Comparison and Design of Linear and Exponential Integrated Charge Pumps

This paper presents static and dynamic models for linear and exponential integrated charge pumps in both step-up and step-down modes. The static models are used to compare the slow-switching and fast-switching output resistance of various configurations, considering optimized and non-optimized capacitors and switches. In the dynamic models, the self-loading capacitance is determined using a simpler approach than previous works, allowing for a more straightforward comparison of the start-up time and charging efficiency. To highlight the differences between linear and exponential charge pumps, the working voltages of capacitors and switches are calculated, with these expressions guiding the selection of the most appropriate devices for each configuration. Additionally, parasitic capacitances and leakage currents are modeled and analyzed across the circuit configurations, and their impact on overall efficiency is assessed. The procedure for optimally sizing capacitors and switches using different device types is then discussed. Finally, two design examples in 65-nm CMOS technology are presented to validate the models, demonstrate design procedures, and highlight the advantages and limitations of practical implementations of each circuit.