Research On The Readout Integrated Circuit For Silicon Nanowire Bio-Sensors

Now,the sensors fabricated by silicon process have been used more and more widely in the field of biology and medicine.Due to the complexity,time-consuming and label needed of traditional detection methods,the detection of biological substance such as pH,protein,DNA,RNA and cells is replaced by sensors.Silicon nanowire bio-sensors become the focus of all the sensors because of its characteristic of real-time,efficient and label-free.The characteristic size of silicon nanowire is nano-meter level,which is close to the size of biological substances.It provides the possibility for the detection of biological substances,especially for low concentration detection.And because of the large ratio of specific surface area,it is easy for silicon nanowire to absorb more effective units,and the resolution of nanowire is further improved.The disadvantage of silicon nanowire sensors is that the signal is so weak that it is difficult to detect substances offchip because of the environmental noise and fluctuations.So it is a trend to integrate nanowire and readout circuit on a single chip.In this paper,a readout circuit is designed using the process of CSMC 0.18μm.The readout circuit includes preamplifier and analog to digital conversion.The preamplifier consists by a sampling structure and an amplifier.A CASCODE current mirror is used to sampling output signals of silicon nanowire with a constant current.The amplifier includes a GM trans-conductor,a capacitance feedback trans-resistance amplifier and a correlation double sampling.A cyclic ADC is also designed to convert the analog signal to digital signal.The circuit chip is to linearize the input and output of silicon nanowire,amplify the weak signal and realize A/D conversion.Firstly,the theory of silicon nanowire bio-sensor is introduced using the pH detection as an example.And then,the design of circuit is introduced in detail.A PCB is also designed to test the chip.Also by writing Verilog code,the control sequence can be got from FPGA.Finally the whole readout chip is tested to see whether it can work.Through the test,the linearity of preamplifier is 97.45%,and the resolution is 475μV.When the input is smaller than 475μV,the signal can be distinguished but the output fluctuates greatly because there is no power management in this chip.There are no signals from ADC test and the chip will burn down because of the order of supply voltages.