Highly-linear voltage-to-time converter (VTC) circuit for time-based analog-to-digital converters (T-ADCs)

Time-based ADC is an essential block in designing software radio receivers because it exhibits higher speed and lower power compared to the conventional ADC, especially, at scaled CMOS technologies. In time-based ADCs, the input voltage is first converted to a pulse delay time by using a Voltage-to-Time Converter (VTC) circuit, and then the pulse delay time is converted to a digital word by using a Time-to-Digital Converter (TDC) circuit. In this paper, a novel VTC circuit is proposed which achieves high linearity and large dynamic analog input range. This new VTC circuit can be used in a 5 bit time-based ADC with no sample and hold circuit for analog input frequencies up to 4 GHz.