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.

Phase-locked loop frequency synthesizer including compensated phase and frequency modulation

Abstract: A phase-locked loop is disclosed that exhibits flat modulation characteristics over a wide range of carrier frequencies for either frequency or phase modulation at rates that are both within and outside the loop bandwidth. The disclosed arrangement is a programmable divide-by-N phase-locked loop frequency synthesizer wherein the feedback path includes a second phase-locked loop that serves as a tracking filter 20. Modulation is supplied to the main phase-locked loop via a first modulation path that couples the modulating signal to the frequency control terminal 50 of the phase-locked loop voltage-controlled oscillator 12 and via a second modulation path that couples the modulating signal to the phase-locked loop phase detector 22. To configure the system so that flat modulation is attained. the gain factors of the first and second modulation paths are established in accordance with specific relationships and the second modulation path includes a compensator network 44 having a transfer function that at least approximates that of the phase-locked loop 20 which is embedded in the system feedback path. Additionally, the modulation signal coupled to both modulation paths is adjusted on the basis of carrier frequency to compensate for frequency-related variation in the transfer characteristics of the main loop VCO. The transfer characteristic of the main loop phase detector 22 is controlled to maintain a constant loop bandwidth.

A Modulation Strategy to Operate Multilevel Multiphase Diode-Clamped and Active-Clamped DC–AC Converters at Low Frequency Modulation Indices With DC-Link Capacitor Voltage Balance

Abstract: This paper proposes a modulation strategy for multilevel multiphase diode-clamped dc–ac converters (also applicable to other functionally equivalent topologies) able to keep the dc-link capacitor voltages balanced under passive front ends, low frequency modulation indices (i.e., low number of switching transitions per fundamental cycle), any value of the amplitude modulation index, and any ac-side displacement power factor. A suitable phase voltage pattern with minimum number of switching transitions is presented for the n -level three-phase case. Subsequently, it is extended to higher number of switching transitions per fundamental cycle and to higher number of phases. Simulation results with three, four, and five levels; three and five phases; and several frequency-modulation-index values are presented to validate the proposed modulation strategy. Experimental results obtained with a four-level three-phase dc–ac converter prototype are also provided. The proposed modulation strategy enables the use of this type of converters in applications where the ac fundamental frequency may be close to the switching frequency, such as in high-power systems and variable-speed motor drives.

Advanced random pulse width modulation technique for voltage-controlled inverter drive systems

Abstract: The principles of an advanced random pulsewidth modulation (ARPWM) technique are presented. The means to alleviate the current deterioration at a low modulation index are investigated, along with the problem of the feasibility of the RPWM technique at supersonic, i.e., on the order of tens of kHz, switching frequencies. The results of computer simulation of the improved ARPWM technique and an experimental investigation of a prototype modulator are presented. Simple in practical realization, the ARPWM technique yields high-quality output current in voltage-controlled, three-phase inverters. The blurred harmonic spectra of the output voltage and current improve the acoustic and electromagnetic interference (EMI) characteristics of the inverter and can stave off resonant torsional vibrations in AC drive systems. >

10-Gb/s millimeter-wave signal generation using photodiode bias modulation

Abstract: We present a simple 120-GHz-band millimeter-wave (MMW) modulation method that uses the bias-voltage dependence of unitraveling-carrier-photodiode output power, which we call photodiode (PD) bias modulation. We investigated the dependence of the output-power-saturation mechanisms on the bias voltage. We used a lowpass filter in the bias circuit to increase the modulation bandwidth, and the 3-dB modulation bandwidth was over 7 GHz. We demonstrated the modulation of 120-GHz MMW signals at a data rate of 10 Gb/s using PD bias modulation.

Pulse width modulation speaker amplifier

Abstract: An open-loop speaker amplifier and a dynamic range reduction circuit are disclosed. The speaker amplifier includes a bridge driver and a bridge circuit. The bridge circuit includes a first set of switches and a second set of switches. When the first set of switches are activated, a positive current flows through a speaker load. When the second set of switches are activated, a negative current flows through the speaker load. The bridge driver generates a pulse width modulated signal and a delayed pulse width modulated signal to drive the first and second set of switches of the bridge circuit responsive to a modulation signal. The modulation signal may be, for example, a plurality of pulse code modulated samples representing sound. The dynamic range reduction circuit modifies a selected signal to reduce the dynamic range of the sound reproduced based on the modulation signal. The selected signal is either the modulation signal or a reference signal. In one embodiment, the dynamic range reduction circuit modifies the selected signal by processing the selected signal based on a smooth saturating function. In another embodiment, the dynamic range reduction circuit modifies the amplitude of the reference signal based on an envelope size of the modulation signal.