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A 5-bit time to digital converter using time to voltage conversion and integrating techniques for agricultural products analysis by Raman spectroscopy

Rezvanyvardom, Mahdi, Nejad, Tayebeh Ghanavati, Farshidi, Ebrahim
Information processing in agriculture 2014 v.1 no.2 pp. 124-130
Raman spectroscopy, agricultural products, diodes, electric power, energy use and consumption, food analysis, photons, temperature
Time to digital converter (TDC) is a key block for time-gated single photon avalanche diode (SPAD) arrays for Raman spectroscopy that applicable in the agricultural products and food analysis. In this paper a new dual slope time to digital converter that employs the time to voltage conversion and integrating techniques for digitizing the time interval input signals is presented. The reference clock frequency of the TDC is 100MHz and the input range is theoretically unlimited. The proposed converter features high accuracy, very small average error and high linear range. Also this converter has some advantages such as low circuit complexity, low power consumption and low sensitive to the temperature, power supply and process changes (PVT) compared with the time to digital converters that used preceding conversion techniques. The proposed converter uses an indirect time to digital conversion method. Therefore, our converter has the appropriate linearity without extra elements. In order to evaluate the proposed idea, an integrating time to digital converter is designed in 0.18μm CMOS technology and was simulated by Hspice. Comparison of the theoretical and simulation results confirms the proposed TDC operation; therefore, the proposed converter is very convenient for applications which have average speed and low variations in the signal amplitude such as biomedical signals.