Showing papers on "Pulse-frequency modulation published in 1986"

An Efficient Algorithm for Spectral Analysis of Heart Rate Variability

Abstract: We present a simple efficient algorithm for the derivation of a heart rate signal from the electrocardiogram. We demonstrate that the amplitude spectrum of this heart rate signal more closely matches that of the input signal to an integral pulse frequency modulation (IPFM) model of the heart's pacemaker than do the spectra of other ECG-derived heart rate signals. The applicability of this algorithm in cross-spectral analysis between heart rate and other physiologic signals is also discussed.

Water-Wave Modulation

Abstract: Accurate numerical computations of wave trains with small modulations that grow are described. The range of wave steepness and modulation lengths that give breaking waves are determined. The number of wave crests is reduced for a time at greatest modulation but frequency downshifting is not observed. Near-breaking wave-group structure is always similar, with energy concentrated into one or two wavelengths.

FM-CW laser radar system

Abstract: A scanning laser radar system utilizing a frequency modulated (fm)-continuous wave (cw) beam to coherently detect echo signal returns from an object in a predetermined region. The frequency of the beam is repeatedly changed as a function of time to produce a symmetrical triangular-shaped frequency modulated waveform. The echo signals received are frequency shifted, as a function of range and Doppler shift, from the signal being transmitted at that time. The frequency shift is detected by homodyning a portion of the instantaneous transmitted signal with the received echo signal to produce an output signal having a frequency which is substantially constant during a portion of the frequency modulation period. The constant frequency portion of the output signal is related to the range and Doppler speed of the target. Target information such as range, Doppler speed, intensity and angle information are derived by processing the output signal. The signal to noise ratio of the output signal is improved by using a frequency modulation period greater than the scanning time across an arc of a size equal to a predetermined multiple of the beamwidth because with such relationship the time duration of the constant amplitude portion of the output signal is increased. Further, with such arrangement, because of the relatively long modulation period, the ambiguity in detection of the range to the target is reduced. The system is particularly useful in terrain following or obstacle avoidance applications.

Electronic sound synthesizer

Abstract: An electronic source synthesizer that employs frequency modulation. Wave-form data of both a fundamental wave and a modulated wave are stored in a RAM as 6-bit digital data. A sine wave signal is produced by modulation wave frequency data and the wave-form data from the RAM. The sine wave signal is multiplied with amplitude data of the modulation wave to obtain the modulation index data (J(t)). The frequency data (w c ) of the fundamental wave and the modulation index data are multiplied. A result of the multiplication provides a read out address of the RAM for storing the wave-form data of the fundamental wave, thereby changing the read out speed of the RAM. The digital data read out from the RAM is converted to an analog sound signal by a D/A converter. Amplitude data (A) of the fundamental wave is pulse-width modulated, and the digital data from the RAM is gated by the modulated pulse. Thus the output of the D/A converter is activated and, forms a sound signal represented by the equation e=A sin J(t) w c t.

Two-port synthesizer modulation system employing an improved reference phase modulator

Abstract: An improved frequency modulator apparatus for use in phase-locked loop (PLL) frequency synthesizers is disclosed which makes possible high deviation, low distortion, FM signals for a wide range of modulating signals, such as digital data or low frequency tone modulation. In a first embodiment having the improved frequency modulator, this apparatus advantageously injects the modulation signal into two ports, one at the VCO and the other provided in an unmodulated reference source signal chain. By properly balancing the levels into each of these two ports, a cancellation effect occurs which nulls the modulation signal at the output of the phase detector. In a second embodiment, the improved frequency modulator is incorporated in a PLL frequency synthesizer with an offset mixer to achieve relatively wide percentage deviation at a low frequency RF carrier. In a third embodiment, the improved frequency modulator is incorporated in a PLL synthesizer in its feedback loop so as to cancel the modulation components before they reach the phase detector. Thus, in the first two embodiments, the added phase modulator is inserted in the reference source signal path to the phase detector, while in the alternate third embodiment, the phase modulator is inserted into the feedback path and includes a phase inverter stage to correct for the inherent modulation polarity reversal.

Critical modulation frequency based on detection of AM versus FM tones.

Abstract: The ratios between the modulation index (η) for just noticeable FM of a sinusoidally modulated pure tone and the degree of modulation (m) for just noticeable AM at the same carrier and the same modulation frequency were measured at carrier frequencies of 0.125, 0.25, 0.5, 1, 2, 4, and 8 kHz. Signal levels were 20 dB SL and 50 dB SPL or 80 dB SPL. At low modulation frequencies, for example, 8 Hz, AM and FM elicit very different auditory sensations (i.e., a fluctuation in loudness or pitch, respectively). In this case, η and m show different values for just noticeable modulation. Since both stimuli have almost equal amplitude spectra if η equals m ( m<0.3), the difference in detection thresholds reflects differences in the phase relation between carrier and sidebands in AM and FM. With increasing modulation frequency, the η–m ratio decreases and reaches unity at a modulation frequency called the ‘‘critical modulation frequency’’ (CMF). At modulation frequencies above the CMF, the same modulation thresholds are obtained for AM and FM. Therefore, it can be concluded that the difference in phase between the two types of stimuli is not perceived in this range. At center frequencies below 1 kHz, where phase errors caused by headphones and ear canal presumably are small, the CMF is useful in estimating critical bandwidth.

Method and device for measuring the propagation of a wave

Abstract: A method and device are provided for measuring the propagation time of a wave, wherein a wave is transmitted modulated in amplitude by a modulation signal. The wave reflected by an obstacle is received after a propagation time and the amplitude thereof is detected. The average value of the product of the detected signal and a reference signal is calculated and the delay with respect to the modulation signal is controlled so as to cancel out the average value. The modulation signal and the reference signal comprise a succession of elementary signals chosen so as to allow, in a single measurement, a long propagation time to be determined without ambiguity and with high accuracy.

Frequency modulation spectroscopy using dual frequency modulation and detection

Abstract: FM laser spectroscopy apparatus includes a single modulator for modulating a laser beam with first and second modulation signals (ω1, ω2). The two modulation signals are generated by mixing a signal from a first oscillator (ω1 +ω2)/2 and a signal from a second oscillator (ω1 -ω2)/2 and producing the two modulation signals (ω1, ω2). The modulator produces three groups of sidebands on the laser beam at the laser frequency plus and minus the two modulation frequencies and at plus and minus the difference between the two modulation signal frequencies. The apparatus provides practical high frequency FM spectroscopy as required for the observation of pressure broadened spectral features.

Frequency-modulation characteristics of semiconductor lasers: deviation from theoretical prediction by rate equation analysis

Abstract: The frequency modulation characteristics of 1.3 ?m InGaAsP DFB BH lasers are measured when the bias current is slightly modulated by a sinusoidal waveform. Two deviations from the prediction by the rate equations are observed. One is that the phase difference between the frequency deviation and the modulation current approaches 180° below the relaxation resonance, and the other is that the ratio of the frequency modulation index to the amplitude modulation index has a strong frequency dependence. Both of the results are well explained by the two-section model, in which the inhomogeneous distribution of the spectral width enhancement factor ? is assumed.

Pulse width modulator for AM-RF 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 frequency triangular 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.

Direct frequency modulation of vapor phase transported, distributed feedback semiconductor lasers

Abstract: The frequency modulation (FM) due to injection current modulation of vapor phase transported distributed feedback (VPT DFB) semiconductor lasers is measured as a function of modulation frequency from 10 kHz to 1 GHz. A large frequency modulation response of 350 MHz/mA is obtained for the modulation frequency range of 10 to 1000 MHz. Demodulation of optical frequency shift keying (FSK) at 560 Mb/s is demonstrated, indicating that frequency modulation due to thermal modulation does not pose a significant limitation at this bit rate or higher. The large FM response together with modulation bandwidths up to 8 GHz makes the VPT DFB laser an attractive source for high bit rate optical FSK transmission.

A novel digital frequency multiplier

Abstract: This paper presents a digital frequency multiplier having many features not yet found together in existing multipliers. Its acquisition time is within one period of the input signal and it can follow the input frequency over more than three decades. The relative frequency error on its synchronized output signal is independent of the multiplication factor N and is noncumulative. The maximum value of this error is given by f in /f c where f in is the input frequency and f c a master clock frequency. This represents a decrease in the error value by a factor N over many existing digital frequency multipliers.

An optimum delta modulation strategy for inverter operation

Abstract: An improved PWM inverter waveform synthesis technique for harmonic control in delta modulation (DM) process is presented. Filtering approach is incorporated in the DM technique to reduce harmonics of lower frequencies and suppress the unwanted subharmonics. Analytical method is described to determine the performance of multistage delta modulated inverter and the results are substantiated by experimental verification.

Multimode noise generator using digital fm

Abstract: A pseudorandom noise generator which operates in different modes The pseudorandom noise generator (10) includes circuitry (11, 13) for providing a digital signal having a pseudorandom sequence at a selected clock rate; a modulation control circuit (15, 17, 20, 23) for selectively providing a modulation control signal that corresponds to either a non-filtered of filtered version of the digital signal, and for controlling the mode of operation of the noise generator; a modulation circuit (27, 29, 31, 33) responsive to the modulation control signal for providing a modulation signal; and a voltage controlled oscillator (VCO) (35) responsive to the modulation signal for providing a VCO output having a relatively constant output spectrum and high spectral containment for each mode of operation pursuant to control by the modulation control circuit and the modulation circuit

Digital-to-analog converter system

Abstract: A D/A converter system for converting digital signal to analog signal includes a circuit for converting digital signal such as PCM signal to pulse density modulation signal, and an analog low-pass filter for converting the pulse density modulation signal to analog signal by removing noise from the pulse density modulation signal.

Method and apparatus therefor in motor speed control

Abstract: A pulse width control apparatus and method for controlling motor speed wherein the number of pulses relating to more speed feedback data is counted so as to control the speed of the motor in accordance with a speed command data and a pulse width modulation signal based on the counted number of pulses. A free-running hardware timer and a soft-timer on a program controlled by an instruction execution time of a microcomputer are arranged so that ON-time data and OFF-time data of the pulse width modulation signal are selectively set in one and the other of the hardware and soft-timers in dependence on values of the ON and OFF times, respectively. The ON and OFF states of the pulse width modulation signal are changed when the contents of the hardware and soft-timers reach predetermined values so as to control the pulse width thereof.

Instantaneous deviation limiter with pre-emphasis and zero average value

Abstract: A modulation limiter that eliminates over-deviation otherwise caused by asymmetrical modulation signals in a frequency modulated (FM) transmitter. The output signal from a conventional modulation clipper is integrated, multiplied by a gain constant, and subtracted from the input, which causes the clipper output to have zero average and a high-pass frequency response with a time constant determined by the feedback gain. The zero average value allows the clipped modulation signal to be coupled to a modulator without over-deviation caused by shifts in the average value of the clipped signal, and the high-pass response can be used to give the modulation signal pre-emphasis.

Frequency modulation characteristics of coupled stripe laser diode array

Abstract: Time-dependent changes in the cavity resonance frequency were measured in a ten-element gain-guided coupled stripe array using a new technique based on injection locking. Sensitivity of the frequency to changes in the array current was 0.7 GHz/mA at dc and 0.04 GHz/mA for 1.0 MHz sine-wave modulation. The current-to-frequency modulation transfer function for the array was determined, and it was concluded that the transition from thermal to carrier-induced frequency modulation occurs in the region between 105and 106Hz.

Receiver of a digital communication apparatus

Abstract: A receiver for a digital communication apparatus which utilizes a time division multiplexed signal of a single or a plurality of pulse width modulation signal(s) and a synchronous signal or of a plurality of pulse width modulation signals, includes: a signal separation circuit including flip-flops and logic gates for separating each said pulse width modulation signal and said synchronous signal or separating each said pulse width modulation signal, from said time division multiplexed signal.

Controller for pwm inverter

Abstract: PURPOSE: To reduce electromagnetic noise of an induction motor by using a carrier signal generator as a frequency modulation signal generator. CONSTITUTION: A frequency modulation signal generator 17 generates a carrier signal obtained by frequency-modulation of a functional waveform such as triangular wave according to an instantaneous value of pulsating current such as sine wave. Said carrier signal is compared with a modulated signal from multipliers A1, A2, A3 by comparators 6a, 6b, 6c. Thus, if a carrier signal generator is used as a frequency modulation signal generator, many sidebands are generated in a higher harmonic of output voltage of PWM inverter 2 decrease its peak value. Therefore, electromagnetic noise of an induction motor is reduced without changing a frequency of said carrier signal. COPYRIGHT: (C)1988,JPO&Japio

Influence of frequency modulation on the interaction of pulses in fiber waveguides

Abstract: It is shown that regular phase modulation reduces a nonlinear interaction between optical solitons and suppresses an "interference" signal due to the interaction between multisoliton pulses.

Pulse width modulator

Abstract: PURPOSE: To generate a natural intermediate tone picture whose center of recording dots is coincident by providing a pulse generating means comparing a code signal converted by a code conversion means with a code signal commanding a pulse width of a modulation signal and generating a pulse width modulation signal having a prescribed pulse width in a laser beam printer. CONSTITUTION: A comparison result signal HH of a comparator 22 is outputted to a glitch elimination circuit 24. A pulse signal II is outputted from the glitch elimination circuit 24. A code converter 1 converts counts C(0∼7) outputted from a counter 23 into code signals B(6,4,2,0,1,3,5,7). Thus, while the timewise center phase of the width of the pulse width modulation signal II is kept nearly constant, the output data A is changed with respect to the input data D(O-7). The center of phase is deviated slightly in comparison with an ideal pulse width, but when the input data D is a 6-bit signal to express, e.g., 64-gradation, the center of the pulse width modulation signal II approaches limitlessly the ideal form. COPYRIGHT: (C)1987,JPO&Japio

Frequency agile signal generator for emulating communications environments

Abstract: A frequency agile signal generator provided for emulating a communication signal of predetermined frequency and modulation characteristics including frequency hopping. The signal generator includes a digital controller such as a microprocessor or microcomputer for generating digital command signals specifying the desired characteristics of the output signal. In response to the digital command signals, a base digital frequency signal representing the desired base or center frequency of the output signal is generated by a number controlled oscillator in response to a digital frequency control signal. The digital command signals also control the generation of an analog modulation signal having desired modulation characteristics. For frequency modulation, the analog modulation signal is converted to a digital signal in the frequency domain and is algebraically summed with the frequency control signal to control the frequency of the number controlled oscillator output signal as a function of both the digital frequency control signal and the digital modulation signal. The number controlled oscillator output signal is converted to analog form to provide an analog output signal. The analog output signal can be amplitude modulated and/or attenuated as commanded by the digital command signals. For amplitude modulation, the analog modulation signal in the time domain is used directly under the control of the digital command signals as a mixer input to amplitude modulate the analog output signal or for on/off keying.

RF amplitude modulator/mixer

Abstract: A method and apparatus are disclosed for offsetting the DC level of a modulating signal input to a dual balanced modulator. The circuit is adapted to offset a high frequency modulation signal by an amount sufficient to provide the optimum percent modulation of a carrier signal applied to the dual balanced modulator. The offset level to be applied is dependent upon the desired percent modulation and is further affected by the operating modulation and carrier frequencies as well as their respective input power levels.

Linearizer circuit for frequency modulation oscillator

Abstract: A system for frequency modulation by a signal, the system including an oscillator having a known linearity distortion, a circuit for selecting one from a plurality of predetermined constants, a circuit for operating on the signal with the selected constant, and a digital to analog converter in an embodiment where the signal is digital, for converting the signal having been operated on to an analog signal for modulating the oscillator is disclosed. One embodiment includes a circuit for determining the magnitude of the input signal.

Single-sideband modulator and broadcast transmitter

Abstract: A broadcast transmitter with single-sideband modulation for transmitting a message with a band width and carrier power which is lower in comparison with double-sideband modulation. To be able to operate a high-power single-sideband transmitter with only one transmitting tube, a single-sideband modulator (1) is used which generates, as a function on a modulating LF signal (2), a zero-phase modulator amplitude signal (9) which amplitude-modulates the anode (23) of an RF output stage tube (26) via a digital/analog converter (21), constructed as a switching amplifier with pulse step modulation, and an RF filter (22). The single-sideband modulator (1) also supplies a modulator phase signal (19) which is preferably not amplitude-dependent and which is fed to the control grid of the RF output stage tube (26), if necessary via a frequency converter (25). The single-sideband modulator (1) can be of digital or analog construction; at its input it has a Hilbert transformer which splits the modulating input signal (2) into two component signals which are phase-shifted by 90° and at its output it is also provided with an amplitude computer, a cyclic switch having a clock frequency (fT) which is preferably equal to 4 times the carrier frequency (f1) and, if necessary, a quotient computer and a subsequent band-pass filter. A residual carrier signal can be added to the input signal (2) or to the output signals of the Hilbert transformer.

Analysis of the dynamic frequency characteristic of a ring laser based on the Floquet theory

Abstract: A method is proposed for calculating the frequency characteristic of a ring laser with a periodically varying frequency nonreciprocity of the resonator on the basis of the Floquet theory valid for an arbitrary ratio of the modulation frequency to the width of the parametric locking bands. Rectangular modulation of the frequency nonreciprocity is considered as an example and it is shown that the parametric locking bands are located on the quasistatic characteristic. If the constant component of the frequency nonreciprocity is comparable with the modulation amplitude, the bands approach very closely one another and their width reaches a maximum value which is approximately equal to twice the modulation frequency.

Frequency-doubling PFM system to prolong the distance of optical fibre TV programme transmission

Abstract: In the square-wave PFM system for transmission of TV programmes through optical fibres, square-wave PFM pulses are generated at the transmitter with a relatively low centre frequency, whereas double-frequency equal-width narrow pulses are produced in the receiver before the demodulating low-pass filter, at both the rising and falling edges of the transmitted pulses. The use of the frequency-doubling technique in such a system results in narrow transmission bandwidth and high receiver sensitivity, thus prolonging the transmission distance significantly as compared with ordinary PFM. In the experiment, the system is operated at 1.3 μm with multimode fibre having bandwidth 700 MHz km, a laser diode as optical source and a PIN/FET as detector. It can effectively transmit the high-quality broadcast TV programme with accompanying sound channel to a distance of 50.7 km. Experimental results are: receiver sensitivity −40 dB m, weighted SNR for video 59.3 dB, differential gain and differential phase less than 1% and 1°, respectively.

Modulation of the emission frequency of a single-mode homojunction laser by an injection current

Abstract: A study was made of the emission spectra of a cooled single-mode homojunction laser used in scanning interferometers under conditions when a sinusoidal component of frequency ƒm up to 1.2 GHz was superimposed on a constant injection current. It was found that a strong frequency modulation could be achieved for a fairly small depth of amplitude modulation amounting to M ≲ 10%. The frequency modulation coefficient Kfm was within the range 0.1–0.8 GHz/mA, depending on the degree of excess above the threshold and on the frequency ƒm. The physical mechanisms governing the dependence Kfm(ƒm) were analyzed.

Device for transmitting high-frequency pulses in a certain pattern and a radio-navigation system including such a device

Abstract: This device comprises a high-frequency signal generator (5) fitted with a modulation control input (10) to supply said pulses at its output in relation to a modulation signal applied to its modulation input and a modulation generator (15) to provide the modulation input with the modulation signal. This device also includes a replica circuit (18) to supply a replica of the pulse transmitted, a management circuit (25) to compare this replica wtih said pattern and to alter the modulation signal from the modulation generator so that the pattern complies with the replica.