Showing papers on "Pulse-frequency modulation published in 1975"

New sinusoidal pulsewidth-modulated invertor

Abstract: Sinusoidal p.w.m. invertors depend intrinsically for their operation on quite complex modulation processes. An in-depth study of these modulation processes is presented and the sources of possible operational problems are identified. These problems are shown to be manifest in low-frequency harmonic distortion and the possible existence of subharmonics at noninteger frequency ratios, particularly at low-frequency ratios. These problems restrict the viable invertor-output frequency range. A new method of control is presented which overcomes these problems and allows the possibility of low-frequency-ratio operation, resulting in significantly wider invertor-output frequency ranges. An analytic comparison of both the existing and new methods of control is presented, using a 3-dimensional modulation-model approach. The results of this analysis provide the system designer with generalised frequency-spectra characteristics for any particular frequency ratio and modulation depth by direct inspection.

Novel approach to the analysis and synthesis of modulation processes in power convertors

Abstract: It is axiomatic that frequency changing, whether it be in communications or power convertors, can only be achieved by a process of modulation. The paper presents a powerful method of analysing and synthesising these complex modulation processes using a 3-dimensional modulation-model approach, which provides a lucid geometric interpretation of the processes involved. The application of the new approach is demonstrated by deriving new frequency-spectra results for the p.w.m. and p.a.m. convertors, thereby providing essential design information.

Pulsewidth Modulated Inverter Motor Drives with Improved Modulation

Abstract: The performance of inverter drives, which use the pulsewidth modulated (PWM) technique to control motor applied voltage and frequency, are critically influenced by the choice of the modulation policy used in the control circuits. This paper deals with practical inverter drives for squirrel cage induction motors and presents some basic considerations on modulation requirements. The advantages and limitations of popular modulation methods are discussed, and an improved modulation scheme, which allows us to extend the practical speed range of PWM ac drives, is presented.

Transistor inverter motor drive having voltage boost at low speeds

Abstract: A transistor inverter drive provides variable frequency and variable voltage power to an electric motor and pulse width modulates a predetermined number of harmonic-reduced constant volt/hertz pulses per cycle of motor frequency to selectively vary the motor stator voltage so that constant torque over a wide speed range can be accomplished and increases the number of constant volt/hertz PWM pulses per motor frequency cycle at low motor speeds to boost the stator voltage and thereby compensate for decrease in magnetizing current and in torque which would otherwise occur at low frequencies Particularly, the drive has first and second oscillators for respectively deriving trains of first and second clock pulses whose frequencies vary at different rates as a function of an analog speed signal; a frequency switch which selects the higher frequency train of clock pulses; a volt/hertz integrator which derives ramp pulses whose leading edges are established by the pulses from the frequency switch and which vary in magnitude as a function of the time integral of the inverter bridge output voltage; a first comparator for deriving a first control pulse when each ramp signal becomes equal to a first reference voltage; a three phase generator for deriving three phase reference waves synchronized to the first clock pulses and displaced 120° and each of whose period includes a predetermined number of first clock pulses; and means for controlling the fundamental output voltages of individual phases of the inverter bridge in accordance with respective reference waves and including pulse width modulation chopping means for controlling conduction of transistors of the bridge inverter by variable width PWM pulses whose leading edges are at the output pulses from the frequency switch and whose trailing edges are at the first control pulses, whereby the number of PWM pulses in each fundamental voltage cycle is controlled by the higher frequency pulse train and provides a boost in motor terminal voltage at low motor speeds

Optimizing the PWM Waveform of a Thyristor Inverter

Abstract: An optimization method, which will be of use in selecting the modulation technique and Carrier frequency for a PWM inverter system, is presented. The difficult decision, concerning the tradeoff between efficiency and unfiltered harmonic content, can be made with the help of this method. A relation between second-order filter rating and unfiltered harmonic attentuation, for optimum component values, is also obtained. The optimization method is used for illustration to select the optimum modulation technique and its carrier frequency for the modified McMurray inverter [1] to be used in a rapid transit auxiliary power converter. The design aim is to obtain a constant sine wave output with a specific input supply voltage variation. The inverter efficiency is predicted for various carrier frequencies using two modulation schemes. The Schonung and Stemmler [2] modulation approach, with a carrier frequency of 900 Hz, is found to be optimum as it results in low filter rating and an efficient inverter.

Integrated electro‐optic intracavity frequency modulation of double‐heterostructure injection laser

Abstract: Integration of a taper‐coupled GaAs‐AlxGa1−xAs laser with a linear electro‐optic modulator permits efficient optical frequency modulation of the laser emission. The pulsed room‐temperature threshold current density of the device was 8 kA/cm2. Frequency modulation depth in excess of 15 GHz (corresponding to a wavelength shift of 0.4 A) was obtained with a reverse bias change of 20 V across the modulator. Conversion of frequency modulation into intensity modulation was demonstrated with a characteristic power P0 of 10 μW/MHz for 90% intensity modulation. It is shown that reduction of P0 by an order of magnitude is easily feasible.

Time domain modelling and stability analysis of an integral pulse frequency modulated DC to DC power converter

Abstract: Using state variable representation a nonlinear, discrete-time system is derived that models the converter exactly. This system is linearized about its steady state solution, and converter stability, transient response and audio susceptibility are studied. The steady state solution of the converter is stable if and only if all the roots of the linearized system are absolutely less than unity. Excellent agreement with laboratory test data has been observed.

Injection-induced modulation of laser light by the interaction of laser diodes

Abstract: The experimental investigation of laser-light modulation by injecting laser light of a frequency, which is slightly different from the cavity resonant frequency, into a laser-diode cavity is reported. For this investigation, the interaction of two laser diodes was used and the relation between the oscillation frequency spectra and the lasing frequency difference of the two diodes was measured where the frequency difference was greater than the locking frequency range. The sidebands generated by the injection of laser light were measured to judge an appearance of the injection-induced modulation of light intensity. Modulation in the frequencies from 10 to 90 GHz was achieved by using laser diodes of 60-130-\mu m length. It was experimentally shown that the upper frequency limit of the injection-induced modulation was related to the Q value of the laser-diode cavity.

Limitation on the efficiency of frequency doublers of picosecond light pulses

Abstract: A theoretical analysis is made of the influence of the phase modulation of the fundamental-frequency radiation on the second-harmonic generation. The phase modulation must be allowed for in the calculations of the field intensities from known values of the energy of a pulse and the width of its frequency spectrum. Moreover, in the case of a mismatch between the group velocities the phase modulation results in deviation from the optimal phase relationships (loss of the coherence of the interaction between pulses) and then the harmonic energy is pumped back to the fundamental-frequency radiation. This mechanism imposes basic limitations on the doubler efficiency. The results are given of numerical calculations of the excitation of the second harmonic of Gaussian pulses with a linear variation of the instantaneous frequency; the width of the frequency spectrum and the peak amplitude are fixed in one series of calculations and the energy in another series.

VLF radio position location system

Abstract: A low frequency radio position location system for aircraft or other vehicles for operating in conjunction with ground stations transmitting at a first VLF radio frequency which is shifted in frequency by a small amount to a second frequency at fixed intervals with the shifting being carried out coherently with a defined transition point at the frequency signal is made up of an RF receiver and amplifier, a phase-locked loop for providing a continuous output frequency signal precisely locked to the first frequency, a detector for deriving a signal at the modulation frequency, a phase comparator for comparing the phase relationship of the derived modulation frequency signal to the phase relationship of the output frequency signal and the second frequency signal. The derived modulation frequency signal and its phase information is then available for providing distance and position information in relation to the ground stations.

Frequency control circuits such as for use in modulation measurement

Abstract: A circuit responsive to an input signal having an unspecified frequency for converting it to a predetermined and constant means frequency, and particularly suitable for incorporation in a modulation measuring instrument, comprises a sampling mixer controlled by a variable frequency oscillator for sampling the input signal to produce an intermediate signal. The mean frequency of the intermediate signal is then compared with a reference representing a predetermined frequency value whereby to produce an error signal, and means responsive to the error signal adjusts the frequency of the oscillator in such a direction as to tend to hold the mean value of the frequency of the intermediate signal at the predetermined frequency value while preserving therein variations in amplitude and/or frequency due to amplitude and/or frequency modulation.

Methods and apparatus for speed-control of induction motors

Abstract: A method of energizing a single-, three-, or poly-phase A.C. motor for continuously-variable speed control from a fixed-frequency supply of corresponding phase. Each phase is modulated by a continuously-variable modulation wave of sub-supply frequency to provide two continuously-variable sideband frequencies, either of which can be used to supply the motor. The modulation wave is sampled in each cycle of the A.C. supply and a full-wave rectified resultant modulation wave compared with a cosine wave of supply frequency. Each phase is gated by solid-state switch means for current flow from amplitude equality to next-following cosine zero. Optionally, secondary modulation, by a square wave of supply frequency, is used.

Arrangement for compensating duty factor variations in an optical video disc

Abstract: Processing optical video discs may result in modulation of the duty factor of the pits and lands which constitute a spatial representation of a stored carrier signal frequency modulated with program information. Such modulation of duty factor introduces spurious components that are detrimental to image reproduction if the frequency of the stored carrier signal is not at least twice the highest video frequency component to be reproduced. A correction signal is developed and used to at least partially cancel the effect of such spurious components.

Signal identification system

Abstract: A signal identification system, in which a signal of a specified frequency included in an analog signal indicated by an input pulse train converted from the analog signal is detected from the pulse train. The input pulse train is multiplied by two reference wave pulse trains having peak valves following the signal of the specified frequency but displaced by π/2 in phase from each other, respectively. The results of the multiplications are separately accumulated. The signal of the specified frequency is identified by utilizing a fact that the absolute value of at least one of the accumulated values exceeds a predetermined threshold value in the range of a permissible frequency deviation of the signal of the specified frequency and in the range of its permissible level fluctuation. The decision of the above fact may be performed when the accumulation is achieved at a certain number of times, which is predetermined in view of a permissible frequency deviation and a permissible level fluctuation of the signal of the specified frequency.

The Frequency Modulation Spectrum of an Exponential Voltage-Controlled Oscillator

Abstract: As the amplitude of a modulating voltage to an exponential VCO is increased, the pitch of the modulated signal rises, making dynamic depth FM unrealistic. The pitch rise is proportional to /o, the first of the modified Bessel functions. Higher order terms involving additional modified Bessel functions can be used to compute the entire spectrum. Various methods of correcting for the pitch shift are possible, but the most useful solution to the dynamic depth FM problem with exponential VCO's is to add some form of auxiliary linear control.

Theoretical limitations and extensions of a modulation technique for lineshape analysis

Abstract: The technique of differentiation by modulating the independent variable of an experimental signal and its application to increasing the accuracy of experimental measurements has been studied via a computer simulation. The modulation derivative (the approximate derivative obtained using this method) has been found to be accurate to 1% or better when the amplitude of modulation is 5% or less of the full width of the transfer function. The dependence of the width and amplitude of the first and second modulation derivatives upon the amplitude of modulation has been studied, and methods have been found for ascertaining the width of the transfer function and its first derivative without using the small amplitudes of modulation usually necessary. The approach described is general and is applicable to any experiment where the modulation technique can be utilized.

Stability of single sign integral pulse frequency modulation control systems

Abstract: Developed herein are detailed mathematical expressions for the stability analysis of single sign integral pulse frequency modulation (SSIPFM) control systems by the dual input describing function (DIDF). The necessary conditions, the d.c. condition and the a.c. condition, for producing limit cycle oscillations in the system, under zero or step inputs, are presented. This work suggests that for such a system it is more efficient to use the DIDF than the DF (describing function) method. The advantages of using this particular method in studying the stability of certain neurophysiological control systems is emphasized.

Optical frequency modulation demodulator

Abstract: A laser beam frequency modulation demodulator is disclosed utilizing the highly linear frequency versus voltage characteristic of the absorption resonance provided by a Stark-effect cell. An error signal, generated by dither modulation of the Stark-effect cell voltage, is fed back to the Stark-effect cell via a low-pass filter to cause the absorption resonance to track the instantaneous frequency of the laser beam. The feedback signal applied to the Stark-effect cell has an amplitude proportional to the frequency modulation on the laser beam.

Introducing threshold modulation in Bayly's integral pulse frequency modulation in the neuron

Abstract: Bayly's model of integral pulse frequency modulation in the neuron is considered to have more possibilities than the original paper pointed out. Threshold modulation in it is introduced and discussed.

Method and apparatus for determining AM modulation factor

Abstract: The modulation factor for an AM signal wherein the modulation signal is an A. C. wave is determined by demodulating the AM signal, obtaining the average D. C. level and peak deviation therefrom for the demodulated signal and then dividing the latter by the former.

Frequency modulation transfer system and method

Abstract: A system for transferring operation of a mechanism from one control signal to another control signal utilizing frequency modulation is disclosed. A rate multiplier generates pulses at an increasing frequency during a first portion of the transfer period up to a predetermined maximum frequency; and controlled to generate pulses at a decreasing frequency during the final portion of the transfer period. During the first portion of the transfer period, the peak and base of each pulse, corresponds to the value of the one and the other signal, respectively. During the final portion of the transfer period, the peak and base of the pulses are reversed to correspond to the opposite control signals. A filter averages the peaks and bases of the applied pulses during both portions of the transfer period to change gradually the average signal from the one control signal to the other.

A Nonlinear Modulator Using Delta Modulation Principles

Abstract: A delta modulator in which the clock is replaced by voltage sources and the comparator is modified to have some controlled hysteresis is shown to behave like a relay-mode multivibrator whose "on" and " off" periods are functions of input voltages. Both approximate and exact analysis of the circuit are included. Under different input conditions, the circuit behaves as an A//D converter or square law or linear frequency modulator and a reconstruction filter.

Signal-to-noise ratio improvement of analog pulse-position modulation over analog intensity modulation in optical communication links*

Abstract: This paper presents a comparison of the performance of optical communication links employing analog pulse-position modulation and analog intensity modulation. In particular, the theoretical output signal-to-noise ratios for the two types of modulation are compared assuming "equivalent" optical links. Analog pulse-position modulation offers signal-to-noise ratio improvement over intensity modulation at the expense of increased system complexity and expanded transmission band-width. The effect of timing errors on the signal-to-noise ratio of the pulse-position modulation receiver is considered, and it is shown that these errors can degrade performance significantly from theoretical .© (1975) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new look at unstable resonators

Abstract: gated using a scanning Fabry-Perot interferometer. The data consisted of multiple scans of a single Fabry-Perot fringe which were photographically recorded over various exposure times. The frequency variations exhibited by these multiple traces indicate that over a period of 1 sec, long term frequency stabilities of better than 3 parts in 10’ are achievable with a relatively straight forward resonator design. Similar data obtained over shorter time durations indicated an approximate inverse square root dependence upon the observation time. For times shorter than 100 msec, the frequency stability was less than 1 part in 10’ and could not be resolved by the present scanning FabryPerot technique. I The frequency spectrum produced by heterodyning two identical H F mixing lasers, both operating on P,-1 (6) , was displayed on a low frequency spectrumaqalyzer. Thedataindicated that the frequency stability of the present device is predominantly limited by the low frequency disturbances coupled to the mechanical resonator structure from the environment and not by the mixing within resonator medium. Consequently, significantly better frequency stability should be attainable by further sophistication of the resonator’s mechanical properties before the influence of the active medium imposes limitations upon the device’s performance. To evaluate the suitability of these chemical lasers for applications such as laser communications, where frequency and amplitude stability is required over very long time periods, active stabilization techniques wereinvestigated. A particularly attractive technique which was developed is that of locking the HF laser output to the minimum of the Lamb dip by using active dither stabilization. The laser cavity was tuned in frequency such that the dither was symmetrically applied about the minimum of the Lamb dip which was located at the center of the 300 MHz Doppler broadened gain curve. A comparison of the open and close loop performance of the chemical laser was made. In the open loop mode when the cavity length was changed due to thermal or mechanical influences, substantial variations in both the intensity and frequency of the laser were observed. However, when the laser was actively locked to the Lamb dip by means of an electronic servo system, the laser intensity and frequency remained constant within the limits associated with the dither stabilization over periods in excess of an hour and for a wide range of conditions. Data will also be presented comparing the performance of a premixed, CW electricallyinitiated, chemical laser* with that of the chemical mixing laser and the suitability of these CW chemical lasers as frequency-stable local oscillators for mid-IR heterodyne applications will be discussed.

A.M. carrier transmission method - uses signals which are modulated on bunched signal channels and transmitted through optical fibres

Abstract: Pulse frequency modulation is used for transmission of analogue signals. A voltage controlled oscillator is used in the transmitter which has limited output amplitude, and which is connected to the light producing device at the end of the glass fibre line. The pulse frequency modulated signal is reconverted by the light receiver and is applied to a phase controlled loop consisting of connected in cascade phase shifter, low-pass filter and a voltage controlled oscillator. The pulse frequency modulated signal is applied to one input of a phase comparator and the voltage controlled oscillator output is applied to its other input; the low-pass filter output signal is the demodulated frequency modulated signal.

The power spectrum of an FSK signal due to fast random jitter in the carrier frequency

Abstract: A mathematical expression is derived for the power spectrum of an FSK signal in the presence of fast random variations in the carrier frequency. Several curves are drawn to illustrate this effect for different modulation indices, when the modulating signal is a penny-toss square wave.

Elimination of extraneous modulation from VHF omnirange receiver

Abstract: A VHF omnirange receiver subject to extraneous amplitude modulation of the carrier close to the frequency of a variable phase VOR modulation signal with a subcarrier frequency modulated by a fixed phase signal at the frequency of the variable phase signal is adapted for elimination of the effect of the extraneous modulation. Amplitude modulation of the subcarrier is detected and amplified with phase reversal with amplification in an amount equal to the ratio of the carrier amplitude to the subcarrier amplitude to produce a cancellation signal. The cancellation signal is added to the composite received signal to eliminate the effects of unwanted modulation at the frequency on the carrier.

Novel analytic technique for obtaining the spectrum associated with piecewise-linear frequency modulation

Abstract: A new analytic method is presented for determining the frequency spectra associated with frequency-modulated waves. A piecewise-linear approximation to the modulation is used, the spectra being calculated for each piece. The sum of these spectra gives the total spectrum for the modulated signal.