Electronic Feedback Circuit Research Articles

Self-synchronized reflection-mode acousto-optic imaging system utilizing nanosecond laser pulses.

We present an acousto-optic imaging system operating in reflection-mode and utilizing a pair of compact, triggerable lasers with 532 and 1064 nm wavelength and nanosecond pulse duration. The system maps the fluence rate distribution of light transmitted through optically scattering samples. The imaging is performed using an acousto-optic probe comprising an ultrasound linear array with attached optical fiber on one side and a camera on the other. The described hardware configuration images samples with access restricted to one side only and ensures mobility of the entire setup. The major challenge of the introduced approach is mitigating the effects of laser parameter instabilities and precise synchronization of ultrasound and laser pulses. We solved this issue by developing an electronic feedback circuit and a microcontroller-based synchronization and control system triggering the ultrasound scanner. Schematics and details regarding control algorithms are introduced. The imaging performance of the system is demonstrated on examples of results obtained for solid, acoustically-homogeneous and optically scattering phantoms with and without light absorbing inclusions present. Adjusting the size and location of the region of interest within the camera sensor matrix and the number of laser pulses illuminating every frame allows for significant improvements in terms of the achievable peak signal to noise ratio. We demonstrate that the developed synchronization algorithm and system play a crucial role in ensuring imaging quality and accuracy.

Residual phase noise suppression for Pound-Drever-Hall cavity stabilization with an electro-optic modulator

We propose a simple method to suppress residual frequency/phase noise in Pound-Drever-Hall (PDH) cavity stabilization setups. This method makes use of the electro-optic modulator that is commonly used in PDH setups, and hence, only requires the addition of a simple electronic feedback circuit. Here, we apply this method to stabilize a commercially available continuous wave (cw) laser to a high-finesse cavity, and we demonstrate additional phase noise suppression of ~30 dB and more from DC to 100 kHz, compared to the use of a fast-piezo actuator alone. This method can be applied to almost all PDH systems to achieve feedback bandwidths in the multi-MHz range. Furthermore, this method does not require additional actuators, such as acousto-optic modulators, and it does not introduce parasitic amplitude modulation to the first order. The limitations and drawbacks of this approach are also discussed.

Experimental examination of frequency locking effect in acousto-optic system

The optoelectronic system containing collinear acousto-optic cell fabricated on the base of calcium molybdate crystal and positive electronic feedback circuit was examined. The feedback signal is formed due to the optical heterodyning effect that occurs on the cell output and takes place in the special regime of collinear acousto-optic diffraction. It was discovered that three operation modes that may exist in this system. The boundaries between the modes were determined. The positions of the boundaries depend on the main parameters of the system—the incident light intensity and the feedback gain value. The new for acousto-optics phenomenon of acousto-optic system self-oscillations frequency locking by the RF generator signal was discovered and examined experimentally. Such an effect has never been observed before in the acousto-optic systems. It was experimentally shown that frequency locking effect may be used to select one of the multimode semiconductor laser longitudinal modes to improve laser radiation spectral composition.

Fundamentals of Electronics: Book 4 Oscillators and Advanced Electronics Topics

This book, Oscillators and Advanced Electronics Topics, is the final book of a larger, four-book set, Fundamentals of Electronics. It consists of five chapters that further develop practical electronic applications based on the fundamental principles developed in the first three books. This book begins by extending the principles of electronic feedback circuits to linear oscillator circuits. The second chapter explores non-linear oscillation, waveform generation, and waveshaping. The third chapter focuses on providing clean, reliable power for electronic applications where voltage regulation and transient suppression are the focus. Fundamentals of communication circuitry form the basis for the fourth chapter with voltage-controlled oscillators, mixers, and phase-lock loops being the primary focus. The final chapter expands upon early discussions of logic gate operation (introduced in Book 1) to explore gate speed and advanced gate topologies. Fundamentals of Electronics has been designed primarily for use in upper division courses in electronics for electrical engineering students and for working professionals. Typically such courses span a full academic year plus an additional semester or quarter. As such, Oscillators and Advanced Electronics Topics and the three companion book of Fundamentals of Electronics form an appropriate body of material for such courses.

Parametric noise squeezing and parametric resonance of microcantilevers in air and liquid environments

In this work, parametric noise squeezing and parametric resonance are realized through the use of an electronic feedback circuit to excite a microcantilever with a signal proportional to the product of the microcantilever's displacement and a harmonic signal. The cantilever's displacement is monitored using an optical lever technique. By adjusting the gain of an amplifier in the feedback circuit, regimes of parametric noise squeezing/amplification and the principal and secondary parametric resonances of fundamental and higher order eigenmodes can be easily accessed. The exceptionally symmetric amplitude response of the microcantilever in the narrow frequency bandwidth is traced to a nonlinear parametric excitation term that arises due to the cubic nonlinearity in the output of the position-sensitive photodiode. The feedback circuit, working in both the regimes of parametric resonance and noise squeezing, allows an enhancement of the microcantilever's effective quality-factor (Q-factor) by two orders of magnitude under ambient conditions, extending the mass sensing capabilities of a conventional microcantilever into the sub-picogram regime. Likewise, experiments designed to parametrically oscillate a microcantilever in water using electronic feedback also show an increase in the microcantilever's effective Q-factor by two orders of magnitude, opening the field to high-sensitivity mass sensing in liquid environments.

Biomolecular Mimic Circuit for an Allosterically Regulated Enzyme of Pyrimidine Biosynthetic Pathway

A general type of molecular level metabolic control that is common to all living organisms is the feedback inhibition, wherein an increase in the product of a metabolic pathway regulates an enzyme upstream in the cascade by binding to it and decreasing enzyme activity. The de novo pyrimidine biosynthetic pathway provides a specific example for the feedback inhibition. Aspartate transcarbamoylase (ATCase) catalyzes the first step in the biosynthesis of pyrimidines and one of the best understood allosteric enzymes. The structure of ATCase is roughly triangular in shape, similar to the symbol of an op-amp IC. Since most of the enzymatic properties were analogous to the properties of IC, this inspired us to mimic the enzyme (EC 2.1.3.2) with an IC (PIN μ A741CN) in our circuit design. The Michaelis-Menten model, Lineweaver-Burk equation and the equation for the non-inverting amplifier were theoretically related and used for our model. As a result, an electronic feedback circuit was designed and tested. The biomolecular mimic circuit will develop a new level of understanding of the metabolic complexity in the cell.

Electronic Feedback System for Stabilization of Fiber Ring Resonator

We propose a simple technique to stabilize the optical output intensity of a fiber ring resonator. The electronic feedback circuit system, which consists of two voltage control oscillators, a phase comparator, and a low pass filter, is applied to the fiber ring resonator in order to compensate the optical phase shift in the ring loop. The reference electrical signal determines the operating condition of the fiber ring resonator for the desired optical output signal. The experimental results within the operating range agree well with the analytical results. The simulated performance of the proposed model is also compared with that of other existing models and shows significant improvement over them.

Fast-response, wide-dynamic-range optical equalisation based on silicon photonic platform

Fast optical power equalisation using a monolithic integrated germanium photodetector and a silicon variable optical attenuator on a compact silicon photonic platform is demonstrated. With an external electronic feedback circuit, the output power of the device is stabilised within a residual deviation of 2.7 dB for 22 dB input power variation. For a surge pulse, a sudden input power increase of over 16 dB can be suppressed within 50 ns for a 3 dB recovery.

TOAD를 이용한 40 Gbit/s OPLL Clock Recovery 시스템에 대한 연구

10 GHz clock recovery from 40 Gbit/s optical time-division-multiplexed(OTDM) signal pulses was experimentally demonstrated using an optical phase lock loop based on a terahertz optical asymmetric demultiplexer(TOAD) with a local-reference-oscillator-free electronic feedback circuit. The 10 GHz clock was successfully extracted from 40 Gbit/s signals. The SNR of the time-extracted 10 GHz RF signal to the side components was larger than 40 dB. Also we performed numerical simulation about the extraction process of phase information in TOAD. The lock-in frequency range of the clock recovery is found to be 10 kHz.

Clock recovery from 40 Gbps optical signal with optical phase-locked loop based on a terahertz optical asymmetric demultiplexer

10 GHz clock recovery from 40 Gbps optical time-division-multiplexed (OTDM) signal pulses is experimentally demonstrated using optical phase lock loop based on a terahertz optical asymmetric demultiplexer (TOAD) with a local-reference-oscillator-free electronic feedback circuit. The clock pulse that was used as the control pulse had energy of 800 fJ and the SNR of the time-extracted 10 GHz RF signal to the side components was larger than 40 dB.

Wall Heat Flux Behavior of Nucleate Pool Boiling Under a Constant Temperature Condition in a Binary Mixture System

The objective of this work is to measure space and time resolved wall heat fluxes during nucleate pool boiling of R113/R11 mixtures using a microscale heater array in conjunction with a high speed CCD. The microscale heater array is constructed using VLSI techniques, and consists of 96 serpentine platinum resistance heaters on a transparent quartz substrate. Electronic feedback circuits are used to keep the temperature of each heater at a specified temperature and the variation in heating power required to keep the temperature constant is measured. Heat flux data around an isolated bubble are obtained with triggered CCD images. CCD images are obtained at a rate of 1000frames/second. The heat transfer variation vs. time on the heaters directly around the nucleation site is plotted and correlated with images of the bubble obtainedby using the high speed CCD. For both of the mixture(R11/R113) and pure system(pure R11, pure R113), the wall heat fluxes are presented and compared to find out the qualitative difference between pure and binary mixture nucleate boiling.

Stretching DNA with optical tweezers

Force-extension (F-x) relationships were measured for single molecules of DNA under a variety of buffer conditions, using an optical trapping interferometer modified to incorporate feedback control. One end of a single DNA molecule was fixed to a coverglass surface by means of a stalled RNA polymerase complex. The other end was linked to a microscopic bead, which was captured and held in an optical trap. The DNA was subsequently stretched by moving the coverglass with respect to the trap using a piezo-driven stage, while the position of the bead was recorded at nanometer-scale resolution. An electronic feedback circuit was activated to prevent bead movement beyond a preset clamping point by modulating the light intensity, altering the trap stiffness dynamically. This arrangement permits rapid determination of the F-x relationship for individual DNA molecules as short as -1 micron with unprecedented accuracy, subjected to both low (approximately 0.1 pN) and high (approximately 50 pN) loads: complete data sets are acquired in under a minute. Experimental F-x relationships were fit over much of their range by entropic elasticity theories based on worm-like chain models. Fits yielded a persistence length, Lp, of approximately 47 nm in a buffer containing 10 mM Na1. Multivalent cations, such as Mg2+ or spermidine 3+, reduced Lp to approximately 40 nm. Although multivalent ions shield most of the negative charges on the DNA backbone, they did not further reduce Lp significantly, suggesting that the intrinsic persistence length remains close to 40 nm. An elasticity theory incorporating both enthalpic and entropic contributions to stiffness fit the experimental results extremely well throughout the full range of extensions and returned an elastic modulus of approximately 1100 pN.

A highly accurate, hand-held clamp-on current transformer

The design, operation, and performance of a 1000:5 A highly accurate, hand-held, clamp-on-type current transformer are presented. This precision current transformer uses a sensitive magnetic circuit to detect transformer ampere-turn unbalance between the primary and secondary circuits. The unbalance represents an error in the ratio and phase angle of the transformer. The largest of the errors is due to the core magnetization current and magnetic reluctance caused by the cutting of the core material. After sensing the errors, electronic feedback through a magnetic circuit is used to provide an error-correcting current. This reduces the overall errors dramatically. These types of devices are referred to as "active" current transformers because of the use of electronic amplifier and feedback circuits. The device described has a novel feature of an openable, split core. This "clamp-on" capability enables use of the transformer on a bus or cable without the complications or need to open the current-carrying circuit to be measured. Commonly used "clamp-on"-type current transformers generally have uncertainties from about 1 to 5% at full-scale rated current. This paper describes a commercialization of active current transformers having a ratio uncertainty of less than /spl plusmn/0.05% over a current range from full-scale rated to 1% of full-scale. Additionally, this product has a small phase angle which is an important consideration when measuring electric power, energy, and power factor. It is intended to be used by electric utilities, standards laboratories, testing laboratories, and in applications where high measurement accuracy and the split-core, clamp-on feature are attractive considerations.

High-precision BESOI-based resonant accelerometer

A uniaxial resonant acceleration sensor for high-precision measurements, made in bulk micromachining, is presented. The high symmetry of the device structure eliminates rotational acceleration components and diminishes cross-axis sensitivities. Silicon direct bonding, and the use of commercial BESOI (bond and etch back silicon on insulator) wafers, form the sensor structure, which is a silicon-silicon sandwich. The vibrating element is a silicon beam that is driven electrothermally and sensed piezoresistively. Closed-loop operation of the resonator by means of an electronic feedback circuit is demonstrated. Also in closed-loop operation, static and dynamic measurements of prototypes have been performed, showing the very good mechanical properties of the device. The method employed for dynamic testing of a resonant accelerometer on a vibrating table is described.

Heating stage for in situ studies of thin-film reactions

We describe a method for measuring and controlling the temperature of thin ceramic plates which are used as substrates for the deposition of thin films in high vacuum. The ceramic plates have an embedded platinum resistor which acts as both heating element and thermometer. The temperature of the substrate is controlled by an electronic feedback circuit. This arrangement enables accurate measurements of the thin-film temperature. In addition, the system has a fast response time and excellent long-term temperature stability. We describe an application where the temperature control system is combined with ac resistance measurements to study the kinetics of a solid-state interdiffusion reaction in Ni-Zr multilayers.

Parallel Neighborhood Operation System by Optical Parallel Logic Gate and Optical Interconnection with Prisms

Parallel neighborhood operations are very useful for image processing. A system that optically implements the operations is presented. The system consists of an optical parallel logic gate, a simple multiple-imaging system and electronic feedback circuits. The experimental results of several binary image processings are presented by use of the system, and a new algorithm for extraction of corners is proposed.

Fast automatic polarization control system

A fast polarization control system using a lithium niobate electrooptic polarization transformer and a simple electronic feedback circuit is reported. The system produces general elliptical phase retardation at a maximum rate of 6300 rad/s and allows continuous transformations from any general varying input polarization into any desired output state. The automatic stabilization of a rapidly varying polarization state at rates of up to 4900 rad/s was achieved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Demonstration of data transmission using coherent correlation to reconstruct a coded pulse sequence

An optical pulse sequence derived from a single pulse can be summed coherently by a delay network provided that delay lengths are strictly controlled. Coherent correlation was demonstrated experimentally, using an electronic feedback circuit to interferometrically stabilize fiber delay lengths. The potential for application to code-division multiple access (CDMA) networks is demonstrated by using coherent correlation to distinguish a data sequence from an incoherent background signal. >

Mass-flow sensor using aerodynamic damping

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The increasing-temperature hot-plate test: An improved test of nociception in mice and rats

The increasing-temperature hot-plate test has several advantages compared to the conventional hot-plate test, but available equipment has been impractical and restricted with regard to stimulus control. We now describe an apparatus consisting of an aluminum plate that is heated and cooled by Peltier elements in contact with its lower surface. Several plates can be used simultaneously, individually controlled by electronic proportional feedback circuits. The set temperature of the feedback circuit is controlled by a computer program run on an IBM XT-compatible PC, so that a linear increase in temperature is achieved. Experiments were performed using rats and mice, with hindpaw licking as an end-point criterion. Experiments with various heating rates showed that 3.0° C/min is the lowest rate that can be applied without signs of stress in the animals. On the basis of the recorded data, nociceptive temperature thresholds were calculated to be approximately 44.5°C for both rats and mice. Inspection of the paws after analgesic treatment and exposure to different end-point temperatures suggested that a cutoff temperature of 50°C should be employed to minimize tissue damage. Testing at ambient temperatures of 18° and 28°C yielded similar results for rats, whereas mice responded at significantly higher plate temperatures in the colder environment. Dose-related antinociceptive effects were demonstrated for morphine and paracetamol in both species. The results confirm that the increasingtemperature hot-plate test is a valuable test of nociception, which is also suitable for demonstrating the antinociceptive effects of nonopioid analgesics. The test may also be used to estimate the nociceptive temperature threshold.