing all active mixers and implementing a mixer using a new version of the bias-offset technique. The quadrature generator uses active inductors embodied in the LO buffer, and provides easy tuning by relaxing the coupling between amplitude and phase tuning of the outputs. It also provides reduced power consumption by eliminating the buffers located between the quadrature generator and the mixers. A prototype implemented in a 0.18 ?m CMOS technology occupies an area of 0.44 × 0.3 mm2, operates from a 1V power supply and features an IIP3 of +3.5 dBm, an IIP2 of better than +48 dBm, an input compression point of ?5.5 dBm, a power conversion gain of +6.5 dB for the mixers and a quadrature phase and amplitude matching of better than 1.5° and 1 dB respectively over a bandwidth of 100 MHz after tuning. The overall power consumption of the quadrature downconverter is 25.8 mW.

Forces between chemically structured substrates mediated by critical fluids

We consider binary liquid mixtures close to their critical points confined by two parallel, geometrically flat, and chemically structured substrates. Universal order parameter profiles are calculated within mean field theory for periodic patterns of stripes with alternating preferences for the two species of the mixture and with different relative positions of the two substrates. From the order parameter profiles the effective forces between the two plates are derived. The tuning of Casimir amplitudes is discussed.

Nonlinear acoustic landmine detection: Comparison of ‘‘off target’’ soil background and ‘‘on target’’ soil-mine nonlinear effects

When airborne sound at two primary tones, f1, f2 (closely spaced near a resonance) excites the soil surface over a buried landmine, soil wave motion interacts with the landmine generating a scattered surface profile which can be measured over the ‘‘target.’’ Profiles at f1, f2, and f1−(f2−f1), f2+(f2−f1), 2f1−(f2−f1), f1+f2 and 2f2+(f2−f1) (among others) are measured for a VS 1.6 plastic, inert, anti-tank landmine, buried at 3.6 cm in sifted loess soil. It is observed that the ‘‘on target’’ to ‘‘off target’’ contrast ratio for the sum frequency component can be ∼20 dB higher than for either primary. The vibration interaction between the top-plate interface of a buried plastic landmine and the soil above it appears to exhibit many characteristics of the mesoscopic/nanoscale nonlinear effects that are observed in geomaterials like sandstone. Near resonance, the bending (softening) of a family of increasing amplitude tuning curves, involving the vibration over the landmine, exhibits a linear relationship between the peak particle velocity and corresponding frequency. Tuning curve experiments along with two-tone tests are performed both on and off the mine in an effort to understand the nonlinearities in each case. [Work supported by U.S. Army RDECOM CERDEC, NVESD.]

Measurements of a Persistent-Current Qubit Driven by an On-Chip Radiation Source

Monolithic integration of control electronics with superconducting qubits will facilitate scalability of a superconducting quantum computer by reducing the room temperature electronics necessary for performing quantum state manipulation. We report the experimental results of the monolithic integration of an on-chip radiation source with a persistent-current (PC) qubit and dc SQUID measurement device. The devices were fabricated at MIT Lincoln Laboratory in a Nb/Al/AlOx/Nb trilayer process. The two PC qubit states were detected by measuring the switching current of an underdamped dc SQUID magnetometer inductively coupled to the qubit. The radiation source comprised an overdamped dc SQUID operating in the voltage state and inductively coupled to the qubit and measurement SQUID through a low-Q RLC filter. The oscillator was designed to have tunable amplitude and frequency to satisfy the requirements for coherent quantum manipulation of a superconducting PC qubit. We will discuss the measurements in the millikelvin regime and the effects of the oscillator noise on the state of the qubit.

Nonlinear acoustic experiments involving landmine detection: Connections with mesoscopic elasticity and slow dynamics in geomaterials, Part II

In nonlinear acoustic detection, airborne sound at two primary tones, f1, f2 (chosen several Hz apart from resonance) insonifies the soil surface over a buried landmine, and due to soil wave interactions with the landmine, a scattered surface profile can be measured by an LDV. Profiles at f1, f2, f1−(f2−f1) and f2+(f2−f1) exhibit a single peak while profiles at 2f1−(f2−f1), f1+f2 and 2f2+(f2−f1) are attributed to higher order mode shapes. The lowest resonant frequency for a VS 1.6 plastic, inert, anti-tank landmine, buried at 3.6 cm deep is ∼125 Hz. The ‘‘on target’’ to ‘‘off target’’ contrast ratio, for some of the nonlinearly generated combination tones, is roughly 15–20 dB higher compared to either primary component. Near resonance, the bending (softening) of a family of increasing amplitude tuning curves, involving the surface vibration over the landmine, exhibits a linear relationship between the peak particle velocity and corresponding frequency. The tuning curves exhibit hysteresis effects. Landmine-soil vibrations exhibit similar characteristics to nonlinear mesoscopic/nanoscale effects that are observed in geomaterials like rocks or granular materials. Nonlinear mechanisms of soil and the soil interacting with the top-plate of the mine case are compared. [Work supported by U.S. Army RDECOM CERDEC, NVESD.]

Using spectral decomposition as a hydrocarbon indicator tool in the Norwegian Sea

Investigation of two deepwater gas accumulations in the Norwegian Sea indicate that phase and amplitude spectra derived using spectral decomposition can be used as hydrocarbon indicators. Specifically, this technique enhances the ability to evaluate phase and amplitude anomaly conformance to structure and complements the more traditional utilization of spectral decomposition for thin bed analysis. The 6707/10-1 Luva well on the Nyk High encountered a 156 m thick column of dry thermogenic gas and was the first deepwater discovery in Norway. Despite the fact that the accumulation is characterized by a well developed flat event, examination of partial stack broadband 3D reflectivity data proved inconclusive in substantiating the presence of an amplitude anomaly conformant with structure at all offset ranges. Amplitude and phase tuning cubes were derived using spectral decomposition from near, far and full offset-stack 3D seismic data. Strong amplitude anomalies most notably at frequencies less than 10 Hz, structurally conformant with the observed gas/water contact, are observed at all offset ranges. Phase instability, associated with rock property differences between the gas charged and brine saturated portions of the reservoir, results in an anomaly in the phase tuning cube that is also most evident at low frequencies and is also conformant with the observed gas/water contact. Similar spectral decomposition evaluation of seismic data over the Ormen Lange gas discovery gave equally dramatic results. Traditional amplitude extraction methodologies on the full stack broadband data set show an ambiguous amplitude anomaly with limited conformance to structure. Spectral decomposition of the same full stack data set show well defined anomalies at frequencies less than 12 Hz, in both amplitude and phase tuning cubes, conformant with the gas water contact proven by drilling. 3D forward models built using rock properties from the Luva and Ormen Lange wells have been processed with the same spectral decomposition software and substantiate observed results. Spectral decomposition analysis of untested prospects in other areas of the Norwegian Sea show both phase and amplitude anomalies at low frequencies that appear conformant with structure.

Nonlinear acoustic experiments involving landmine detection: Connections with mesoscopic elasticity and slow dynamics in geomaterials, Part III

In nonlinear acoustic detection schemes, airborne sound at two primary tones, f1, f2 (closely spaced near an 80-Hz resonance) excites the soil surface over a buried landmine. Due to soil wave interactions with the landmine, a scattered surface profile can be measured by a geophone. Profiles at f1, f2, f1−(f2−f1) and f2+(f2−f1) exhibit single peaks; those at 2f1−(f2−f1), f1+f2 and 2f2+(f2−f1) involve higher order mode shapes for a VS 2.2 plastic, inert, anti-tank landmine, buried at 3.6 cm in sifted loess soil [J. Acoust. Soc. Am. 116, 3354–3369 (2004)]. Near resonance, the bending (softening) of a family of increasing amplitude tuning curves, involving the vibration over the landmine, exhibits a linear relationship between the peak particle velocity and corresponding frequency. Results are similar to nonlinear mesoscopic/nanoscale effects that are observed in granular solids like Berea sandstone. New experiments show that first sweeping up through resonance and then immediately sweeping back down result in different tuning curve behavior that might be explained by ‘‘slow dynamics’’ where an effective modulus reduction persists following periods of high strain. Results are similar to those described by TenCate et al. [Phys. Rev. Lett. 85, 1020–1023 (2000)]. [Work supported by U.S. Army RDECOM CERDEC, NVESD.]

Direct digital synthesiser with tunable phase and amplitude error feedback structures

The error feedback (EF) technique is used to suppress phase and amplitude spurs in direct digital synthesisers (DDSs). It allows the reduction of wordlengths of the phase-to-amplitude converter and the D/A converter. The drawback of the conventional phase EF technique is that it reduces the phase spurs only at DDS output frequencies, which are near DC or half the sampling frequency. New phase EF structures with arbitrary centre frequency for cosine and quadrature output DDSs are introduced. The cosine and quadrature DDS with tunable phase and amplitude EF were designed and implemented on a programmable logic device. The experimental results show their desired operation and performance.

Calcium Secretion Coupling at Calyx of Held Governed by Nonuniform Channel–Vesicle Topography

Phasic transmitter release at synapses in the mammalian CNS is regulated by local [Ca2+] transients, which control the fusion of readily releasable vesicles docked at active zones (AZs) in the presynaptic membrane. The time course and amplitude of these [Ca2+] transients critically determine the time course and amplitude of the release and thus the frequency and amplitude tuning of the synaptic connection. As yet, the spatiotemporal nature of the [Ca2+] transients and the number and location of release-controlling Ca2+ channels relative to the vesicles, the "topography" of the release sites, have remained elusive. We used a time-dependent model to simulate Ca2+ influx, three-dimensional buffered Ca2+ diffusion, and the binding of Ca2+ to the release sensor. The parameters of the model were constrained by recent anatomical and biophysical data of the calyx of Held. Comparing the predictions of the model with previously measured release probabilities under a variety of experimental conditions, we inferred which release site topography is likely to operate at the calyx: At each AZ one or a few clusters of Ca2+ channels control the release of the vesicles. The distance of a vesicle to the cluster(s) varies across the multiple release sites of a single calyx (ranging from 30 to 300 nm; average approximately 100 nm). Assuming this topography, vesicles in different locations are exposed to different [Ca2+] transients, with peak amplitudes ranging from 0.5 to 40 microm (half-width approximately 400 microsec) during an action potential. Consequently the vesicles have different release probabilities ranging from <0.01 to 1. We demonstrate how this spatially heterogeneous release probability creates functional advantages for synaptic transmission.

Real-time integrated process supervision

This paper presents the use of a micro-controller-based integrated process supervision (IPS) system as a real-time platform for investigative work in structuring expert control. Two different control approaches, based on classical and artificial intelligence techniques, were integrated within IPS and serve as practical examples of the structured approach to expert control. The IPS is a refinement of the expert control architecture. It allows the integration of several control techniques in a single generic framework. Specifically, the paper presents the extensive experimental results derived from a micro-controller-based implementation of IPS on the real-time control of a typical industrial heat-exchanger process. The classical approach, based on auto-tuning techniques, was implemented under the IPS framework. Three auto-tuning techniques, namely Ziegler–Nichols tuning, amplitude tuning and phase tuning were incorporated. In addition, neural-network-based control techniques using the modified cerebellar model articulation controller (MCMAC) were also seamlessly incorporated within the IPS scheme. The real-time experimental results using the IPS architecture significantly demonstrated the effectiveness of IPS in handling varying operating conditions. Furthermore, the inclusion of both AI and classical control techniques within a common supervisory framework adequately shows the generality of the architecture.

Spatiotemporal Frequency and Direction Sensitivities of Human Visual Areas Measured Using fMRI

Using functional magnetic resonance imaging (fMRI) we have studied the variation in response magnitude, in each visual area (V1–V5), as a function of spatial frequency (SF), temporal frequency (TF) and unidirectional motion versus counterphase flicker. Each visual area was identified in each subject using a combination of retinotopic mapping fMRI and cortical flattening techniques. A drifting (or counterphasing) sinusoidal grating was used as the stimulus in a study in which we parametrically varied SF between 0.4 and 7 cycles/degree and TF between 0 and 18 Hz. For each experiment we constructed fMRI amplitude tuning curves, averaged across subjects, for each visual area. The tuning curves that resulted are consistent with the known physiological properties of cells in the corresponding macaque visual areas, previous functional imaging studies, and in the case of V1, the psychophysically determined contrast sensitivity functions for spatial and temporal frequency. In the case of V3A, the SF tuning functions obtained were more similar to those found in single cell studies of macaque V3 rather than macaque V3A. All areas showed at least a moderate preference for directed versus counterphasing motion with V5 showing the largest preference. Visual areas V1, V2, V3, and V3A showed more direction sensitivity at low spatial frequencies, while VP, V4, and V5 had the highest drifting versus counterphasing ratios for higher spatial frequencies.

Mechanical nonlinearity in the apical turn of the guinea pig organ of Corti

Confocal microscopy was used to view the sealed apical turn of the cochlea in a living guinea pig, and to identify the cochlear structures through the intact Reissner’s membrane. X, Y and Z coordinates for each point of interest were recorded. A confocal laser heterodyne interferometer measured the cellular vibration in response to acoustical signals applied to the ear. Velocity time waveforms were recorded at 32 frequencies between 25 and 2500 Hz at each point of measurement. To characterize the vibration pattern of the organ of Corti, vibrations at multiple locations along a radial track of the reticular lamina were measured before and after sacrificing the animal. Amplitude and phase tuning curves of the fundamental and the second harmonic, velocity time waveforms, and FFTs of time waveforms are compared before and after sacrifice. The results show that a sharply tuned nonlinear part of the response disappears shortly after sacrifice.

Generation of Tunable Amplitude-Squeezed Light by Injection Locking of a Laser Diode

Tunable amplitude squeezing around the D2 line of cesium has been experimentally accomplished at room temperature in a quantum-well laser diode with light injection from a single-mode distributed Bragg-Reflector laser diode. While the master laser frequency is tuned, amplitude squeezing of the output light from the slave laser can be maintained at about 0.9 dB throughout a tunable range of ∼ 1.7 GHz around the cesium D2 line.

Cladding-mode resonances in hybrid polymer-silica microstructured optical fiber gratings

We examine the cladding-mode resonances of fiber gratings UV written into the core of a novel microstructured fiber whose air regions are subsequently infused with polymer. The cladding spectrum changes with temperature because of the strong temperature dependence of the polymer refractive index and we show that these changes can be understood qualitatively using a simple model of the polymer-silica waveguide. Our results imply wavelength and amplitude tuning regimes for long period gratings written into this fiber with tunability enhanced over conventional long period gratings because of the small effective inner cladding diameter of our fiber.

Properties of saccade-related neurons in the cat superior colliculus: patterns of movement fields and discharge timing.

The discharge characteristics of saccade-related neurons in the superior colliculi (SC) of trained cats were investigated in order to understand the involvement of the SC in dynamic control of saccades. In particular, two aspects of saccade-related collicular activity in relation to visually guided saccades were quantitatively analyzed: the bounded pattern of amplitude tuning and the timing of neural activity in relation to saccade offset. In order to determine whether the amplitude tuning of SC cells is bounded or unbounded, we characterized it with a quantitative index, the unbounded-field (UF) index. Analysis of the characteristics of the distribution of this index, including the absence of unbounded fields for cells within the central 10 degrees, suggested that all cells form a single class and that apparent unbounded amplitude tuning is an artifact occurring when the range of gaze shift is truncated by restraining the head. This interpretation is supported by the results of a computer simulation based on truncation of gaze-shift range that closely replicated the experimental data. Analyses of relative location of peak motor activity in the spatial and temporal dimensions revealed that the peak discharge was more closely linked to the midpoint of the saccade than to the offset of saccade, regardless of the pattern of amplitude tuning. These results do not support the proposal advanced by the moving-hill hypothesis: the bounded pattern of amplitude tuning is inconsistent with rostral migration of the activity locus during execution of a saccade, and the relative location of the peak motor activity is inconsistent with the idea that the SC activity encodes dynamic motor error (the difference between desired and current gaze directions).