Study On Compact Short-wave Infrared Ingaas Spectral Sensor With Digital Output

Spectral analysis is widely used in various fields such as agriculture and medicine to provide fast,non-destructive access to material composition information.In recent years,with the prosperity of the Internet of Things(IoT)and cloud computing technology,the spectral sensing IoT node,which developed by combining IoT with spectral analysis technology can realize remote spectral information sensing and online monitoring of material composition.The short-wave infrared spectrum band contains a wealth of spectral information and has a wide range of applications in many fields.Traditional short-wave infrared spectroscopy equipment is bulky and expensive.It causes poor mobility and high cost if applied directly to the IoT spectral nodes.Indium gallium arsenide(InGaAs)spectral sensor is capable of perceiving short-wave infrared spectral information.It encapsulates the InGaAs focal plane detector and micro-spectroscopy components in the package,which is small in size,light in weight and relatively inexpensive.InGaAs spectral sensors are more suitable for spectral sensing IoT nodes than traditional infrared spectroscopy devices.At present,most of the InGaAs products on our market are integrated with analog voltage output,which need to use commercial analog-to-digital converters(ADCs)to digitize the output signals for digital signal processing.On-chip digital output is a trend in the miniaturization of InGaAs focal planes.The focal plane integrates on-chip digital output circuit can effectively shorten the analog signal transmission path,reduce the effects of noise and signal crosstalk.In this paper,InGaAs spectral sensor with digital output is studied and a digital read-out integrated circuit(DROIC)is designed at first.Secondly,a new InGaAs digital output spectral component is developed based on the DROIC chip.Finally,a miniature IoT spectral node is designed.The IoT spectral nodes have initially realized the remote spectral information perception function.The details are as follows:(1)Digitalization is the underlying technology for sensors intelligence and miniaturization.A 128×1 DROIC is designed for InGaAs spectral sensor.The circuit integrates a 14-bit successive approximation register(SAR)analog-to-digital conversion circuit.Since the SAR ADC has a unit capacitor array,the parasitic capacitance of capacitor routes will seriously affect the capacitor array matching accuracy.A new layout routing scheme is proposed to reduce the parasitic capacitance of the capacitor array,which reduces the maximum mismatch rate from 9.1%to 2.3%.The DROIC was fabricated in 0.18?m CMOS process.The results show that the DROIC performance meet the design requirements.(2)Based on the 128×1 DROIC chip,the domestic first InGaAs spectral sensor with digital output is developed.The sensor can percept short-wave infrared spectrum information and convert it to digital voltage signal.The spectral sensor uses a 256×1InGaAs chip as the photosensitive element and a linear gradient filter as the spectral element.The sensor embeds 202 spectral channels with a spectral range of 950-1700nm and a spectral resolution of 11-16 nm,which can meet the demands of short-wave infrared spectroscopy applications.(3)A new miniature IoT spectral perceptual node is developed based on the digital spectral sensor.The node realizes the collection and wireless transmission of spectral data.The node uses a three-layer laminate structure to reduce system size.The volume and weight of the node is 42×70×42 mm~3 and 68 g,respectively.Test results show that the performance of the node meets the design requirements.It can meet the application of short-wave infrared spectroscopy and provide technical support for short-wave infrared IoT applications.