Showing papers on "Pulse-frequency modulation published in 1992"

Pulsewidth modulation-a survey

Abstract: Pulse-width modulation (PWM) is surveyed with reference to performance criteria, feedforward schemes, and feedback PWM control. It is stressed that the implementation of PWM techniques in the design of AC motor drive systems depends on the machine type, the power level, and the semiconductor devices used in the power converter. It is ultimately performance and cost criteria which determine the choice of a PWM method in a specific application. >

On separating amplitude from frequency modulations using energy operators

Abstract: To estimate the amplitude envelope and instantaneous frequency of an AM-FM signal the authors developed a novel approach that uses nonlinear combinations of instantaneous signal outputs from an energy-tracking operator to separate its output energy product into its amplitude modulation and frequency modulation components. This energy separation algorithm is then applied to search for modulations in speech resonances, which the authors model using AM-FM signals. The theoretical and experimental results demonstrate that the energy separation algorithm, due to its low computational complexity and instantaneously adapting nature, is very useful in detecting modulation patterns in speech and other time-varying signals. >

Detection of combined frequency and amplitude modulation

Abstract: Zwicker [Acustica 6, 356–381 (1956)] proposed that amplitude modulation (AM) and frequency modulation (FM) are coded by a common mechanism. To test this, the detection of simultaneously occurring AM and FM is discussed. In a two‐alternative forced‐choice task, thresholds for detecting AM alone were determined. Then, thresholds for detecting FM were determined for stimuli which had a fixed amount of AM in the signal interval only. The amount of AM was always less than the threshold for detecting AM alone. The FM thresholds depended significantly on the magnitude of the coexisting AM. For low modulation rates (4, 16, and 64 Hz), the FM thresholds did not depend on the relative phase of modulation for the FM and AM. For a high modulation rate (256 Hz) strong effects of modulator phase were observed, which can be explained by assuming that detection of modulation at high frequencies is based on detection of the lower sideband in the modulated signal’s spectrum. In a second experiment, psychometric functions w...

A new method of modulation classification for digitally modulated signals

Abstract: A modulation model representation of a signal is used to provide a convenient form for subsequent analysis. The modulation model is formed by estimating the instantaneous frequency and bandwidth using autoregressive spectrum analysis. In particular, the instantaneous bandwidth and derivative of the instantaneous frequency prove to be valuable parameters in estimating modulation type. This method performed extremely well for input carrier-to-noise ratios as low as 15 dB. Additionally, since the autoregressive fit to the frequency spectrum is second order, the autoregressive polynomials coefficients and corresponding roots can be computed with closed-form expressions. Thus, the method is computationally efficient. >

Speech information extractor

Abstract: A method and apparatus for extracting information from human speech are disclosed. A speech signal is received into a bank of bandpass filters and the instantaneous amplitude modulation and frequency modulation of each harmonic in the speech waveform is determined. A logarithm of the instantaneous frequency of the speech fundamental frequency is determined, for example, by computing a weighted average of the frequency modulations of the harmonics. An output signal is formed having the logarithm of the frequency of the thus determined speech fundamental and the logarithms of the amplitude modulation for the ten lowest frequency speech harmonics and/or the speech envelope.

PWM strategy for high frequency carrier inverters eliminating current clamps during switching dead-time

Abstract: The switching dead time to protect the inverter main transistors from the arm shortage is investigated. The dead time causes not only waveform distortion, but also zero clamping phenomena. The zero clamping phenomena increase as the switching frequency increases. The inductance model was used to clarify the mechanism of the zero-clamping phenomena, and the dependencies of the phenomena on dead time and load power factor were investigated. A pulse width modulation (PWM) strategy to avoid the phenomena is proposed. The new PWM strategy is combined with the split-zero-vector method. The control scheme is discussed in detail, and experimental results are presented. >

Modulation properties of a near travelling-wave semiconductor laser amplifier

Abstract: The amplitude and phase or frequency modulation properties for pump current modulation of a near travelling-wave semiconductor laser amplifier are examined. The investigations are performed numerically in the time domain with large-signal analysis and in the frequency domain with small-signal analysis. It is shown that the modulation bandwidth is increased by high pump current or high input power and that the small-signal modulation efficiency is increased by low pump current or low input power. The validity of the simulations is supported by experimental results. >

A pulse frequency modulated PWM inverter for induction motor drives

Abstract: A PWM pulse pattern optimization method using pulse frequency modulation (PFM) is described. In conventional PWMs the pulse frequency is kept constant. In the proposed PFM, however, the pulse frequency is adjusted. The PFM technique is intended to not only reduce the magnetic acoustic noises of driven motors but also to improve the performance of sinusoidal inverters. The PWM pulse patterns are basically controlled so that the time-integral function of the voltage vectors in the space vector notation may draw a circular locus. In addition to this, the pulse frequency, of PWM is also controlled so that the performance index (PI), which represents the degree 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 employed. The method is implemented using a single-chip microprocessor, and the experimental results demonstrate its validity. >

Constant frequency ZVS converter with integrated magnetics

Abstract: The author introduces a high-frequency DC-DC converter which provides zero-voltage-switching (ZVS) and allows control of the output by pulse width modulation (PWM) at constant frequency. The topology is very tolerant to leakage inductance in the isolating transformer, and it is possible to combine the transformer and filter choke into a single integrated magnetic assembly yielding several additional benefits. The converter has been operated with ZVS to reduce losses at the switching transition, and this has allowed high-frequency operation even with high frequency and high input voltage. A control scheme has been defined whereby constant frequency operation and PWM produce a linear control to output transfer function with minimal interaction of load. >

Modulation signal amplitude adjustment for an ink jet printer

Abstract: A method is provided for adjusting the operating amplitude of a modulation signal which influences the separation of drops from an ink jet of an ink jet printer. The method includes (1) determining the phase relationship between the modulation signal and the instants when successive drops separate from the ink jet for a plurality of amplitudes of said modulation signal (2) identifying the amplitude of the modulation signal at a predetermined characteristic point in the function of the phase relationship with the amplitude from the magnitude of the change of the phase relationship with the change of the amplitude; and (3) selecting the operating amplitude for the modulation signal in accordance with the amplitude identified in step (2). An ink jet printer is also provided which has control means for identifying the predetermined point from the magnitude of change of the phase relationship between the modulation signal and the instants when successive drops separate from the ink jet with change in the amplitude of the modulation signal.

Waveguide nonlinear optical frequency converter with integral modulation and optimization means

Abstract: An optical, waveguide, quasi-phase-matching frequency converter has integral means to vary the efficiency of the quasi-phase-matching frequency conversion process resulting in intensity modulation of the device output; said frequency converter has integral means to optimize the quasi-phase-matching frequency conversion process resulting in optimum device output; and said frequency converter has integral input signal polarization mode conversion means in optional combination with the conversion optimization means for modulating the optimized device output. Methods for modulating and optimizing the quasi-phase-matching frequency converted signal by electro-optically controlling the dispersion of the frequency converting medium are also disclosed.

Merits and limitations of resonant and soft-switched converters

Abstract: An attempt to classify resonant and soft-switching pulse width modulation (PWM) techniques based on their operation principle and origin is presented. General properties of the most prominent families are summarized. The merits and limitations of the classified families are discussed with the objective of defining their most suitable area of application. >

Digital modulators for use with sub-nyquist sampling of raster-scanned samples of image intensity

Abstract: Apparatus useful in electronics for the tape recording of a video signal, which is a baseband signal of a prescribed bandwidth extending up to a prescribed maximum frequency, processes the video signal to generate a folded-spectrum video signal. The video signal is digitized and supplied to a digital band-splitting filter with a cross-over frequency at one-half said prescribed maximum frequency, for separating the digitized video signal into samples of a lower-frequency-band component and into samples of a higher-frequency-band component. A balanced modulator is connected for modulating a folding carrier wave of the prescribed maximum frequency, which modulation is done in accordance with the higher-frequency-band component to generate a balanced modulation signal; and the balanced modulation signal is linearly combined with the lower-frequency-band component to generate the folded-spectrum video signal. Preferably, the sampling rate of the digitized video signal is exactly the Nyquist rate of the prescribed maximum frequency, reduces the balanced modulation of a suitably phased folding carrier wave to multiplication of successive samples of the modulating signal alternately by plus one and by minus one. Such multiplications are done without having to use a digital multiplier.

The role of amplitude modulation in distress-call

Abstract: The decoding process of distress calls uses many parameters. In our experiment we establish that amplitude modulation was not taken into consideration by the birds in the experiment, even if other parameters were altered. The decoding process that discards amplitude modulation appears well adapted to transmission at long range because amplitude modulation is always subject to degradation.

Electronic musical instrument using fm sound generation with delayed modulation effect

Abstract: A computer having one or more wave tables stored therein is used to synthesize sounds represented by a series of digital samples produced at a sample rate by specifying parameters including a carrier frequency, a modulating frequency and an index of modulation. At each sample time, a modulation value determined during an immediately preceding sample time is scaled to produce a digital control signal. Also at each sample time the modulation value to be used during an immediately succeeding sample time is read from a location of a wave table determined by the modulating frequency, and a carrier value used to produce the digital samples is read from a location of a wave table determined by the carrier frequency and the digital control signal. Modulation effects are therefore delayed by one sample in order to speed execution of the method using the computer. Phase accumulation is performed using a multiplier making it unnecessary to store the sum of all of the previous steps as would be otherwise be required using an additive approach.

Electric power converter arrangement and electric rolling stock control device using the same

Abstract: An electrical power converter having a phase converter constituted by positive side semiconductor switching elements connected in series and negative side semiconductor switching elements connected in series which converts a DC voltage to an AC output phase voltage having at least three potential levels, resulting in three possible modulation modes: dipolar, partial dipolar and unipolar. Dipolar modulation is realized by alternating positive and negative output pulses. Unipolar modulation is realized by output pulses having only the same polarity as the corresponding fundamental modulation wave. Transition is accomplished via partial dipolar modulation which is realized by alternating positive and negative output pulses in a first period of a half cycle by outputting alternating positive and negative pulses and in a second period by outputting pulses having only the same polarity as the corresponding fundamental modulation wave. A control unit for the converter turns the semiconductor switching elements on and off depending on an input voltage amplitude command for a fundamental modulation wave. The intervals of the first and second periods in the half cycle of the AC output phase voltage varies dependent upon the voltage amplitude command.

Programmable intensity smart laser system capable of being fabricated on a semiconductive substrate

Abstract: A laser recorder for recording images on a substrate in response to a video signal (36) having a frequency which defines a pixel time (during which a single pixel is imaged) includes a duty cycle modulating digital to analog (D/A) converter (32) which outputs a variable duty cycle high frequency signal, based upon an intensity controlling N-bit input (34), to a power controller (26) which then controls the intensity of a light beam output by a laser based upon the variable duty cycle high frequency signal. The duty cycle modulating D/A converter outputs a high frequency variable duty cycle bitstream including a repeating cycle of fixed amplitude pulses, a total duration of all of the pulses in each cycle varying based upon the N-bit input signal. The high frequency of the variable duty cycle is sufficiently high so that the cycle of fixed amplitude pulses repeats multiple times within each pixel time, so that the intensity level with which pixels are formed on a substrate varies based upon the number of pulses output during each pixel time and the total duration of all pulses in each cycle. Preferably, the laser, power controller, and duty cycle modulating D/A converter are formed in a common semiconductive substrate. A detector (24) for detecting the intensity of light output by the laser is also preferably formed in the common semiconductive substrate, and provides feedback to the power controller. In a preferred embodiment, the duty cycle modulating D/A converter varies the total duration of the fixed amplitude pulse within a cycle by varying a number of fixed amplitude, fixed width pulses output during each cycle based upon the N-bit input signal.

A pulse-width modulation device

Abstract: A pulse-width modulation device for controlling shapes of dots printed out by a printer by regulating shapes of pulses of pulse-width modulation signals, which respectively represent gray levels of pixels of input image, according to code signals respectively indicating shapes of pulses of pulse-width modulation signals, each of which has a duration composed of time slots respectively corresponding to bits of image data representing a gray level of a pixel. The pulse-width modulation device is provided with a code converter for converting image data corresponding to each pixel of an input image into a predetermined code indicating a shape of a pulse of a corresponding pulse-width modulation signal and for outputting a code signal representing the predetermined code. The indicated shape of the pulse is formed by making the corresponding pulse modulation signal have a high level at a predetermined number of time slots thereof, which are serially counted from the time slot corresponding to the most significant bit of the image data or from the time slot corresponding to the least significant bit of the image data according to a gray level of each pixel. The pulse-width modulation device is further provided with a pulse generating circuit for receiving the code signal and for generating the pulse of the predetermined pulse-width modulation signal according to the code in response to a predetermined clock signal.

Numerically-controlled modulated oscillator and modulation method

Abstract: A numerically-controlled modulated oscillator and modulation method which selectively provides frequency modulation, phase modulation or amplitude modulation with minimal circuitry. A numerically-controlled modulated oscillator is provided having a tuning register for receiving a center frequency parameter, an adder for receiving at one input the frequency parameter, a phase accumulator for receiving a phase increment number from the adder and producing a waveform phase number, a waveform memory for producing a waveform amplitude number in response to the phase number, and a digital-to-analog converter for producing an analog signal in response to the waveform amplitude number. Another input is provided to the adder from an angle modulation register which provides an angle modulation parameter. This parameter can perform either phase or frequency modulation. In the case of frequency modulation, the angle modulation represents the current amplitude of the modulation signal and is added to the center frequency parameter on every clock cycle. In the case of phase modulation, the angle modulation parameter is provided at a periodic rate and then for only one clock cycle. In this case, the value of the angle modulation parameter is relative to the previous angle modulation parameter. Amplitude modulation is provided by an amplitude modulation register which receives an amplitude modulation parameter and applies it to a multiplier disposed between the waveform memory and the digital-to-analog converter.

A PWM ASIC using stochastic coding

Abstract: The authors describe an application-specific integrated circuit (ASIC) design implementing a novel pulse width modulation (PWM) technique. This PWM function is based on the stochastic coding of the driving pulses. This approach allows a small IC area and high-speed generation of pulse sequences. The validity of the proposed PWM has been studied with simulation and experiment. Several limiting operation conditions of the ASIC are also defined. Using the stochastic PWM a three-voltage inverter is shown to be a more efficient solution than the classical PWM and a dual-voltage inverter; fewer harmonics are generated in current and voltage. >

DC motor control using frequency and pulsewidth modulation

Abstract: The flow of power through a field effect transistor to a DC motor is controlled by the output of a frequency modulator having a low frequency pulsed signal applied to one input thereof and a high frequency pulsed signal applied to a second input thereof. The pulse width of each "on" pulse of the low frequency pulsed signal is varied in response to a signal representing a desired motor speed. Optionally, the pulse width of each "on" pulse of the high frequency pulsed signal can also be varied in response to the signal representing the desired motor speed. A filter circuit can be employed to prevent rapid changes in the pulse width of the low frequency pulsed signal. Similarly, a filter circuit can be used to avoid rapid changes in the pulse width of the high frequency pulsed signal. A freewheeling diode can be used to minimize inverse voltage spikes across the motor.

Radio communication apparatus having an automatic frequency control circuit for controlling a transmission frequency on the basis of a reception frequency

Abstract: A radio communication apparatus comprises a detecting circuit for detecting a change of a received frequency of a radio communication channel during a communication and outputting a digital detection signal, a pulse width modulating circuit, and a smoothing circuit. The pulse width modulating circuit pulse-width modulates a pulse signal having a predetermined frequency in accordance with the digital detection signal output from the detecting circuit. The smoothing circuit smoothes the pulse-width modulated circuit output from the pulse width modulating circuit and generates an analog control signal. A transmission local oscillating frequency is controlled in accordance with the analog control signal.

Control of pulse width modulated resonant DC link inverter

Abstract: Control techniques for synthesis of AC waveforms using pulse-width-modulated resonant DC link inverters are presented. The performance characteristics achieved with the use of pulse width modulation as opposed to discrete pulse modulation in resonant DC link inverters with respect to waveform spectrum, component stresses, and control complexity are discussed. The use of a hybrid modulation strategy in order to maximize the performance is examined. Detailed control strategies backed up by experimental results from a passively clamped resonant DC link inverter are presented. >

Confidence on the second difference estimation of frequency drift: a study based on simulation

Abstract: Simulation is used to compare the confidence in estimating frequency drift in the presence of stochastic noise between two different estimators: (1) a mean second difference using neighbouring data, and (2) a single second difference over the entire data set. In each case 100-s data sampling and 10000 samples (11.5 days of data) are simulated. The two estimators show a similar confidence when the noise is purely random walk frequency modulation, but when there is also white frequency modulation, as is common in oscillators, method (2) is more efficient. An advantage of (1) is that it provides an internal confidence to an estimate on a single data set. When a typical rubidium gas cell frequency standard is simulated, the confidence of the drift estimate is ten times better for method (2) as compared to method (1). >

Pulse width modulated series resonant converter

Abstract: A pulse-width-modulated (PWM) extension of the series resonant converter is presented which reduces the dead time and improves the modulation strategy of this type of converter. With the addition of one thyristor and one diode to the 12 thyristors of a series resonant converter, pulses of link current of arbitrary width can be created. Simulations show that good waveform quality can be achieved, and experimental results also show a reduction in the effective dead time. The proposed control scheme has the following advantages over previous methods: inverter switching and external PWM signals can be synchronized; high-frequency DC link current regulation remains possible, allowing line current power factor control; and device stresses are typically lower than in the normal series resonant DC link converter when a PWM technique is employed. >

Modulation techniques for quasi resonant DC link PWM converters

Abstract: The performance limitations of the quasi-resonant DC link inverter at very low load current are discussed. It is shown that substantial benefits can be obtained by suitable improvements in modulation strategy, without affecting the power circuit structure. Further substantial benefits can be obtained by introducing an intermediate phase voltage status, allowed by the converter structure, which is valid at low load current. This gives an extra degree of freedom, thus overcoming all practical limitations to the working range of this kind of converter. The proposed solutions are of general validity, and can be applied to different modulation techniques (both analog and digital), irrespective of operating conditions. Converter performance was simulated in a wide range of situations. Efficient and reliable operation was demonstrated by extensive experimental tests. >

Characterization of the modulation and noise properties of a three-electrode DFB laser

Abstract: The modulation and noise properties of a three-electrode DFB laser have been measured. At proper biasing, the frequency modulation response could be chosen to be in phase or 180 degrees out of phase with respect to the intensity modulation by selecting the modulated electrode. Applying a first order equalization/filter, a flat frequency modulation response was measured up to 5 GHz. A 20-dB broadband suppression of the intensity modulation was accomplished when modulating two sections in push-pull. The spectral densities of the FM and intermodulation noise were measured showing remarkably flat intermodulation and FM noise spectra. >

Method for measuring frequency modulation rate characteristics for a swept frequency signal

Abstract: A method for characterizing frequency modulation rate parameters for a swept frequency signal is based on zero crossing counting and digital signal processing. The method is easy to implement and does not require batch processing so as to be suitable for real time tracking of frequency variations in a variety of applications.

An extended system approach to dynamical pulse-frequency-modulation control of nonlinear systems

Abstract: The design of stabilizing pulse-frequency-modulation (PFM) controllers is addressed, in all generality, for the case of nonlinear single-input single-output analytic systems. Both static and dynamical PFM control strategies are developed, in full detail, on the basis of an elementary scalar system result. A dynamical PFM controller design is carried out for chemical process control as an illustrative example in which smoothed (i.e., implementable) inputs are obtained. >

Closed loop fiber optic gyroscope with fine angle resolution

Abstract: A closed loop fiber optic gyro features signal processing wherein square wave phase modulation is added to a modulation drive signal after overflow logic so that the square wave modulation will not cause a phase modulation ramp to exceed overflow/underflow logic limits. The arrangement is such that the phase modulation causes a retrace with each modulation period when the amplitude of the ramp is within predetermined limits. Corrections to the retrace limit are implemented so as to scale a digital output, which enables the determination of accumulated gyro angle with a finer resolution than simple output pulse accumulation as has heretofore been the case.