Effective Design Techniques for High Density On-Chip Switched Capacitor Power Converters Aalay Kapadia Nishtha Sharma Department of Electrical Engineering Department of Electrical Engineering University of Texas at Dallas University of Texas at Dallas Richardson, Texas-75080, USA Richardson, Texas-75080, USA adk130330@utdallas.edu nxs135730@utdallas.edu Abstract - Power converter is a key component in micro-scale energy harvesting systems. Micro-scale energy harvesting has become an increasingly viable and promising area for powering ultra-low power systems [7]. Switched-capacitor (SC) power converters that use capacitors as energy storage elements offer much better power density than switched-inductor counterparts and are thus attractive in low-power area-constrained applications [hoi lee]. Switched-capacitor (SC) converters have shown tremendous promise in this regard due to favorable device utilization and scaling trends, and the emergence of high-density silicon-compatible capacitor technologies [8]. With the rising integration levels used to increase digital processing performance, there is a clear need for multiple independent on-chip supplies in order to support per-IP or block power management [11]. The growing demand for both performance and battery life in portable consumer electronics requires SoCs and power management circuits to be small, efficient, and dynamically powerful [10]. This paper first reviews various design techniques for implementing high density On-chip Switched-capacitor (SC) power converters and secondly suggests the best technique to solve aspects of power converter design: Area Density, Power Consumption & Efficiency. Index Terms - auto-reconfiguration; multiple-output switched- capacitor power converters; resonant converters; Favrat cell. I. INTRODUCTION Due to increasing integration of analog, digital and RF circuits in modern systems-on-chip (SoCs), there is a demand for a wide range of unique power supplies to work for various functionalities. Hence, an on-chip power management unit (PMU) is necessary to efficiently convert and provide these wide ranges of power supplies from a single source. With the progress of CMOS scaling, the minor supply voltage (V dd ) of the transistors has substantially decreased. For modern CMOS processes the nominal supply voltage is around 1V. With standard CMOS process, from the perspective of circuit designs, the most effective techniques to achieve high density, on-chip SCPC’s are reviewed. Switched capacitor is one of the DC-DC type converters. Similar to the switch mode power converter, a SC converter also consists of two major components, the power stage (also known as the charge pump), along with a closed loop feedback controller (and/or a feed-forward controller). The charge pump is an array of capacitors, which act as energy storage elements [6]. The use of power switches and clock control signals leads to appropriate switching actions that cause charge storage on the pumping capacitors and then charge transference to output load, with an ultimate goal to maintain a desired voltage value. The major benefit of SC power converters is their capability for monolithic integration at low power levels, since they employ capacitors as energy storage devices, instead of bulky, off-chip inductors. One major drawback of traditional SC DC–DC converters is their ability to provide only a single Conversion Gain (CG), which is defined as the ratio of the output voltage to the input voltage of the converter [6]. If the output voltage moves from this desired level, the efficiency of the SC converter reduces. If the variation is large, the power loss becomes unacceptably high due to charge redistribution. Hence, to accommodate a large output voltage range and to be capable of powering Dynamic Voltage Frequency Scaling (DVFS) based applications, a SC power converter with a fixed CG does not suffice. To overcome this drawback, state-of-the-art SCPC designs involve the use of reconfigurable power stages to supply variable output voltages. While such converters are capable of delivering multiple voltage levels, it is done so efficiently only at certain discrete levels, depending on the topology of the reconfigurable charge pump and its corresponding switching actions. Reconfigurable SC power converters can be implemented using Series-Parallel switched capacitor (SPSC) or Sequential switched capacitor (SQSC) based on your application for which you are using. SPSC is a reconfigurable SC power converter combined with interleaving technique, which is popular among the most of the designs. II. SC POWER STAGE DESIGN BASED TECHNIQUES A) ON-CHIP PUMPING CAPACITOR SIZING TECHNIQUE: System miniaturization and low-power operation is of critical importance for self powered microsystems. Hence, the design of two low-power reconfigurable SC power converters is done using adaptive control method. The first converter is a monolithic multiple gain step-down SC power converter with on-chip pumping capacitor sizing. The second converter further improves upon this design to provide both step-up and step-down voltage control [6]. The expression for V out of the reconfigurable SC power converter is given by Vout = 2Vin 3 + Ts 2 RoutCp (1)