A Successive Approximation Switched Capacitor DC DC Converter With Resolution of $V_{\text{IN}{2^N} for a Wide Range of Input and Output Voltages
A fully integrated successive approximation (SAR) switched capacitor (SC) DC DC converter is presented that overcomes the coarse output voltage resolution limitation of traditional SC converters. An SAR SC converter cascades multiple stages of 2:1 SC converters, and achieves a fine grained conversion ratio resolution of VIN/2N, where VIN is the input voltage and N is the number of stages. As the SAR SC converter generates the output voltage through SAR, each stage of 2:1 SC converter provides a fixed voltage level, requiring minimal configuration change for regulation. Analysis shows that the SAR SC converter has a slow switching limit output impedance increasing proportionally to log2 (number of resolution) and switching loss of bottom plate parasitic capacitor decreasing with the number of stages. As a test chip, an SAR SC converter with 7 b resolution is fabricated in 180 nm CMOS process and implemented by cascading 4:1 and five 2:1 two phase interleaving SC stages. It achieves 31.25 mV voltage resolution with output voltages over 0.4 V at VIN 4 V. Using this fine grain voltage regulation approach, line and load regulations are implemented with a feedback/feedforward controller with peak efficiency of 72% for load currents from 0 to 300 mA. The test chip occupies 1.69 mm2 and utilizes on chip capacitors of 2.24 nF in total.
IEEE Journal of Solid State Circuits