6-bit 1.6GS/s ADC with low input capacitance in a 0.18um CMOS

Chun-Chieh Chen,  Yu-Lun Chung,  Chen-I Chiu
Department of Electronic Engineering, Chung-Yuan Christian University.


Abstract

This work presents a novel flash analog-to-digital converter (ADC) with low input capacitance. Utilizing the proposed distributed track-and-hold pre-comparators (THPCs) architecture, the loading capacitances of the ADC front-end sampling sub-circuits can be markedly reduced, thereby improving operation speed. In a standard 0.18┬Ám CMOS process, a 1.6GS/s 6-bit flash ADC is implemented to demonstrate the feasibility of the proposed distributed THPC architecture. The equivalent input capacitance of each input port of the proposed flash ADC is only 400fF, which is an easily driven interface. Furthermore, clocked timing buffers are inserted in the encoder to accelerate the operational speed of the proposed flash ADC.

Post-layout simulation results demonstrate that the proposed ADC achieves an SNDR of 35.81dB, which is 5.66 ENOB at 1.6GS/s with a 793.8MHz input signal frequency. The proposed ADC consumes 300mW from a 1.8-V supply at full operating speed.