Showing papers on "Pulse-frequency modulation published in 2008"

Controller of multi-phase electric motor

Abstract: A controller of a multi-phase electric motor has a drive section having an upper arm switching element and a lower arm switching element for driving the multi-phase electric motor, a single current detection section for detecting a current value of the multi-phase electric motor, a pulse width modulation signal generation section for generating plural pulse width modulation of each phase within one control period based on the current value detected by the current detection section and a carrier signal, and a phase movement section for moving the pulse width modulation signal of a predetermined phase generated by the pulse width modulation signal generation section by gradually changing a movement amount of the phase in one control period, and outputting the resultant pulse width modulation signal to the drive section.

Digital PWM/PFM controller with input voltage feed-forward for synchronous buck converters

Abstract: This paper describes a digital pulse-width modulation/pulse-frequency modulation (PWM/PFM) controller with input voltage feed-forward for synchronous buck DC-DC converters. The controller includes automatic PWM/PFM mode switching and effective synchronous operation with a minimum number of active components and without the need for current sensing in PFM mode of operation. Input-voltage feed-forward improves efficiency and dynamic performance over a wide range of input voltages. Controller parameters, including the PWM switching frequency, the PFM pulse period, and the mode transition point are programmable, which enables efficiency optimization. Experimental results are shown for a synchronous buck converter with 5-to-12 V input voltage, and 1.3 V, 0 - 10 A output.

System And Method For Controlling A Current Limit With Primary Side Sensing Using A Hybrid PWM and PFM Control

Abstract: A hybrid constant current control system that uses both pulse width modulation (PWM) and pulse frequency modulation (PFM) control. When transitioning from constant voltage mode to constant current mode the present invention can continue to control using PWM. Thereafter, when the voltage has dropped, the present invention smoothly transitions to PFM mode. The point of transition is based upon the switching frequency and the lowest rated voltage of operation. The system and method avoids very short (narrow) Ton times which ensures accurate constant current (CC) control with bipolar junction transistor (BJT) devices. The present invention also avoids acoustic noise because the switching frequency is maintained at a high enough level to avoid such acoustic noise even when the energy transferred through the transformer is still substantial and the output voltage is not too low. In addition the output current limit is insensitive to variation in the inductance-input voltage ratio, and is minimized against leakage inductance.

Pulse width modulation: A novel readout scheme for high energy photon detection

Abstract: In standard PET scintillation detection, the energy, timing, and location of the incoming photon are recovered using analog signal processing techniques The energy and location information are processed using an analog-to-digital (ADC) converter that samples an analog value that is proportional to the integral of the charge created by the scintillation event We propose to change the paradigm and modulate the width (rather than amplitude) of a digital pulse to be proportional to the integral of the charge created The analog value of the outgoing digital pulses is recovered by using a time-to-digital converter (TDC) in the back-end electronics, without the need for an ADC Note that in this new scenario the same TDC used to record the time of the event is used to recover the amplitude The main performance parameter that must be optimized is the dynamic range versus the dead-time of the front-end detector The goal is an 8-bit dynamic range for this pulse-width modulation (PWM) scheme, which is adequate for high resolution PET systems based on semiconductor detectors such as avalanche photodiodes (APD) or cadmium zinc telluride (CZT) A novel circuit has been designed, fabricated, and tested for the proposed PWM readout scheme This circuit is different than previously developed time over threshold pulse width modulation circuits used in high energy physics PWM techniques simplify the routing to the back end electronics without degrading the performance of the system A readout architecture based on PWM processes digital rather than analog pulses, which can be easily multiplexed, enabling one to achieve very high channel density required for ultra-high resolution, 3-D positioning PET detector systems

Flyback constant voltage converter having both a PWFM mode and a PWM mode

Abstract: A flyback AC/DC switching converter has a constant voltage (CV) mode. The CV mode has sub-modes. In one sub-mode (“mid output power sub-mode”), the output voltage (VOUT) of the converter is regulated using both pulse width modulation and pulse frequency modulation. Both types of modulation are used simultaneously. In a second sub-mode (“low output power sub-mode”), VOUT is regulated using pulse width modulation, but the converter switching frequency is fixed at a first frequency. By setting the first frequency at a frequency above the frequency limit of human hearing, an undesirable audible transformer humming that might otherwise occur is avoided. In some embodiments, the converter has a third sub-mode (“high output power sub-mode”), in which pulse width modulation is used but the switching frequency is fixed at a second frequency. By proper setting of the second frequency, undesirable EMI radiation and other problems that might otherwise occur are avoided.

Large-signal analysis of analog intensity modulation of semiconductor lasers

Abstract: Large-signal analog intensity modulation of semiconductor lasers (SLs) is characterized based on numerical integration of the rate equations. The modulation dynamics are classified into seven types with regular and irregular signals. The classification is made in terms of the time trajectory of the laser intensity, phase portrait, and fast Fourier transform (FFT) spectrum. The operating region of each type is defined in a diagram of the modulation index versus modulation frequency. The accuracy of applying the approximate small-signal analysis to study analog modulation is assessed. The validity of identifying the dynamic types by the large-signal modulation response is examined. The laser emits continuous and regular signals under weak modulation. When the modulation index exceeds one half, the laser emits picosecond-pulses. Under strong modulation with frequencies around the relaxation frequency, both continuous and pulsed signals exhibit period-doubling.

Grating lobes suppression in stepped-frequency pulse train

Abstract: Frequency stepping is one of the known techniques employed by modern radars to achieve high range resolution. The main advantage of this approach is that the actual instantaneous bandwidth of a radar is quite small compared with the total processing bandwidth. This allows the transmission of waveforms with extremely wide overall bandwidth (and, as a consequence, the attainment of high range resolution) without the usage of the expensive hardware needed to support wide instantaneous bandwidth. Unfortunately, the autocorrelation function of uniform frequency stepped pulse trains can have undesirable peaks, known as "grating lobes." We address this issue, using an approach which allows us to suppress grating lobes below a desired threshold level in the case of appropriately chosen stepped frequency waveforms. We discuss in detail how to choose relevant parameters in order to produce such waveforms with small grating lobes, and give examples of waveforms with small overlap ratio. We also discuss the issue of high sidelobes in the vicinity of the mainlobe, which are inevitable in a stepped frequency train of linear frequency modulated (LFM) waveforms with small overlap ratio, and show that it is possible to suppress these, as well as the grating lobes, by means of nonlinear frequency modulation (NLFM).

Analysis of small-signal intensity modulation of semiconductor lasers taking account of gain suppression

Abstract: This paper demonstrates theoretical characterization of intensity modulation of semiconductor lasers (SL’s). The study is based on a small-signal model to solve the laser rate equations taking into account suppression of optical gain. Analytical forms of the small-signal modulation response and modulation bandwidth are derived. Influences of the bias current, modulation index and modulation frequency as well as gain suppression on modulation characteristics are examined. Computer simulation of the model is applied to 1.55-µm InGaAsP lasers. The results show that when the SL is biased far-above threshold, the increase of gain suppression increases both the modulation response and its peak frequency. The modulation bandwidth also increases but the laser damping rate decreases. Quantitative description of the relationships of both modulation bandwidth vs. relaxation frequency and maximum modulation bandwidth vs. nonlinear gain coefficient are presented.

Direct Duty Ratio Pulse Width Modulation Method for Matrix Converters

Abstract: This paper presents a new carrier based pulse-width modulation (PWM) method for matrix converters. By using the concept of average over one switching period, the modulation algorithm and the required equations are derived to synthesize the desired output voltage and to achieve the controlled input power factor. The proposed method uses a continuous carrier and the predetermined duty ratio signals to directly generate the gating signals and, thus, is referred to as "direct duty ratio PWM (DDPWM)". The feasibility and validity of the proposed method were verified by simulation and experiment.

A new PWM/PFM control technique for improving efficiency over wide load range

Abstract: This paper proposed a novel controlling technique of pulse width modulation (PWM) mode and pulse frequency modulation (PFM) mode to keep the high efficiency within width range of loading. The novel control method is using PWM and PFM detector to achieve two modes switching appropriately. The controlling technique can make the efficiency of current mode DC-DC buck converter up to 88% at light loading and this paper is implemented by TSMC 0.35 mum CMOS process.

A quasi fixed frequency constant on time controlled boost converter

Abstract: Continuous conduction mode (CCM) boost converter is difficult to compensate due to the right half plane (RHP) zero. This paper presents a quasi fixed frequency constant on time (COT) controlled boost converter, it has no loop compensation requirement. With the proposed COT control, pulse frequency modulation (PFM) comes free at light load, which improves the light load efficiency compared with traditional PWM control. A compact on-time generator that controls the operation frequency is proposed. And a current sink based feedback circuit is used to improve the quality of feedback signal.The COT controller is designed with 1.5 mum BCD process. Simulation results demonstrate that the COT boost converter has fast load transient response and quasi fixed frequency operation.

Method and system for pulse frequency modulated switching mode power supplies

Abstract: A pulse frequency modulation (PFM) controller for controlling a switching mode power supply. The controller includes an output terminal for providing a control signal to turn on and off a current in the power supply to regulate an output of the power supply. A first input terminal receives a feedback signal related to the output of the power supply, the feedback signal exhibiting a ringing waveform when the current in the power supply is turned off. The controller also includes a control circuit configured to provide the control signal in response to the feedback signal. The control signal is adapted to turn on the current in the power supply when the feedback signal is substantially at a valley of the ringing waveform of the feedback signal. In an embodiment, such a PFM controller can reduce turn-on transition loss in a power supply and provides frequency dithering to reduce electromagnetic interference.

A monolithic step-down SC power converter with frequency-programmable subthreshold z-domain DPWM control for ultra-low power microsystems

Abstract: This paper presents a fully integrated switched-capacitor (SC) power converter for ultra-low power microsystems. The design features an efficient step-down charge pump and a frequency-programmable digital feedback controller. The controller is designed in the subthreshold region to reduce power dissipation significantly. It employs a programmable switching frequency digital pulse-width modulation (DPWM) to maintain high efficiency under various loading scenarios, without causing random noise spectrum as in pulse-frequency modulation (PFM). The monolithic implementation effectively suppresses switching noises and glitches introduced by parasitic components from traditional bonding, packaging and PCB wiring. The test prototype was designed and fabricated with a 0.35-mum digital CMOS N-well process. It supplies a variable power output from 0.8 to 1.5 V and from 400 muW to 7.5 mW precisely, with a variable switching frequency ranging from 200 KHz to 1 MHz. The converter achieves 66.7% efficiency with a controller power of only 147.5 muW.

Clock dithering process for reducing electromagnetic interference in d/a converters and apparatus for carrying out such process

Abstract: A process and apparatus for generating an output signal whose frequency varies according to a modulation scheme, the process including the steps of providing a dither generator for receiving a first input signal representative of a clock frequency and for generating, according to the modulation scheme, a dithered output signal representative of the first signal at a dithered frequency; providing a DSP for receiving the following input signals: the signal at the dithered frequency and a second signal representative of a clock frequency, the DSP adapted to generate a processed output signal representative of the maximum frequency of the second signal; wherein the modulation scheme has a periodic ultrasonic modulating wave.

Method and apparatus for frequency modulating a periodic signal of varying duty cycle

Abstract: A method and apparatus for frequency modulating a PWM involves 1) generating a high frequency carrier signal much greater in frequency than the PWM signal; 2) modulating the high frequency signal to generate a spread spectrum carrier signal; and, 3) retiming a PWM signal with this high frequency SS carrier signal so that the binary transitions of the PWM signal are aligned with the frequency varying carrier signal. In another embodiment, a PWM oscillator is driven by a second, FM oscillator having spread spectrum characteristics. In another embodiment a PWM oscillator is driven and modulated by a counter/frequency divider comprised of modules.

Multiple switch node power converter control scheme that avoids switching sub-harmonics

Abstract: A method of and system for modulating buck and boost modulation ramps of a multiple switch node power converter without overlap. As the pulse width or duty cycle of the signal to a modulated complementary switching pair approaches a pre-established reference pulse width or duty cycle, plural fixed-width or fixed duty cycle pulses are generated and introduced to a nonmodulated complementary switching pair. A controller detects proximity to the pulse width or duty cycle limit and, correspondingly, initiates prematurely a pseudo-buck-boost mode in the power converter by generating fixed-width or fixed duty cycle pulses to the nonmodulated complementary switching pair while the duty cycles or pulse widths to the modulated complementary switching pair are still controlled by the appropriate modulation ramp. The net effect is that the power converter reaches its optimal operating point without overlap and eliminates any sub-harmonic switching.

Pulsed frequency modulation techniques for high-precision ultra wideband ranging and positioning

Abstract: In this paper a novel approach for a high precision local positioning radar using an ultra wideband technique is presented. The concept is based on the standard FMCW (frequency modulated continuous wave) radar principle combined with short pulses to fulfill the emission limits given by the official regulatory authorities. The system combines the advantages of FMCW radar systems and the advantages of the use of a wide bandwidth. With this concept, a high accuracy in dense multipath indoor environments can be achieved, ideally suited for 1D, 2D, and 3D localization. A prototype was fabricated which operates around the center frequency of 7.5 GHz utilizing a bandwidth of 1 GHz. With the setup presented in this paper the distance between two wireless units can be measured achieving a low standard deviation.

Current source ZCS PFM DC-DC converter for magnetron power supply

Abstract: This paper presents the design of zero current switching ZCS pulse frequency modulation type DC-DC converter for magnetron power supply. A magnetron serving as the microwave source in a microwave oven is driven by a switch mode power supply (SMPS). SMPSs have the advantages of improved efficiency, reduced size and weight, regulation and the ability to operate directly from the converter DC bus. The demands of the load system and the design of the power supply required to produce constant power at 4 kV. A magnetron power supply requires the ability to limit the load current under short circuit conditions. The current source series resonant converter is a circuit configuration which can achieve this. The main features of the proposed converter are an inherent protection against a short circuit at the output, a high voltage gain and zero current switching over a large range of output power. These characteristics make it a viable choice for the implementation of a high voltage magnetron power supply.

Transmitter and control method for transmitting and calibrating a phase signal and an amplitude signal

Abstract: A transmitter for transmitting and calibrating a phase signal and an amplitude signal. The transmitter comprises a phase modulation path, an amplitude modulation path, and a control unit. The phase modulation path transmits the phase signal. The amplitude modulation path transmits the amplitude signal. The control unit delays the signal on at least one of the phase modulation path and the amplitude modulation.

Spectral lineshape and noise of semiconductor lasers under analog intensity modulation

Abstract: Intensity and frequency fluctuations of semiconductor lasers under analog intensity modulation are theoretically investigated in both time and frequency domains. The spectral properties of the relative intensity noise (RIN) and the frequency noise (FN) as well as the associated lineshape are examined as functions of the modulation frequency and strength. The study is based on a numerical solution of the stochastic rate equations of semiconductor lasers. Based on the time variation of the photon number and the phase portrait of the photon number versus the electron number, the modulation dynamics are classified into six distinct types. The results showed that the high-frequency regimes of both RIN and FN are higher and the lineshape is more broadened when the signal is pulsed than when it varies continuously with time. The low-frequency components of RIN and FN are considerably enhanced and the laser coherency is extremely deteriorated when the laser emits irregular spike-like pulses under low-frequency strong modulation.

Optical device and optical modulation method

Abstract: The disclosed device and method include varying phases of two data signals at a first predetermined frequency, performing multi-level phase modulation of a light based on the two data signals whose phases are varied at the first predetermined frequency, extracting a component having the first predetermined frequency from an optical signal subjected to the phase modulation, and controlling the phases of the two data signals based on the component extracted from the optical signal.

Dc-dc converter and power supply system

Abstract: A DC-DC converter prevents localization of switching operations at light loads and is able to improve power conversion efficiency. The DC-DC converter of some variations performs pulse frequency modulation control at light loads, and includes a reducing circuit configured to skip an oscillation frequency signal at light loads and to generate a skipped signal.

Method and apparatus for reducing the amplitude modulation of optical signals in external cavity lasers

Abstract: The present invention concerns a laser apparatus (200) comprising an external cavity laser (ECL) in which the optical signal is modulated by an electrical modulation signal with the purpose of modulating in frequency the laser output signal. The modulation in frequency produces in turn a modulation of intensity (power) of the laser output signal, also denoted amplitude modulation (AM). A method is described of control of the AM amplitude of a signal emitted by an ECL that comprises a gain medium (205), a phase element (206) with variable transmissivity induced by the modulation and a spectrally selective optical filter (209) and that selects and keeps the AM amplitude below a certain desired value or minimizes such value. A control method and a laser apparatus (200) are also described in which the reduction of the AM component of the output power is achieved by acting on the gain of the gain medium of the ECL in such way that the variation of transmissivity caused by the modulation applied to a phase element (206) is at least partially compensated by a corresponding variation of the gain current of the gain medium so as to reduce or to minimize the variation of the loop gain of the laser cavity induced by the modulation.

A 28.6dBm 65nm Class-E PA with Envelope Restoration by Pulse-Width and Pulse-Position Modulation

Abstract: This paper introduces a Class-E PA that overcomes the various limitations using pulse-width and pulse-position modulation (PWPM).

Method and apparatus for active power factor correction

Abstract: A power factor correction method and apparatus which use Pulse Frequency Modulation (PFM) to control an AC/DC converter is disclosed. The average current drawn by the AC/DC converter is compared with a reference sinusoidal signal and the error is used to determine the switching frequency. The switching frequency varies with the sinusoidal reference signal such that the converter emulates a resistive load. By using PFM control, EMI is spread over a range rather than concentrated at a few frequencies. Since the switching frequency decreases with the loading of the converter, the switching loss decreases with the loading as well. Thus, the need of meeting efficiency standards, e.g. the 80 PLUS and Energy Star, can be fulfill without extra circuitry.

Performance evaluation of a miniaturized unconstrained digital on-off switching valve

Abstract: The technology of pneumatic valves is progressing from large-scale and heavyweight industrial valves to the development of miniaturized valves with less weight. The size and weight of valves are no longer problems due to the development of microelectromechanical system (MEMS) fabrication processes. The limitations of micro valves are their low flow rate and manufacturing complexity. In this paper, we discuss an unusual method of miniaturization using piezoelectric actuated unconstrained valves with comparatively higher flow rate and a simple construction process. Integration of a piezoelectric actuator driver and a microcontroller into the valve unit was accomplished, which allowed reduction of the overall size. Moreover, microcomputer-embedded valves have a digital nature, which enables direct pulse width modulation (PWM) control from the valve. The characteristics of the valve, design parameters, flow tendency and valve response time are discussed. Experimental results of pulse width and pulse frequency modulation are evaluated. The behavior and versatility of unconstrained modulated digital switching valve in control systems are presented in detail, with descriptions of the advantages and disadvantages of unconstrained valve.

Pulse width modulation method and digital analogue converter using the same

Abstract: In a pulse width modulation method of the present invention, a digital signal is modulated and a pulse width modulation signal is generated in a pulse width modulator by using a digital signal output unit and the pulse width modulator The pulse width modulation method includes: outputting to the pulse width modulator a first value corresponding to the input signal as a first digital signal at a first timing by the digital signal output unit; determining a limited value range based on the first value by the digital signal output unit; determining a second value corresponding to a new input signal by the digital signal output unit; judging whether or not the second value is included in the limited value range, and when the second value being judged to be included, outputting the second value to the pulse width modulator as a second digital signal, and when the second value being judged not to be included, outputting a value included in the limited value range to the pulse width modulator as the second digital signal at the second timing at which at least one cycle has elapsed from the first timing by the digital signal output unit; and modulating the pulse width of the second digital signal and generating the pulse width modulation signal, by the pulse width modulator.

Carrier-suppressed optical pulse train generating device and method

Abstract: The device is structured to have a first electric modulation signal generator, a second electric modulation signal generator, a two-mode beat light source and an optical intensity modulator. The first electric modulation signal generator generates and outputs a first electric modulation signal. The second electric modulation signal generator generates and outputs a second electric modulation signal of a same frequency as the first electric modulation signal and to which a phase difference of δ radians is provided (δ is a real number satisfying 0≦δ≦π). The two-mode beat light source is driven by the first electric modulation signal, and generates and outputs two-mode beat light. The two-mode beat light is inputted to the optical intensity modulator, and the optical intensity modulator generates and outputs a CS optical pulse train. Light transmittance of the optical intensity modulator is modulated by the second electric modulation signal.

DC-DC converter for pulse frequency modulation control and power supply system

Abstract: A DC-DC converter prevents localization of switching operations at light loads and is able to improve power conversion efficiency. The DC-DC converter of some variations performs pulse frequency modulation control at light loads, and includes a reducing circuit configured to skip an oscillation frequency signal at light loads and to generate a skipped signal.