REDUCTION OF PVT EFFECTS ON A SWITCHED-CAPACITOR DCIDC CONVERTER USING DIGITAL FEEDBACK CONTROL FOR RF HARVESTING APPLICATIONS

RF-harvesting wireless sensors are under a tight power budget due to the limitations of RF energy transmission. To optimize power delivery and increase voltage headroom for succeeding blocks, a step-up switched-capacitor DC/DC (SC DC/DC) converter is used for efficient power delivery under variable input and output conditions. This work presents a 700-mV output SC DC-DC regulator in 65rnn CMOS process designed for very low loading conditions, targeted to operate with a variable supply and input voltage of 450-600mV. The SC DC/DC converter (Fig. 1) is a switch network operating with clock signals controlled by a feedback loop for load detection. Regulation of the output voltage is done by accurately detecting the load current and setting the output impedance to the corresponding value by manipulating one or more of the following-s-switching frequency, switch on-resistance and/or duty cycle [1]. Simulations of a simple switch network using hysteretic feedback control [2] with no modifications show that the target specifications have been met. The output voltage across different process comers (Fig. 2) obtains a maximum ripple voltage of 100mV and minimum output of650mV. The maximum converter efficiency achieved in the simulations is 80%. Further testing shows that this can further be improved and optimized over the operating range. Current implementations of SC DC-DC converters rely on the optimization of analog blocks to improve regulator efficiency. These methods are impractical and expensive for RF harvesting applications. This work aims to lessen the area and power overhead of implementing reliable but complex analog circuitry using digital assistance for cheaper processing and computation