A high-speed high-accuracy voltage-to-time-difference converter for time domain analog-to-digital converters

In this paper, a novel high-speed, high-accuracy voltage-to-time-difference converter (VTC) is presented. The proposed VTC addresses a load tuning scheme in order to fine tune the delay time of the symmetrical delay cell. This allows further improvement in its linearity. The load tuning circuit also provides a process sensing circuit which dynamically shifts the control voltage of the delay cell to mitigate overloading the following TDCs circuit. The VTC circuit is designed using a 0.18 μm CMOS process and simulation results show that the accuracy is 7 to 8 bits. The bandwidth can be up to 250 MHz. The VTC can be used in a high speed time based data converter with a sampling frequency up to 500 MHz.