A Novel Quadrature-Phase Sampling Technique for Filterless, Low-Complexity, High-Alias-Suppression in VCO-ADCs

Next-generation LiDAR systems demand unprecedented resolution, requiring wide signal bandwidth and high-density pixel arrays that constrain each pixel circuit to <tex-math notation="LaTeX">≤ 0.01 </tex-math> mm2. This limits the complexity and power available for anti-aliasing filtering in the receiver front-end, even though strong attenuation of interference and alias noise is critical to preserve signal fidelity. Voltage-controlled oscillator (VCO)-based analog-to-digital converters (ADCs) offer inherent anti-aliasing through spectral shaping, but for bandwidths <tex-math notation="LaTeX">≥ </tex-math>50 MHz, the attenuation is insufficient, necessitating dedicated analog filters that undermine area and power. To resolve this, we propose a novel sampling technique for VCO-ADCs, employing quadrature clocks instead of conventional clocking. The resulting output spectrum exhibits a quasi- <tex-math notation="LaTeX">sinc³ </tex-math>-shaped response that improves alias attenuation by ~10 dB to 80 dB at 50 MHz bandwidth—the highest reported to date—eliminating the need for analog filters. We derive an analytical expression for this response, accounting for non-idealities and offering insight into the parameters governing the shaping behavior. The technique is demonstrated with a proposed filterless, low-complexity VCO-ADC circuit in CMOS 65 nm, occupying just 0.0017 mm2—43% smaller than the state-of-the-art—and dissipating only 0.42 mW at 2 GHz sampling in simulation. Benchmarking shows a figure-of-merit of 56 fJ/conversion-step, <tex-math notation="LaTeX">~ 1.1× </tex-math> better than the best reported design.