Showing papers on "Pulse-frequency modulation published in 2009"

A Comprehensive Study of a Hybrid Modulation Technique for the Neutral-Point-Clamped Converter

Abstract: This paper presents a hybrid modulation technique for the three-level neutral-point-clamped converter. A modulation strategy, based on two modulation signals per phase, was presented previously. This strategy completely removes the low-frequency voltage oscillations that appear at the neutral point (NP) in some operation conditions. However, it also has a major drawback: it significantly increases the switching losses of the converter. The proposal in this paper combines such a modulation strategy with sinusoidal pulsewidth modulation (SPWM). The main characteristic of this hybrid modulation is the reduction in switching losses at the cost of some low-frequency voltage oscillations at the NP. The amplitude of these oscillations can be controlled by varying the combination of the two strategies. The performance of the hybrid modulation is analyzed and compared with the original strategies. Power losses and oscillation amplitudes on the dc-link capacitors are evaluated. Experimental results show how the hybrid modulation performs by balancing the dc-link capacitors.

Voltage-Balance Compensator for a Carrier-Based Modulation in the Neutral-Point-Clamped Converter

Abstract: This paper presents an optimal voltage-balancing compensator for a specific modulation technique applied to a neutral-point-clamped converter. The technique uses two modulation signals per phase, and it is called double-signal pulsewidth modulation. It completely eliminates low-frequency oscillations in the neutral-point voltage. However, it does not provide natural voltage balancing; therefore, a compensation loop is required. The proposed control generates a feedback compensation signal that correctly modifies the three-phase modulation signals. The optimal compensation signal is calculated by a dynamic limiter according to the intrinsic limitations of the system related to the variability range of the modulation signals. It significantly improves the voltage balancing under all operating conditions of the converter. In addition, this compensation strategy does not increase the switching frequencies of the power devices. The algorithm is tested and verified using both simulation and experimentation.

Pulse width modulation scheme for the Modular Multilevel Converter

Abstract: The Modular Multilevel Converter (M2C) is an emerging and highly attractive multilevel converter topology for medium and high voltage applications. In this paper, a new pulse width modulation (PWM) scheme will be derived. For this pulse width modulation scheme, characteristic simulated waveforms are described and analyzed.

Modified dimming LED driver

Abstract: A driver circuit produces variable current output for an LED lighting system providing improved dimming capability and greater power efficiency when responding to industry standard lighting dimmers, through the use of an input voltage monitoring circuit which variably controls the current output of a switching regulator. Output current modulation methods such as analog, PWM, Pulse Frequency Modulation, or other digital modulation, and combination or hybrid methods such as that disclosed in U.S. Pat. No. 7,088,059 B2 may be employed. The current invention marries such output modulation techniques with a control method which is derived through intelligent monitoring of the input voltage waveform. The circuit and method described is adapted to higher current applications such as LED lighting systems using the latest high-power LEDs.

Five-level single-leg flying capacitor converter voltage balance dynamics analysis

Abstract: The attractive feature of a flying capacitor converter is the natural voltage balance property The reported voltage balance dynamics analytical research methods are based on heavy frequency domain transformations (Fourier transform, Bessel functions etc) and are rather algorithmic and difficult to use in an everyday engineering practice Suggested time domain approach uses stitching of piece-wise analytical solutions for consecutive switching intervals The small parameter analysis of a five-level single-leg converter yields physically meaningful, simple, and accurate expressions for average voltage balance dynamics giving an in-depth insight into parameters, carrier frequency, and modulation strategy impact for both DC and AC PWM

Valley-mode switching schemes for switching power converters

Abstract: An improved valley-mode switching (VMS) scheme and circuitry for implementing the improved VMS switching scheme in a switch-mode power converter are disclosed. For a given switching cycle, a desired switch turn-on time is determined based on a pulse width modulation, pulse frequency modulation, or other suitable power converter control scheme. Also, one or more times corresponding to local minimums (valleys) are predicted for the voltage across a power switch of the switching power converter. The power switch is turned on at a valley immediately subsequent or otherwise subsequent to the desired switch time determined according to the power converter control scheme. Thus, the improved VMS scheme enables low-voltage switch operation to reduce switching loss and EMI noise without restricting the control scheme of the power converter.

Residual amplitude modulation mechanisms in modulation transfer spectroscopy that use electro-optic modulators

Abstract: Three independent mechanisms are described that contaminate the phase-modulated pump beam of an optical frequency reference stabilized by modulation transfer spectroscopy (MTS) with residual amplitude modulation (RAM). The electro-optic modulator, the beam geometry and the absorption of the saturated medium all separately generate undesired RAM that degrades the accuracy of the optical frequency reference. An analysis is presented that shows how frequency shifts introduced by the different mechanisms can be evaluated in typical MTS set-ups and minimized. The analysis also shows how the detector phase can be used to measure the total RAM in the system and how the phase required to remove any remaining frequency offsets can be evaluated.

LED Dimming Techniques Using Spread Spectrum Modulation

Abstract: Circuits and methods of LED dimming are disclosed. Frequency modulation using controlled modulation depth generates deterministic sidebands of both the fundamental frequency and its harmonics. Various filters including low-pass, band-pass, high-pass and combinations of those are used to selectively filter the deterministic frequency components generated by the frequency modulation to achieve LED dimming.

System and method for wireless power transfer

Abstract: A wireless transmission system having a transmitter and receiver is described. In one embodiment, the transmitter includes an electronically-controlled switch controlled by a first pulse width modulation control circuit, the switch configured to pull current through a first inductor when the switch is closed, the first pulse width modulation control circuit outputting a PWM output signal to control the switch. A first feedback signal obtained from a control input of the switch. A second feedback signal obtained from a terminal of the inductor, wherein a control feedback signal is computed, at least in part, as a difference between the first feedback signal and the second feedback signal is provided to the first pulse width modulation control circuit. In one embodiment, the receiver includes a second pulse with modulation controller, the second pulse width modulation controller controlling the receiver switch to deliver a desired power from the receiving coil to a load.

Method and apparatus to measure differential phase and frequency modulation distortions for audio equipment

Abstract: A testing method or apparatus utilizes multiple frequencies applied to a device under test for measuring newly discovered frequency modulation effects. An embodiment may include a lower frequency signal with a smaller amplitude higher frequency signal to test a dynamic change in frequency response, gain, and or phase. This dynamic test can reveal frequency modulation effects. Another embodiment may include the use of a multiple frequency signal to dynamically induce a time varying phase or frequency distortion for the device that has differential phase distortion. The device's output is then measured with an FM detector to measure a shift in one of the frequencies used in the test signal or to measure frequency modulation effects of any signals, including distortion products, from the device. Yet another embodiment of the invention may include biasing a device with a voltage to span the output voltage range of the device while measuring harmonic or intermodulation distortion or phase or frequency response at the various operating points.

Characteristic Analysis for Multisampled Digital Implementation of Fixed-Switching-Frequency Closed-Loop Modulation of Voltage-Source Inverter

Abstract: In this paper, a fixed-switching-frequency closed-loop modulation of a voltage-source inverter (VSI), upon the digital implementation of the modulation process, is analyzed and characterized. The sampling frequency of the digital processor is considered as an integer multiple of the modulation switching frequency. An expression for the determination of the modulation design parameter is developed for smooth modulation at a fixed switching frequency. The variation of the sampling frequency, switching frequency, and modulation index has been analyzed for the determination of the switching condition under closed loop. It is shown that the switching condition determined based on the continuous-time analysis of the closed-loop modulation will ensure smooth modulation upon the digital implementation of the modulation process. However, the stability properties need to be tested prior to digital implementation as they get deteriorated at smaller sampling frequencies. The closed-loop modulation index needs to be considered maximum while determining the design parameters for smooth modulation. In particular, a detailed analysis has been carried out by varying the control gain in the sliding-mode control of a two-level VSI. The proposed analysis of the closed-loop modulation of the VSI has been verified for the operation of a distribution static compensator. The theoretical results are validated experimentally on both single- and three-phase systems.

DC converter which has switching control unit to select PWM signal or PFM signal

Abstract: A DC (direct current) converter includes a PWM (pulse width modulation) pulse generation unit outputting a PWM pulse signal whose duty ratio is controlled in accordance with an output voltage, a PFM (pulse frequency modulation) pulse generation unit outputting a PFM pulse signal whose pulse output interval is controlled in accordance with an output voltage, a selection circuit selecting and outputting any one of the PWM pulse signal and the PFM pulse signal in response to a selection signal, a drive circuit unit driving a load and generating an output voltage on the basis of a signal outputted from the selection circuit, and a switching control unit outputting the selection signal. When the selection signal is in a second state, the switching control unit detects a fact that the number of pulses of the PFM pulse signal in a measurement period increases to or above a set value of the maximum number of pulses, and switches the selection signal to a first state.

Experimental Demonstration of Metamaterial-Based Phase Modulation

Abstract: Phase modulation is critical due to its applicability in varied RF devices such as phased array antennas, radars to name a few. In this paper, we report experimental data on phase modulation in the X-band frequency using tunable metamaterials such as a planar design of stacked dual split ring resonators (DSRRs) of 3 mm thickness at 8.5 GHz. Modulation was brought about by switching between the open and closed states of the rings causing a net change in the effective refractive index and thereby producing a phase variation. One and two dimensional free-space scanning experiments were carried out where a phase modulation of 62 degrees was demonstrated. The measured data matched well with the numerically simulated results.

Compensation of frequency modulation to amplitude modulation conversion in frequency conversion systems

Abstract: Frequency modulation to amplitude modulation (FM-to-AM) conversion is an important issue that can prevent fusion ignition with high power lasers such as the Laser MegaJoule (LMJ). On LMJ, most of the FM-to-AM conversion is expected in the so-called frequency conversion and focusing system, which is a nonlinear system. However, we propose linear transfer functions to compensate the effect of frequency conversion on FM-to-AM conversion. We show that most of AM distortion can be reduced by practical systems: for beam intensity up to 3 GW/cm2, the FM-to-AM conversion level can be divided by at least 2, and we almost cancel intensity modulation for intensities below 1 GW/cm2.

High energy photon detection using pulse width modulation

Abstract: Methods and systems for processing an analog signal that is generated by a high energy photon detector in response to a high energy photon interaction A digital edge is generated representing the time of the interaction along a first path, and the energy of the interaction is encoded as a delay from the digital edge along a second path The generated digital edge and the delay encode the time and energy of the analog signal using pulse width modulation

An Exact Current-Mode PFM Boost Converter With Dynamic Stored Energy Technique

Abstract: A novel pulse frequency modulation step-up dc-dc converter with maximum power conversion of 9191% and steady-state accuracy of 033% is presented in this letter The high efficiency and exact output are achieved by a dynamic stored energy technique that enhances utility rate of energy with less power consumption This technique uses a dynamic sensing current controller and a load current detector that accurately generates different energy according to various load conditions The boost converter has been designed and fabricated with a standard TSMC 33/5 V 035- mum 2P4M CMOS technology Experimental results show that the output up-ripple voltage variation was 25 mV (61-86 mV), whereas its fixed energy counterpart was 394 mV (86-48 mV) The proposed boost converter has 16% higher power conversion efficiency than the conventional fixed energy technique at 1 mA load current

Estimation of the center frequency of the highest modulation filter.

Abstract: For high-frequency sinusoidal carriers, the threshold for detecting sinusoidal amplitude modulation increases when the signal modulation frequency increases above about 120Hz. Using the concept of a modulation filter bank, this effect might be explained by (1) a decreasing sensitivity or greater internal noise for modulation filters with center frequencies above 120Hz; and (2) a limited span of center frequencies of the modulation filters, the top filter being tuned to about 120Hz. The second possibility was tested by measuring modulation masking in forward masking using an 8kHz sinusoidal carrier. The signal modulation frequency was 80, 120, or 180Hz and the masker modulation frequencies covered a range above and below each signal frequency. Four highly trained listeners were tested. For the 80-Hz signal, the signal threshold was usually maximal when the masker frequency equaled the signal frequency. For the 180-Hz signal, the signal threshold was maximal when the masker frequency was below the signal fr...

Control multiplexor for a switch mode power supply

Abstract: A digital circuit directs operation of a pulse width modulation or pulse frequency modulation controller varying its control between closed loop and open loop topology. An exemplary control plant could embody a step-down switch mode power supply providing a precise sequence of voltages or currents to any of a variety of loads such as the core voltage of a semiconductor unique compared to its input/output ring voltage. A state machine monitors pulse width or pulse frequency from the pulse width modulation or pulse frequency modulation controller, respectively, while either type of controller operates in its closed loop topology, to determine if the present power state of the system matches the predicted load as characterized from a predetermined model used in conjunction with design automation tools. The state machine averages pulse widths or pulse frequencies monitored in the closed loop topology. If the average deviates from the predicted pulse width or pulse frequency for the present power state, the state machine updates a corresponding value in a table of pulse width or pulse frequency values from which an open loop controller applying pulse width modulation or pulse frequency modulation, respectively, generates a near critical damped step response during system power state transitions or maintains a maximally flat voltage during system current transients.

Two-point modulation polar transmitter architecture and method for performance enhancement

Abstract: A polar transmitter includes a two-point modulation phase-locked loop (PLL) for producing an RF signal with a wide bandwidth. The PLL includes a first input for receiving a phase signal of a variable-envelope modulated signal and providing the phase signal along a first signal path to produce a first frequency modulation signal and a second input for receiving the phase signal and providing the phase signal along a second signal path to produce a second frequency modulation signal. The PLL further includes a voltage controlled oscillator (VCO) having two modulation points, one for receiving the first frequency modulation signal and the other for receiving the second frequency modulation signal. The VCO is controlled by an aggregate of the first frequency modulation signal and the second frequency modulation signal to up-convert the phase signal from an IF to an RF to produce the RF signal with a wide bandwidth.

High Efficiency Charge-and-Add Adjustable DC-DC Converter

Abstract: A charge-and-add DC-DC voltage converter design using a switch network that toggles between two states, either simultaneously charging a flying capacitor (one or any number) or creating a DC voltage on the output capacitor by connecting all flaying capacitors in series thus adding the input voltage to remaining voltages on flying capacitors after they were charged. A pulse generator delivers a train of pulses to toggle the switch network. Depending on the applications, the train of pulses can be continuous when a fixed unregulated voltage must be delivered, or a defined number of pulses when voltage (power) surge is to be produced. The charge-and-add converters should be capable of delivering a regulated output voltage, and in this case, pulse-width modulation (PWM) or pulse frequency modulation (PFM) can be used.

Class D power amplifier

Abstract: A class D power amplifier includes: a signal input terminal for receiving an analog signal; an analog signal processing unit for amplifying the analog signal; an integrating circuit for integrating the analog signal received from analog signal processing unit; a PWM circuit for providing pulse width modulation to an integration signal received from the integrating circuit, and outputting a resulting pulse width modulation signal having a duty ratio falling within a first duty ratio range; a duty ratio adjusting circuit for adjusting the pulse width modulation signal, received from the PWM circuit, to have a pulse width falling within a second duty ratio range narrower than the first duty ratio range; a first driver and a second driver each for processing the pulse width modulation signal received from the duty ratio adjusting circuit; and power transistors.

Resonator optical gyroscope having input beam modulation optimized for high sensitivity and low bias

Abstract: Systems and methods for optimizing input beam modulation for high gyro sensitivity and low bias errors. The present invention is a resonator optical gyroscope having an optimized phase-modulation amplitude (frequency) for a selected modulation frequency (amplitude) that maximizes the gyro signal-to-noise (S/N) sensitivity. For selected values of the phase modulation amplitude, the polarization cross-coupling induced intensity modulation can be nulled. By setting the phase modulation amplitudes substantially close to these nulling points (e.g. M= 3.832 or 7.016 radians, which causes the first order Bessel function to be zero J 1(M) = 0) and then optimizing the modulation frequency, the intensity modulation induced bias is reduced to zero and gyro S/N sensitivity is maximized.

Quantum cascade laser linewidth investigations for high resolution photoacoustic spectroscopy

Abstract: High detection selectivity is extremely important for gas analyzers in order to correctly identify the measured compound. Therefore, laser-based systems require a high optical resolution, which primarily depends on the spectral linewidth of the radiation source. This study examines the effective linewidth (chirp) of a pulsed distributed feedback (DFB) quantum cascade laser (QCL) in a photoacoustic (PA) gas detection system. The influence of the QCL operating parameters pulse duration and pulse current as well as the impact of the modulation technique are investigated. Effective QCL linewidths for pulse gate modulation, pulse frequency modulation, and chopper modulation are compared. The investigations are performed by measuring the PA spectra of nitrogen monoxide absorption lines. The results prove the strong influence of pulse duration and pulse current. They also demonstrate that the modulation technique has a considerable influence and, consequently, affects the detection selectivity of the PA analyzer. The aim of this research is to determine optimum operational parameters for high resolution PA spectroscopy.

Research on zero-sequence signal of space vector modulation for three-level neutral-point-clamped inverter based on vector diagram partition

Abstract: This paper proposes a novel method for analyzing the zero-sequence signal of three-level voltage-source inverter based on vector diagram partition. The inherent relationship between carried-based PWM and SVPWM is demonstrated. It is shown that the two method can worked equivalently through proper selection of active time for the redundant vector in the case of space vector modulation, or zero-sequence signal injections in the case of carried-based modulation. Furthermore, a novel balancing control strategy of NP potential is proposed based the zero-sequence signal injections. Both simulation and experiment result verify the effectiveness of proposed approach.

A multiple phase demodulation method for high resolution of the laser scanner

Abstract: To have higher resolution of distance in the laser scanner using the phase demodulation method, signal should be modulated with a high frequency. In the signal processing of modulation and demodulation, it is inevitable to amplify the signals. However, it is not easy to amplify the high frequency since the amplifying gain is restricted by the frequency bandwidth. It is advantageous to demodulate using an intermediate frequency in which high gain amplification as well as less contaminated signal is obtained. Analytical and experimental results are presented to show how the intermediate frequency demodulation method works and how good performance is obtained in the time and frequency domains.

Multiple output of dual half bridge LLC resonant converter using PFM-PD control

Abstract: This paper proposes the multiple output of dual half bridge LLC resonant converter using PFM-PD control. For the main output, dual half bridge LLC resonant converter controlled by pulse frequency modulation (PFM) is used. For the sub output, multiple outputs scheme is configured and operated by phase delay (PD) control. Since the control variables, PFM and PD, have little mutual effect, the sub output voltage can be regulated for a wide input and load range. All MOSFETs achieved ZVS and all rectifier diodes attained ZCS for the whole load range. The modes of operation are investigated and then steady state characteristics of the proposed converter are analyzed. A 320V- 400V input, 24V/20A, 5V/16A hardware prototype is realized with dsPIC33FJ16GS502 and tested to verify the performances of the proposed multiple output converters‥

LED Brightness Control by Variable Frequency Modulation

Abstract: Perceived intensity (brightness) of light from a light emitting diode (LED) is controlled with a pulse train signal having fixed pulse width and voltage amplitude and then increasing or decreasing the frequency (increasing or decreasing the number of pulses over a time period) of this pulse train signal so as to vary the average current through the LED. This reduces the level of electro-magnetic interference (EMI) at any one frequency by varying the pulse train energy spectrum over a plurality of frequencies.

A single-inductor dual-output switching converter with low ripples and improved cross regulation

Abstract: This paper proposes a novel fly capacitor method for single-inductor dual-output (SIDO) switching converters to reduce the output ripples and spikes. An adaptive common-mode control is presented to suppress the cross regulation problem. The converter can automatically switch between pulse-width modulation (PWM) and pulse-frequency modulation (PFM) control to improve the efficiency. The SIDO converter is specified for one channel 1.2 V/400 mA and the other 1.8 V/200 mA with input voltage ranging from 2.7 V to 5 V. The chip has been fabricated on a 0.25 μm CMOS mixed signal process. The conversion efficiency is 82% at a total output power of 840 mW while the output ripples are about 20 mV and spikes less than 40 mV.

Modulation instability of narrow-band nanosecond pulses propagating in anomalous-dispersion fibre

Abstract: We demonstrate that, in the presence of noise, propagation of narrow-band 100-ns pulses through a 6-km long optical fibre sharply reduces their amplitude when a threshold power (~0.2 W) is exceeded. The effect is due to the development of modulation instability and is sensitive to the noise level in the spectral region ~100 GHz in width around the central frequency.

Method and System for Frequency Down-Conversion and Frequency Up-Conversion

Abstract: A method and system is described wherein a signal with a lower frequency is up-converted to a higher frequency. In one embodiment, the higher frequency signal is used as a stable frequency and phase reference. In another embodiment, the invention is used as a transmitter. The up-conversion is accomplished by controlling a switch with an oscillating signal, the frequency of the oscillating signal being selected as a sub-harmonic of the desired output frequency. When the invention is being used as a frequency or phase reference, the oscillating signal is not modulated, and controls a switch that is connected to a bias signal. When the invention is being used in the frequency modulation (FM) or phase modulation (PM) implementations, the oscillating signal is modulated by an information signal before it causes the switch to gate the bias signal. In the amplitude modulation implementation (AM), the oscillating signal is not modulated, but rather causes the switch to gate a reference signal that is substantially equal to or proportional to the information signal. In the FM and PM implementations, the signal that is output from the switch is modulated substantially the same as the modulated oscillating signal. In the AM implementation, the signal that is output from the switch has an amplitude that is a function of the information signal. In both embodiments, the output of the switch is filtered, and the desired harmonic is output.