Showing papers on "Pulse-frequency modulation published in 1996"

Stabilized power converter having quantized duty cycle

Abstract: A multi-slice power converter (10) employs a digital circuit (22) to generate phase-delayed pulse width modulated (PWM) signals, which results in the duty cycle of the PWM signals having only a certain number of possible values. The quantization of the duty cycle is shown to result in two types of instabilities which are unique to power converters having a digital control loop, in addition to the conventional analog-type of instabilities. This invention provides novel methods and apparatus for stabilizing the digital control loop of the power converter through the use of a periodic dither signal having a frequency that is less than the PWM frequency and greater than a bandwidth frequency of the converter. The dither signal functions to effectively increase the number of possible duty cycles by a factor given by the ratio of the dither frequency to the bandwidth frequency.

Cues for discrimination of envelopes

Abstract: Thresholds for detection of sinusoidal amplitude modulation at a signal modulation frequency were measured in the presence of a masker modulation frequency, with broadband noise carriers Broad tuning for modulation frequency was observed For maskers half or twice the signal frequency, thresholds depended on the relative phases of the signal and masker These results were used to determine what aspects of envelopes listeners might be using in making decisions Simulations were performed using an envelope detector model, consisting of bandpass filtering, half‐wave rectification, and low‐pass filtering Decisions were based on envelope statistics that have been used to predict other data These statistics were (1) rms power, (2) ratio of maximum to minimum amplitude (max/min), (3) crest factor, (4) fourth moment, and (5) average slope The max/min statistic was successful at predicting the major trends in the data, without requiring the presence of channels tuned to modulation frequency

Optical frequency control system and method

Abstract: Method and apparatus for controlling the frequency of a laser in an optical transmission system which involves applying a frequency modulation to the laser, determining an amplitude modulation present in the signal downstream of the laser and attributable to the frequency modulation, and discriminating a portion of the amplitude modulation which is substantially in phase quadrature with the applied frequency modulation. The frequency of the laser is controlled on the basis of the discriminated quadrature portion. An optical component downstream of the laser may have a response which converts FM to AM. The response and the frequency output of the laser can be locked to one another, without errors caused by unwanted AM in the transmitted signal modulation frequency.

Method and apparatus for coherent burst ranging

Abstract: A high resolution ranging method is described utilizing a novel modulated waveform, hereafter referred to as coherent burst modulation In the coherent burst method, high frequency modulation of an acoustic or electromagnetic transmitter, such as a laser, is performed at a modulation frequency This modulation frequency is transmitted quasi-continuously in the form of interrupted bursts of radiation Energy from the transmitter is directed onto a target, interacts with the target, and the returning energy is collected The encoded burst pattern contained in the collected return signal is detected coherently by a receiver that is tuned so as to be principally sensitive to the modulation frequency The receiver signal is processed to determine target range using both time-of-flight of the burst envelope and phase shift of the high frequency modulation This approach effectively decouples the maximum unambiguous range and range resolution relationship of earlier methods, thereby allowing high precision ranging to be conducted at arbitrarily long distances using at least one burst of encoded energy The use of a receiver tuned to the high frequency modulation contained within the coherent burst vastly improves both sensitivity in the detection of the target return signal and rejection of background interferences, such as ambient acoustic or electromagnetic noise Simultaneous transmission at several energies (or wavelengths) is possible by encoding each energy with a separate modulation frequency or pattern; electronic demodulation at the receiver allows the return pattern for each energy to be monitored independently Radial velocity of a target can also be determined by monitoring change in phase shift of the return signal as a function of time

Orthogonal modulation scheme

Abstract: The modulation scheme has two versions that can transform two data streams into two mutually orthogonal modulated signals within the same carrier-frequency band. In one embodiment, the modulation scheme is a quadrature-phase shift-keying (QPSK) modulation scheme having an in-phase part and a quadri-phase part. In this embodiment, one version of the QPSK modulation scheme conforms to the IS-95 telecommunications standard. In this version, the in-phase part is applied to a first data stream to generate an in-phase signal that is multiplied by a cosine function of the carrier frequency. In a parallel path, the quadri-phase part is applied to the first data stream to generate a quadri-phase signal that is multiplied by a sine function of the carrier frequency. The resulting signals are combined to generate a conventional IS-95 signal. In this embodiment, the other version of the QPSK modulation scheme is designed to transform a second data stream into a second modulated signal that is orthogonal to the IS-95 signal, even though the second modulated signal is within the same carrier-frequency band and even if the second data stream is encoded using the same Walsh code sequence as the first data stream. In one implementation of the second version, the logical negation of the quadri-phase part of the QPSK modulation scheme is applied to the second data stream to generate an quadri-phase signal that is multiplied by the cosine function of the carrier frequency. In a parallel path, the in-phase part of the QPSK modulation scheme is applied to the second data stream to generate an in-phase signal that is multiplied by the sine function of the carrier frequency. The resulting signals are combined to generate a modulated signal that is orthogonal to the IS-95 signal and which therefore will not interfere with the IS-95 signal, even though the two modulated signals exist within the same carrier-frequency band and may in fact be based on two data streams that were encoded using the same Walsh code sequence. Those skilled in the art will understand that the modulation scheme of the present invention can be implemented in contexts other than the IS-95 standard.

Multifrequency lightwave source using phase modulation for suppressing stimulated Brillouin scattering in optical fibres

Abstract: Spectral broadening over a large range using PM (Phase Modulation) is achieved by a lightwave source without the need for a large phase modulation index and without expending a large amount of modulator RF drive power. In this lightwave source, a laser output signal is externally phase modulated by one or more modulation signals. The phase modulation employs one or more frequency drive signals (i.e., the modulation signals) each of whose amplitude is judiciously selected to produce an output spectrum having substantially equal spectral components over a predetermined range of frequencies. The predetermined frequency range is centered about the source frequency for the laser and resembles a comb. Each frequency drive signal is also selected to have a frequency (or frequency spacing from other drive signals) so that adjacent spectral components in the output spectrum of the modulated signal are produced with a frequency spacing which exceeds the SBS (Stimulated Brillouin Scattering) interaction bandwidth at the transmission wavelength of interest.

A new method to extend linearity of a sinusoidal PWM in the overmodulation region

Abstract: A new method to extend the linearity of a sinusoidal pulsewidth modulation (PWM) is presented. A square wave is added to each of the phase voltage commands in the pulse dropping region. Addition of the square wave maintains the fundamental component gain of the PWM in the pulse dropping region and extends the PWM linearity all the way to the six-step mode of operation. The method eliminates the need to overmodulate the phase voltage commands to extend linearity, resulting in increased dynamic range for the associated control. The magnitude of the square wave is governed by a function of the modulation index. Analytical expressions are derived for the required function. A simple approximation of this function is suggested and its effectiveness demonstrated for actual implementation. All analytical results are experimentally verified on a 100 kW three-phase AC-DC converter.

Hearing assist system employing time variant modulation transmission to hearing aid

Abstract: A short range magnetically coupled wireless communication system employs time variant modulation of a high repetition rate pulse stream and magnetic coupling between a transmission magnetic element and a receiving magnetic element. The pulse stream is modulated by an input audio frequency signal in the time domain, for example, through pulse position modulation, pulse width modulation or pulse symmetry modulation. The receiving magnetic element is coupled to a demodulator circuit which detects the transmitted pulses induced in the receiving magnetic element and reproduces the audio frequency signal. Transmission over short range is thus efficiently accomplished through magnetic coupling in a simple, low cost, low power consumption communication system.

Hybrid pulse width modulation/sigma-delta modulation power digital-to-analogue converter

Abstract: A new digital signal processing technique is presented for power digital-to-analogue converters which offers high linearity and a substantial reduction in clock frequency compared to conventional pulse width modulation converters. The basis of the technique is to group together pulses from the output of a single bit sigma-delta modulator. A model is derived which shows that the system output is essentially a pulse width modulated sequence. Noise and distortion are introduced by the pulse grouping but are considerably reduced using noise shaped feedback around the pulse grouper. Simulation results are presented which validate the model and indicate the performance of the technique with ideal and nonideal output stages.

Synchronous polarization and phase modulation using a periodic waveform with complex harmonics for improved perfomance of optical transmission systems

Abstract: A method and apparatus is provided that yields improved performance by modulating the optical phase and polarization of an optical signal with a periodic waveform having harmonic content that is more complex than that associated with a simple sinusoidal waveform. A phase modulator receives an optical signal onto which data has been modulated at a predetermined frequency. The phase modulator modulates the phase of the optical signal in a continuous manner with the periodic waveform with complex harmonics where the fundamental phase modulation frequency is equal to the same predetermined frequency at which the data is modulated onto the optical signal. In another illustrative embodiment of the invention, a polarization modulator further processes the optical signal by modulating the state-of-polarization of the signal in a continuous fashion with the periodic waveform with complex harmonics where the fundamental polarization modulation frequency is equal to the same predetermined frequency at which the data is modulated onto the optical signal. In addition to being continuously modulated, the polarization modulation is performed so that the average value of the state of polarization over each modulation cycle is substantially equal to zero.

Power losses for space vector modulation techniques

Abstract: Space vector modulation (SVM) allows 15% more bus utilization than sinusoidal pulse width modulation (PWM). In addition, variations of the SVM method can offer 33% less switching edges. With power losses in the inverter being a significant concern, a reduction in modulation losses can be a significant benefit. Different SVM techniques are discussed along with the calculations for determining both switching losses and conduction losses in the transistors and diodes. Equations for the average and RMS transistor and diode currents are derived based on a quantitative analysis of the current waveforms. The switching losses are plotted against power factor to illustrate the effect of power factor on switching losses for the various SVM techniques. The results are discussed and compared. In at least one case, an analysis of the strategy can lead to specialized power electronics optimized to the switching strategy.

A universal space vector modulation strategy based on regular-sampled pulse-width modulation [invertors]

Abstract: A universal space vector modulation (USVM) strategy based on regular-sampled PWM technique is presented which minimizes the switching losses. It is shown that the reduction of the switching losses results from the selected null switching states inverter control. Moreover, it is shown that the simple universal space vector modulation strategy can be implemented in software using a digital signal processor in real-time. Simulation and experimental results are presented to confirm the theoretical analysis.

Phase-change optical recording method using pulse width modulation technique

Abstract: When recording data according to the PWM recording system by modulating signals, pulse modulation for pulse modulation for recording for recording a 0 signal or the like having a signal width of nT (T: Clock time) after modulation is a continuous electro-magnetic wave at a power level e, a record signal pulse array for recording a 1 signal or the like having a signal width of nT after modulation comprises a pulse section fp having a time width x and a power level a, a multi-pulse section mp in which a low level pulse at a power level b and a high power pulse at a power level c having a time width T in total alternately appear (n-n') times in all with a duty ratio y, and a pulse section op having a time width z and a power level d, and x, y, z are integers satisfying the conditions of 0.5 T≦x≦2 T, 0.4≦y≦0.6 and 0.5 T≦z≦1 T, and n' is a positive integer which is equal to or smaller than n, and controls are provided so that the condition of (a and c)>e >(b and d) is satisfied.

Detection of frequency-modulated tones in electromagnetic signals

Abstract: An apparatus and method for detecting a channel of a fiber-optic system. According to one embodiment, a filter is adapted to receive an electromagnetic signal resulting from modulation of a carrier frequency over a frequency range by a modulation signal. The filter has a plurality of transmissivity peaks over the frequency range, whereby the filter generates a plurality of intensity pulses as frequency of the electromagnetic signal varies over the frequency range. A detector is adapted to detect the modulation signal based on the plurality of intensity pulses. According to another embodiment, an electromagnetic signal corresponding to a channel and resulting from modulation of a carrier frequency over a frequency range by a modulation signal is received. A plurality of intensity pulses are generated as frequency of the electromagnetic signal varies over the frequency range, and the channel is detected in accordance with the intensity pulses.

The Effect of Carrier Frequency Modulation of PWM Waveforms on Conducted EMC Problems in Switched Mode Power Supplies

Abstract: SummaryElectromagnetic compatibility (EMC) remains an issue which can present many problems to designers of high frequency power converter circuits. Usual techniques for alleviating the problems of interference generation by power converters involve the use of screening materials and filters, however, the effectiveness of such measures depends on the frequency the interference and the power density at each frequency of interest. As pulse width modulation (PWM) generates high frequency harmonics at multiples of the switching frequency, modulation of the switching frequency may be used to spread the spectral power density present at these harmonic frequencies. This paper presents a technique of frequency-hopping spread-spectrum modulation which may be applied to switched-mode power converters (SMPC’s) to reduce the spectral power density at harmonics of the switching frequency. The influence of the peak frequency deviation, the modulation sequence length and the type of modulating sequence on the resultant ...

Digital frequency demodulator

Abstract: A digital frequency demodulator includes a first counter and a second counter measuring the instantaneous and mean values of the period of a frequency modulated signal. A comparator compares the values measured and creates a binary signal of the same frequency as the modulation signal. The measurement of the instantaneous value of the frequency modulated signal is effected by counting the number of reference clock pulses during a period of the modulated signal, and the measurement of the mean value is effected by counting the number of pulses of a clock signal of frequency N times lower than the reference clock during N periods of the modulated signal.

Vehicle-mounted radar system and detection method

Abstract: Modulation frequency setting device sets the modulation frequency on the basis of the vehicle speed data from a vehicle speed detector and the detected range data, causing a low frequency oscillator to generate a low frequency signal of the set frequency. A transmitter transmits an electromagnetic wave (e.g., infrared light) which have been modulated with the low frequency signal. A phase comparator detects the phase difference between the low frequency signal and a detector output, and a range operating device produces range data. Relative speed operating unit finds the relative speed based on the range data. In case of a high vehicle speed, the modulation frequency is set low to extend the detection range. If an object in a short distance is detected, the modulation frequency is set high to limit the detection range to a short range, thereby enhancing the range resolution.

A frequency modulator, transmitter and TRANSCEIVER incorporating the frequency modulator

Abstract: A frequency modulator (50, 150) for modulating a carrier signal according to a modulation data signal to provide a modulated output signal (RFout), comprises a reference signal generator (54, 154) coupled to receive the modulation data signal for generating a reference signal modulated according to the modulation data signal, and a main synthesizer (52, 152) coupled to receive the modulated reference signal and the modulation data signal for providing the modulated output signal at an output. Preferably, the modulated reference signal has a first modulation gain (Kr) and the modulated output signal has a modulation gain (KV) which is substantially proportional to the first modulation gain (Kr).

FM signal generation using delta-sigma oscillators

Abstract: A frequency modulation signal generator based on delta-sigma oscillators is presented. The signal, mixed with out-of-band quantization noise, is encoded in a single bit stream. The design is entirely digital except for a 1-bit DAC. It therefore exhibits many digital circuit qualities such as programmability, accuracy, low sensitivity to process variations and mature testing methods. It is more efficient in terms of silicon area than other digital synthesis methods as it does not require a ROM or a multiplier. While the carrier frequency is fixed to a quarter of the clock frequency, this generator allows a wide range of modulated signal frequency and modulation index. It can be used as a stimulus for built-in self-test of wireless communication systems.

Method and arrangement for frequency modulation of a high-frequency signal

Abstract: In a method and an arrangement for frequency modulation of a high-frequency signal, where the high-frequency signal is generated with an oscillator which is controlled by comparison of an actual frequency signal with a variable set frequency signal, the actual frequency signal contains pulses with an average repetition frequency which corresponds to an actual frequency, with one pulse being derived from one edge of the high-frequency signal and its phase angle being determined by a predetermined clock pulse. The set frequency signal comprises pulses with an average repetition frequency which corresponds to a set frequency. The pulses increment or decrement an up/down counter from whose count a control voltage is derived for the oscillator.

Digital pulse interval and width modulation

Abstract: This article investigates the implementation of a new digital pulse-time modulation (PTM) technique based on a digital pulse internal and width modulation (DPIWM) scheme. Original expressions are presented for code characterization, channel capacity, and power spectral density. These illustrate the advantages of this scheme compared with conventional pulse-code modulation (PCM). Both theoretical and simulated spectral results are given, and are shown to be in close agreement.

Phase sensitive detection of light reflected from a Fabry-Pérot interferometer

Abstract: We present an analysis of the Fabry–Perot response to a phase‐modulated light in the reflection mode, by considering the general problem of the lock‐in detection at the pth harmonics of the rf modulating frequency. Suitable frequency modulation conditions for servo‐locking purposes are obtained and the values of modulation index which maximize the sensitivity for the first, third, and fifth harmonics are found. Moreover, we investigate the effects of the residual amplitude modulation introduced by the electro‐optic frequency modulator, the presence of laser amplitude and frequency noise, and the dependence of the achievable closed‐loop frequency fluctuation spectrum on the modulation index and detection noise.

Integrators in pulse width modulation [switching circuits]

Abstract: Many control methods for power convertor switching circuits employ an integrator to realize PWM. Depending how the integrator is used, the dynamic performance differs greatly. This paper presents a systematic evaluation of the function of integrators in some representative integrator related PWM methods, such as ASDTIC control, delta/delta-sigma modulation, modulated integral control and one-cycle control. In general, zero steady-state error is granted for all methods. Further, the variable frequency control methods are able to achieve one-cycle dynamic response. In the constant frequency category, however, only the one-cycle control method achieves one-cycle dynamic response, i.e., it realizes zero dynamic tracking error in the cycle average sense. In this paper, performance enhancement rules were explored for variable frequency control method in order to reduce the frequency variation. For the one-cycle control method, a pulse position modulation effect is identified which deteriorates the perturbation rejection ability of the single-side modulated one-cycle control method in the high frequency range. As a result, a double-side modulation is proposed that effectively reduces this effect. In addition, a fast reset mechanism is suggested that improves the switching error correction. This paper also provides a general approach to use integrators in PWM to realize arbitrary function.

Low-Noise Design of Cross-Flow Fan Based on Frequency Modulation.

Abstract: The aerodynamic noise generated by the rotating blade row of an electric fan generally consists of a broad-band vortex noise and a narrow-band rotational noise. The rotational noise, called blade passing frequency (BPF) noise, is annoying and its suppression has been considered at the design stage of many types of fans. The authors propose new design methods to reduce BPF level based on sinusoidal frequency modulation and M-sequence frequency modulation. Comparison by means of numerical simulation revealed that M-sequence frequency modulation is superior to sinusoidal frequency modulation with respect to spectral dispersion. Furthermore, it was confirmed that M-sequence frequency modulation realizes successful reduction of the BPF level of the cross-flow fans used in air conditioners.

Minimum Vibration Maneuvers Using Input Shaping and Pulse-Width, Pulse-Frequency Modulated Thruster Control.

Abstract: : Minimizing the modal vibration induced by on-off thrusters is a challenging problem designers of flexible spacecraft. This thesis presents the first study of Pulse Width, Pulse Frequency (PWPF) modulated thruster control using the method of command input shaping. Input shaping systems with linear actuators has been successfully developed to reduce modal vibrations. Recently this method has been extended to systems with on-off actuators to some degree. However, exist approaches require complicated nonlinear optimization and result in bang-bang control action. Bang thruster operation on flexible spacecraft is propellant-intensive and causes frequent thru switches. In this thesis, a new approach integrating command input shaping with PWPF-modulated thruster control is developed to minimize residual vibration in maneuvers and to reduce propel consumption. To realize this approach, an in-depth analysis of the PWPF modulator is first conducted to recommend parameter settings. Next, command input shapers are designed and integrated with PWPF modulator. Simulation verifies the efficacy of this technique in reducing modal vibration. Lastly, robustness analyses are performed and demonstrate the method's insensitivity to frequency damping uncertainty.

Modulation for AC-to-AC resonant link converters with active filtering

Abstract: Modulation methods for AC-to-AC pulse-modulated series-resonant power converters are analyzed. A novel control approach based on space vector dynamical equations is suggested. The obtained equations prescribe the dynamics of the complete power converter including its filters. The derived modulator base can overcome the drawbacks of pulse modulation techniques. The sliding mode control is considered to control the power factor of the pulse-modulated power converter. The suggested modulation mechanism and philosophy is generally applicable for the entire class of the pulse-modulated soft-switching power converters.

Bragg-assisted parametric amplification of short optical pulses

Abstract: Parametric amplification of pulses in Bragg gratings is investigated numerically. Gain is observed for a much larger range of parameters than in uniform media. This is explained in terms of grating-assisted phase matching. In contrast to that for cw results, the input signal pulse need not be tuned to a particular frequency. Rather, through cross-phase modulation the signal self-locks to the correct frequency for growth.

Pulse width modulation load controller

Abstract: PROBLEM TO BE SOLVED: To provide a pulse width modulation load controller capable of reducing a power source voltage change as compared with the prior art. SOLUTION: In the case of PWM controlling a plurality of loads 1 to 4 by a PWM(pulse width modulation) signal, the pulses of pulse width modulation signals PWM1 to PWM4 for driving the loads 1 to 4 are dispersed substantially at equal intervals by, for example, deviating the phase at 90 degrees by a timing control circuit 21. Thus, the superpositions of the pulses of the signals PWM1 to PWM4 are reduced, and superposition periods are dispersed. When the pulse widths are small, the period that all the pulses of the signals PWM1 to PWM4 are not excited (a common pulse interval period) is finely segmented by the pulses of the PWM signals. The change of the current flowing from a battery is enhanced in frequency, and the change is reduced. On the other hand, the impedances of a power source system or the loads have electrostatic capacity or inductance and hence the discharging current of the battery is not continuously discharged for a long period or paused for discharging, but can be easily averaged.

Circuit for 2-level/4-level frequency shift key modulation

Abstract: A circuit for two-level/four-level frequency shift keying modulation, which may be used for a paging transmitter, is compatible with earlier two-level non-return to zero frequency shift keying modulation circuits and includes; a voltage leveling circuit for generating four voltage levels to selectively allow the two-level and four-level frequency shift keying modulation; a decoder for decoding the least significant bit and most significant bit data inputs to generate a decoded signal output; an analog switch for selecting the four voltage levels in accordance with the two-level or four-level frequency shift keying modulation, in response to the decoded signal; an adder for adding the selected voltage level to a reference voltage to generate a corresponding digital output voltage; an audio amplifier for amplifying an audio signal input; an input/filter selector for selecting the digital output voltage or the amplified audio signal in response to an input selection control signal and for selecting one of two filtering paths of a following stage in association with a control signal for selecting the two-level or four-level frequency shift keying modulation to generate the selected digital output voltage or the amplified audio signal via the selected filtering path; and a baseband filter for performing a first or a second filtering with a respective bandwidth for the two-level or four-level frequency shift keying modulation and for filtering the digital output voltage or the audio signal supplied through the selected one of the filtering paths.

Dynamic analysis of the fixed-frequency PWM LCC-type parallel resonant converter using discrete time domain modeling

Abstract: Dynamic analysis of the fixed-frequency pulse width modulated LCC-type parallel (or series-parallel) resonant power converter is presented using discrete time domain modeling. First, the large-signal state-space model is derived and used to study the large signal behavior of the power converter in the event of large, nonlinear transient conditions. The results are verified using SPICE. The steady-state solution is obtained. Finally, the large signal equations are linearized about the steady-state equilibrium point to derive a linear small-signal model, which is used to study the small signal dynamic behavior of the power converter.