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 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.

Dynamic Voltage Balancing Algorithm for Modular Multilevel Converter: A Unique Solution

Abstract: The modular multilevel converter (MMC) has several submodules in cascade. To control the submodule capacitors voltage, a new generalized dynamic voltage balancing algorithm along with a simple pulse width modulator structure is proposed in this paper. With proposed pulse width modulator structure, the dynamic voltage balancing algorithm can be easily implemented with any type of carrier based pulse width modulation (including level-shifted and phase-shifted pulse width modulation) scheme without any modifications. This method does not require the sorting technique for selection of submodule capacitors voltage. The performance of the proposed voltage balancing algorithm is presented for MMC with three-level flying capacitor submodules (MMC-3L-FC). The proposed method is also applicable to the conventional two-level half bridge submodules as well. The effectiveness of the proposed voltage balancing algorithm is verified with the phase-shifted carrier-based pulse with modulation scheme. The results obtained from the MATLAB/SIMULINK simulations on 6-kV/ 2.5-MW system and the dSPACE DS1103-based laboratory prototype of 208-V/3-kVA MMC-3L-FC system are in close relationship, and thus, the proposed methodology is validated.

Effects of carrier frequency, modulation rate, and modulation waveform on the detection of modulation and the discrimination of modulation type (amplitude modulation versus frequency modulation).

Abstract: Initially, psychometric functions were measured for the detection of amplitude modulation (AM) or frequency modulation (FM), using a two-alternative forced-choice (2AFC) task. Carrier frequencies were 125, 1000, and 6000 Hz, and modulation rates were 2, 5, and 10 Hz. For the two lower carrier frequencies, FM detection tended to be best at the lowest modulation rate while AM detection was best at the highest rate. For the 6000-Hz carrier, both AM and FM detection tended to be poorest at the lowest modulation rate. Then, pairs of values of AM and FM were selected that would be equally detectable, and psychometric functions were measured for the discrimination of AM from FM, again in a 2AFC task. For carrier frequencies of 125 and 1000 Hz, the ability to discriminate AM from FM was always poorest at the highest modulation rate (10 Hz); at this rate some subjects were essentially unable to discriminate AM from FM when the detectability of the modulation was relatively low (d' of 1.16 and below). For a modulation rate of 2 Hz, and when the detectability of the modulation was moderate (d' up to about 2), some subjects discriminated the type of modulation rate varied across subjects, but there was still a trend for poorer discrimination of modulation type at the highest modulation rate. It is suggested that FM detection at a 10-Hz modulation rate is based largely on changes in excitation level for all carrier frequencies. For a 2-Hz modulation rate, and for the two lowest carrier frequencies, an extra mechanism, possibly based on phase locking, may play a role in the detection and discrimination of FM. This mechanism may be ineffective at modulation rates above about 5 Hz because the stimuli spend insufficient time at frequency extremes. To check on this, psychometric functions were measured for the detection of FM and AM using quasitrapezoidal modulation with a rate of five periods per second and carriers of 250, 1000, and 6000 Hz. This produced improvements in performance relative to that obtained with 5-Hz sinusoidal modulation and, for the two lower carrier frequencies only, the improvements were markedly greater for FM than for AM detection. This is consistent with the idea that the use of of phase-locking information depends on the time that the stimuli spend at frequency extremes.

Avoiding spectral efficiency loss in unipolar OFDM for optical wireless communication

Abstract: Unipolar orthogonal frequency division multiplexing (U-OFDM) has recently been introduced for intensity modulation and direct detection (IM/DD) systems. The scheme achieves higher power efficiency than the conventional direct-current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) at the expense of half the spectral efficiency for the same M-ary quadrature amplitude modulation (M-QAM) order. This paper presents a modulation approach which doubles the spectral efficiency of U-OFDM and still allows it to achieve better performance in terms of both electrical power and optical power dissipation compared to DCO-OFDM. The simulation results and the theoretical analysis suggest that the performance improvement of the proposed scheme over DCO-OFDM increases with the modulation order. This trend is different from the inherently unipolar state-of-the-art techniques such as U-OFDM, asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and pulse-amplitude-modulated discrete multitone modulation (PAM-DMT). It is typical for these schemes to exhibit a loss in the power efficiency as the spectral efficiency is increased. The novel approach is very promising for the achievement of high data rates in IM/DD systems. To the best of the authors' knowledge, this is the first design of a strictly unipolar orthogonal frequency division multiplexing (OFDM) scheme which requires no biasing and is able to demonstrate significant energy advantage over DCO-OFDM without sacrificing spectral efficiency.

Integrated circuit for controlling power converter by frequency modulation and pulse width modulation

Abstract: An integrated circuit contains the gate drivers and the control components for constructing a DC power supply in any of the most popular converter topologies. Multi-function elements in the control circuit minimize the area of the chip. The integrated circuit drives both the upper and lower switches of a half-bridge converter and separately regulates two power supply output voltages, one by pulse width modulation and the other by frequency modulation.