Study Of A Readout Circuit For Self-assembling Monolayers Biosensor Micro Arrays

Self-assembled monolayers (SAMs) biosensor micro arrays are micro biosensors by using high performance SAMs as biologic identification films.It is an important cross-disciplinary research area over both biochemical field and microelectronic field. It has been attracting much attention as a novel technology of this century. This paper presents an interface circuit that is tuned to the needs of 1×4 SAMs amperometric biosensor micro arrays and an integration strategy for the CMOS readout circuit and transducing micro arrays. The study of this project may play a positive role in the application of biosensor chip.Based on SAMs amperometric biosensor micro arrays, this paper analyzes the characteristic of output signal of the micro arrays and presents a circuit model of transducing micro electrodes according to its reaction characteristic.The potentiostat current integration unit is a very important part of the readout circuit, the potentiostat circuit in this unit could play a role in importing the transducing signal of micro electrodes to the CMOS readout circuit and separating the readout circuit and the transducing micro arrays, making sure there is no interference between the two parts. So, the biosensor micro arrays can work in a stable state. At the same time, four amplifiers in the potentiostat circuit share a common half-circuit, with this method, the power supply could be reduced and the IC layout area of the circuit could be saved. The four amplifiers are working at the negative feedback state, and then the stability of the circuit can be ensured. The unit is simulation verified under PSpice environment.The automatic data selector unit of the readout circuit consists of a 4 bit CMOS shift-register and four CMOS transmission gates. This unit can send 4-way integration signal to correlated double sampling (CDS) unit in turn, achieve the goal of serial output, save output ports and provide convenience for following signal processing. The shift-register is the hardcore part of this unit. This paper has compared the two shift-registers, and found that the parastatic CMOS shift-register has better performance with good transferability and simple input clock signal.CDS is a widespread noise reduction method for discrete-time output signal. A new CDS circuit is designed and simulation verified. The output buffer of the readout circuit adopts a source-follower to improve the impedance matching ability.After the whole CMOS readout circuit is simulation verified, layout of the CMOS readout circuit is designed with 0.6μm DPDM N-well CMOS process. Post layout simulation results of the readout circuit are presented in this paper.Driving signals are essential for the readout circuit, and the driving signals have been designed and simulation verified in this paper.At last, we analyze four possible integration strategies for CMOS readout circuit and micro arrays, and a feasible strategy is presented according to the truth of our micro biosensor.