CMOS SPAD Line Sensor With Fine-Tunable Parallel Connected Time-to-Digital Converters for Raman Spectroscopy

Abstract

A 256-channel single-photon avalanche diode (SPAD) line sensor was designed for time-resolved Raman spectroscopy in 110-nm CMOS technology. The line sensor consists of an 8 × 256 SPAD array and 256 parallel connected time-todigital converters (TDCs). The adjustable temporal resolution and dynamic range of TDCs are 25.6-65 ps and 3.2-8.2 ns, respectively. The median timing skew along 256 channels is 43.7 ps, and TDC bin boundaries can be fine-tuned at the ps-level to enable precise timing skew compensation. The sensor is capable of real-time dark count measurement (two dark measurements for each excitation pulse) that gives accurate data for dark count compensation without any increment in measurement time. The maximum excitation pulse rate with realtime dark count measurement is 680 kHz. Raman spectra of six different samples were measured to prove the performance of the sensor in time-resolved Raman spectroscopy.

Towards time-domain diffuse optics with extreme photon rate

“…As detection chain, we used the chip described in Ref. [8], composed of 8x256 CMOS SPADs and 256 7-bit Time-to-Digital Converters (TDCs), each one reading a line of 8 SPADs and with a time bin of about 60 ps . The repetition rate of the laser was limited to 2 MHz since the chip cannot operate at higher frequency.…”

0.5 Billion Counts per Second Enable High Speed and Penetration in Time-Domain Diffuse Optics

“…At 2 MHz laser pulse rate, the maximum saturated PCR is 512 Mcps, resulting from 256 TDC conversions (i.e., 1 for each TDC) every 500 ns. Further details on the device can be found in [15]. 2 MHz laser pulses are provided by a commercially-available laser source composed by a laser control unit (PDL 828 Sepia II, Picoquant GmbH, Germany) connected to a 670 nm laser head (LDH-P-C-670M).…”

“…Generally speaking, the capability to follow deep and fast tissue dynamics requires to combine a high diffuse optical responsivity with a high throughput, thus obtaining a high signal-to-noise ratio not only at short source detector separations. Towards this objective, in this work we present the first application in time-domain diffuse optics of a fully-integrated detection chain (i.e., detector array and TCSPC electronics) initially designed for Raman spectroscopy [15]. Thanks to its superior diffuse optical responsivity (i.e., 2.25 10 -7 m 2 sr at 670 nm) and high throughput (i.e., saturated PCR = 512 million of cps), we demonstrate the possibility to perform both phantoms and in-vivo measurements reaching a PCR of ~435 million of cps at 2 cm source detector separation.…”

Multipoint Raman Spectrometer Based on a Time-Resolved CMOS SPAD Sensor

“…Data read-out and controlling of sensor operation are done with an Opal Kelly XEM7310-A200 FPGA integration module. A detailed description for the sensor is given in [14].…”