The present invention provides an n-bits successive approximation register (SAR) analog-to-digital converting (ADC) circuit, comprising: an n-bits SAR control logic, a p-type capacitor network including a DAC_p array and a sampling capacitor C_Sp, an n-type capacitor network including a DAC_narray and a sampling capacitor C_Sn; and a comparator for comparing outputs from the p-type capacitor network and the n-type capacitor network, wherein a power supply and ground are directly connected to the p-type capacitor network and the n-type capacitor network without using reference voltages produced by a reference voltage generator. The n-bits SAR control logic comprises n shift registers, n bit registers, and a switching logic. The comparator comprises a first pre-amplifier, a second pre-amplifier and a dynamic latch. Alternative, the comparator comprises a four-input pre-amplifier and a dynamic latch.