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.

Control method and circuit of double-module modulation and mode smooth conversion switching power supply

Abstract: The invention relates to a control scheme of double-module operation of a direct current switching power supply, which is used for direct current voltage stabilization and improves the efficiency when the power supply is in underloading. Under heavier load, a system adopts a pulse width modulation (PWM) mode. When in underloading, the system automatically enters a pulse frequency modulation (PFM)mode, and outputs stable direct current voltage according to detected current and load voltage by corresponding logic. Under the PFM mode, equivalent switching frequency of the power supply is lowered following the reduction of the load, and the switching loss is reduced, thereby improving the efficiency when in underloading. When the load is jumped, the system automatically performs the smooth transition between the PFM mode and the PWM mode and ensures the rapid dynamic response of the output voltage. Under the PWM mode, the system integrates feedforward control of the input voltage and increases the capacity of resisting the jump of the input voltage by the load voltage. The invention is suitable to power supply control of a portable media player, an intelligent mobile phone, a load point power supply and the like.

Fm-cw radar device

Abstract: An FM-CW radar device in which an FM modulated wave outputted from a modulated signal generator has a gradient (modulation gradient) of frequency variation with respect to the time axis. The radar device comprises means for controlling the modulated frequency width or modulation period of a modulation signal to vary the modulation gradient. Further comprised is means for detecting a signal component changing with a change of the modulation gradient to discriminate the signal from a target object from other signals. In the case of an FM-CW radar device in which the transmission, the reception, or the transmission and reception are carried out by a time-division ON-OFF control, there is further comprised means for detecting the signal which changes with a change, if made, of the frequency for the ON-OFF control, thereby to discriminate the signal the target object from other signals.

Self-phase modulation and compression of few-optical-cycle pulses

Abstract: The nonlinear propagation of few-optical-cycle pulses through a dispersive Kerr medium, as, e.g., fused silica, is studied theoretically using a global approach to dispersion without applying the slowly varying envelope approximation. Contrary to amplitude self-steepening, a nearly triangular pulse shape with the steep side on the leading front is predicted. The calculation of the ultrawide spectrum and the spectral phases demonstrates that half-cycle pulses with a full width at half maximum as short as 0.5 fs and single-cycle pulses can be generated by the application of an appropriate broadband modulator for the compensation of the frequency-depending phase.

Grating lobes suppression in stepped-frequency pulse train

Abstract: Frequency stepping is one of the known techniques employed by modern radars to achieve high range resolution. The main advantage of this approach is that the actual instantaneous bandwidth of a radar is quite small compared with the total processing bandwidth. This allows the transmission of waveforms with extremely wide overall bandwidth (and, as a consequence, the attainment of high range resolution) without the usage of the expensive hardware needed to support wide instantaneous bandwidth. Unfortunately, the autocorrelation function of uniform frequency stepped pulse trains can have undesirable peaks, known as "grating lobes." We address this issue, using an approach which allows us to suppress grating lobes below a desired threshold level in the case of appropriately chosen stepped frequency waveforms. We discuss in detail how to choose relevant parameters in order to produce such waveforms with small grating lobes, and give examples of waveforms with small overlap ratio. We also discuss the issue of high sidelobes in the vicinity of the mainlobe, which are inevitable in a stepped frequency train of linear frequency modulated (LFM) waveforms with small overlap ratio, and show that it is possible to suppress these, as well as the grating lobes, by means of nonlinear frequency modulation (NLFM).

High pass modulation of a phase locked loop

Abstract: A radio frequency modulator based on direct frequency/phase modulation of output signal of a controllable oscillator ( 724 ) that is a part of a phase locked loop (PLL) provides a direct modulator that is able to operate over a wide frequency range with a flat frequency response. A modulation signal is digitally processed ( 721, 730 ) before injection to a high-pass path of a direct modulator. Applicability of digital signal processing is based on the fact that the modulation signal is a base band signal. Therefore, the modulation signal ( 702 ) occupies such a band in the frequency domain so that a sufficient ratio of a sampling rate to an upper edge frequency of the modulation signal can be achieved. Digital processing is used for compensating an effect of non-flat high-pass PLL transfer function and/or to perform pre-distortion of the input signal of a controlled oscillator to compensate an effect of non-linearity of a controlled oscillator.