Frequency Modulation Scheme Research Articles

Efficient Hybrid Carrier Based Space Vector Modulation for a Cascaded Multilevel Inverter

This paper presents a novel hybrid carrier based space vector modulation for cascaded multilevel inverters. The proposed technique inherits the properties of carrier based space vector modulation and the fundamental frequency modulation strategy. The main characteristic of this modulation are the reduction of power loss, and improved harmonic performance. The carrier based space vector modulation algorithm is implemented with a TMS320F2407 digital signal processor. A Xilinx Complex Programmable Logic Device is used to develop the hybrid PWM control algorithm and it is integrated with a digital signal processor for hybrid carrier based space vector PWM generation. The inverter offers less weighted total harmonic distortion and it operates with equal electrostatic and electromagnetic stress among the power devices. The feasibility of the proposed technique is verified by spectral analysis, simulation, and experimental results.

Experimental study of the CPT magnetometer worked on atomic energy level modulation

We have set up a coherent population trapping (CPT)-based atomic magnetometer experimental system worked with 87Rb atoms, and with this system experimentally investigated the behaviour of a CPT magnetometer prototype proposed by us, which worked with the atomic energy level modulation scheme. Through systematical comparison with generally used microwave frequency modulation scheme, the experimental results reveal that the energy level modulation scheme not only extends the detection range, but also improves the sensitivity of magnetic field detection.

Intracavity wavelength modulation of an optical parametric oscillator for coherent Raman microscopy

We present a novel intracavity frequency modulation scheme in a tunable, picosecond optical parametric oscillator (OPO). The OPO signal wavelength can be modulated with a depth of more than 10 nm at a rate of 38 MHz (one half its repetition rate). We discuss the design and construction of the light source and its application to the recently-developed frequency modulation coherent anti-Stokes Raman scattering (FM-CARS) and stimulated Raman scattering (SRS) techniques. The new light source allows for real time subtraction of the interfering background signal in coherent Raman imaging, yielding images with purely chemical contrast.

Integrated CMOS system and thermally actuated optical switch for wavelength modulation/lock in communication network

AbstractThe advancement of communication technology and growth of internet traffic have continuously driven the fast evolution of networks. Compared to the traditional optoelectronic switch, all-optical switch provides high throughput, rich routing functionalities, and excellent flexibility for rapid signal exchange in fiber optical network. Among various all-optical switches, thermal actuated ring switch provides the advantages of high accuracy, easy actuation, and reasonable switching speed. However, when scale up, thermal ring switch may encounter issues related to fabrication error, non-accurate wavelength response, and large terminal numbers in the control circuit. In this research, we propose the employment of an integrated CMOS control circuit to compensate the fabrication error and tune as well as lock the wavelength in a thermal-actuated ring-type optical switch through a frequency modulation scheme. Additional functionalities can also be added in this circuit by tailoring externally the roundtrip loss or coupling constants of the ring. The design concept can be easily scaled up for large array optical switch system without much change in the terminal numbers thanks to the three-dimensional hierarchy of control circuit design, which effectively reduces the terminal numbers into the cubic root of the total control unit numbers. The integrated circuit has been designed, simulated, as well as fabricated, and demonstrated a decent performance with free spectral range (FSR) equal to 1.5 nm at 1534 nm and very accurate wavelength modulation to 0.3 nm within 0.01 nm fluctuation for thermal actuated ring type optical switch.

Detection of extracellular potentials using a mechanical-based nanosensor

Event Abstract Back to Event Detection of extracellular potentials using a mechanical-based nanosensor Implantable high density microelectrode arrays hold enormous promise as tools for understanding neuronal circuits in vivo. At present, a limitation of this technology arises in signal extraction from the recording site to the macro-scale. This is typically carried out via lithographically defined wiring. In order to minimise tissue damage, higher density electrode arrays will require narrower wiring with submicron dimensions. However, the effects of impedance and capacitive coupling prohibit an arbitrary reduction in size. Realising ultra-high resolution extracellular recordings over large volumes will thus require novel methods of signal extraction. Here we present a new paradigm that allows parallel signal extraction from potentially hundreds to thousands of electrodes through a single output, by transducing signals in the frequency-domain. Our approach relies on the use of nanoscale, piezoelectrically coupled transducers known as D-NEMS (depletion-mode nanoelectromechanical systems). A key feature of these devices is that they exhibit mechanical resonance effects; their precise structural dimensions determine their characteristic vibrational frequencies. The piezoelectric effect enables conversion of an electric field into mechanical strain. The devices we constructed were beam structures of different lengths, analogous to the strings on a guitar. Each beam was coupled to a different microelectrode, and as they were of varying lengths, they exhibited dissimilar resonant frequencies when driven in the RF range. Much like the tones of guitar strings can be modulated by stress, a voltage applied through the coupled microelectrode can be used to shift the vibrational frequency of the piezoelectric beam resonator by altering the tension within it. This presentation discusses our early attempts to harness this effect to develop a nanoscale, mechanical-based detection scheme for extracellular potentials. In a proof-of-concept experiment, the mechanical displacement of the resonators were measured in parallel using laser interferometry. All mechanical transduction thus occurred via a single, optical signal transmission path. As the fundamental frequency of each microelectrode-coupled resonator is set much further apart than the variation that occurs during signal detection, each of the microelectrodes is addressable. The mechanical response is linear, and thus microelectrode signals can be transduced back into an amplitude post-extraction. Extracellular action potentials in the thoracic ganglia of the locust were successfully recorded using the frequency modulation scheme, with our devices coupled to multi-channel neural probes. In addition, multiplexed voltage detection was demonstrated with two recording electrodes coupled to separate piezoelectric resonators. Finally, the response of the system was systematically characterised, and its limitations and prospects for improvement are presented. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster and Short Oral Presentation Topic: Poster and Short Oral Presentations Citation: (2009). Detection of extracellular potentials using a mechanical-based nanosensor. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.304 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Feb 2009; Published Online: 04 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Multiple frequency modulation for low-light atom measurements in an optical cavity

We present a frequency modulation scheme to detect atoms dispersively in a high-finesse optical cavity at low-light levels with immunity to cavity length fluctuations. We use multiple cavity resonances to provide common mode noise rejection, keeping the high intensity carrier off-resonant from all cavity modes. The method has applications in atomic squeezed state generation and quantum metrology.

Multilevel Optimal Modulation and Dynamic Control Strategies for STATCOMs Using Cascaded Multilevel Inverters

A multilevel optimal modulation strategy was developed for static synchronous compensators (STATCOMs) using cascaded multilevel inverters. In this strategy, besides the minimized harmonic distortion level, the inverter units' fundamental output voltages are also equalized. Therefore, all the inverter units in each phase leg can equally share the exchanged active and reactive power with the utility grid. This greatly helps the DC-link voltages balancing control. A special gating-pattern swapping scheme was developed to further maintain the DC capacitors' charge balance and equalize the current stress of the switching devices. The modulation strategy also includes a redundant operation scheme and a transformer DC magnetization prevention scheme. The performance of the proposed strategy was compared with the conventional fundamental frequency modulation strategy. To implement a fast and robust control of reactive power, a nonlinear feedback linearization controller with a direct voltage control capability was employed. The scheme of modulation index controlling and the operating modulation index range are presented. The effects of the system uncertainties on the closed loop dynamic performance are also discussed. A plusmn30 kVAr 21-level STATCOM prototype was developed. All the modulation and dynamic control strategies were verified using the experimental results from the scaled prototype.

High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser

The quantum cascade laser is a powerful, narrow linewidth, and continuous wave source of terahertz radiation. The authors have implemented a distributed feedback device in a spectrometer for high-resolution gas phase spectroscopy. Amplitude as well as frequency modulation schemes have been realized. The absolute frequency was determined by mixing the radiation from the quantum cascade laser with that from a gas laser. The pressure broadening and the pressure shift of a rotational transition of methanol at 2.519THz were measured in order to demonstrate the performance of the spectrometer.

Unified SPICE compatible model for large and small-signal envelope simulation of linear circuits excited by modulated signals

The envelope-simulation method, developed earlier for large-signal simulation [time domain (TRAN)] is extended to include small-signal envelope simulation (ac) and dc sweep simulation (steady state for a range of carrier frequencies). The model is derived for amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM) modulation schemes and is demonstrated on a piezoelectric transformer circuit. The model is based on the equivalent circuit approach and can be run on any modern electronic circuit simulator. An excellent agreement was found between the simulation results according to the new unified envelope model, full simulation, and experimental results.

Modeling of Variable Switching Frequency Controlled STATCOMs and Active Filters

This paper introduces an average circuit model for switch mode shunt converters coupled with power systems such as active filters (AF) and static compensators (STATCOM). These devices absorb or deliver reactive power to the utility network by employing a variable switching frequency modulation scheme (e.g. hysteresis current control). Analysis and simulation of these exact devices could be complex under transient and steady state conditions. Here the variable switching frequency shunt devices are modeled using an averaging approach, deriving averaged mathematical and circuit models. Further, the ripple is approximated to provide a correction to the average model. The resulting models produce much faster simulations than their exact devices. Theoretical considerations show that the averaged model agree well with the original system, and this is confirmed by PSpice and MATLAB simulations, as well as experimental results.

Optical frequency modulation and intensity modulation suppression in a master-slave semiconductor laser system with direct modulation of the master laser

An injection-locked laser system where the master laser is directly modulated is analyzed using rate equations. Both quasi-static and dynamic analyses are carried out in order to ensure that the parameters lie inside the locking range. The analysis is valid for all injection levels. The quasi-static analysis provides a good basis for explaining the phenomena. It is shown that, for a given detuning frequency, maximum suppression of intensity modulation (IM) occurs at a specific value of the injection ratio. At low frequencies, the frequency modulation (FM) index of the slave laser bears a constant ratio to the FM index of the master laser of less than unity. It is illustrated that the direct FM scheme is only viable for modulation frequencies up to about 100 MHz. Large IM suppression can only be achieved for large values of the linewidth enhancement factor of the slave laser, small magnitude of the detuning frequency, and low injection ratio. The latter two conditions are associated with narrow limits on stable operation, and care should be taken to avoid instability.

A high-sensitive digital photosensor using MOS interface-trap charge pumping

A high-sensitive CMOS photosensor based on a pulse frequency modulation (PFM) scheme is presented. We propose and demonstrate the high-sensitive PFM photosensor, whose output frequency is proportionate to the incident light intensity, that utilizes MOS interface-trap charge pumping (ITCP) as a frequency-controlled ultra-low current. The proposed pixel sensor consists of only 4 transistors: a transistor as an ultra-low current source; a sense amplifier transistor; a selection transistor; and, a reset transistor. The prototype device is fabricated using 0.6-µm standard CMOS technology. High sensitivity 4.0 × 105Hz/(W·m-2), which is larger than two orders of magnitude compared to previous works, was obtained.

Detection of electron paramagnetic resonance absorption using frequency modulation

A frequency modulation (FM) method was developed to measure electron paramagnetic resonance (EPR) absorption. The first-derivative spectrum of 1,1-diphenyl-2-picrylhydrazyl (DPPH) powder was measured with this FM method. Frequency modulation of up to 1.6 MHz (peak-to-peak) was achieved at a microwave carrier frequency of 1.1 GHz. This corresponds to a magnetic field modulation of 57 μT (peak-to-peak) at 40.3 mT. By using a tunable microwave resonator and automatic control systems, we achieved a practical continuous-wave (CW) EPR spectrometer that incorporates the FM method. In the present experiments, the EPR signal intensity was proportional to the magnitude of frequency modulation. The background signal at the modulation frequency (1 kHz) for EPR detection was also proportional to the magnitude of frequency modulation. An automatic matching control (AMC) system reduced the amplitude of noise in microwave detection and improved the baseline stability. Distortion of the spectral lineshape was seen when the spectrometer settings were not appropriate, e.g., with a lack of the open-loop gain in automatic tuning control (ATC). FM is an alternative to field modulation when the side-effect of field modulation is detrimental for EPR detection. The present spectroscopic technique based on the FM scheme is useful for measuring the first derivative with respect to the microwave frequency in investigations of electron-spin-related phenomena.

Bluetooth receiver based on zero-crossing demodulation

Bluetooth is a short-range communication system facilitating ad hoc networking, using a digital frequency modulation scheme termed Gaussian frequency shift keying. Presented is a novel receiver structure for Bluetooth which is based on zero-crossing demodulation in combination with a decorrelating matched filter. Its performance is analysed.

A vision sensor with on-pixel ADC and in-built light adaptation mechanism

In this paper we propose an on-pixel Analogue-to-Digital Converter (ADC) based on pulse frequency modulation (PFM) scheme. This PFM based converter presents a viable solution for pixel-level based ADC. It uses a simple and robust circuit that can be implemented in a compact area resulting in a 23% fill-factor for a digital vision sensor in 0.25μm CMOS technology. An in-built light adaptation mechanism has also been implemented which allows the sensor to better adapt to low-light intensity or to adjust the sensor saturation level. As a consequence, the proposed sensor features a programmable dynamic range. Image lag is eliminated since a reset of the photodetector is performed after the conversion period. A prototype comprising a 32×32 pixel array has been implemented in CMOS 0.25μm technology. Each pixel occupies an area of 45×45μm2 with an average power consumption of 85μW per pixel.

System-level microwave design projects

The teaching laboratory can be an invaluable component of an undergraduate electromagnetics curriculum. This goal of this article is to illustrate several simple but effective microwave-design laboratory projects, involving both system- and component-level design experiences, based upon radar and wireless communications applications. The projects highlighted include a Doppler radar, a simple synthetic aperture radar (SAR), and wireless links using amplitude and frequency-modulation schemes. Students use modern computer-aided design (CAD) tools, coupled with planar technology.

Development of a novel fast frequency modulation scheme for the Joint European Torus multichannel reflectometer

A novel frequency modulation scheme has been developed for the multichannel reflectometer used to measure density profiles and density fluctuations on the Joint European Torus (JET) tokamak. This reflectometer normally uses slow frequency sweeping (6 ms), combined with fixed-frequency operation, to measure the group delay, as well as plasma fluctuations, at ten different microwave frequencies. The novel scheme uses continuous frequency modulation on a time scale much shorter (1/65 μs) than that of plasma fluctuations, the main aim being to make the group delay measurement more robust against plasma fluctuations. This article discusses the theoretical background of the scheme, gives a detailed description of the system, and presents results from plasma measurements. Although the implementation used suffered from an excessive power-dependent group delay distortion (resulting in a positional error of 10 cm), the main objectives have been achieved.

Radar sensor using low probability of interception SS-FH signals

One of the best known weakness of radar sensors in defense and security applications is the necessity to radiate a signal, which can be detected by the target, so being possible (easy in fact) that the target is alerted about the presence of a radar before the radar is alerted about the presence of a target. In this context, Low Probability of Interception (LPI) Radars try to use signals that are difficult to intercept and/or identify. Spread spectrum signals are strong candidates for this application, and systems using special frequency or polyphase modulation schemes are being exploited. Frequency hopping, however, has not received much attention. The typical LPI radar at this moment of the technology is a CW-LFM radar. The simplicity of the technology is its best point. Polyphase codes, on the other hand have the inherent advantage of high instantaneous bandwidth regardless of observation time. But the complexity of the hardware is also higher. FH signals have traditionally been considered of lower performance but higher complexity, due to the difficulties to compensate the individual dopplers for the individual range cells in the receiver. One important point is that an FH radar must be clearly distinguished from an agile frequency radar. In the latter, a pulsed signal is transmitted using different frequencies from pulse to pulse. In an FH radar the frequency changes must be during the pulse. In fact, in an LPI FH radar, a CW frequency hopped signal is used. A radar system concept is proposed in which it shows how these problems can be overcome in a tracking application. Also, the signal format is analyzed under the scope of future decade digital interceptors, showing that, in fact, this kind of signal exhibits improvement in some performances and requires a hardware that is only slightly more complex than that needed for CW-LFM systems.

Analysis and spectral characteristics of a spread-spectrum technique for conducted EMI suppression

Frequency modulation (FM) and random switching methods have been used for reducing conducted electromagnetic interference (EMI) in power converters. Limited theoretical studies and comparisons of these schemes, however, are available. In this paper, a detailed analysis and the spectral characteristics of a random carrier-frequency (RCF) technique for suppressing conducted EMI in an offline switched-mode power supply are presented. The analysis provides a theoretical platform for studying the characteristics of this random switching scheme. The level of randomness is defined for the RCF scheme and varied in the converter example so that the effects on the power spectra can be demonstrated. Theoretical predictions of the spectral characteristics of this scheme are confirmed with measurements. The RCF scheme has been compared with the standard constant-frequency pulsewidth modulation (PWM) scheme and the FM scheme. Comparisons of their spectral performance show that the RCF scheme has better conducted EMI suppression than the FM and standard PWM schemes.

Single-switch electronic ballast with continuous input current charge pump power-factor correction

This paper presents a single-switch electronic ballast with continuous input current charge pump power-factor correction. The ballast circuit is composed of a series/parallel inverter, a charge pump power-factor corrector, and a dimming controller. The characteristics and design considerations of this ballast are discussed in this paper. Dimming control is achieved by varying the switching frequency. The frequency-modulation scheme is used to reduce the low-frequency output current ripple. A prototype of a 36WT8 fluorescent lamp ballast has been implemented and tested. Experimental results verify the analytical derivations.