An integrated 9×9 SPAD array with a 10-channel TDC and a CMOS laser diode driver for a wearable time-domain diffuse optics optode
A 9×9 Single-Photon Avalanche Photodiode (SPAD) array with a 10-channel time-to-digital converter and an integrated laser diode driver fabricated in 0.35 μm HV- CMOS technology were used to carry out time domain diffuse optics measurements of optical phantoms. The average optical power of 20 μW was achieved by the laser diode transmitter at the repetition rate of 500 kHz with a pulse width of 80 ps. The resolution of the TDC and the measured instrument response function (IRF) of the system were ~65 ps and ~190 ps, respectively. The power consumption of the proposed system was 180 mW. Measurements showed that with the proposed system a perturbation with a different absorption property than in surrounding material at the depth of 15 mm could be recognized. In addition, in in vivo measurement with the proposed components, hemodynamic changes in volunteer’s arm during a venous occlusion were detected.