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.

System And Method For Controlling A Current Limit With Primary Side Sensing Using A Hybrid PWM and PFM Control

Abstract: A hybrid constant current control system that uses both pulse width modulation (PWM) and pulse frequency modulation (PFM) control. When transitioning from constant voltage mode to constant current mode the present invention can continue to control using PWM. Thereafter, when the voltage has dropped, the present invention smoothly transitions to PFM mode. The point of transition is based upon the switching frequency and the lowest rated voltage of operation. The system and method avoids very short (narrow) Ton times which ensures accurate constant current (CC) control with bipolar junction transistor (BJT) devices. The present invention also avoids acoustic noise because the switching frequency is maintained at a high enough level to avoid such acoustic noise even when the energy transferred through the transformer is still substantial and the output voltage is not too low. In addition the output current limit is insensitive to variation in the inductance-input voltage ratio, and is minimized against leakage inductance.

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.

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.

Grain loss monitor

Abstract: A grain loss monitor for a combine harvester derives a grain loss rate signal in accordance with the number of grains impinging on a transducer and a ground speed signal proportional to the ground speed of the combine and divides the former by the latter to derive an analog of grain loss per unit area which is independent of time. The preferred embodiment includes a one-shot multivibrator which is triggered to its unstable state to generate a fixed width pulse each time a grain kernel strikes the transducer, a tachometer coupled to the combine wheels and a period timed integrator triggered by tachometer pulses for deriving a unidirectional ground speed voltage inversely proportional to frequency of the tachometer pulses, a pulse frequency modulation chopper circuit turned on and off by the fixed width one-shot pulses and having its peak voltage controlled by the unidirectional ground speed signal for accomplishing division of grain loss rate by combine ground speed, and an averaging circuit for determining the average voltage of the chopper output pulses as an analog of grain loss per unit area.

A DCM-Only Buck Regulator With Hysteretic-Assisted Adaptive Minimum-On-Time Control for Low-Power Microcontrollers

Abstract: A 40-mA buck regulator operating in the inherently stable Discontinuous Conduction Mode (DCM) for the entire load range is presented. A pulse frequency modulation control scheme is implemented using a proposed hysteretic-assisted adaptive minimum-on-time controller to automatically adapt the regulator to a wide range of operating scenarios in terms of input, output, and passive component values while ensuring compensationless DCM operation with minimized inductor peak current. Thus, compact silicon area, low quiescent current, high efficiency, and robust performance across all possible scenarios can be achieved without any calibration. Moreover, power gating is employed in the analog circuits of the proposed controller to further improve efficiency at sub-mA loads. The regulator is integrated within a low-power microcontroller in 90-nm CMOS to power its digital core while allowing maximum flexibility in the powering options of the microcontroller and the choice of the passive components. It occupies 0.1 mm2 and achieves 92% peak efficiency, and 78.5% and 86% efficiency at 200-μA and 40-mA loads, respectively. It handles an input in the range of 1.8–4.2 V, an output in the range of 0.9–1.4 V, an inductor in the range of 4.7–10 μH, and an output capacitor in the range of 2.2–10 μF without any calibration or reoptimization.