A time-gated 4×128 SPAD array with a 512 channel flash 80 ps-TDC for pulsed Raman spectroscopy

A time-gated 4×128 single photon avalanche diode (SPAD) array with a 512 channel flash time-to-digital converter (TDC) has been designed and realized for pulsed Raman spectroscopy in a high voltage 0.35 μm CMOS technology. The time-to-digital converter uses a coarse digital delay line with an interpolation structure to achieve a resolution better than the gate-delay of the technology. The delay lines are stabilized by using replica delay lines. The arrival of photons can be measured channel wise with a resolution and range of 80 ps and 3.5 ns, respectively. The maximum variation of the 80 ps resolution through the spectral rows was measured to be ± 33 ps. The main error source of Raman spectroscopy measurement, a high fluorescence can be rejected effectively with this resolution when a typical used pulse width of the laser is approximately 150 ps.