Design Of Multifunctional Infrared Focal Plane Readout Circuit

With the development of modern science and technology,infrared detection technology has been widely used in military and civil fields.Infrared Focal Plane Array(IRFPA)is an important part of Infrared photoelectric detection system,which mainly includes Infrared detector Array and Readout Integrated Circuit(ROIC).The infrared photoelectric detector is responsible for collecting the infrared radiation of the target and converting the optical signal into electrical signal.As the front-end processing circuit,the ROIC needs to amplify,sample and denoise the weak current signal generated by the detector.It determines the quality of the entire infrared imaging and is the focus of current research at home and abroad.Aiming at the problem of single function of traditional focal plane readout circuit,a multifunctional infrared focal plane readout circuit is designed in this paper,which realizes four functions of daylight standard imaging,weak light high-gain imaging,asynchronous laser pulse detection and two-dimensional distance measurement under the restriction of compact pixel area.The readout circuit integrates both active and passive imaging methods at the same time to collect laser signals and thermal infrared signals at the pixel level.Aiming at the passive detection mode of infrared thermal imaging,a capacitive transimpedance amplifier(CTIA)is constructed,which uses different capacitors to switch to achieve wide dynamic range imaging.The full well capacity and noise characteristics of the circuit are analyzed and optimized.At the same time,a structure to eliminate the leakage effect is proposed to improve the accuracy of weak current detection.Aiming at the active laser detection mode,this paper selects the asynchronous pulse current detection circuit and the photon time-of-flight(TOF)measurement circuit with the resistance-feedback transimpedance amplifier(RTIA)as the input stage,and designs and verifies a doublesampling TAC circuit separately to realize the wide range and high precision TOF of single frame detection.Finally,according to the working mode of multifunctional ROIC,the readout mode of ITR is proposed.In this paper,TSMC 0.35?m standard CMOS process is used to complete the design and the wafer verification of the multifunctional readout circuit.The post-simulation results show that the area of the pixel unit circuit is30?m×30?m,and the dynamic range of the CTIA circuit in high and low gain mode is 62.4d B and 70.42 d B,respectively.The amplitude sensitivity of the asynchronous laser pulse detection circuit is 0.74?A,the pulse width sensitivity is 1.8ns,and the quantization resolution of TOF is up to 2ns.The linearity of passive infrared imaging mode is greater than 99%,and the absolute relative error rate of TOF based on TAC laser active detection imaging is less than 1%.The test results show that the readout circuit can realize four basic functions.The dynamic range of CTIA circuit in high and low gain mode is 60 d B and 67.94 d B respectively,which basically meets the design requirements.The amplitude sensitivity of the asynchronous pulse detection circuit is 0.8?A,and the pulse width sensitivity is 2.1ns,which is slightly degenerated than the post-simulation results,but can still meet the application requirements of laser pulse.The linearity of both high and low gain modes of CTIA circuit is above 98%,which can basically meet the application requirements of passive infrared imaging.Due to the limitation of test conditions,the quantization resolution of TOF could not be verified,and the relative error rate of TOF was between 1% and3%.