Showing papers on "Pulse-frequency modulation published in 2000"

A high-precision magnetoencephalographic study of human auditory steady-state responses to amplitude-modulated tones.

Abstract: The cerebral magnetic field of the auditory steady-state response (SSR) to sinusoidal amplitude-modulated (SAM) tones was recorded in healthy humans. The waveforms of underlying cortical source activity were calculated at multiples of the modulation frequency using the method of source space projection, which improved the signal-to-noise ratio (SNR) by a factor of 2 to 4. Since the complex amplitudes of the cortical source activity were independent of the sensor position in relation to the subject’s head, a comparison of the results across experimental sessions was possible. The effect of modulation frequency on the amplitude and phase of the SSR was investigated at 30 different values between 10 and 98 Hz. At modulation frequencies between 10 and 20 Hz the SNR of harmonics near 40 Hz were predominant over the fundamental SSR. Above 30 Hz the SSR showed an almost sinusoidal waveform with an amplitude maximum at 40 Hz. The amplitude decreased with increasing modulation frequency but was significantly different from the magnetoencephalographic (MEG) background activity up to 98 Hz. Phase response at the fundamental and first harmonic decreased monotonically with increasing modulation frequency. The group delay (apparent latency) showed peaks of 72 ms at 20 Hz, 48 ms at 40 Hz, and 26 ms at 80 Hz. The effects of stimulus intensity, modulation depth, and carrier frequency on amplitude and phase of the SSR were also investigated. The SSR amplitude decreased linearly when stimulus intensity or the modulation depth were decreased in logarithmic steps. SSR amplitude decreased by a factor of 3 when carrier frequency increased from 250 to 4000 Hz. From the phase characteristics, time delays were found in the range of 0 to 6 ms for stimulus intensity, modulation depth, and carrier frequency, which were maximal at low frequencies, low intensities, or maximal modulation depth.

Improved heart rate variability signal analysis from the beat occurrence times according to the IPFM model

Abstract: The heart rate variability (HRV) is an extended tool to analyze the mechanisms controlling the cardiovascular system. In this paper, the integral pulse frequency modulation model (IPFM) is assumed. It generates the beat occurrence times from a modulating signal. This signal is thought to represent the autonomic nervous system action, mostly studied in its frequency components. Different spectral estimation methods try to infer the modulating signal characteristics from the available beat timing on the electrocardiogram signal. These methods estimate the spectrum through the heart period (HP) or the heart rate (HR) signal. The authors introduce a new time domain HRV signal, the Heart Timing (HT) signal. They demonstrate that this HT signal, in contrast with the HR or HP, makes it possible to recover an unbiased estimation of the modulating signal spectra. In this estimation the authors avoid the spurious components and the low-pass filtering effect generated when analyzing HR or HP.

Random modulation techniques with fixed switching frequency for three-phase power converters

Abstract: This paper proposes a new family of random modulation techniques for three-phase power converters which operate with a fixed switching frequency. The techniques are based on adjusting the duration of the zero-vectors or adjusting the three pulse positions in a switching period. Three methods are selected for experimental tests because they preserve the fixed switching frequency known from standard PWM techniques. The new methods are also compared with random switching frequency modulation and with fixed switching frequency modulation. Voltage, current and acoustic noise spectra are used for comparison and it is concluded that two of the techniques are especially useful at lower fundamental frequencies. The techniques can substitute classic random modulation techniques with variable switching frequency in some applications.

Series resonant ZCS-PFM DC-DC converter with multistage rectified voltage multiplier and dual-mode PFM control scheme for medical-use high-voltage X-ray power generator

Abstract: In general, high-voltage DC power supplies employing a variety of high-frequency inverters are implemented for constant value control schemes. In particular, their good transient and steady state performances cannot be achieved under wide load variations for a medical-use high-voltage X-ray generator, ranging from 20 kV to 150 kV in the output voltage and from 0.5 mA to 1250 mA, respectively. A high-voltage DC power supply designed for X-ray power generator applications is considered, which uses a series resonant inverter-linked multistage DC voltage multiplier instead of a conventional high-voltage diode module rectifier connected to the secondary side of a high-voltage transformer. A constant on-time/variable frequency control scheme of this converter operating at zero-current soft switching mode is described. Introducing the capacitor-diode cascaded multistage voltage multiplier, the secondary turn numbers and secondary-side stray capacitance of the high-voltage, high-frequency transformer, as well as the rectifier diode voltage ratings, can be greatly reduced. It is shown that the proposed converter control scheme of the two-step selective changed frequency selection switching is more effective for improving the output voltage responses. The series resonant high frequency transformer-linked voltage-multiplying rectifier is evaluated for an X-ray high-voltage generator on the basis of simulation analysis and observed data in experiment.

Delta-sigma based dual-port modulation scheme and calibration techniques for similar modulation schemes

Abstract: PLL frequency synthesizers and their calibration techniques are described. The PLL frequency synthesizers are used to generate digital modulation of a carrier signal. A digital frequency divider in the feedback path of the loop has its division ratio controlled by a digital Δ-Σ modulator. The modulation of the carrier is achieved by applying a modulation signal to the input of the Δ-Σ modulator and to the input of the voltage-controlled oscillator of the PLL. The high frequency path and low frequency path of the modulation signal must be adjusted with respect to one another in order to obtain a good modulation. As the low frequency path can be accurately set, the calibration is performed only on the high frequency path. Digital calibration techniques for the high frequency path are described.

Antenna coupling systems and methods for transmitters

Abstract: Multiple radio channel frequency signals that are modulated with respective information modulation are transmitted from a common antenna at multiple radio frequencies. Multiple modulators are provided, a respective one of which corresponds to a respective one of the radio channel frequencies. Each modulator generates at least one constant amplitude, phase modulated drive signal at the corresponding radio channel frequency from the respective information modulation, such that the at least one constant amplitude, phase modulated drive signal corresponds to the information modulation for the corresponding radio frequency. At least one saturated power amplifier is provided for each of the at least one constant amplitude, phase modulated drive signals. A respective saturated power amplifier is responsive to the corresponding constant amplitude, phase modulated drive signal, to produce a corresponding amplified output signal at an output thereof. A coupling network connects the outputs of the saturated power amplifiers in series, to produce a combined signal that is applied to the common antenna, such that the common antenna radiates the radio channel frequency signals that are modulated with the respective information modulation. In first embodiments, the at least one constant amplitude, phase modulated drive signal is a single constant envelope modulation drive signal, wherein the information modulation is a constant envelope information modulation. In other embodiments, at least two constant amplitude phase modulated drive signals are provided at the corresponding radio channel frequency, such that the at least two constant amplitude, phase modulated drive signals correspond to the information modulation for the corresponding radio frequency.

Entraining power-dropout events in an external-cavity semiconductor laser using weak modulation of the injection current

Abstract: We measure experimentally the effects of injection current modulation on the statistical distribution of time intervals between power-dropout events occuring in an external-cavity semiconductor laser operating in the low-frequency fluctuation regime. These statistical distributions are sensitive indicators of the presence of pump current modulation. Under most circumstances, we find that weak low-frequency (in the vicinity of 19 MHz) modulation of the current causes the dropouts to occur preferentially at intervals that are integral multiples of the modulation period. The dropout events can be entrained by the periodic perturbations when the modulation amplitude is large (peak-to-peak amplitude /spl ges/8% of the dc injection current). We conjecture that modulation induces a dropout when the modulation frequency is equal to the difference in frequency between a mode of the extended cavity laser and its adjacent antimode. We also find that the statistical distribution of the dropout events is unaffected by the periodic perturbations when the modulation frequency is equal to the free spectral range of the external cavity. Numerical simulations of the extended-cavity laser display qualitatively similar behavior. The relationship of these phenomena to stochastic resonance is discussed and a possible use of the modulated laser dynamics for chaos communication is described.

Self-phase modulation and compression of few-optical-cycle pulses

Abstract: The nonlinear propagation of few-optical-cycle pulses through a dispersive Kerr medium, as, e.g., fused silica, is studied theoretically using a global approach to dispersion without applying the slowly varying envelope approximation. Contrary to amplitude self-steepening, a nearly triangular pulse shape with the steep side on the leading front is predicted. The calculation of the ultrawide spectrum and the spectral phases demonstrates that half-cycle pulses with a full width at half maximum as short as 0.5 fs and single-cycle pulses can be generated by the application of an appropriate broadband modulator for the compensation of the frequency-depending phase.

Envelope simulation by SPICE-compatible models of electric circuits driven by modulated signals

Abstract: SPICE-compatible equivalent circuits were developed to facilitate the analysis and envelope simulation of electric circuits driven by modulated signals. The circuits are based on a novel complex phasor domain transformation. The proposed method facilitates fast simulation of any general linear circuit driven by a modulated signal, such as amplitude, frequency, or phase modulation.

Method and apparatus for implementing improved pulse width modulation

Abstract: A method and apparatus for implementing an improved pulse width modulation circuit is disclosed. In particular, a circuit and method is provided to generate a pulse width modulated signal, wherein the circuit and method significantly reduce susceptibility to transient noise effects. The pulse width modulator according to the present invention operates at high frequencies and over a full duty cycle range of 0% to 100%. Furthermore, automatic self-correction logic is also disclosed for pulse width modulated circuits wherein the self-correction logic prevents fault conditions.

Device and method for compensating polarization mode dispersion in an optical communication system

Abstract: An optical communication system comprising: a transmitter for sending a digital signal, an optical transmission line, a receiver comprising a modulation and dispersion device, the said modulation and dispersion device comprising: a) a modulation device for modulating the phase of the said digital optical signal by a modulation having: a1) a predetermined modulation frequency, a2) a periodic variation in time, a3) a maximum amplitude of said periodic variation; b) a chromatic dispersion element providing an anomalous dispersion when the said periodic variation has a positive modulation amplitude and a normal dispersion when the said periodic variation has a negative modulation amplitude.

Modulation identification device

Abstract: A modulation identification device can be used for detecting the modulation type of a wirelessly transmitted and modulated RF signal without a-priori information on the kind of modulation used. The modulation identification device (1) comprises a n-port junction (17), n being an integer equal to or larger than three. The n-port junction (17) is supplied with the modulated RF signal (2) and a second RF signal (3) from a local oscillator. The n-port junction (17) outputs at least one third RF signal to at least one power detector (18). A signal processing unit (6) processes the power detected output of the n-port junction (17) to generate at least one flag (10) indicating the identified modulation type.

Modulation technique providing high data rate through band limited channels

Abstract: A digital data modulator is coupled to a source of a digital data signal. An encoder encodes the digital data using a variable pulse width code. A pulse signal generator generates pulses representing edges of the encoded digital data signal. A carrier signal generator generates a carrier signal having carrier pulses corresponding to the pulses from the pulse signal generator. A corresponding digital data demodulator is coupled to a source of a modulated signal having carrier pulses spaced relative to each other to represent a variable pulse width encoded digital data signal. A detector generates a variable pulse width encoded signal in response to received carrier pulses. A decoder decodes the variable pulse width encoded signal to generate the digital data signal.

New control method of piezoelectric transformer converter by PWM and PFM for wide range of input voltage

Abstract: A new control method of a piezoelectric transformer (PT) converter by PWM and PFM is presented. The combination of an active-clamp circuit and a resonant circuit makes it possible to control the output voltage of the PT converter by PWM at a fixed switching frequency and PFM at a fixed duty ratio. The PT converter implemented on a printed circuit board was experimentally evaluated and a good controllability was successfully achieved.

Two sided latched pulse width modulation control

Abstract: A control scheme is presented in which both edges of the PWM signal are modulated. The PWM signal is latched to prevent multiple transitions. The sawtooth ramp is replaced by a triangular wave derived from a digital clock, which is particularly suitable for high frequency operation. Additionally, the two sided PWM halves the response time.

Detection of quasitrapezoidal frequency and amplitude modulation

Abstract: It has been proposed that the detection of frequency modulation (FM) of sinusoidal carriers can be mediated by two mechanisms; a place mechanism based on FM-induced amplitude modulation (AM) in the excitation pattern, and a temporal mechanism based on phase locking in the auditory nerve. The temporal mechanism appears to be “sluggish” and does not play a role for FM rates above about 10 Hz. It also does not play a role for high carrier frequencies (above about 5 kHz). This experiment provided a further test of the hypothesis that the effectiveness of the temporal mechanism depends upon the time spent close to frequency extremes during the modulation cycle. Psychometric functions for the detection of AM and FM were measured for two carrier frequencies, 1 and 6 kHz. The modulation waveform was quasitrapezoidal. Within each modulation period, P, a time TSS was spent at each extreme of frequency or amplitude. The transitions between the extremes, with duration Ttrans had the form of a half-cycle of a cosine f...

Class d digital amplifier

Abstract: A digital amplifier having a PWM modulator for modulating an analog input signal with a modulation signal so as to produce at an output thereof a pulse width modulated signal. A high power switch is responsively coupled to the output of the PWM modulator for switching between high level d.c. positive and negative voltages in accordance with a logic level of the pulse width modulated signal so as to produce a high power modulated switched signal, and a low pass filter is coupled to an output of the high power switch for filtering out the high frequency components of the signal. A feedback control loop is provided from the output of the high power switch to the analog input signal, and the modulation signal is of generally triangular shape.

Novel converters for electric ship propulsion system and shipboard power distribution

Abstract: This paper presents a novel propulsion system concept with numerous advantages. The heart of the concept is a motor drive and control topology we call "pulse frequency modulation (PFM)" The PFM concept is a fundamentally different method of distributing and converting electrical power that is well suited for any motor type and power distribution topology, including permanent magnet motors (PM). Many benefits accrue from using PFM topologies in future ship designs. Three of those benefits are particularly important to reconfigurable electric ship design: (1) very high power density (a minimum factor-of-five increase); (2) very low harmonic distortion (less than one percent); and (3) reconfigurable electric ship compatibility. Compatibility with the reconfigurable electric ship stems from the fact that by using the PFM topology, power system designers have flexibility never before available. With minor hardware variations, the system designer is able to change AC frequencies, to connect AC to DC easily, to convert both AC and DC voltages up or down, to inject out-of-phase harmonics to compensate for slot noise, to provide uninterruptable power, to handle PM motor faults efficiently, to provide full four-quadrant operation, to provide programmable interconnects between the ship's service zones and the propulsion modules, and to level loads throughout the system.

Asynchronous superconductor serial multiply-accumulator

Abstract: An oscillator/multiply-accumulator AID converter ( 100 ) which simultaneously provides frequency downconversion, band pass filtering and analog-to-digital conversion of an analog signal, where the analog signal includes a carrier wave modulated with information by any known modulation technique The converter ( 100 ) uses a superconducting, Josephson single flux quantum circuit operating as a voltage controlled oscillator ( 102 ) The voltage controlled oscillator ( 102 ) receives the analog signal to be converted, and generates a series of sharp, high frequency pulses based on the characteristics of the carrier signal The series of pulses are applied to a gate circuit ( 104 ) that either passes or blocks the pulses depending on a gate control signal ( 103 ) When the pulses are passed by the gate circuit ( 104 ), a multiply-accumulator ( 106 ) multiplies the pulse by a binary coefficient ( 109 ) and accumulates the products ( 111 ) resulting from the multiplication during a predetermined time period The predetermined time period includes at least one sampling period Each sample is multiplied by a different weight and their products ( 111 ) are accumulated This operation eliminates the DC response, and leads to an improved frequency response

Power supply for silent discharge type load

Abstract: Since silent discharge in gas has been recognized as one of the most effective ways for ozone, ultraviolet and excimer laser generation, development of low cost and high effective driver for silent discharge load becomes a task of great importance. This paper presents a switched-mode power supply designed for such a type of load. A voltage source type resonant inverter operating under ZVS (zero voltage switching) principle and developed for driving a silent discharge (SD) type high-frequency ozone generation tube is introduced. PDM (pulse density modulation) and PFM (pulse frequency modulation) hybrid control strategy applied in this inverter allows achievement of zero voltage switching in all power regulating ranges (10-100%) that reduces total switching losses and EMI noises and increases total system efficiency. The developed inverter type ozonizer system has superior performances, simple power regulating scheme and appears to be promising in industrial ozone generation applications, however the same principles can be applied in the domestic units with lower power, which will be widely applied in the near future. The developed scheme has proven high performances for the ozone generation system both by simulation and experiment and now it is under implementation for the ultraviolet generating system. This paper introduces the design principles of such a power supply along with its structure, regulation method and operating performances.

Wide frequency range PLL clock generating circuit with delta sigma modulating circuitry for reducing the time changing ratio of the input voltage of a voltage controlled oscillator

Abstract: A clock generation circuit of the present invention extracts a phase error signal of a digital signal obtained from a recording medium ( 1 ) by a phase comparator ( 4 ), filters the phase error signal by a loop filter ( 5 ). In a first embodiment it converts the signal into an analog signal by a minute control D/A converter ( 6 ), detects whether the signal is within a set range by a range detector ( 9 ), generates a modulation reference signal by a modulation reference signal generator ( 10 ), modulates the modulation reference signal by a pulse width modulator ( 11 ), adds a frequency set value and the modulation reference signal by an adder ( 12 ), converts the addition result into an analog signal by a rough control D/A converter ( 13 ), cuts high-band components of the analog signal by a low-pass filter ( 14 ), adds the analog signals output from the minute control D/A converter ( 6 ) and the low-pass filter ( 14 ) by an analog adder ( 7 ), and outputs a clock signal by a voltage controlled oscillator ( 8 ) on the basis of an output signal of the analog adder ( 7 ). Thereby, a clock signal which can continuously lock a wide frequency range can be generated. In a second embodiment the loop filter output is oversampled ( 15 ), then interpolated ( 16 ) and modulated by a multivalued delta sigma modulator.

System for measuring the distance and the relative velocity between objects

Abstract: System for measuring the distance and the relative speed between objects using electromagnetic waves, having means for emitting electromagnetic waves from a first object and having means for receiving reflected electromagnetic waves from at least one second object, the frequency of the emitted signal being modulated in such a way that the modulation frequency, during a first time segment, increases approximately linearly from a first to a second modulation frequency value, that the modulation frequency, during a second time segment, is approximately constant, that the modulation frequency, during a third time segment, decreases approximately linearly from the second to a third modulation frequency value, that the modulation frequency, during a fourth time segment, is approximately constant, and that these time segments recur repeatedly, at least one of the modulation frequency values and/or the duration of at least one time segment being changeable.

On the voltage pulse-width modulation control of L-C filters

Abstract: Pulse-width modulation is broadly used to control electric and electronic devices. The operation of many of these devices is based on the control of the output voltage of a passive filter. Their controllers are designed from the approximate linearization of the dynamics of the joint system, filter-pulse width modulation strategy, which is strongly nonlinear. Common linearization techniques work fine when the modulation frequency is much larger than the natural frequencies of the filter, but fail when that frequency is of the same order of magnitude or smaller than these filter frequencies, as happens in power electronic circuits. This paper develops a new linearization technique that allows a very precise control of these devices when small modulation frequencies have to be used. Our method permits the design of power electronic circuits with very fast output dynamic responses. An experimental circuit is developed to test this and results are reported.

Apparatus and method of pulsed frequency modulation for analog optical communication

Abstract: A method and apparatus for pulse frequency modulation for analog optical communication. A train of optical pulses is generated. The spectrum of the optical pulses in the train of optical pulses can be broadened to provide a train of broad spectrum optical pulses. The broadening can be provided by self-phase modulation. Alternatively, broad spectrum optical pulses can be provided by merely having the optical pulses be less than 1 ps duration. A desired optical frequency slice from the train of spectrum broadened optical pulses is selected by a tunable Fabry-Perot filter. A desired optical frequency slice from the broad spectrum optical pulses is selected by a tunable Fabry-Perot filter. The tunable Fabry-Perot filter has a pair of Distributed Bragg Reflectors separated by an electro-refractive section. The electro-refractive section has tuning electrodes for applying transverse electric fields to the electro-refractive section, corresponding to an analog waveform being applied to the tuning electrodes, to provide a pulse-frequency modulated train of optical pulses.

Frequency limitation and overload detection in a voltage regulator

Abstract: The method describes the generation of a regulated output voltage and an output current by using a switching device for providing the output current and controlling the switching device with the first control circuit functioning in a pulse width modulation (PWM) mode and in an alternative manner with a second control circuit functioning in a pulse frequency modulation (PFM) mode, wherein a second feedback circuit is enclosed in the second control circuit and a time delay is introduced in the second feedback circuit in order to introduce a limitation of the pulse frequency.

Pulse-Modulated Vision Chips with Versatile-Interconnected Pixels

Abstract: This paper proposes and demonstrates novel types of vision chips that utilize pulse trains for image processing. Two types of chips were designed using 1.2 µm double-metal double-poly CMOS process; one is based on a pulse width modulation (PWM) and the other is based on a pulse frequency modulation (PFM). In both chips the interaction between the pixels were introduced to realize the image pre-processing. The basic experimental and simulation results are shown for the PWM and PFM chips, respectively. Also the comparison between two types is discussed.

Microwave phase modulator

Abstract: A phase modulator for direct wideband linear phase modulation of a microwave continuous wave carrier signal which is suitable for many analog and digital phase or frequency modulation techniques. Linear phase modulation range in excess of 360 degrees is provided as a result of linear variation in the modulating signal. A conditioned baseband modulating signal is injected into a highly linear fractional range phase shifter, operating at a subharmonic of the desired output frequency. A nonlinear circuit is used to perform frequency and instantaneous phase multiplication, thus expanding the linear phase modulation range to greater than 360 degrees at the desired output frequency. With special conditioning of the baseband modulating signal, the phase modulator can be made frequency agile in ultra-small frequency steps, without requiring a stable, frequency agile reference signal or frequency synthesizer.