Showing papers on "Pulse-frequency modulation published in 1987"

Potentials evoked by the sinusoidal modulation of the amplitude or frequency of a tone

Abstract: Steady state responses to the sinusoidal modulation of the amplitude or frequency of a tone were recorded from the human scalp. For both amplitude modulation (AM) and frequency modulation (FM), the responses were most consistent at modulation frequencies between 30 and 50 Hz. However, reliable responses could also be recorded at lower frequencies, particularly at 2-5 Hz for AM and at 3-7 Hz for FM. With increasing modulation depth at 40 Hz, both the AM and FM response increased in amplitude, but the AM response tended to saturate at large modulation depths. Neither response showed any significant change in phase with changes in modulation depth. Both responses increased in amplitude and decreased in phase delay with increasing intensity of the carrier tone, the FM response showing some saturation of amplitude at high intensities. Both responses could be recorded at modulation depths close to the subjective threshold for detecting the modulation and at intensities close to the subjective threshold for hearing the stimulus. The responses were variable but did not consistently adapt over periods of 10 min. The 40-Hz AM and FM responses appear to originate in the same generator, this generator being activated by separate auditory systems that detect changes in either amplitude or frequency.

Multielectrode distributed feedback laser for pure frequency modulation and chirping suppressed amplitude modulation

Abstract: A new concept for operation of distributed feedback lasers with multielectrodes is proposed and its capability for amplitude or frequency modulation is demonstrated. The device has electrically separated electrodes so that carrier density distribution along the laser cavity can be controlled artificially by adjusting the current distribution for each electrode. The lasing frequency can be controlled by changing the current ratio applied to the electrodes. Frequency modulation experiments disclose that neither frequency modulation efficiency nor phase delay depend on modulation frequency. It turned out that the frequency shift under modulation showed blue shift or red shift depending on bias current distribution and the position of the modulation applied electrode. Using these characteristics, chirping suppressed amplitude modulation and frequency modulation with constant output power are realized.

A versatile power converter for high frequency link systems

Abstract: The single-phase high frequency link appears to be an attractive alternative to the dc link commonly employed in power conversion systems. This paper proposes a power converter suitable for one-step conversion of the single-phase high frequency link voltage to the three-phase low frequency voltages typically required for interfacing with system sources and loads. The converter is utilizes zero voltage switching principles to minimize switching losses and uses an easy to implement technique of pulse density modulation for the control of the amplitude, frequency and the waveshape of the synthesized low frequency signals. Adaptation of the proposed topology for power conversion to single-phase ac and dc voltage or currents outputs is shown to be straight forward. The feasibility of the proposed power circuit and the control technique have been experimentally verified.

Self-amplitude-modulation of optical pulses in nonlinear dispersive fibers

Abstract: We consider propagation of optical pulses in the anomalous dispersive region of single-mode fibers after including the effects of Kerr-type nonlinearity. It is found that the pulse develops an internal structure with deep amplitude modulation. We show that this self-amplitude-modulation of pulses is related to the modulation instability of continuous-wave optical beams in nonlinear dispersive fibers. The initiation of this phenomenon does not require an external probe or spontaneous emission. Numerical results show that self-phase-modulation broadens the power spectrum enough to encompass the frequency at which self-amplitude-modulation provides the maximum gain. The amplification of these sidebands manifests as a breaking of the optical pulse into several subpulses. For negligible loss, the pulse breakup may also be viewed as the internal structure of a high-order soliton. However, modulation instability appears to provide a simpler interpretation and explains the features of numerical simulation and experiments.

Pulse width modulation for analog fiber-optic communications

Abstract: The pulse width modulation (PWM) technique has been revisited and analyzed to evaluate its merits for application to analog signal transmission in fiber-optic links. Fourier analysis of the PWM signal reveals that it can be used as a vehicle to launch an analog signal onto optical fiber when a symmetrical natural sampling process is used. The SNR of the modulated signal depends on the timing jitter of the carrier pulses and a wide-band (45 MHz) SNR of 45 dB has been obtained with a commercially available multimode laser transmitter. A linear dynamic range of over 50 dB has been experimentally demonstrated. The full fiber bandwidth can be utilized by using a very high pulse carrier frequency, while a more popular pulse frequency modulation technique provides about a 10-MHz analog signal bandwidth when 1 km of multimode fiber is used in conjunction with a short wavelength (0.87 μm) LED transmitter. Analog transmission capability was experimentally demonstrated by constructing a simple video link using common laboratory equipment. The performance of the video link supports the PWM modulation theory developed here and elsewhere. The experimental results indicated that PWM is potentially very attractive for low-cost broad-band local area network (LAN) application, including future highly interactive offices, hospitals, and automated factory floors.

Perception of amplitude and frequency modulated signals (mixed modulation)

Abstract: This article discusses the detection of mixed modulation, i.e., simultaneous amplitude and frequency modulation (MM). The investigations have incorporated both a sine wave modulating signal and an irregular modulating signal, a very narrow noise band, of a specified center frequency. The results revealed that for a sinusoidal low‐frequency modulating signal, amplitude and frequency changes that were separately subthreshold could be detected by listeners in mixed modulation. This indicates summation of sensations caused by simultaneous AM and FM modulation. This effect was not observed in the case of the irregular modulating signal. A hypothesis is advanced that the perception of modulated signals is governed by two mechanisms, viz., temporal and spectral. The operation of the two mechanisms depends mainly on the modulating frequency. The type of modulation does not play any significant role in this case.

Image processing apparatus in which the minimum and maximum widths of a pulse-width modulated signal can be independently adjusted in accordance with predetermined data signals

Abstract: An image processing apparatus includes a D/A converter for generating an analog image signal, a variable resistor for changing an output range of the analog image signal generated by the D/A converter, and a comparator for processing the analog image signal generated by the variable resistor by using an analog pattern signal and for outputting a pulse width modulated signal. The analog pattern signal may be a triangular wave signal, a saw-tooth wave signal, a sine wave signal, or a trapezoidal wave signal. In another version, selection is performed between predetermined data and a generated image signal and the selected signal is processed using an analog pattern signal (e.g., a triangle wave) to output a pulse width modulated signal. A D/A converter may be used to convert the output of the selection. The output range of the DAC may be variable.

Transmission of signals through analog channels using adaptive frequency modulation

Abstract: Improved effifiency of frequency-modulated (FM) transmission of signals through analog channels, i.e., achievement of a higher bandwidth and/or signal-to-noise ratio (SNR) in the received signal for a given channel bandwidth and channel carrier-to-noise ratio (CNR), is accomplished by adaptive adjustment of the modulation index in such a manner that the spectrum of the channel signal more nearly occupies the entire channel more of the time than it would otherwise. Data is transmitted, along with the signal, to enable the receiver to calculate the modulation index at each instant so that the signal can be properly demodulated. The invention has application to FM transmission of signals representing visual image or other information, such as sound, for which human perception of noise is greatest in areas of low amplitude and/or frequency and reduced in and immediately adjacent to areas of high amplitude and/or frequency.

Method of generating a tone signal

Abstract: A tone generation system and method generates tone signals having complex harmonic components while reducing aliasing noise resulting from sampling of high frequency harmonics. In a first step, waveshape data which has been sampled with a second sampling frequency which is higher than a first sampling frequency is obtained. Then a predetermined tone synthesis modulation operation is performed, using this waveshape data as at least one of a signal to be modulated and a modulating signal. By performing this modulation operation in accordance with the higher second sampling frequency, occurrence of an aliasing component contained in a tone signal obtained as the output of the modulation operation in a frequency band below a frequency which is 1/2 of the first sampling frequency can be prevented. Then, the frequency band of the output signal of the modulation operation is limited to a frequency band below the frequency which is 1/2 of the first sampling frequency. By this arrangement, even if an aliasing noise component concerning the second sampling frequency occurs in a frequency region which is higher than the frequency which is 1/2 of the first sampling frequency, such aliasing noise component will be eliminated. Lastly the output signal of the third step is resampled with the first sampling frequency. In this manner, in a tone signal generated in response to the resampled signal, an aliasing component concerning the first sampling frequency becomes higher than 1/2 of the first sampling frequency so that it does not appear as the aliasing noise.

Method and apparatus for selectively controlling an operation mode of a PWM inverter between an asychronous mode and a synchronous mode modulation

Abstract: A method and apparatus are disclosed for controlling a pulse width modulated (PWM) inverter controlled for ignition by a (PWM) pulse produced with a carrier wave and a modulation wave. The method comprises sampling an amplitude of the modulation wave at a cycle rate related to the frequency of the carrier wave. The modulation wave and the carrier wave are synchronized when the sample modulation wave amplitude has a peak value greater than an amplitude of the carrier wave. The modulation wave and the carrier wave are asynchronized when the sampled modulation wave has a peak value less than the amplitude of the carrier wave.

Methods and apparatus for analog to digital conversion

Abstract: An analog-digital converter includes a source of high frequency pulses comprising a variable frequency oscillator having an output frequency f which is a function of an analog condition. Also included is a source of a reference signal, preferably pulses, having a fixed frequency whose value is a fraction of the value of the frequency of the variable frequency oscillator. The first named souce also includes a counter-divider to which the output of the variable frequency oscillator is applied. The counter-divider has an output which is either f/N or f/N-M where N and M are whole integers and M is less than N. A phase comparator is responsive to the reference signal and to the output from the counter-divider for measuring the phase difference between the reference signal and the output pulses from the counter-divider. The dividing ratio of the counter-divider is under control of means responsive to the measure of phase difference such that the counter-divider is adjusted to bring the pulses from the counter-divider toward an in-phase relationship with the reference signal as seen at the phase comparator. The selection of the dividing ratio is carried out by a logic means which responds to the output of the variable frequency oscillator and the output of the source of the reference signal to provide for a selection of the counter-divider division ratio for each cycle of the reference signal. The output or measure of phase difference is in the form of a single-bit digital function and this function is applied to a digital low-pass filter to produce a binary word.

Laser vision sensor

Abstract: PURPOSE: To enable measurement of a distance at a high speed and with high precision by enabling modulation of a laser light by a plurality of modulation frequencies, by conducting primary measurement of a long distance by a low modulation frequency and by conducting highly-precise distance measurement by a high modulation frequency. CONSTITUTION: A laser light emitted from a laser oscillator 1 is modulated in intensity by a light modulator 2. In order to conduct modulation by a plurality of frequencies, two light-modulating elements 202 and 203 are provided. A distance range for measure ment is divided in a plurality and a long distance is measured primarily at a low modulation frequency, while the range of a relatively short distance is measured with high precision at a high modulation frequency. By combining these two measurements, it is made possible to measure the long distance with high precision. By raising the ratio of the modulation frequencies to (n)th power of 2, in addition, a value of the distance measured by the low modulation frequency is recorded in upper bits, while a value of the distance measured by the high modulation frequency is recorded in lower bits, and they are read out as continuous data, whereby distance measurement of a wide dynamic range is conducted. As the result, high-speed and highly-precise measurement of distances can be realized. COPYRIGHT: (C)1991,JPO&Japio

Errors in Determining the Center of a Resonance Line Using Sinusoidal Frequency (Phase) Modulation

Abstract: The errors in determining the center of a resonance line, which are due to residual imperfections in practical high-precision electronic systems using sinusoidal Frequency or phase modulation, are reviewed. In particular, the effects of residual amplitude modula- tion, baseline distortion, and harmonic distortion in the modulation process and the demodulator are qualitatively analyzed for a Loren- tzian line in the limit of small modulation index. This permits one to calculate analytically the frequency offsets as a function of modulation index, the transfer function of the fundamental, and various harmon- ics of the modulation frequency. Using this model one can easily for- mulate accurate tests for experimentally measuring the Frequency er- rors in practical servosystems, even if the original assumptions about small modulation index and a pure Lorentzian line are not exactly ful- filled.

Multi-frequency acousto-optic modulation process and apparatus

Abstract: A process for acousto-optic modulation of a monochromatic light beam, delivered by a laser, consists in deflecting the light beam in an acousto-optic modulator which receives a composite electric signal The composite signal has at least one modulation frequency It further includes two compensation components The overall acoustic power applied to the modulator is maintained at a substantially constant value by servo-controlling the electric power of the two compensation components having frequencies which are mutually different and different from the modulation frequency or frequencies

Formulas for direct frequency modulation response of two-electrode diode lasers: proposals for improvement

Abstract: Semiconductor lasers, ModulationFormulas for the frequency and amplitude small-signal modulation response are given with nonlinear gain taken into account. The importance of the phase characteristic is discussed. Curves are shown of the modulus and phase of the frequency modulation for some selected cases and a method is proposed to obtain nearly ideal response.

Frequency demodulator operable with low frequency modulation carriers

Abstract: A frequency demodulating device is arranged to supply a frequency modulated signal and a separately generated signal to an analog multiplying circuit and to perform frequency demodulation by supplying the output signal of the analog multiplying circuit to a frequency demodulation circuit via a high-pass filter.

Demodulator for psk-modulated signals

Abstract: A demodulator is disclosed for a PSK-modulated transmission signal in which the time average value of the frequencies thereof are equal to the carrier frequency. A mixer receives and mixes the PSK-modulated transmission signal with a signal from a local variable frequency oscillator (1) and the output thereof is converted (5) to a square wave which is used to reconstruct the original digital modulation data. A pulse counter (8) receives and counts the square wave signal for every period of time which is n times a time slot of a digital signal and a subtractor (11) provides a difference between the count value from the pulse counter and a reference count number. The subtractor output is converted (12) to an analog signal which controls the local oscillator frequency.

Non-linear analogue-to-digital conversion through PWM

Abstract: A method for finding non-linear functions digitally is described. The design is based on pulse width modulating (PWM) the analogue signal by applying a specially shaped reference waveform in the modulator. The number of pulses of a high frequency clock entering in a binary counter during the high state period of the PWM will provide a digital number proportional to the first, square, cubic or forth order root at the input voltage. Exponential form functions also can be found digitally.

Interferometric generation of high‐power, microwave frequency, optical harmonics

Abstract: A new technique for sinusoidal intensity modulation of light at microwave frequencies using a frequency modulated semiconductor laser and an interferometer is described. This technique can be more efficient than direct amplitude modulation and, since sidebands at harmonics of the modulation frequency are generated, is capable of reaching higher frequencies than direct modulation. The highest observed frequency (18 GHz) was generated by direct modulation of a laser diode at 9 GHz, and was limited by the bandwidth of available detectors. Frequencies in excess of 100 GHz can be obtained using suitable detectors.

Method and device for focusing, on one point to be examined, the antennae of an antenna array

Abstract: A method and device are provided for focusing the antennae of an array on a point to be examined. Each microwave signal received by an array antenna is subjected to amplitude modulation by means of a phase shifted low frequency modulation signal. The modulated signals are summed and the result of the summation is subjected to microwave detection then to low frequency demodulation by means of the modulation signal. The focusing point depends on the phase law by which the modulation signal is phase shifted so as to obtain each phase shifted modulation signal.

System for transmitting low frequency analog signals over AC power lines

Abstract: A system for transmitting low frequency analog signals over AC power lines using FM modulation A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an AC power line The modulation signal frequency range in selected to be within the response band of the FM transmitter The FM modulated carrier signal is received by an FM receiver coupled to the AC power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal

Method and apparatus for controlling a pwm inverter

Abstract: A method and apparatus are disclosed for controlling a pulse width modulating (PWM) inverter controlled for ignition by a PWM pulse (E U , E V , E W ) produced with a carrier wave (g) and a modulation wave (e). The method comprises sampling an amplitude of the modulation wave (e) at a cycle rate related to the frequency of the carrier wave. The modulation wave and the carrier wave are synchronized when the sample modulation wave amplitude has a peak value (V R ) greater than an amplitude (H) of the carrier wave. The modulation wave and the carrier wave are asynchronized when the sampled modulation wave has a peak value less than the amplitude of the carrier wave.

Modulation frequency stabilizing circuit for pulse frequency modulator

Abstract: PURPOSE:To stabilize a modulation frequency by extracting and demodulating only a horizontal synchronizing part out of the pulse frequency modulation signal of a video signal and monitoring the DC voltage and amplitude value of said demodulation signal so as to control the modulation frequency. CONSTITUTION:A modulation signal 4a is inputted to a horizontal synchronizing part extraction circuit 6. An output signal 5a from a horizontal synchronizing pulse generator circuit 5, which can be obtained from the video signal 1a, extracts the horizontal synchronizing part of the modulation signal 4a to obtain an output signal 6a. A demodulator circuit 7 demodulates said output signal 6a into the horizontal synchronizing part included in the video signal corresponding to the modulation signal 4a, thereby obtaining an output signal waveform 7a. A comparator 8 compares the DC voltage (a) of the output signal waveform 7a with a reference voltage Vref1, and its error amplification output voltage Va controls the horizontal synchronizing tip clamp voltage Vc of a video signal horizontal synchronizing tip clamp circuit 3. Thus a compensation circuit with a closed loop constitution can control the power source and temperature of a pulse frequency modulator and the fluctuation of the modulation frequency due to a secular change, whereby the modulation frequency can be stabilized at high accuracy.

Adaptive Array Behavior with Periodic Phase Modulated Interference

Abstract: We consider a least mean square (LMS) adaptive array [1] receiving a phase modulated interference signal. The phase modulation is assumed to be periodic and to have finite bandwidth. Under these assumptions, we determine the time-varying array weights, the modulation on the array output desired signal, and the time-varying output interference-to-noise ratio (INR) and SINR (signal-to-interference-plus-noise ratio). We present numerical results describing the behavior of a 2-element adaptive array that receives an interference signal with sinusoidal phase modulation. We show how each signal parameter (arrival angle, power, modulation index, and modulation frequency) affects the performance of the array.

Method and device for focusing an antenna array at a test point

Abstract: Chaque signal microonde (s j ) recu par une antenne de reseau est soumis a une modulation en amplitude (2) a l'aide d'un signal de modulation basse frequence dephase (C j ). Each microwave signal (s j) received by an array antenna is subjected to amplitude modulation (2) with a low frequency modulation signal of phase (C j). Les signaux modules (s' j ) sont sommes, et le resultat de la sommation soumis a une detection microonde (6) puis a une demodulation basse frequence (8) a l'aide du signal de modulation (D). The modulated signals (s' j) are summed, and the result of the summation subjected to microwave detection (6) and at a low frequency demodulator (8) with the modulation signal (D). Le point de focalisation depend de la loi de phase (A x ) selon laquelle on dephase le signal de modulation (D) pour obtenir chaque signal de modulation dephase (C j ). The focusing point depends on the phase law (A x) that is the phase shift modulation signal (D) for each of phase modulation signal (C d). L'invention s'applique en particulier aux systemes d'imagerie microonde et aux antennes a balayage electro-' nique. The invention applies in particular to microwave imaging systems and electronic scanning antennas' lunch.

Stability of interconnected systems with combined pulse frequency and pulse width modulation

Abstract: Sufficient conditions for finite pulse stability of interconnected systems with combined pulse frequency and pulse width modulation are developed in this paper using a direct method The stability criteria established provide upper bounds on the number of pulses emitted by each modulator The results are also applicable to those systems which contain a finite number of pulse frequency modulators and a finite number of combined pulse frequency and pulse width modulators

New methods of spectral analysis for pulse width modulators

Abstract: Pulse width modulation (PWM) forms the basic control technique for many audio frequency switching amplifiers and static power converters. As the switching frequencies that can be employed in the higher power ranges are relatively low, every effort is made to improve the spectral performance of the modulation technique. Adequate tools of analysis are clearly a prerequiste. To date the Fourier series or double Fourier series have been the major analysis tools in this area. These methods give analytical expressions for the spectra resulting from simple forms of modulation. They cannot provide solutions in the more complex cases such as two tone sinusoidal modulation. These cases are of interest if the pulse modulator is to operate in the presence of output feedback. Feedback is often required to improve low frequency linearity and attenuate low frequency components generated by the modulation process. Two new methods of spectral analysis for pulse width modulators are discussed. These are based upon. (a) A direct analysis of pulse position modulated (PPM) waveforms and hence pulse modulated waveforms using the properties of the Fourier Transform and the impulse function. (b) A modification of the 'Existence Function' technique which has been previously only applied to the spectral analysis of sine wave sourced cycloconverters. Expressions for the spectra of common pulse width modulators for two tone sinusoidal modulation are presented. Some observations on the modelling of both naturally and uniformly sampled pulse width modulators in closed loop applications are made.

Am radio transmitter

Abstract: An Rf-AM transmitter of the type including a power pulse amplifier driving an RF amplifier with a modulating voltage via a low pass filter includes a pulse width modulator for deriving variable frequency pulses having a frequency that is a direct function of an RMS like function of the amplitude and frequency of an information source; the width of the pulses is determined by the instantaneous amplitude of the information signal source. The pulse width modulator includes a constant amplitude, variable frequencytriangular wave voltage controlled oscillator responsive to a DC signal representing the frequency and amplitude of the information source. In response to amplitude crossovers between the variable frequency triangular wave and the information source, transitions in the pulse width modulated wave are derived.

Modulation waveform for 1200 BAUD DFSK paging transmitter

Abstract: A Continuous Phase Digital FM with premodulation shaping for Digital Paging Systems is presented. Some theoretical considerations and experimental results are included in order to validate this modulation scheme.