Showing papers on "Pulse-frequency modulation published in 1991"

Feedback control of electrically stimulated muscle using simultaneous pulse width and stimulus period modulation

Abstract: The closed-loop control of electrically stimulated muscle using simultaneous pulse width and frequency modulation is considered. It is shown how the addition of pulse frequency modulation to pulse width modulation can improve controller performance. In single muscle operation, the combination of pulse width and stimulus pulse frequency modulation results in better control of transient responses than with pulse width modulation alone. In the case of costimulation, the controller modulates the pulse stimulus periods of the antagonists in a reciprocal manner, to ensure stable and fast responses. This feedback controller was evaluated in animal experiments. Step responses with rapid rise times but without overshoot were obtained by the combined modulation. Good steady-state and transient performance were obtained over a wide range of static lengths and commands, under different loading conditions and in different animals. >

Across-channel Masking of Changes in Modulation Depth for Amplitude- and Frequency-modulated Signals:

Abstract: This study examines a form of masking that can take place when the signal and masker are widely separated in frequency and cannot be explained in terms of the traditional concept of the auditory fi...

Advanced random pulse width modulation technique for voltage-controlled inverter drive systems

Abstract: The principles of an advanced random pulsewidth modulation (ARPWM) technique are presented. The means to alleviate the current deterioration at a low modulation index are investigated, along with the problem of the feasibility of the RPWM technique at supersonic, i.e., on the order of tens of kHz, switching frequencies. The results of computer simulation of the improved ARPWM technique and an experimental investigation of a prototype modulator are presented. Simple in practical realization, the ARPWM technique yields high-quality output current in voltage-controlled, three-phase inverters. The blurred harmonic spectra of the output voltage and current improve the acoustic and electromagnetic interference (EMI) characteristics of the inverter and can stave off resonant torsional vibrations in AC drive systems. >

Microwave modulation of laser diodes with optical feedback

Abstract: It is shown theoretically and experimentally that significant variations in the microwave modulation responses of laser diodes occur due to optical feedback from the transmission fiber. These variations decrease if the laser spectrum is less coherent; this can be achieved, for example, by increasing the intensity modulation index. In a recent letter the authors (1989) discussed the small-signal transfer functions; large deviations in the amplitude and the phase response resulted from optical feedback. For large-signal modulation, weaker feedback-induced deviations of the transfer function were predicted by W.I. Way and M.M. Choy (1988). The microwave modulation characteristics are considered in more detail, including the effects of higher modulation indexes. For a typical intensity modulation index of 26%, variations of up to 3 dB in amplitude and 60 degrees in phase were observed. >

Five-stepped PWM inverter used in photovoltaic systems

Abstract: A PWM (pulse-width-modulated) inverter that has five-stepped output-voltage levels is introduced. In this inverter, the waveform of the output voltage has a smaller harmonic content than that of a conventional PWM inverter. A novel PWM technique is analyzed. The PWM pulses included in the waveform of the output voltage are formed using a criterion based on the calculation that each area of voltage pulses is equal to the integrated value of each time shared area of a reference sinusoidal waveform. This PWM technique for the five-stepped PWM inverter is superior to the conventional PWM technique, and the experimental results coincided with the calculation obtained using the fast Fourier transform. In addition, the relations between the number of PWM pulses and the harmonic contents of the output voltage are described. >

Interferometer phase modulation controller apparatus using ratios of two pairs of harmonic signals

Abstract: A phase modulation control apparatus is taught in combination with an interferometer excited by a coherent light source providing a light beam to the interferometer having first and second optical paths. The interferometer senses a physical quantity such as pressure. The interferometer is coupled to provide an optical signal containing information providing a measure of the physical quantity via first and second interfering beams to a detector. The detector provides a composite output signal. The invention phase modulation control apparatus has a modulation means responsive to a modulating frequency signal and a phase modulation control signal to provide a frequency modulating factor signal for frequency modulating at least a portion of the light beam to provide a phase modulation between the first and second interfering beams at a carrier frequency. The composite output signal has at least four harmonic signals referenced to the carrier frequency. A synchronous detection means responsive to the carrier frequency signal and to the composite output signal provides a pair of even harmonic filtered signals and a pair of odd harmonic filtered signals. A reference channel means and quadrature channel means each respond to the even and odd harmonic pairs of filtered signals and respectively provide first and second integrator input error signals which have null values in response to their respective harmonic pairs having a predetermined ratio. An integration means combines and integrates the first and second integrator input error signals to provide the phase modulation control signal to the modulation means.

Random pulse width modulation of delta inverter for automotive applications

Abstract: An analysis of PWM strategies for a delta inverter, with a stress on a random PWM technique, is presented. The delta inverter, based on three power switch/freewheeling diode pairs and requiring three independent DC supply sources, has been found particularly suitable for automotive applications due to the reduced extent of the power circuit. The random modulation of output voltage pulses improves noise and vibration characteristics of the AC drive system. Results of an experimental investigation of randomly modulated delta inverter are provided. >

Pulse width modulation circuit

Abstract: A pulse width modulation circuit includes an operation unit which generates a compensation signal based on the product of a deviation of an input signal from a first reference value and a deviation of a power supply voltage from a second reference. A level change unit changes the level of at least one of an error signal from an error amplifier and a reference wave signal generated by a reference wave signal generator in accordance with the compensation signal so that a relative level defined by a level difference between the error signal and the reference wave signal changes in accordance with the compensation signal. The pulse width modulation circuit also includes a unit for comparing the level of the error signal and the level of the reference wave signal having a changed relative level with each other and for generating a pulse width modulated signal based on a comparison result.

Digitally compensated modulation system for frequency synthesizers

Abstract: A digitally compensated modulation system for frequency synthesizers has a single modulation input line with flat frequency response to zero hertz. The above is accomplished while eliminating circuit components and adjustments by integrating reference oscillator temperature compensation, modulation compensation for changes in the voltage controlled oscillator modulation sensitivity and modulation compensation for changes in the reference oscillator modulation sensitivity. Signals requiring modulation enter a microprocessor and are summed together with a microprocessor generated signal and a temperature compensation input to create a composite modulation signal. The composite modulation signal is then multiplied by appropriate constants and sent to the synthesizer.

Modulation mode recognition for baseband signal transformation - subjecting intermediate signal, or couples band signal to parameter estimation

Abstract: The modulation mode recognition methods has a modulated, complex base band signal, initially of unknown modulation mode, which is transformed into numerous, independent intermediate signals, forming a base for the determination of the modulation mode in an evaluation circuit. The individual intermediate signals, and/or the original complex base band signal, are subjected to parameter estimation of an autoregressive model. From the estimated parameters, and/or derived prediction errors the modulation mode is determined by intercomparison or comparison with preset threshold values. USE/ADVANTAGE - For signal transmission systems, with simple and effective layout, and high reliability.

Negative feedback using a nonlinear mirror for the generation of a long train of short light pulses

Abstract: A nonlinear mirror is used to provide a passive negative feedback in an actively mode-locked pulsed Nd:YAG laser. Trains of 250 ps pulses with a total length of up to 50 microseconds were generated. The train duration is limited only by the flashlamp pump pulse length.

Instantaneous frequency and conditional moments in the time-frequency plane

Abstract: The conditional moments of frequency of a time-frequency distribution are discussed, and it is shown that they may be related to the derivative of the log of the corresponding signal, a complex function whose imaginary part is the instantaneous frequency. For the complex energy spectrum, a general form for the moments is obtained. For a signal which is the sum of several other signals, the instantaneous frequency will always demonstrate erratic behavior. >

Effect of amplitude modulation on profile detection

Abstract: The effect of amplitude modulation on profile detection was examined in three experiments. The observer’s task was to determine in which observation interval an increment was added to the 1000‐Hz target component of a multitone complex in which the components were equally spaced on a logarithmic frequency scale from 200 to 5000 Hz. The target was unmodulated throughout the study. In some conditions, all nontarget components of the standard were modulated in phase; in other conditions, they were modulated with random phase. In experiment 1, the threshold was measured as a function of the modulation rate. The results show that, at low modulation rates, 5 Hz for example, modulation elevates threshold by about 13 dB. The threshold decreases as the modulation rate increases, with the threshold elevation being only 3 dB at 80 Hz. In experiment 2, threshold was measured as a function of modulation depth for both 21‐ and 5‐component complexes. The results show that for a 5‐Hz modulation rate the threshold decreases as the modulation depth decreases, and that the rate of decrease is greater for the 21‐component complex than for the 5‐component complex. In experiment 3, the effects of random‐phase modulation were explored; the phase of the modulation waveform was randomly chosen for each component. The results show that there is no difference between in‐phase and random‐phase modulation when each component occupies a different critical band. If, however, two or more components occupy the same critical band, then randomizing the phase of modulation reduces the effective depth of modulation within that critical band, and the effect of modulation is thereby lessened.

Modulation circuit for a light emission device

Abstract: A modulation circuit for controlling a light emission device to produce an intensity-modulated light signal based on an input modulation signal. The modulation circuit includes a level detector and an attenuator. The level detector produces an electrical signal corresponding to an amplitude level of the input modulation signal. The attenuator attenuates the input modulation signal based on the electrical signal, and applies the attenuated input modulation signal to said light emission device.

The 'inverted' gain-levered semiconductor laser-direct modulation with enhanced frequency modulation and suppressed intensity modulation

Abstract: A gain-levered semiconductor laser has enhanced efficiencies in both intensity modulation (IM) and frequency modulation (FM). It is shown that by inverting the bias points of the gain and modulation sections, a mode of operation referred to as 'inverted' gain-lever, the FM efficiency is suppressed. The large FM-to-FM ratio makes it a desirable source for an FM optical transmitter. >

Method and apparatus for optical fiber length determination

Abstract: In a method and apparatus for measuring length of an optical fiber, a light source of a selected wavelength transmitted along the fiber is modulated by both a first and a second light modulation signal, which light modulation signals each differ in frequency from a first modulation frequency by a fixed amount. A time detector responds, alternately during a period, to the light signal as modulated by of each of the first and second light modulation signals by using each of the light signal modulation frequencies as a reference. Consequently, the output of the time detector has a phase responsive to the effective length of the fiber. A phase sensitive detector receives as a signal input an output of the time detector means. A second modulation frequency defines the period of alternation of response and provides a reference input to the phase sensitive detector. The phase sensitive detector measures the ac component of time detector output in phase with the second modulation frequency to provide an indication of fiber length.

Acceleration effects in crystal filters-a tutorial

Abstract: The quasi-static method for the analysis of vibration-induced modulation in crystal filters is briefly reviewed. A dynamic method, in which the filter is treated as a linear network with time-varying elements, is introduced. The method, which allows determination of both amplitude and phase modulation due to vibration, is illustrated by examples. It is then applied to the analysis of the spectrum clean-up case, consisting of a frequency source with an output filter, both of which are undergoing the same acceleration. >

A pulse frequency modulated PWM scheme for sinusoidal inverters

Abstract: A pulsewidth modulated (PWM) pulse pattern optimization method using pulse frequency modulation (PFM) is described. The PFM technique is aimed at not only reducing the magnetic acoustic noise of driven motors, but also at improving the performance of sinusoidal inverters. The PWM pulse patterns are controlled so that the time-integral function of the output voltage in the space vector notation may draw a circular locus. The pulse frequency of PWM is controlled so that the performance index (PI), which represents the degrees of achieved objectives, may be minimized. Two PIs, one for minimizing the distortion of output currents and the other for minimizing the torque pulsation of driven motors, are used. The method is implemented using a single-chip microprocessor, and experimental results demonstrate its validity. >

Voltage modulation factor of the magnetic flux control PWM method for inverter

Abstract: The voltage modulation factor of the magnetic flux control pulse-width modulation (PWM) method is discussed. The modulation factor is derived from a theoretical study on the flux locus produced from the inverter output voltage. The derivation is based on the fact that the fundamental component of the inverter output voltage is proportional to the radius of the flux locus. It is shown theoretically that the voltage modulation factor is expressed by the content of a zero vector in one cycle of the selected PWM pattern of the space vector expression. The modulation factor of the magnetic flux control PWM method is calculated. The modulation factor can be varied from zero to 12/ pi /sup 2/. The output voltage of the magnetic flux control PWM method can be controlled by the modulation factor linearly from zero up to overmodulation. The simulation and experimental results are also shown. >

Pulse width modulation decoder

Abstract: The present invention relates to a pulse width modulation (PWM) decoder, and more particularly to a PWM decoder which demodulates a pulse width modulated signal for proper interface with the operational characteristics of an object to be controlled. The present invention includes a PWM input terminal for receiving a PWM signal, an integrator for converting the PWM signal to a linear analog signal, and a transfer characteristic converter for changing the slope of the transfer characteristic of the integrator, so that a microcomputer can be interfaced with a signal processor without changing the microcomputer's internal design.

Vectorial PWM methods, implementation and results for some AC-DC converter structures

Abstract: A list of vectorial pulse-width modulation (PWM) methods was derived for three-phase AC-DC converters, namely, the full-bridge, the delta inverter, and the incomplete bridge. Significant results of these techniques are reported for each converter, consisting of commutation rates, maximum attainable amplitudes, and harmonic spectra. A digital implementation scheme is also presented. >

Two types of control in the current mode resonant converter

Abstract: The authors report the results of an in-depth study of the operation of a circuit controlled by pulsewidth modulation (PWM) through experiments and using a model. The experiment used an open-loop circuit to observe the relationship between the control current and output current. The circuit was analyzed by classifying the operation of the resonant circuit controlled by pulse frequency modulation (PFM) and/or PWM into four modes and comparing the results. The upper- and lower-frequency limits of PFM control were also considered. This analysis clarifies the mechanism which determines the gain phase characteristics of a series resonant converter under PFM and PWM control modes. The theoretical results agree closely with the experimental results. When the circuit is under PWM control, the lower limit for control frequency can be raised and the output current can be controlled from normal current to 0 A. >

Optical transmission system for transmitting analog signals

Abstract: To transmit analog modulated signals via an optical transmission fibre (such as AM-modulated TV signals via a local optical network), it is important that the noise is minimal. External modulation of the laser signal (a) is therefore preceded by filtering out the noise signal at least in the frequency range of the modulation signal (m), with the result that the modulated signal (c) is free of noise. The occurrence of distortion as a consequence of external modulation by means of, for example, a Mach-Zehnder modulator is compensated for by adding the harmonics normally introduced by such a modulator to the modulation signal in phase opposition.

A 45MHz VCO Combining High Linearity With High Modulation Bandwidth

Abstract: A fully monolithic 45MHz Voltage-Controlled Oscillator (VCO) is described, that achieves high linearity (differential gain below 1%) at frequency sweeps up to 25MHz. This has been accomplished by way of a new compensation method that cancels the effect of Switching Time Delay (STD). Because a forward compensation method is applied, the modulation bandwidth is not affected. The circuit has been integrated in a 3GHz bipolar semi-custom process.

Demonstration of a novel wide-band optical signal generator by deep phase modulation in a fiber coupler

Abstract: A simple method for wide bandwidth optical signal generation has been realized by applying a deep phase modulation signal in a fiber coupler which acts as an all‐fiber Michelson interferometer. The output of the interferometer displays a discrete spectrum with a nearly leveled output and frequency bandwidth up to a hundred times that of the frequency of the modulation signal. In this first demonstration, we have generated frequency components up to 4 MHz (with external modulation) and 50 MHz (by direct modulation of the laser diode) respectively. Multigigahertz operation is possible in the future with wideband integrated‐optic phase modulators.

In-pulse frequency modulation mode detecting circuit

Abstract: PURPOSE:To detect an in-pulse frequency mode in real time at the time of one-pulse measurement by providing a multiplier for spectrum width and pulse width outputted by a compressive receiving and a pulse width measuring circuit and a comparator which decides whether or not the output of the multiplier is larger than a constant value. CONSTITUTION:The subject circuit consists of the compressive receiving circuit 2 which outputs the spectrum width 4 with an input signal 1, the pulse width measuring circuit 3 which outputs the pulse width 5 similarly, the multiplier 6 for both their outputs, the comparator 7 which compares its output with the constant value, etc. Then the signal 1 passes through the circuits 2 and 3 to obtain the spectrum width 4 and pulse width 5, which are supplied to the multiplier 6 and comparator 7 to obtain a status 8 indicating whether or not the input signal is a frequency chirp signal. The comparator 7 outputs the status 8 which is '1' indicating the chirp signal when the output of the multiplier 6 is larger that the constant value, but '0' indicating a fixed signal when the output of the multiplier is nearly equal. Consequently, the in-pulse frequency mode can be detected in one-pulse measurement.

Transient analysis of forward multi-resonant converter using EISCAP

Abstract: A circuit simulator, EISCAP, is introduced for the efficient development and design of switching circuits. The transient state of a forward multiresonant power converter was simulated by EISCAP. The magnetizing current of the transformer has a great effect on the converter operation. The most interesting effect was that peak voltage across the main switch increased for the transient state. The peak voltage across the main switch was changed by the pulse frequency modulation (PFM) control method of the main switch. The relation between the stress of the main switch and the PFM control method of the switch in the transient state was revealed. >