A very high light-load efficiency low-ripple-voltage pulse-frequency modulation (PFM) buck converter for Internet of Things applications is presented in this article. The PFM buck converter is widely ...used because of its higher light-load efficiency. However, it has a higher ripple voltage than its pulsewidth modulation counterpart. Although the ripple voltage of a PFM buck converter can be reduced by increasing the output capacitance, we find that this leads to a decrease in the light-load efficiency due to increased controller loss. This problem is analyzed and verified by IC measurements in this article. The proposed PFM buck converter remarkably reduces the controller loss even at low ripple voltages by replacing the static comparator with a dynamic comparator, which provides a high voltage gain, fast evaluation speed, and low power consumption. In addition, to further reduce the controller loss, a dynamic shutdown control method, which selectively turns off control circuits, is used. The proposed PFM buck converter was fabricated with 0.35-μm CMOS technology. The magnitude and variation of the output ripple voltage are 3 and 2 mV, respectively, and the light-load and peak efficiencies are 81.1% and 94.8%, respectively.
Abstract The acquisition of frequency modulation in self-mixing interferometry opens the way to a new generation of instruments, with significantly superior performance compared to traditional ...self-mixing interferometers. In this work, we experimentally confirm the noise limit dependence of this kind of interferometer on the laser source linewidth. The obtained results confirm the theoretical prediction, opening the way for a deeper improvement in sensitivity, by employing narrow-line lasers in this interferometric configuration.
In this paper, we propose a fully-integrated reconfigurable charge pump in a 0.18-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> CMOS process; this converter is ...applicable for self-powered Internet-of-Things applications. The proposed charge pump uses a two-dimensional frequency modulation technique, which combines both the pulse-frequency modulation (PFM) and pulse-skip modulation (PSM) techniques. The PFM technique adjusts the operating frequency of the converter according to the variations in the load current, and the PSM technique regulates the output voltage. The proposed two-dimensional frequency modulation technique can improve the overall power conversion efficiency and the response time of the converter under light load conditions. A photovoltaic cell was chosen as the input source of the proposed converter. To adapt to the variations in the output voltage of a photovoltaic cell under different light illumination intensities, we built a reconfigurable converter core with multiple power conversion ratios of 2, 2.5, and 3 for the regulated output voltage of 1.2 V when the input voltage ranged from 0.53 V to 0.7 V. Our measurement results prove that the proposed capacitive power converter could achieve a peak power conversion efficiency of 80.8%, and the efficiency was more than 70% for the load current that ranged from <inline-formula> <tex-math notation="LaTeX">10~\mu \text{A} </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">620~\mu \text{A} </tex-math></inline-formula>.
The recently proposed orthogonal time-frequency-space (OTFS) modulation technique was shown to provide significant error performance advantages over orthogonal frequency division multiplexing (OFDM) ...over delay-Doppler channels. In this paper, we first derive the explicit input-output relation describing OTFS modulation and demodulation (mod/demod). We then analyze the cases of: 1) ideal pulse-shaping waveforms that satisfy the bi-orthogonality conditions and 2) rectangular waveforms which do not. We show that while only inter-Doppler interference (IDI) is present in the former case, additional inter-carrier interference (ICI) and inter-symbol interference (ISI) occur in the latter case. We next characterize the interferences and develop a novel low-complexity yet efficient message passing (MP) algorithm for joint interference cancellation (IC) and symbol detection. While ICI and ISI are eliminated through appropriate phase shifting, IDI can be mitigated by adapting the MP algorithm to account for only the largest interference terms. The MP algorithm can effectively compensate for a wide range of channel Doppler spreads. Our results indicate that OTFS using practical rectangular waveforms can achieve the performance of OTFS using ideal but non-realizable pulse-shaping waveforms. Finally, simulation results demonstrate the superior error performance gains of the proposed uncoded OTFS schemes over OFDM under various channel conditions.
This paper presents a power management unit that meets the need of small-form-factor net-zero energy systems by aggregating the maximum available power from three different energy sources while ...simultaneously regulating three output power rails over a wide dynamic load range, while also managing the charging and discharging of a battery, all in a single-stage single-inductor converter. The proposed architecture uses hysteresis control to regulate the voltage of each harvester at their respective maximum power points (MPPs) using pulse-frequency modulation (PFM) and adaptive inductor ON-time, all via a low-power event-driven controller. The converter, fabricated in 28-nm fully-depleted silicon-on-insulator (FDSOI), achieves a peak efficiency of 89% and supports an output power range from <inline-formula> <tex-math notation="LaTeX">1~\mu \text{W} </tex-math></inline-formula> to 60 mW with efficiency >75% at <inline-formula> <tex-math notation="LaTeX">V_{\text {out}}=1 </tex-math></inline-formula> V and >69% at <inline-formula> <tex-math notation="LaTeX">V_{\text {out}}=0.6-0.9 </tex-math></inline-formula> V, all with a quiescent power of only 262 nW.
In this paper, we propose underwater acoustic (UWA) communications using a generalized sinusoidal frequency modulation (GSFM) waveform, which has a distinct ambiguity function (AF) and correlation ...function characteristic. For these reasons, it is more robust in multipath channels than the conventional chirp spread spectrum (CSS) with a linear frequency modulation (LFM) waveform. Four types of GSFM waveforms that are orthogonal to each other are applied for each symbol in the proposed method. To evaluate the performance of the proposed method, we compared the performances of the proposed method and conventional method by conducting diverse experiments: simulations, lake trials and sea trials. In the simulation results, the proposed method shows better performance than the conventional method. The lake trial was conducted with a distance of 300~400 m between the transmitter and receiver. As a result of the experiment, the average bit error rate (BER) of the proposed method is 3.52×10−2 and that of the conventional method is 3.52×10−1, which shows that the proposed method is superior to the conventional method. The sea trial was conducted at a distance of approximately 20 km between the transmitter and receiver at a depth of 1500 m, and the receiver was composed of 16 vertical line arrays (VLAs) with a hydrophone. The proposed method had a BER of 0.3×10−2 in one channel and was error free in the other.
Chaotic sinusoidal pulse width modulation (SPWM) can be used to suppress the electromagnetic interference in power converters. In this paper, a mathematical method for estimating power losses in ...insulated-gate bipolar transistors and freewheeling diodes occurring under chaotic frequency modulation SPWM (CFM-SPWM) switching is proposed. This method is based on the features of the chaotic mapping and uses semiconductor datasheet information to calculate the power losses in a discrete way. Analytical expressions and approximations for estimating the losses for the cases of SPWM and CFM-SPWM switching, respectively, are presented. This paper includes a quantitative comparison of the losses under the two previously mentioned cases. It is confirmed that CFM-SPWM does not result in higher power losses when it greatly improves electromagnetic compatibility of power converters, and hence, its adoption will not require any modified converter thermal design. Experimental results taken from a single-phase ac-dc converter are presented to prove the validity of the proposed method and associated results.
This article proposes an autonomous pulse frequency modulation (APFM) scheme for wireless battery charging in which the self-excited oscillating (SEO) wireless power transfer (WPT) system can offer ...output power regulation with reliable zero-voltage switching (ZVS). The key is to utilize the self-excited oscillation feature to adjust the WPT operating frequency autonomously so as to deliver more power in the strong coupling region than the traditional forced oscillating (FO) WPT system while the transmission efficiency can maintain at a high level. In the weak coupling region, the system becomes equivalent to the FO-WPT system. The pulse frequency modulation enables the system to adjust the output power by changing its duty ratio. Besides, reliable ZVS is achieved by extracting and processing the current signal at the primary side. Both theoretical analysis and experimental verification are provided to support the feasibility of the proposed APFM for SEO-WPT system.
This article presents a low-quiescent current, high-efficiency buck converter. A dynamic pulse frequency modulation control with adaptive off -time was proposed to increase efficiency. An ultra-low ...power system can be achieved with minimized quiescent current in each block and a low-power bandgap reference. The entire proposed buck converter consumed a quiescent current of 464 nA with a peak efficiency of 93.7% over the load range from 0 to 50 mA. In addition, a maximum converter output ripple of only 28 mV was achieved at this ultra-low quiescent current.
High switching frequency is an effective method to improve power density for LLC resonant converters. However, conventional digital controllers, such as general-purpose digital signal processors and ...microprocessors, have limited frequency resolution, which induces high primary- and secondary-side current variation and leads to poor output voltage regulation. In this paper, a hybrid control method combining pulse frequency modulation (PFM) and pulse width modulation is proposed to overcome the limited frequency resolution issue. The proposed hybrid control method focuses on steady-state operation, and its operating principles are introduced and analyzed. In addition, the proper magnetizing inductance and dead time duration are derived to ensure that the power mosfets achieve zero voltage switching with the proposed control method. The improved voltage regulation performance is compared with the conventional PFM control and verified through simulation and experimental results using a 240 W prototype converter operating at a switching frequency of 1 MHz.
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