Fibonacci Switched Capacitor Converters Research Articles

Analysis and Design of an Output Adjustable Resonant Switched Capacitor Converter

This article proposes an output adjustable resonant switched capacitor converter (OARSCC) based on resonant voltage doubler. The proposed OARSCC works in regulated mode with on time fixed frequency modulation. The output is regulated through controlling the power stored in resonant capacitor. With proper converter configuration, the conversion ratio is approximate to a straight line. When OARSCC works in nonregulated mode, the efficiency is higher, but the ratio is fixed. The loads of different stage are derived with load equivalent method to build an accurate model of the topology. The load equivalent method is also applicable to other types of multistage switched capacitor converter (SCC), such as Fibonacci SCC. A 100-W converter with a maximum boost ratio of eight times is made to verify the proposed topology and load equivalent method.

Constrained minimization of switched capacitor converter equivalent resistance by adjusting transistor sizes and duty cycles

This paper presents a novel optimization technique for Switched Capacitor Converters (SCCs). The optimization focuses on minimizing the SCC equivalent resistance by adjusting MOSFET widths and switching duty cycles. The optimized SCC parameters are obtained from numerical optimization with constant total transistor width and switching period constraints. The transistor carrier mobilities and gate-to-source voltages are accounted during the optimization. A Fibonacci SCC with two flying capacitors is used as an example and is simulated in a 65 ​nm low-power process. By comparing SCC parameters before and after the optimization, we obtain certain performance improvements. Particularly, at a switching frequency of 10MHz and 50Ω load, the optimized design shows improvement in average and minimum output voltage parameters by 2.5% and 4.1%, respectively, which are caused by 20.6% reduction of the equivalent resistance. The output voltage ripple is also decreased by 22.4%. By sweeping the duty cycle and transistor widths in simulation, the optimized parameters show nearly the best performance.

Analysis of parallel connected Fibonacci switched capacitor converter

Switched capacitor converter (SCC) is a power converter without magnetic components. SCCs have been used in various portable electric products such as flash memories and energy harvesting systems. Conservative SCCs separately charge and discharge their output capacitors during one operating cycle. This operation reduces power efficiencies and increases output ripple voltages. To improve this problem, a parallel connected Fibonacci SCC (PFSCC) was suggested. The symmetric structure of the PFSCC can lead to its better output performance. As a preliminary stage to design a hardware and a controller for the PFSCC, this paper performs an analysis of the PFSCC to derive parameters such as its optimized capacitance and power stage transfer function. Also, simulations and comparisons with 4 different SCCs are conducted to verify its performance.

An Analytical Approach for Design of a Cross-Connected Fibonacci Switched Capacitor Converter

Switched capacitor converters (SCCs) are used for low-power applications because they are designed without magnetic components. Among various types of SCCs, the Fibonacci SCC (FSCC) features a small size and high voltage gain. However, the FSCC performance can be more improved, which leads to suggest a cross-connected FSCC (CCFSCC). However, in the considered four-terminal equivalent circuit model for analyzing the CCFSCC, some circuit parameters, such as the operation frequency and capacitor capacitance of the SCC are neglected. In this paper, we propose an analytical approach to optimize the CCFSCC circuit parameters by deriving its voltage gain function. The validity of the addressed methodology is confirmed by comparing the outcomes with the results of simulations and experiments. It is shown that the average errors between the calculated and experimental voltage gains are 9%, and the average absolute errors between the calculated and simulated ones are under 0.1.

A Monolithic Voltage-Scalable Fibonacci Switched-Capacitor DC–DC Converter With Intrinsic Parasitic Charge Recycling

Switched-capacitor converter (SCC) features a compact solution due to its magnetic-less structure, which fulfills the high density requirement in low power applications. Compared to other SCC topologies, Fibonacci switched-capacitor converter (FSC) utilizes the least number of flying capacitors to perform any voltage conversion. This paper proposes a monolithic voltage-scalable FSC, which can be used in energy harvesting applications. The challenges to implement on-chip FSC are addressed. The parasitic charge loss is substantial in FSC. Therefore, a charge recycling technique exploiting the presence of parasitic capacitors in each other phase of FSC has been employed resulting in 27% reduction in the power loss, which improves the overall efficiency by 12.7%. For a proof of concept, the proposed converter is implemented in 0.5-μm CMOS technology on 4-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> die area. The postlayout simulation is carried out using Virtuoso ADE. With 0.3-V input voltage, the system achieves 47.5% peak power efficiency with 5-μW load.

A Family of Step-Up Resonant Switched-Capacitor Converter With a Continuously Adjustable Conversion Ratio

In this paper, a family of step-up resonant switched-capacitor converters (RSCs) with a continuously adjustable conversion ratio is proposed based on the Cuk dual-resonance core (DRC) featuring two resonant paths. By adopting the on-time fixed frequency modulation, the two resonant paths can conduct simultaneously and satisfy the charge balance of the flying capacitor during the overlapping period. As a result, the conversion ratio—upper bounded by two determined by the circuit configuration—can vary continuously and efficiently even at the light load condition (1/10 of the rated power). A comprehensive analysis—the operation principle, voltage-gain curve, and voltage/current stresses—about the DRC is given. In addition, the Cuk DRC was extended to the series–parallel switched-capacitor converter (SCC), Fibonacci SCC, and voltage doubler to form a family of step-up RSCs, whose voltage-gain curves of different topologies are derived. Moreover, a characteristic comparison between the Cuk DRC and the traditional “direct” and “indirect” resonant core is given. Then, a 48 to 62–94.6 V resonant core with peak efficiency 97.8% and maximum power 120 W under the open loop condition was built. The analyses were verified by both experimental and simulation results.

Multiphase Fibonacci Switched Capacitor Converters

A simple algebraic approach to synthesize Fibonacci switched capacitor converters (SCC) is analyzed and the expected losses are estimated. The proposed approach reduces the power losses by increasing the number of target voltages. The synthesized Fibonacci SCC is compatible with the binary SCC and uses the same switch network. This feature is exceptionally beneficial as it provides the option to switch between the binary and Fibonacci target voltages, increasing thereby the resolution of attainable conversion ratios. The theoretical results were verified by experiments.

Unified algebraic synthesis of generalised Fibonacci switched capacitor converters

A unified algebraic approach to the synthesis of generalised Fibonacci switched capacitor converters (SCC) has been developed. The proposed approach reduces the power losses by increasing the number of target voltages. It is shown that the binary and Fibonacci SCC are special cases of the proposed approach. Furthermore, the proposed generalised SCC is built around the same switch network as the binary and Fibonacci SCC. This feature is extremely beneficial, since it provides the option of switching between the different target voltages, thereby increasing the resolution of attainable conversion ratios. In the case of three flying capacitors, six new conversion ratios were introduced, in addition to the 13 that had already been realised. The theoretical results were verified experimentally.