An opamp-free second-order noise-shaping SAR ADC with 4x passive gain using capacitive charge pump

This paper presents a compact and robust opamp-free noise shaping (NS) successive approximation register (SAR) analog-to-digital converter (ADC). The proposed NS SAR ADC adopts extra one passive feed-forward path summing in realizing second-order noise shaping with the minimum modification to a standard SAR. Compared with previous works, the noise sources of residue sampling and first-order integration on filter capacitors are obviated. It implements 4x passive gain by capacitive charge-pump techniques that compensates the partial loss of residue voltage and relaxes the specifications of comparator. According to the behavioral modeling and simulation results, an ENOB of 16.88-bit is achieved based on a 10-bit DAC array, at the OSR of 16. Through utilizing the Monte Carlo simulation, the proposed ADC architecture is proven to be a robust system.