Showing papers on "Pulse-frequency modulation published in 1977"

Dynamic properties of Renshaw cells: Frequency response characteristics

Abstract: The dynamic properties of Renshaw cells located in the lumbar spinal cord of intercollicular decerebrate cats were measured. The responses of these interneurones were recorded extracellularly, while the ventral root was stimulated with sinusoidally frequency-modulated trains of electrical pulses. The frequency of the Renshaw cell discharges resulting from such stimulation varied sinusoidally. The amplitude of modulation about the average (or "carrier") rate of discharge exhibited a linear dependence on the modulation amplitude of the stimulus pulse train. Renshaw cells were able to follow modulated stimulus trains in the entire range of modulation frequencies (0.2 to 80 Hz) encompassed by the present study. Above modulation frequencies between 20 and 50 Hz, the amplitude of modulation of the responses declined. Frequency responses measured at low average frequencies of the stimulus pulse train (centre frequencies 30 and 40 Hz) showed comparatively little dependence on modulation frequency. The higher the centre frequency, however, the greater was the enhancement of the modulation amplitudes at high modulation frequencies compared with those observed at low modulation frequencies. Some aspects of the functional implications of these results are considered and an approximate formula for the transfer function of Renshaw cells is presented.

Optical Pulse Position Modulation with Multiple Positions per Pulsewidth

Abstract: This concise paper determines the required laser power to achieve a given probability of bit error using a pulse-interval modulation (PIM) (discrete pulse position modulation) system with resolution much smaller than a laser pulsewidth. An approximation to the first crossing density for a threshold detector operating on a filtered Poisson process is used. Both analytic and computer simulation results are presented.

Frequency stabilization utilizing multiple modulation

Abstract: A system and method is disclosed for achieving frequency stabilization. A tunable element, such as a cavity structure, is stabilized through the use of multiple modulation to stabilize both the resonant frequency of the cavity structure and the probe signal coupled to an atomic, molecular or other reference resonance line. Said reference resonance line can be internal or external to the cavity structure. A local oscillator provides a carrier signal, which typically can be at a frequency of 5 MHz, with the carrier signal being phase or frequency modulated by multiple modulating signals, such as, for example, by modulating signals with frequencies of 12.2 KHz and 0.4 Hz, and the multiple modulated carrier signal then processed and the resulting probe signal coupled to the cavity structure substantially at a preselected frequency, which frequency can be approximately 1420 MHz for a hydrogen frequency standard useful for atomic clocks. The output signal coupled from the cavity structure is amplitude modulated with the modulation at the fundamental and odd harmonics of the first modulation frequency having a level proportional to any frequency offset between the probe signal and the atomic, molecular or other reference resonance line, and the modulation at the fundamental and odd harmonics of the second modulation frequency having a level proportional to any frequency offset between the cavity frequency and the frequency of the probe signal. The output signal from the cavity is processed and ultimately rectified so that various amplitude modulations on the output signal can be recovered. The error signal resulting from synchronous detection of the amplitude modulation signal of the second frequency, 12.2 KHz in this example, or odd harmonics thereof, is coupled to the tuning element of the cavity tuning control circuitry to precisely tune the resonant frequency of the cavity to the frequency of the probe signal and the error signal resulting from synchronous detection of the amplitude modulation signal of first frequency, 0.4 Hz in this example, or odd harmonics thereof, is coupled to the local oscillator to adjust the frequency so that the probe signal is maintained at the center of the resonance of the atomic, molecular or other reference resonance and to thereby stabilize the resonant frequency of the cavity and the output frequency of the device over a long term.

Radio frequency pulse width amplitude modulation system

Abstract: Amplitude modulation of a radio frequency carrier is achieved by generating a rectangular wave pulse train at the carrier frequency, the pulses of which vary in width as a function of the amplitude of the audio input signal. The audio frequency input wave is subjected to an arc sine conversion process prior to the generation of the rectangular wave pulse train. The radio frequency pulse width modulated wave is amplified and then filtered to pass the fundamental radio frequency voltage and its modulation side bands.

A Digital Method of Frequency Multiplication and Its Application to Numeric Spectrum Analysis of Periodic Signals

Abstract: A digital way to produce an integral multiple of the frequency of periodic trigger pulses is described. This procedure is used to generate the sampling pulses for the ADC of a time-series analyzer. The device which implements this method is called sampling frequency generator (SFG). A comparison is made between this digital method and the analog frequency multiplication method by means of a PLL.

Time delay modulator

Abstract: A time delay modulator is disclosed in which the instantaneous time base of a carrier signal is varied in accordance with a modulating signal. In one embodiment, modulation is achieved through the use of charge transfer delay lines and variable frequency clocks in which a carrier wave signal is applied to the input of the delay line and the carrier wave signal is propagated through the delay line at a rate determined by the output frequency of an oscillator which deviates from a nominal frequency by an amount proportionate to the magnitude of the modulating signal. In another embodiment, an analog-to-digital converter, a shift register and a digital-to-analog converter in serial configuration are each controlled by a voltage controlled oscillator. The carrier wave signal is connected to the input of the analog-to-digital converter and samples are taken in accordance with a clock input. Parallel digital output signals are applied to an N x M bit shift register, the output of which is applied to the digital-to-analog converter having a serial output. A modulating signal is applied to the voltage controlled oscillator which provides an output deviating from a nominal frequency by an amount proportional to the magnitude of the modulating signal.

Response of auditory‐nerve fibers to sinusoidal amplitude modulation

Abstract: Stimuli consisted of 300‐msec‐long tones at the CF of the unit under study. The tone bursts were amplitude modulated during their second 150 msec, and SPL was varied with percent modulation and modulation frequency held constant. Response firing rates were obtained from PST and period histograms synchronized to the tone bursts and modulating sinusoids respectively. The period histograms were approximately sinusoidal and response modulation was estimated from the amplitude of the fundamental component of the histogram waveform. When SPL was increased the average firing rate increased and then asymptotically approached saturation, while response modulation increased to a maximum and then decreased. The shape of the response modulation function could be predicted by taking increments along the average rate‐intensity function, suggesting that the same saturating nonlinearity limits responses to both constant and modulated stimuli. However, for some units the predicted modulation function had to be shifted as much as 7 dB towards higher intensities in order to match the measured responses. Hence an additional mechanism may be involved which produces a small shift in dynamic range.

Method for stabilizing the mean-frequency and modulation slope of a phase-keyed oscillator

Abstract: A method for stabilizing the mean-frequency and modulation slope of a frequency controlled oscillator used for generating PSK signals is disclosed. A control signal representative of the phase deviation between the PKS signal and a reference signal representative of the base frequency of the carrier signal is generated. The control signal is directly utilized to stabilize the mean-frequency of the PSK signal generated by the frequency controlled oscillator. After the control signal is inverted as a function of a data signal whose information is to be carried by the PSK signal, it is utilized to stabilize the modulation slope of the PSK signal.

Single-mode laser frequency modulation

Abstract: This paper presents an analysis of the frequency response of single-mode laser frequency modulation. The method employed is based on the combined concepts of an active Fabry-Perot interferometer and of internal phase modulation, and is very transparent. The calculation of the sideband amplitudes and phases of the laser output reveals two main regions of the frequency response: for modulating frequencies lower than the cavity mode spacing the laser generates an ideally frequency-modulated signal. At higher frequencies the sideband amplitude versus modulating frequency shows an oscillatory behavior. Here, the response is mainly determined by the cavity mode spacing frequency and by the position of the modulator within the cavity. Comparing the theoretical results with previously reported experiments, very good agreement was found.

Device for measuring the range of a moving target and the speed at which it approaches or recedes

Abstract: A radio range measuring apparatus having a controlled modulation slope in order to keep the beat frequency between the transmitted signal and the received signal constant. The apparatus also measures the speed at which a mobile target approaches or recedes by means of a generator of a fixed frequency which, after frequency division, maintains the duration between the start of two consecutive sawtooth modulation signals fixed. A particular spectral line of the beat signal is demodulated by this fixed frequency via a mixer whose output is filtered by a passband filter. The signal at the output of the filter has a frequency which is equal to the Doppler frequency, proportional to the speed.

Pulse-Frequency Modulation Applied to The Digital Control of a Thyristor

Abstract: An integral pulse-frequency modulator is employed for the direct digital control of a thyristor so that the dc component of the thyristor output is proportional to the numerical output of a digital computer. The modulator reference waveform is proportional to the thyristor anode supply voltage; the modulator output is a train of pulses whose time separation satisfies the condition for linear controller operation. The pulses are counted from the beginning of the positive half-cycle of the reference input; they are gated to the thyristor following detection of coincidence with the number supplied to the digital control input. Sensitivity of the pulse-frequency to disturbances in supply voltage and frequency is reduced by means of phase-lock techniques. The departure from linearity was found experimentally to be less than 1%, and is attributed to the forward saturation voltage drop of the thyristor.

Analog signal delay system and method

Abstract: An analog signal delay system is provided with a bucket-brigade charge transfer device controlled by a clock which supplies pulses at a predetermined frequency to sample an analog signal at its input and to effect a predetermined delay between the signal at the input and the corresponding signal at the output. Analog signals are impressed on the input of the system and are sampled at a pulse rate which may be one-half the frequency of the clock pulses. Periodic calibration or correction pulses are supplied to the brigade device during the intervals between the sampling pulses of the analog signal. One or more amplifiers are provided between the output of the brigade device and the output of the system. In order to correct for D.C. drift errors and gain variations which may result from temperature changes, the correction pulses are compared to a reference to generate error signals which are fed to control circuits to correct the D.C. level and gain. This effects the accurate reproduction of the delayed signals in the conformation of the corresponding input signals. The correction pulses are removed from the signal output of the system by gating techniques into an output capacitor.

A white-noise photostimulator by using a pulse frequency modulation method

Abstract: A photostimulator of which radiant power is controlled in the form of white-noise is described and examined in order to study the visual color system, and it has excellent linearity and spectral constancy. Glow modulator tubes (R1131C; Sylvania and L526; HTV) were examined for the purpose of being used for the light source. The spectral concentration of the tube was measured at different current levels of 10, 30 and 50 mA. It is shown that the spectral concentration was changed with the variation of the driving current. The current control method is usually used to control the radiant power, but had the above imperfection for the experiments of the color vision. Another method, the pulse frequency modulation (PFM) method was also tested. These two methods were compared at different levels of the radiant power for five colors. By the usage of the PFM method, linearity and spectral constancy were remarkably improved, and this method was used in a white-noise photostimulator. How the eye responds to the flickering light of the PFM method is explained, and an application to the study of the horizontal cell in the carp rentina is described.

Tuning meter for use with a pulse count FM demodulation circuit

Abstract: A tuning meter circuit for use with a pulse count FM demodulator of an FM receiver. The circuitry comprises a limiter circuit for amplitude limiting a frequency modulated input signal to produce a train of pulses the width of which varies in accordance with the frequency modulation of the input signal; a pulse shaping circuit for generating a trigger pulse for each of the pulses of the pulse train; a monostable multivibrator responsive to each trigger pulse for generating a train of pulses of substantially constant width, the number of which per unit time interval varies in accordance with the frequency modulation of the input signal; a low pass filter responsive to the last mentioned pulse train to produce a low frequency signal and thereby demodulate the frequency modulated signal; a difference amplifier also responsive to the last-mentioned pulse train, the difference amplifier having a threshold level at which it changes state; a tuning meter responsive to the direct current component of the output of the difference amplifier; the duty cycle of the monostable multivibrator and the threshold level of the difference amplifier being so related that the tuning indicator indicates the FM receiver is tuned correctly when a signal of exact intermediate frequency is applied to the limiter circuit; and where the monostable multivibrator includes means for varying the duty cycle thereof to compensate for undesired variations in the FM demodulator.

Electro-cochlear potentials elicited by sinusoidally modulated signals.

Abstract: Responses of the guinea pig cochlea to amplitude-modulated stimuli were measured with the aid of a gross electrode. The dynamic characteristics of this part of the auditory system was studied by varying several parameters of the applied signal. The signals used as carriers in our experiments were either white noise or pure tones of 1 and 4 kHz. The modulation frequency, dynamic and intensity characteristics were determined by varying the modulating frequency, the modulation depth and the intensity of the applied signal. To get an idea about possible non-linear aspects of the system under investigation, we always computed the Fourier transform of the response data and plotted the amplitude of the various harmonics and the phase of the fundamental separately as functions of the signal parameter in question. The greatest response was always found at a modulation frequency of about 200 Hz, with a relatively gradual rise up to this frequency and a sharper drop above 200 Hz. The phase of the fundamental changes...

Measured Backscatter Modulation from Linearly Oscillating Metal Disks

Abstract: : The work described in this report was carried out as part of the basic research program directed toward providing an understanding of the radar detection of agitated metals (RADAM). The report describes an experimental equipment and measurement procedure that permits determination of the kind and amount of modulation introduced onto the backscattered electromagnetic signal by a vibrating or oscillating scattering target. Although discussed specifically in terms of equipment realization at 10 GHz, the techniques are general. Provision has been included for determining characteristics of the mechanical motion and correlating mechanical and electromagnetic results in the time and frequency domain. The results of a series of measurements of modulated backscatter cross sections due to a disk executing small rigid translational oscillations show the modulation introduced to be all phase modulation; measured results are in good agreement with those calculated from a soundly-based theory. In addition, it is shown that the modulation amplitude is independent of modulation frequency, that the phase modulation introduced is directly proportional to the amplitude of the mechanical oscillation, and that the spectral components of the modulated signal are monotonically decreasing for simple sinusoidal motion.

A bipolar monolithic analog subsystem for a 4½ digit A/D converter

Abstract: A HIGHLY ACCURATE A/D convcrter has been required in data handling systems for a microprocessor and in digital multimeters. Responding to this recent demand, a CMOS monolithic structure has been widely employed in combination with the dual slope technique’ 7’. The CMOS process, however, places a limitation on the resolution of an A(D converter at 3% digits. In the dual slope technique, on the other hand, a feedback loop is constructed between the analog and the digital subsystems. This arrangement degrades the electrical isolation between the two systems.

Perceptual analysis of the amplitude envelope of AM signals

Abstract: The manner in which the auditory system encodes the “shape” of the amplitude envelope of AM signals was examined. On the basis of modulation frequency tuned channels previously demonstrated for FM signals [R. H. Kay and D. R. Matthews, J. Physiol. (Lond.) 225, 657–677 (1972)] it was thought the auditory system might be responding to the power spectrum of the amplitude envelope. A 500‐Hz carrier was amplitude modulated at 2, 4, or 8‐Hz with either a sine wave or square‐wave signal. The Method of Adjustment was used to determine the “modulation thresholds” for the 6 frequency by waveform conditions. At each of the modulation frequencies, subjects' thresholds were lower for square wave than for sine wave modulation. The mean ratio between the thresholds for the two wave forms was 1.32 with a SD of 0.22, which approximates 4/π (1.27) as would be predicted on the assumption that the auditory system performs a Fourier analysis on the amplitude envelope of the modulated 500‐Hz tone. Additional data suggest that ...

Versatile LDV burst simulator

Abstract: A device for generating burst signals that can be used to determine whether or not a laser doppler velocimeter is operating properly A high frequency signal which corresponds to the information frequency of the laser doppler velocimeter is modulated by a low frequency signal to provide an envelope for the high frequency signal The high frequency signal is modulated by the low frequency signal by any modulator means such as, for example, an analog multiplier The low frequency signal is added to the modulated signal to provide pedestals for the resulting series of burst pulses Then means are provided for selecting different combinations of these burst signals Also means are provided for making the burst signals asymmetrical as desired In addition, means are provided for varying the frequencies and amplitudes of the information, envelope and pedestal frequency signals in the burst signals

High-Rate Optically Isolated Analog Multiplexer Using Amplitude-to-Width Conversion

Abstract: The operating principle and the performances of a new type of isolated analog multiplexer are described. It has a maximum sampling rate of 80 kHz, 2.5-kV isolation, dc CMRR higher than 140 dB, linearity error lower than 0.6 percent, and thermal drift in the order of 100 ?V/°C. Each acquisition channel has a floating pulsewidth modulator driving an optoelectronic coupler. This last controls a generator which injects a reference current into the virtual ground of an integrator common to all the channels. The resulting output analog voltage is digitized by a fast ADC. The analog information through the optical couplers is carried by a pulse of fixed amplitude and variable width. This circumvents the linearity and stability limitations of optical isolators. The described multiplexer has been devoted to analog data logging in electricity generating plants. Its sampling rate and accuracy performances have been optimized in view of this particular application. The system is susceptible of a factor 10 increase in speed with a limited degradation of other characteristics.