Showing papers on "Pulse-frequency modulation published in 2003"

System and method for providing digital pulse width modulation

Abstract: A pulse width modulation system for use in a switching power supply circuit provides high-resolution pulse width modulated signals. The pulse width modulation system is configured to receive a control signal comprising a (m+n)-bit binary word and to provide a pulse width modulated signal with a predetermined average duty cycle having a resolution of substantially 2-(m+n). The pulse width modulation system includes a timing circuit for providing 2m timing signals, a dithering circuit, and a signal generator. Upon receiving the control signal, the dithering circuit is configured to provide a modified control signal, which comprises a series of up to 2n m-bit binary words. The signal generator is configured to receive the timing signals and the modified control signal and to provide the pulse width modulated signal having a duty cycle, which, when averaged over 2n timing cycles, is approximately equal to the predetermined average duty cycle. The pulse width modulated signal is used by a switching power supply circuit to control at least one power switching device.

Amplitude, phase, and hybrid ternary modulation modes of a twisted-nematic liquid-crystal display at ∼400 nm

Abstract: Applicability of a commercial twisted-nematic liquid-crystal display is examined at ∼400 nm. Different modulation modes predicted by Jones-matrix calculus are experimentally tested. High contrast amplitude modulation with negligible loss, high contrast and low loss hybrid ternary modulation, and 1.5π continuous phase delay without intensity modulation and with low loss are presented. Simulation results of a 4f holographic system prove the usefulness of the high contrast for amplitude modulation, and the importance of π phase difference between high transmission white levels in a hybrid ternary modulation.

Variable frequency PWM controller circuit

Abstract: The present invention discloses a circuit that generates a variable frequency pulse width modulation (VF PWM) signal. Different from the conventional PWM controller, the frequency and duty cycle of the output PWM signal vary with the error-amplified voltage of the feedback loop simultaneously in this invention. The higher the error-amplified voltage of the feedback loop is, the lower the duty cycle with lower frequency will be. A very low duty cycle PWM signal can be generated stably while its frequency is very low.

Evaluation of switching frequency modulation in EMI emissions reduction applied to power converters

Abstract: Although most of the power converters are currently designed to operate by using a constant switching frequency and a variable duty-cycle, some attempts were made in order to verify the effect of modulating the switching frequency [F. Lin et al., 1992] and how this modulation affected the power converters EMI emissions. As known, spread spectrum clock generation (SSCG) modulates the originally constant switching frequency by following a certain modulation profile in order to spread the single harmonic energy into an amount of side-band harmonics having the same energy but much smaller amplitudes. This reduction technique has been used and implemented for high frequencies (as those related to clock frequencies in communications and microprocessors systems). This paper is dedicated to SSCG applied to the reduction of EMI emissions in power converters, focusing on the effectiveness of frequency modulation in EMI reduction as a function of the different switching frequency ranges and modulation profiles. Theoretical results were obtained just modulating a sine pure wave following several modulation profiles [A. Santolaria et al., 2002], this one representing each one of the harmonics composing the real square PWM-signal controlling the power converter. A practical arrangement was implemented to generate and measure EMI emissions.

Pixel design of pulsed CMOS image sensor for retinal prosthesis with digital photosensitivity control

Abstract: A newly designed pulse frequency modulation photosensor for use in retinal prosthesis is proposed and demonstrated. The pixel converts the intensity of incident light into biphasic current pulses at frequencies suitable for the electrical stimulation of retinal neurons. Experimental results showed that the device was sensitive over a dynamic range of input light of about 120 dB, and that photosensitivity could be varied from 0 dB to around -40 dB.

Efficient minimum pulse spread spectrum modulation for filterless class D amplifiers

Abstract: Method and apparatus to enable the use of class D amplifiers without the need for an output filter, while maintaining both a high efficiency and a high audio fidelity Using the classic differential Pulse Width Modulation scheme, the high frequency carrier is first suppressed to achieve a ternary modulation, and then re-introduced as a common mode pulse whose width is modulated to provide the necessary output voltage, but whose width never decreases below a well-defined threshold The frequency of the modulator waveform (ramp or triangle) may itself be modulated on a sample-by-sample basis, so that the EMI spectrum of the output waveforms can be made white at high frequencies The combination of the modulation scheme and spread spectrum high frequency behavior allows the user to eliminate the external filter Various embodiments are disclosed

Comparison of three PWM strategies-SPWM, SVPWM & one-cycle control

Abstract: Sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM) are the most popular modulation strategies applied to variable frequency and adjusting speed systems, and there are diverges in comparing the merits and demerits of their own Also there is another modulation strategy called one-cycle control This paper gathers the three strategies and does some comparisons through simulation based on a simulation tool-PSIM, and has drawn some profitable conclusions

Time-bandwidth product of the photonic time-stretched analog-to-digital converter

Abstract: The time-bandwidth product of the photonic time-stretched system is modeled in terms of physical system parameters. Using the time-bandwidth product as figure-of-merit, the performances of optical double-sideband and single-sideband (SSB) intensity modulation are compared, and optical SSB intensity modulation is identified as a potential solution to extend the system's time-bandwidth product. An SSB-modulated time-stretched system is theoretically analyzed and experimentally demonstrated. As an important practical consideration, the analytical model relating the system performance to the phase and amplitude mismatches in the SSB modulator is presented. The results show that the system is tolerant to such unavoidable mismatches. Experiments using commercially available components suggest that the dispersion-induced power penalty can be kept below 2.5 dB over 4 - 20 GHz bandwidth for any stretch factor. Additional experiments demonstrating 120-GSamples/s real-time digitization of a 20-GHz SSB-modulated signal are also reported.

Improvement of group delay measurement accuracy using a two-frequency modulation phase-shift method

Abstract: The modulation phase-shift method is a standard technique for measuring the group delay and dispersion of fiber-optic devices. The wavelength resolution is typically determined by the radio-frequency modulation frequency. Decreasing the modulation frequency improves wavelength resolution at the cost of decreased sensitivity in the measurement of the time delay. We present a technique that simultaneously yields both high wavelength resolution and high time delay sensitivity by combining two measurements made at different modulation frequencies. High-resolution experimental results are shown for a fiber Bragg grating device.

EMI reduction of power converters by way of controlled randomized modulation of oscillating signals

Abstract: A switching control circuit for a switching power converter utilizes an oscillating signal that causes reduced electromagnetic interference by the power converter by way of modulating the frequency of the oscillating signal within a specified frequency range. An output voltage monitor circuit monitors the output voltage of the power converter, thus producing an output voltage monitor signal. Also, a randomized signal generator creates a randomized signal, which is then used to drive a frequency range converter that is employed to produce a frequency modulation signal. The current state of the frequency modulation signal is based on the current state of the randomized signal, with the frequency range converter limiting the current state of the frequency modulation signal so that the oscillating signal will only operate within the specified frequency range. A variable frequency oscillator then generates the oscillating signal whose frequency is based on the current state of the frequency modulation signal. A comparator then compares the oscillating signal with the output voltage monitor signal to produce a switch control signal, which is then employed to control a switching element of the power converter.

Frequency modulator, frequency modulating method, and wireless circuit

Abstract: A voltage controlled oscillator 1, a variable frequency divider 2, a phase comparator 3, and a loop filter 4 form a Phase Locked Loop (PLL). A sigma-delta modulator 5 sigma-delta modulates data obtained by adding a fractional part M2 of the frequency division factor data with modulation data X by using an output signal of the variable frequency divider 2 as a clock. An output signal of the sigma-delta modulator 5 is added to an integral part M1 of the frequency division factor data, and the resultant data becomes effective frequency division factor data 13 of the variable frequency divider 2. An output signal of the sigma-delta modulator 5 also becomes control data 14 after passing through a D/A converter 6, a low-pass filter 7, and an amplitude adjustment circuit 8. The control data 14 is inputted into a frequency modulation terminal of the voltage controlled oscillator 1. Therefore, it is possible to provide a frequency modulator that can use a reference signal source having no frequency modulation function, and perform modulation over a wide range of frequencies based on a digital modulation signal.

Simple valley-fill self-oscillating electronic ballast with low crest factor using pulse-frequency modulation

Abstract: This paper presents an alternative to achieve fluorescent lamp current low crest factor, using the valley-fill filter as a passive power-factor-correction method. Pulse frequency modulation is used to reduce lamp current high crest factor. Self-oscillating electronic ballast is employed in order to avoid complex circuitry. The partial smoothing valley-fill DC-link bus voltage is used to control the switching frequency. Crest factor correction is achieved through a low power bipolar transistor, which connects a low power passive circuit parallel within the self-oscillating gate-driver circuit. The switching frequency changes in order to keep the lamp current crest factor lower than 1.7 and a modified valley-fill filter is used to meet IEC61000-3-2 requirements. Simulations and experimental results are presented to demonstrate the simplicity, and feasibility of the proposed system.

Two-mode overmodulation in two-level voltage source inverter using principle control between limit trajectories

Abstract: A two-mode overmodulation in two-level VSI using the control principle between limit trajectories is presented The control principle between limit trajectories is used to ensure linear modulation from linear range of space vector pulse width modulation to six step mode and two-mode is employed to get better performance of overmodulation The proposed principle is verified by software simulation

Performance comparison of binary and quaternary UWB modulation schemes

Abstract: In this paper we test and compare different modulation strategies to be used in ultra-wide band (IR-UWB) communications. In the UWB systems of interest in this work the information is conveyed by short-duration pulses; the modulation scheme determine how the data stream is to be transmitted over those pulses. Here we test and compare several schemes based on three types of modulation. The first type is the pulse position modulation (PPM), which includes a pulse delay according to the data to be transmitted. The second is the recently proposed pulse shape modulation (PSM), that uses a different pulse shape to each data. The third one, proposed in this paper, is an M-ary modulation scheme that combines the shape and amplitude of the pulse to transmit the data, which we call pulse amplitude and shape modulation (PASM). Other M-ary schemes are tested, including the recent orthogonal M-ary PSM, based on orthogonal Hermite functions, and a new quaternary PPM scheme, also proposed here. All schemes are tested over an AWG channel.

The generalized discontinuous PWM modulation scheme for three-phase voltage source inverters

Abstract: This paper presents analytical techniques for the determination of the expressions for the modulation signals used in the carrier-based non-sinusoidal and generalized discontinuous PWM modulation (GDPWM) schemes for two-level, three-phase voltage source inverters. The resulting modulation schemes are applicable to inverters generating balanced or unbalanced phase voltages feeding either star or delta connected loads. The results presented in this paper analytically generalize the several expressions for the modulation signals already reported in the literature. Confirmatory experimental results are provided to illustrate some of the feasible modulation signals.

Pulse-skipping PFM DC-DC converter using a voltage mode control loop

Abstract: A pulse frequency modulation unit controls upper limit level and lower limit level for an output voltage of a DC-DC converter. A voltage mode control loop uses the upper and lower limit levels in a feedback loop to generate a control signal to enable and disable the converter circuit.

Integrated data jitter generator for the testing of high-speed serial interfaces

Abstract: An integrated data jitter generator for the testing of high speed serial interfaces is provided. A transmit timing generator for use in a transmit data path includes a high frequency clock generator such as a phase-locked loop or a delay-locked loop having an input for receiving an oscillator or reference clock input. A clock modulator receives both an existing low frequency modulation signal and a high frequency modulation signal. A high-speed modulated clock signal is generated to enable jitter testing by a downstream-coupled receiver. Fixed frequencies such as 3, 6, 125, 150, 250, 300, 750, or 1500 MHz are used for the high-speed modulation signal, but any high-speed modulation frequency can be used to generate the desired amount of jitter. Likewise, the amplitude of the high frequency modulation signal can also be varied as desired.

Pulse-skipping switching power converter

Abstract: The invention relates to a pulse-skipping power converter. In one aspect, a power converter has two stages. When the load is high, both stages are enabled. As the load decreases, one or both of the stages may enter pulse-skipping mode to improve efficiency. As the load is reduced further, the one or both of the stages may be disabled. When both stages are disabled, an auxiliary power supply may be enabled. In a further aspect, an error signal is produced by comparing a signal representative of an output voltage or current of the power converter relative to a level. A pulse-width modulation (PWM) signal including a series of pulses is produced by comparing the error signal to a ramp signal. The duty cycle of the PWM signal is compared to a reference duty cycle. If the duty cycle of the PWM signal is less then the reference duty cycle then the next pulse in the PWM signal is skipped.

Suprathreshold effects of adaptation produced by amplitude modulation.

Abstract: This work extends the study of adaptation to amplitude modulation (AM) to the perception of highly detectable modulation. A fixed-level matching procedure was used to find perceptually equivalent modulation depths for 16-Hz modulation imposed on a 1-kHz standard and a 4-kHz comparison. The modulation depths in the two stimuli were compared before and after a 10-min exposure to a 1-kHz tone (adaptor) 100% modulated in amplitude at different rates. For modulation depths of 63% (20 log m=−4) and smaller, the perceived modulation depth was reduced after exposure to the adaptor that was modulated at the same rate as the standard. The size of this reduction expressed as a difference between the post- and pre-exposure AM depths was similar to the increase in AM-detection threshold observed after adaptation. Postexposure suprathreshold modulation depth was not appreciably reduced when the modulation depth of the standard was large (approached 100%). A much smaller or no reduction in the perceived modulation depth...

Method and apparatus for frequency modulation

Abstract: A voltage controlled oscillator (1), a variable frequency divider (2), a phase comparator (3), and a loop filter (4) form a Phase Locked Loop (PLL). A sigma-delta modulator 5 sigma-delta modulates data obtained by adding a fractional part (M2) of the frequency division factor data with modulation data (X) by using an output signal of the variable frequency divider (2) as a clock. An output signal of the sigma-delta modulator (5) is added to an integral part (M1) of the frequency division factor data, and the resultant data becomes effective frequency division factor data (13) of the variable frequency divider (2). An output signal of the sigma-delta modulator (5) also becomes control data (14) after passing through a D/A converter (6), a low-pass filter (7), and an amplitude adjustment circuit (8). The control data (14) is inputted into a frequency modulation terminal of the voltage controlled oscillator (1). Therefore, it is possible to provide a frequency modulator that can use a reference signal source having no frequency modulation function, and perform modulation over a wide range of frequencies based on a digital modulation signal.

Noise radar using random phase and frequency modulation

Abstract: Pulse compression radar is used in a great number of radar applications. Excellent range resolution and high ECCM performance can be achieved by wide-band modulated long pulses, which spread out the transmitted energy in frequency and time. By using random noise as waveform, the range ambiguity can be suppressed as well. The same limit in Doppler resolution is achieved as for a coherent Doppler radar when the time compression of the reference is tuned to that of the target. Mostly, the random signal is transmitted directly from a noise generating HF-source. A sine wave, which is phase or frequency modulated by random noise, is an alternative giving similar performance but higher transmitted mean power when peak-limited transmitters are applied. A narrower modulation noise bandwidth can also be applied to generate the same output bandwidth. For phase modulation, the bandwidth amplifying factor is simply the rms value of the phase modulation, and for a frequency modulating waveform, the output rms bandwidth equals the rms-value of the frequency modulation. The results also show that the range sidelobes can be highly suppressed compared with the sidelobes of the modulating signal. The mean and variance of the correlation integral are derived in terms of the autocorrelation function of the modulation. The combined effects of low range sidelobes and enhanced range resolution make frequency and phase modulation attractive.

Method and system for generating variable frequency cyclic waveforms using pulse width modulation

Abstract: A method and system for generating variable frequency cyclic waveforms using pulse width modulation (PWM) to provide adjustable precision frequency and enhanced resolution is disclosed. The technique includes a plurality of sets of duty cycle values, each set corresponding to the desired waveform profile at a given frequency, coupled with a mechanism for applying a selected duty cycle for a variable number of PWM cycles, to achieve an adjustable fine resolution of the waveform frequency.

Modulation masking produced by complex tone modulators

Abstract: Thresholds were measured for detecting sinusoidal amplitude modulation in the presence of a complex-tone masker modulation. Both modulations were applied to the same sinusoidal carrier. Two different masker modulations were used: (i) a pair of components beating at the difference frequency and (ii) a three-tone complex producing a sinusoidal amplitude modulation of the modulation depth at the difference frequency between adjacent components. Both maskers show a periodicity in the waveform that is not contained in the envelope spectrum itself but can be observed when the envelope of the envelope, referred to as the "venelope" [Ewert et al., J. Acoust. Soc. Am. 112, 2921-2931 (2002)], is calculated. For a signal frequency equal to the masker-venelope periodicity, modulation depth at threshold was measured as a function of the signal phase relative to the phase of the masker-venelope component. Signal frequencies of 5, 30, and 90 Hz were used. It was found that masking was phase dependent for all three signal frequencies. Thresholds were lower for the in-phase condition, where maxima in the signal waveform coincided with maxima in the masker-venelope waveform, than for the antiphase condition. The maximum threshold difference was 15 dB. The results are in contrast to recent data [Moore et al., J. Acoust. Soc. Am. 106, 908-918 (1999)], where lowest thresholds were reported for the antiphase condition in a similar experiment. The present data are in line with the idea that a nonlinearity prior to a modulation filterbank extracts the venelope of the masker modulator. However, a compressive nonlinearity such as that associated with the processing on the basilar membrane cannot account for the empirical findings, since it predicts the opposite phase effect.

Load-dependent variable frequency voltage regulator

Abstract: A pulse width modulation voltage regulator comprises a pulse width modulation circuit and a control circuit (103). The control circuit is operable to reduce a pulse modulation frequency of the pulse width modulation circuit when a load current increases and to increase the pulse modulation frequency of the pulse width modulation circuit when the load current decreases.

Method and apparatus for re-modulation using zero IF

Abstract: The present invention provides for a first modulation at an arbitrary frequency and a second modulation at another arbitrary frequency. To achieve this, the present invention demodulates the first modulation using the same reference oscillator signal that was used in the first modulation. Because modulation and demodulation are achieved using the same reference oscillator signal, a close approximation of the original signals is achieved. With this close approximation, a subsequent re-modulation can be readily achieved at a second arbitrary frequency and can further be achieved using low-cost synthesizer and modulation components. In effect, a first modulation is achieved at a first frequency; the first modulation is then demodulation to zero frequency; and, in turn, a second modulation (i.e., re-modulation) is achieved at a second frequency.

Electronic circuit, modulation method, information processing device, and information processing method

Abstract: A shaped-wave application section inputs a first pulse signal corresponding to transmission data output from a transmission data output section, and applies, to a modulation and amplification section, a signal wave corresponding to a second pulse signal such that the waveform of the first pulse signal is shaped. The pulse signal applied to the base of the transistor of the modulation and amplification section is amplitude-modulated into an amplitude-modulated wave in which the amplitude-modulated portion is strengthened, in accordance with the signal wave corresponding to the second pulse signal applied to the emitter thereof. The amplitude-modulated wave is supplied to an antenna section including a resonance circuit via the collector thereof, and is transmitted as an electromagnetic wave from the antenna section.

Method of frequency limitation and overload detection in a voltage regulator

Abstract: A regulated output voltage and an output current are generated by using a switching device for providing the output current and controlling the switching device with the first control circuit functioning in a pulse width modulation mode and in an alternative manner with a second control circuit functioning in a pulse frequency modulation mode. A second feedback circuit is included in the second control circuit and a time delay is introduced in the second feedback circuit in order to introduce a limitation of the pulse frequency.

Back-illuminated pulse-frequency-modulated photosensor using silicon-on-sapphire technology developed for use as epi-retinal prosthesis device

Abstract: An intra-ocular epi-retinal prosthesis device using a back-illuminated photosensor is proposed and demonstrated for the first time. The photosensor, based on a pulse frequency modulation, is fabricated on a transparent sapphire substrate to detect the backside incident light. Experimental results show that the device is sensitive over a dynamic range of incident light of 30 dB.

Reduction of residual amplitude modulation in frequency-modulated signals

Abstract: One system of the present invention includes a modulated light source subsystem to provide a first light signal with a first modulation index, and a second light signal with a second modulation index. The system also includes a region to receive an analyte for evaluation and direct the first light signal thereto, and a detector responsive to the second light signal and a third light signal from the region to provide an output representative of spectroscopic information. The third light signal further includes noise induced by residual amplitude modulation that is reduced at the detector by the second light signal in accordance with a difference between the first modulation index and the second modulation index.