Dickson-Charge-Pump-Based Voltage-to-Time Conversion for Time-Based ADCs in 28nm CMOS

This article demonstrates a digitally friendly time-based analog-to-digital converter (ADC) exploiting Dickson charge-pump (CP) as part of a voltage-to-time conversion (VTC) implemented in 28-nm CMOS. In the proposed technique, the Dickson CP generates a ramp signal that is compared with the input voltage to generate a pulse of commensurable widths, which is then fed to a D-type flip-flop (DFF)-based time-to-digital converter (TDC). The TDC is composed of CMOS DFFs and digital circuits for digital conversion without any use of analog-intensive circuits, e.g., amplifiers or current sources. Thanks to the robustness of Dickson CP characteristics, the digital outputs of the proposed ADC can be corrected through a low-complexity deterministic digital mapping with improvements of 1.5-bit in peak effective number of bits (ENOB) and 9 dB in peak signal-to-noise-and-distortion ratio (SNDR) verified over three measured sample prototypes.