Design Of Frequency Locking Digital System For Covid-19 Graphene FET Sensor Application

With the outbreak of the Corona Virus Disease 2019,virus detection has become the top priority of epidemic prevention and control,and virus detection is a powerful means to prevent the spread of the virus at present.The existing testing method is the PCR（polymerase chain reaction）testing method.Real-time RT-PCR for molecular diagnosis takes at least 3 hours,and the detection equipment is relatively large and not easy to carry.Therefore,using highly sensitive immunodiagnostic methods to directly detect viral antigens in clinical samples is a necessary requirement for rapid and accurate diagnosis of Covid-19（Corona Virus Disease 2019）.Graphene biosensors are expected to replace existing PCR method because biosensors are more sensitivity than PCR technologies.One of the graphene biosensors is the Covid-19 FET sensor,which is a field-effect transistor（FET）biosensing device for detecting SARS-Co V-2 in clinical samples.Although this FET sensor is very sensitive to Covid-19 virus,the output signal it produced is very weak and is mixed with many other interfering signals.In order to solve these problems,the thesis proposes a frequency locking digital system to extract this weak electrical signal output of the Covid-19 FET sensor from other interfering signals.The proposed method is to use digital frequency locking-in amplifier to pinpoint the weak signal and amplify it.The implementation of the method is by using FPGA,which is able to realize a miniaturization and integration of nucleic acid detection device suitable for domestic used.The design and simulation of this frequency locking digital system is based on Modelsim and the implementation is on a Xilinx FPGA.The measurement results show that the relative error of the system for millivolt signal detection is less than 1% with no addition of man-made noise,and less than 5.2% when the SNR is-26 d B.Compared with OE1201,the detection error of the system applied to the Covid-19 FET sensor is less than 19%,which can be applied to the Covid-19 virus detection.