An Interface Circuit With Gain Automatic Adjustment for SPAD Arrays

In this paper, a gain automatic adjustment interface circuit is proposed for the non-uniform breakdown voltage of single-photon avalanche diode (SPAD) arrays caused by process and materials. In array applications, by monitoring the current of SPAD in different operating modes and feeding back to control bias voltage of SPAD in real time, an equal current is effectively generated for each SPAD pixel with different gain characteristics. Therefore, the gain of SPAD arrays can be adjusted automatically. When avalanche current occurs, the output voltage of current monitoring circuit is sensed by a comparator of the quenching circuit, achieving rapid detection of avalanche signals. Meanwhile, this interface circuit has an important position in array applications due to its compact layout and low number of control signals required. The interface circuit is fabricated in TSMC 0.35μm standard CMOS process and then tested by interconnecting with 1!Q8 SiC APD arrays. Test results demonstrate that the automatic adjustment of SPAD gain has been successfully realized. After adjustment, the consistency of the gain of SPAD arrays is obviously improved and standard deviation of dark count rate (DCR) is decreased from 83.42 to 11.26.