An 8b 1.0-to-1.25 GS/s Time-Based ADC With Bipolar VTC and Sense Amplifier Latch Interpolated Gated Ring Oscillator TDC

Abstract

An 8-bit digital intensive time-based ADC implemented in 5-nm CMOS is presented in this letter. It proposes a bipolar ramp-based voltage-to-time converter (BVTC) to eliminate the reference voltage and to allow a wide input swing of 0.75 $V<pp,diff>$. A redundancy scheme for the input polarity decision taken for 1-bit voltage domain folding is intro- duced against wrong decisions which eliminates comparator calibration in analog domain and allows a more efficient design. Sense amplifier latch (SAL) interpolation technique is presented which reduces the power and area consumption when phase interpolating the time-to-digital converter (TDC) signals. The ADC reaches 1 GS/s sampling rate with 0.7-V supply and 1.25 GS/s with 0.8-V supply and achieves 16.6 and 20.3 fJ/conv-step Walden FoM, respectively. The total active area is 313 $μm^2$.