A 32x32-pixel array with in-pixel photon counting and arrival time measurement in the analog domain

A Time-to-Amplitude Converter (TAC) with embedded analog-to-digital conversion is implemented in a 130-nm CMOS imaging technology. The proposed module is conceived for Single-Photon Avalanche Diode imagers and can operate both as a TAC or as an analog counter, thus allowing both time-correlated or time-uncorrelated imaging operation. A single-ramp, 8-bit ADC with two memory banks to allow high-speed, time-interleaved operation is also included within each module. A 32x32-TACs array has been fabricated with a 50-µm pitch in order prove the highly parallel operation and to test uniformity and power consumption issues. The measured time resolution (LSB) is of 160 ps on a 20-ns time range with a uniformity across the array within ±2LSBs, while DNL and INL are 0.7LSB and 1.9LSB respectively. The average power consumption is below 300µW/pixel when running at 500k measurements per second.