Search

The paper is focused on design of time-to-digital converters based on successive approximation (SA-TDCs-Successive Approximation TDCs) using binary-scaled delay lines in the feedforward architecture. The aim of the paper is to provide a tutorial on successive approximation TDCs (SA-TDCs) on the one hand, and to make the contribution to optimization of SA-TDC design on the other. The proposed design optimization consists essentially in reduction of circuit complexity and die area, as well as in improving converter performance. The main paper contribution is the concept of reducing SA-TDC complexity by removing one of two sets of delay lines in the feedforward architecture at the price of simple output decoding. For 12 bits of resolution, the complexity reduction is close to 50%. Furthermore, the paper presents the implementation of 8-bit SA-TDC in 180 nm CMOS technology with a quantization step 25 ps obtained by asymmetrical design of pair of inverters and symmetrized multiplexer control.

Remote Raman spectroscopy is widely used to detect minerals, explosives and air pollution, for example. One of its main problems, however, is background radiation that is caused by ambient light and sample fluorescence. We present here, to the best of our knowledge, the first time a distance-resolving Raman radar device that is based on an adjustable, time-correlated complementary metal-oxide-semiconductor (CMOS) single-photon avalanche diode line sensor which can measure the location of the target sample simultaneously with the normal stand-off spectrometer operation and suppress the background radiation dramatically by means of sub-nanosecond time gating. A distance resolution of 3.75 cm could be verified simultaneously during normal spectrometer operation and Raman spectra of titanium dioxide were distinguished by this system at distances of 250 cm and 100 cm with illumination intensities of the background of 250 lux and 7600 lux, respectively. In addition, the major Raman peaks of olive oil, which has a fluorescence-to-Raman signal ratio of 33 and a fluorescence lifetime of 2.5 ns, were distinguished at a distance of 30 cm with a 250 lux background illumination intensity. We believe that this kind of time-correlated CMOS single-photon avalanche diode sensor could pave the way for new compact distance-resolving Raman radars for application where distance information within a range of several metres is needed at the same time as a Raman spectrum.