An 8-bit 1.5-GS/s Voltage-Time Hybrid Two-Step ADC With Cross-Coupled Linearized VTC

This brief presents a single-channel 8-bit 1.5-GS/s voltage-time (V-T) hybrid two-step analog-to-digital converter (ADC). Benefiting from the fine quantification in the time domain, the power-to-noise requirement of a comparator and speed limitation in the voltage domain have been significantly relaxed. An efficient cross-coupled linearized technique (CCLT) is proposed in a dynamic voltage-to-time converter (VTC) design as a crucial part of this ADC. This technique helps improve the total harmonic distortion (THD) of VTC by 8 dB across most process-voltage-temperature (PVT) variations by avoiding using a power-harvest current-source (CS)-based VTC. Moreover, a dynamic conversion strategy is proposed in a time quantizer to build a more power-efficient design. Fabricated in a 28-nm CMOS process, the prototype ADC consumes 3.3 mW at 1-V supply with an active area of 0.0035 mm(2). With a Nyquist input, it achieves a signal-to-noise and distortion ratio (SNDR) and spurious-free dynamic range (SFDR) of 45.4 and 60.3 dB, respectively, yielding a Walden figure of merit (FoMW) of 14.4 fJ/conversion-step.