Showing papers on "Pulse-frequency modulation published in 1970"

Direct modulation of semiconductor lasers

Abstract: Methods for direct modulation of semiconductor lasers are reviewed with the objective of indicating the advantages and limitations of each method. Techniques for producing amplitude, pulse, and frequency modulation of the optical wave are included. The modulation capabilities of present pulsed lasers are analyzed with special attention given to their operation at room temperature. In addition, several ways of producing analog position or width modulation of microwave-rate optical pulses are described, and the capabilities of optical frequency modulation by acoustic waves are reviewed. A new way of obtaining mode-locked optical pulses with a semiconductor laser is also suggested.

Use of plasma tube impedance variations to frequency stabilize a CO 2 laser

Abstract: A method for stabilizing the frequency of a single- J - value CO 2 laser to the center of its output power versus frequency curve based upon the variation of the impedance of the plasma tube with the optical power extracted is described. Frequency modulation of the laser produces an ac component of voltage drop across the plasma tube, which is synchronously detected to generate a frequency-error signal.

Generator for producing ultrasonic oscillations

Abstract: An ultrasonic generator with means for automatically adjusting the oscillation frequency to provide maximum power to the load. The generator includes a DC-AC converter operating into a resonant circuit that is coupled to the transducer. The converter includes first and second switching devices alternately switched by the frequency modulated output of a frequency controllable oscillator. The modulation frequency is derived across a resistor in the converter circuit and is compared with the modulation frequency in a phase detector to produce a control signal whose polarity is determined by the phase relationship of the compared signals. This control signal controls the oscillator to a frequency at which the transducer delivers maximum power to a load.

Improved a-d/d-a converter system

Abstract: A system for transmitting digital representations of analog signals which increases resolution without a corresponding increase in the number of bits in the digital data which is transmitted. In one embodiment, the analog input signal is applied to a level change circuit and summed with a square wave having peak-to-peak voltage equal to one-half the magnitude of the value of the least significant bit of the digital representation. The square wave pattern output of the level change circuit is applied to an analog-to-digital converter and the digital output is transmitted to a digital-to-analog converter. The output of the digital-to-analog converter is filtered to provide the analog output signal. During the time that the square wave pattern crosses an analog-to-digital converter threshold value, the resultant digital-to-analog output is a square wave with an average value between the normal discrete analog output levels. This results in twice as many levels at the analog output which is equivalent to the addition of one bit of resolution.

Proposed method for measuring picosecond pulsewidths and pulse shapes in CW mode-locked lasers

Abstract: A new method is proposed for measuring the widths, and possibly even the detailed shapes, of picosecond pulses in CW mode-locked lasers. The pulses are passed through an electro-optic modulator, which is biased for zero transmission with zero applied voltage, and which is driven at a harmonic of the pulse-repetition frequency. The variation in average light transmission through the modulator is monitored while the relative phase between the light pulses and the modulator drive is varied. The pulsewidth may be deduced from one such measurement made at a microwave light-modulation frequency sufficiently high that the pulsewidth is a finite fraction of a period at the modulation frequency. By making such measurements at a number of harmonics, the complete Fourier expansion (including both amplitudes and phases) of the picosecond pulse envelope can, at least in principle, be determined without ambiguity.

The Digital Echo Modulation

Abstract: A new technique for the transmission of binary data over band-limited channels is described. The signaling method is a generalization of Nyquist's telegraph theory, it allows pulse modulation without intersymbol interference within a frequency spectrum centered at any multiple of one quarter of the signaling rate. The signals are derived from pulse trains generated by a combination of logic circuits and weighting resistors. The number of pulses constituting a signal element varies typically from 5 to 9 in function of the desired total bandwidth. Signaling at 80 percent of the Nyquist rate has been easily achieved with 40-dB out-of-band attenuation. The digital echo modulation eliminates the need for precise analog filters and minimizes the effects of component instability; in addition, it gives a great flexibility to the design, allowing special features such as efficient half-speed operation.

Frequency modulation system for transmitting binary information

Abstract: A system for transmitting binary information in the form of a frequency modulated signal is provided The system includes a digital to analog converter for converting a series of input pulses into an output signal consisting of a series of incremental voltage changes which is approximately in the form of a sine wave having a frequency determined by the frequency of the input pulses The system also includes a frequency selecting circuit for controlling the frequency of the input pulses to the digital to analog converter The frequency selecting circuit is operated by a binary input signal and controls the frequency of the output signal produced by the digital to analog converter A filter is connected to the output of the digital to analog converter to eliminate discontinuities from the output signal of the converter

Apparatus for controlling pulse width modulation of inverter circuits

Abstract: The invention comprises apparatus for providing pulse width modulation suitable to single pole, or half bridge, inverter circuits employing electronic switches wherein a comparator circuit responds to a constant magnitude sawtooth input voltage signal and a variable AC square wave input voltage signal by generating inverter switch pulses when the magnitude of the sawtooth voltage and the magnitude of the AC square wave voltage are equal. The magnitude of the square wave voltage determines the degree of inverter pulse width modulation employed and the firing angle of the inverter switches.

Apparent Depth of Modulation as a Function of Frequency and Amplitude of Temporal Modulations of Luminance

Abstract: White light was temporally modulated and subjects gave magnitude estimations of the apparent depth of modulation. Three stimulus parameters were varied: level of time-average luminance, amplitude of modulation, and frequency of modulation. At the lowest luminances, apparent depth of modulation decreased monotonically as modulation frequency increased toward fusion. At the higher luminances, only large amplitudes of modulation produced monotonic functions relating apparent depth of modulation to frequency; smaller amplitudes of modulation produced nonmonotonic functions with maxima in the region of 5–10 Hz. Derived contours relating modulation amplitude to frequency for constant apparent depth of modulation generally resemble functions relating modulation amplitude to frequency for threshold.

Power Amplification for FM and PM Signals with Synchronized IMPATT Oscillators

Abstract: To meet certain requirements for system performance such as broadening the bandwidth, obtaining a high gain for the FM-and PM-signal amplifier, and increasing the power output, the "locking amplifier" composed of cascade-connected and hybrid-combined synchronizing oscillators is described. How the SNR of the amplifier is greatly improved and its gain increased by cascade connection and hybrid combination is discussed. These have been ascertained by experiments. In addition, another broad-band and high-gain synchronizing circuit and its application to pulse code modulation-phase modulation (PCM-PM) signal amplification are also discussed.

A Modulation Scheme for Powder ENDOR

Abstract: The combination of amplitude modulation of the nuclear rf power at a frequency f1 and 180° modulation of the phase of the resonance microwave signal with respect to the reference microwave signal at a frequency f2, where f1≫f2, with successive amplification and phase sensitive detection at the two frequencies, has proved useful in electron‐nuclear double resonance (ENDOR) of unordered solids. The alternative of amplitude modulation alone often results in poor baseline stability, and the alternative of amplitude modulation plus magnetic field modulation results in the complication of summing in an uncontrolled manner ENDOR contributions from crystallites resonating at different fields and with different orientations with respect to the applied dc magnetic field.

Frequency stabilized laser

Abstract: Single frequency laser oscillation is realized by including within the laser cavity a resonant etalon, tuned to the desired laser frequency. This has the effect of suppressing all other modes while permitting the laser to oscillate at the desired single frequency. In addition, the etalon tuning is frequency modulated about the desired frequency, producing an amplitude modulation of the laser signal. The amplitude modulation thus produced is sensed by a phase detector which generates an error signal whenever the laser frequency tends to deviate from the mean, etalon frequency. The error signal is used, in turn, to retune the laser cavity. It is an advantage of the present arrangement that spurious frequency modulation of the laser frequency, introduced by the stabilization system, is substantially less than that produced by comparable prior art stabilization circuits. Furthermore, such modulation can be conveniently reduced, or eliminated, by the addition of a dummy etalon driven in antiphase to the active etalon.

Converter from delta modulation to pulse code modulation

Abstract: A system for the conversion of a delta modulation ( Delta M) signal into a pulse code modulation (PCM) signal and vice versa. The system for the conversion of a Delta M modulation signal into a PCM modulation signal comprises: register means for storing an input signal consisting of n binary digits generated by a Delta M modulator during a time period corresponding to a normal PCM modulation sampling period Ti, each binary digit representing a positive or negative Delta M modulation quantization step of a quantized signal; means for effecting the algebraic sum of the positive and negative quantization steps to obtain the increase or decrease of the quantized signal during the sampling period; means for multiplying the algebraic sum by a constant K representing the ratio of the value of a Delta M modulation quantization step over the value of a PCM modulation quantization step to obtain a binary signal representing the increase or decrease of the quantized signal in pulse code modulation quantization steps; and means for adding the binary signal obtained by the above multiplication to the binary signal obtained during the sampling period Ti 1 to obtain a binary output signal corresponding to the required pulse code modulation signal.

Measuring system for comparing the relative magnitudes of first and second d.c. signals

Abstract: A Measuring system for comparing the relative magnitudes of a first and a second D.C. input signal by symmetrically integrating the first input signal between time period intervals proportional to its magnitude relative to the magnitude of the second input signal so that pulses are generated at a frequency which is a multiple of the integrating cycle. The variable frequency pulses are either counted directly or are converted to a frequency variable train of voltage pulses, each of the pulse cycles of the train of pulses having the corresponding periodicity of the variable input frequency and each voltage pulse having a substantially constant pulse width; the train of pulses are used to modulate a voltage source output signal which, when subsequently averaged, provides an output signal that is proportional to the product of the modulated output signal of the voltage source and the input frequency.

A holographic pulse compression technique employing amplitude modulation

Abstract: This letter discusses a pulse compression technique suggested earlier by Tuttle which modulates the amplitude of a long duration pulse instead of its frequency (as in the "chirp" process). The modulation code is that of a zone plate; the echoes are recorded photographically, and then reconstructed optically, as in side-looking radar, thereby circumventing the need for the complicated matched filters of the chirp process.

Transmission device for the transmission of analog signals by means of pulse code modulation

Abstract: A transmission device for the transmission of analog signals by means of pulse code modulation, particularly in time-division multiplex systems wherein for the purpose of generating the PCM signals the analog signals are applied through a duration modulating device to a counter controlled by clock pulses. In order to reduce the counting speed and the dynamic range of the comparator the duration modulating device is provided with two integrating networks having mutually greatly different time constants for pulse-duration modulation in accordance with four different slopes, each integrating network being connected to a counter controlled by clock pulses which counters provide the pulses of the greatest weight and of the smallest weight, respectively, of the code group characterized by the analog signal.

Signal Transduction with Differential Pulse Width Modulation

Abstract: The Differential Pulse Width Modulation System presented here is a signal transduction scheme applicable to a wide range of data acquisition processes for either large systems such as industrial process control, aircraft flight testing, computerized medical information centers, etc. or individual users seeking low cost, compact measuring instruments. In this scheme, a variable capacitance or equivalent sensor, actuated by the physical quantities to be measured, is combined with an integrated circuit containing mainly logic elements, to generate a series of pulses with fixed height in voltage but varying width in time so that the difference/sum ratio of the width between two adjacent pulses is proportional to the input. Signals thus modulated can be converted readily into analog output by simple low-pass filtering and can also control a simple up-down counter to give digital output, bypassing the conventional analog-digital converter. For portable recording, this differential pulse width scheme facilitates the use of inexpensive tape recorders at no sacrifice in accuracy, since there is no need for precision speed control.

Locking of spontaneously pulsing CW GaAs injection lasers by fractional-harmonic current modulation

Abstract: The effect of injection modulation on CW GaAs junction lasers undergoing coupled mode pulsations at microwave rates is studied. Two types of behavior are observed depending on the values of the power and frequency of the modulating signal: either fractional-harmonic locking to the modulating signal or pulse repetition rate modulation.

The Performance of a PPM/PM Hybrid Modulation System

Abstract: This correspondence applies a new bounding technique to a modulation system described in [1]. The new bound gives tighter location of threshold level. The variation of the bound with the degree of phase modulation indicates that a hybrid system gives improved performance for all signal-to-noise ratios.

Spectrum Conservation and Characteristics of Single-Sideband Phase Modulation

Abstract: Phase modulation with an analytic signal, which is a Gaussian random process, is examined in order to determine the amount of spectrum conservation that may be achieved by using single-sideband phase modulation (SSB-PM) rather than conventional phase modulation (PM). The autocorrelation function is derived and found to be an analytic signal in terms of the autocorrelation function of the actual modulating signal and its Hilbert transform. When the modulating signal strength is very low, the sideband spectral distribution is the same as that of the actual modulating signal or single-sideband amplitude modulation. As the modulating signal mean-square value is increased, the sideband spectrum broadens and approaches a Gaussian shape. The average power output of an SSB-PM system increases exponentially with input modulating signal strength, while the carrier power remains constant. For the same modulating signal mean-square value, a greater fraction of power is in the one sideband of an SSB-PM system than in the two sidebands of conventional PM. Single-sideband phase or frequency modulation always effectuates spectrum conservation in the continuum when it is compared with conventional phase or frequency modulation on the basis of equal relative sideband power. A Fourier transform computer program is used to generate SSB-PM spectral distributions with varying modulating signal mean-square values, when the modulating signal spectrum is a low-pass rectangular spectrum, a narrowband pass spectrum, and the shape of an average voice spectrum. These examples illustrate the power series formulation of the output spectrum as well as the theoretical analysis of bandwidth.

Frequency Measurement Errors of Passive Resonators Caused by Frequency-Modulated Exciting Signals

Abstract: The condition of resonance for a signal with FM is defined in this paper as the condition of maximum power transfer by the resonant device It is shown that if the width of the signal spectrum is small compared to the resonator's linewidth, then the frequency error is proportional to the third moment of the instantaneous signal frequency about its mean One expects that this treatment should, at least, give the leading term for a precise treatment of atomic resonances Experimental results with a cesium beam frequency standard confirm this expectation and add caution to the idea that higher Q atomic resonances make better absolute frequency standards

Interférence et modulation spectrale

Abstract: It has been shown by Mandel that the spectral density shows a cosine modulation with relative amplitude 2(Ī1 Ī2)1/2γ12(0)/(Ī1 + Ī2) when the optical path difference is much longer than the coherence length in a quite general superposition experiment of two quasi-monochromatic, polarized, and partially coherent beams of light. It is shown here that this is equally true for path differences smaller or equal to the coherence length. This conclusion is reached by considering the properly defined visibility of the modulation of the spectral density. Both aspects of the modulation of the spectral density are considered: modulation as a function of path difference for a fixed frequency ν0 and modulation as a function of frequency for a fixed path difference cT0.

Digital frequency modulator

Abstract: Two pulse trains with harmonically related repetition frequencies 1/To, 1/nTo are derived from an original square wave of cadence 2/To, the pulses of each train having the width To/4 of the square-wave pulses. With the aid of a second square wave of cadence To, produced by frequency halving from the original square wave, the two harmonically related pulse trains are additively or subtractively combined so as to produce an irregular pulse sequence with n + OR - 1 pulses in each period nTo of the lower-frequency train. A digital pulse counter derives from this irregular pulse sequency a low-frequency square wave converted, by filtration, into its fundamental sine wave whose frequency can thus be selectively varied, with only minor phase discontinuities, between three predetermined values related to one another as (n+1) : n : (n-1). In an alternative embodiment, the keying frequencies are related to the basic frequency as (2n+1) : 2n : (2n-1). The two pulse trains are generated by progressive frequency division, starting with the original square wave, and selective gating.

Air Damped Capacitance Accelerometers and Velocimeters

Abstract: This is a companion paper serving as an extension of an earlier presentation entitled ``Signal Transduction With Differential Pulse Width Modulation''1. In that paper, a scheme was introduced to streamline the data acquisition system bridging a variety of physical parameters to be measured with several forms of signal processing. The essential part of that scheme involves the generation of a differential pulse width modulated signal with integrated logic circuits utilizing d. c. excitation to produce analog output with significant power, a pulse width modulated signal suitable for transmission or tape recording, or a digital output suitable for computer coupling.

High-speed phase and amplitude modulation of Gunn oscillators

Abstract: Linear phase and amplitude modulation of X band Gunn oscillators up to 3 GHz modulating rates has been observed. The modulating signal was applied through the bias circuit, and typical sensitivities were 0.1 rad/V and 10% depth of modulation/volt, respectively. A simple theoretical explanation of the results is given.

Amplitude Modulation of Microwaves Propagated Through a Periodically Varying Plasma

Abstract: A theory has been developed for the amplitude modulation of microwave signals propagated through a plasma created by an amplitude modulated RF field by taking into account the variations in the electron density and the electron molecule collision frequency of the plasma due to the modulation of the electron temperature. Experimental studies have verified the predicted dependence of the microwave modulation index on the modulation frequency, the exciting field strength, and the carrier modulation index. Slight deviations have been found between the experimental and theoretical values at both very low and very high modulation frequencies. The dependence of the RF conductivity on the exciting field has been suggested as the probable cause for the departures of the experimental values from the theoretical ones.

Method of controlling a polyphase inverter

Abstract: A method of controlling a polyphase inverter intended to supply a polyphase voltage whose frequency and amplitude must be variable independently. A sine wave of fixed frequency is generated and is sampled at a succession of instants at a frequency close to that of the sine wave. From this sampling is obtained a train of width-modulated pulses whose width corresponds to the amplitude of the sine wave at the successive sampling instants. Any variation in frequency of the sampling results in a corresponding variation in frequency of the pulse train and any variation in amplitude of the sine wave correspondingly affects the width of the pulses. As many such pulse trains as there are phases are produced and the leading and trailing edges of the pulses, which are independently variable by virtue of the sampling frequency and the amplitude of the sine wave being independent, are used to control the firing and extinction of rectifier elements in the inverter.

Output power spectral densities for unipolar pulse frequency modulation with white noise input

Abstract: Analysis of pulse-frequency-modulation (PFM) systems has already been carried out for the case of white Gaussian noise input and a resulting output consisting of a train of randomly-spaced unit impulses whose polarity was equally likely to be positive or negative This note extends the analysis by deriving power spectral densities when the output impulse train is unipolar System parameters are chosen to facilitate comparison with the earlier results