Abstract: With the continuous development of large-area gas electron multiplier-time projection chamber detectors, the density and integration of readout electronics are increasingly required. In this paper, a 10 bit, 20 MSPS successive approximation register analog-to-digital converter prototype chip is designed and fabricated by 180 nm CMOS process. Combining the SAR ADC chip with an analog front-end module and a digital signals processor, a fully digital front-end readout application specific integrated circuit for GEM-TPC is realized. The ADC is mainly composed of the DAC module, the dynamic comparator module, the asynchronous clock generation module and the SAR logic module. Simulation results show that when the input signal frequency is 1.836 MHz, the effective number of bits is 8.61 bit, and the core power consumption is about 3.3 mW/Ch.