High-Fill-Factor SPAD Array With 60 Subnanosecond Integrated TDCs

This letter presents a high-fill-factor 60 × 1 linear array of single-photon avalanche diodes (SPADs) and 60 integrated time-to-digital converters (TDCs). The 100-μm diameter SPAD has high photon detection efficiency (50% at 420 nm), very low dark count rate (2.5 kcps at room temperature), and negligible crosstalk (~0.1% between adjacent pixels). The TDC resolution is 250 ps and its single-shot precision of 200-ps rms is limited just by the quantization noise. Very good linearity (DNL = 5% LSB rms and INL = 30% LSB rms) is achieved because of the sliding scale technique. The overall fill-factor of the array is 52%. This chip is suitable for many advanced spectroscopic applications, since it provides 60 independent single-photon detectors and the corresponding counting and timing electronics within just one integrated circuit.