Pulse-frequency modulation

About: Pulse-frequency modulation is a research topic. Over the lifetime, 4151 publications have been published within this topic receiving 53039 citations. The topic is also known as: PFM.

Voltage-boosting wireless power delivery system with fast load tracker by ΔΣ-modulated sub-harmonic resonant switching

Abstract: Recently, many applications have emerged that use wireless power delivery technology. A new standard “Qi” [1] has been established for battery operated portable devices. The rechargeable battery acts as a power buffer and shields the rapid load variation. Therefore, the requirement of the response to load variation is not so stringent and time constant of the power control loop is longer than several tens of milliseconds. Several hundred kHz band is chosen for switching frequency to reduce the power loss and frequency modulation (FM) [2] or pulse-width modulation (PWM) [3] are used for power control because of their relaxed in-band spurious emission regulation.

Temporal compression of light

Abstract: The 5890 A output from a CW dye laser was converted into a train of 0.5 ns pulses by frequency modulation and passage through a near-resonant atomic vapor delay line of Na. The theory of the process is discussed in both the time and frequency domains. Using a modulation index of 120 at a frequency of 17.8 MHz, we obtained values for the temporal compression ratio and intensity enhancement of 112 and 14, easily the largest that have been reported.

Direct modulation architecture for amplitude and phase modulated signals in multi-mode signal transmission

Abstract: Multiple-mode direct phase/amplitude modulation circuitry ( 20 ) for use in a transceiver ( 17 ) of a device such as a wireless handset ( 10 ) is disclosed. The modulation circuitry ( 20 ) includes a modulation loop ( 36 ) for modulating a phase signal into a Gaussian-Minimum-Shift-Keyed (GMSK) signal for transmission in a first mode. The modulation loop ( 36 ) may include a phase-locked loop ( 45 ) with its frequency controlled by a Σ-Δ demodulation of a compensated version of the phase signal, or alternatively may produce a modulated signal from a direct digital synthesis circuit ( 70; 70′ ). An amplitude signal is converted into an analog signal and applied to a single-sideband mixer ( 43 ) for combination with a frequency multiplied version of the phase-modulated signal (GMSK(t); PH(t)), producing an amplitude and phase modulated signal for transmission in a second mode.

Width-modulated square-wave pulses for ultrasound applications

Abstract: A method of output pressure control for ultrasound transducers using switched excitation is described. The method generates width-modulated square-wave pulse sequences that are suitable for driving ultrasound transducers using MOSFETs or similar devices. Sequences are encoded using an optimized level-shifted, carrier-comparison, pulse-width modulation (PWM) strategy derived from existing PWM theory, and modified specifically for ultrasound applications. The modifications are: a reduction in carrier frequency so that the smallest number of pulses are generated and minimal switching is necessary; alteration of a linear carrier form to follow a trigonometric relationship in accordance with the expected fundamental output; and application of frequency modulation to the carrier when generating frequency-modulated, amplitude- tapered signals. The PWM method permits control of output pressure for arbitrary waveform sequences at diagnostic frequencies (approximately 5 MHz) when sampled at 100 MHz, and is applicable to pulse shaping and array apodization. Arbitrary waveform generation capability is demonstrated in simulation using convolution with a transducer?s impulse response, and experimentally with hydrophone measurement. Benefits in coded imaging are demonstrated when compared with fixedwidth square-wave (pseudo-chirp) excitation in coded imaging, including reduction in image artifacts and peak side-lobe levels for two cases, showing 10 and 8 dB reduction in peak side-lobe level experimentally, compared with 11 and 7 dB reduction in simulation. In all cases, the experimental observations correlate strongly with simulated data.

Non-linear constant envelope modulator and transmitter architecture

Abstract: A constant envelope modulator and transmit architecture for a wireless communication system is provided and a method for operating the same. The constant envelope modulator includes a differential encoder which receives data to be transmitted and creates in-phase and quadrature components of a modulation signal to be transmitted. The in-phase and quadrature components are passed through digital filters in order to give the modulation a particular shape. The in-phase and quadrature components of the modulation signal have both phase information and amplitude information on the modulation, where the constant envelope modulator removes the amplitude modulation (AM) information from the modulation signal to provide constant envelope in-phase and quadrature modulation signals and an accompanying AM envelope signal. The resultant constant envelope in-phase and quadrature modulation signals are combined at a radio frequency for transmission into a constant envelope phase modulation signal. The constant envelope phase modulation signal is fed through a non-linear power amplifier to bring the modulation signal to a proper output power level for transmission. The AM content of the modulation signal is then reintroduced into the constant envelope phase modulation signal at the non-linear power amplifier after the point of amplification of the constant envelope phase modulation signal in order to reintroduce the amplitude information into the signal. The constant envelope modulator and transmit architecture of the present invention allows the entire structure to be operated in an efficient, non-linear mode.