Design of an Integrated Near-Infrared Spectroscopy Module for Sugar Content Estimation of Apples

An integrated near-infrared (NIR) spectroscopy prototype module for sugar content estimation of apples is presented. Since this is the first attempt to design an integrated NIR spectroscopy module, we followed the design process as follows. First, we estimated the sugar content of apples using a tungsten halogen light source and a 700 nm–1000 nm NIR spectrometer with a 10 nm wavelength resolution and a 16b analog-to-digital converter (ADC) resolution. Second, we determined the most effective wavelengths among 31 evenly distributed wavelengths while observing the correlation coefficient, R², and then we reduced the ADC resolution 1b by 1b starting from 16b while also observing the R². Lastly, we designed an integrated NIR spectroscopy module with the selected eight wavelengths and a 13 ADC resolution. The module implemented in a 0.18 μm 1P6M CMOS process occupies a die area of 0.84 mm². By utilizing this module with eight off-chip light emitting diodes (LED) and one photo diode (PD), the measured R² and the standard error of calibration (SEC) were 0.365 and 0.686 brix, respectively.