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

Self-assembled monolayers (SAMs) biosensor micro arrays are 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 dissertation presents a thorough study on the weak current readout circuit as well as the integration of ADC used for 1×5 SAMs amperometric biosensor micro arrays which forming some foundation for monolithic integration of biosensors.Firstly, aiming at the SAMs amperometric biosensor micro arrays, the characteristics of the signal from its microelectrodes'output has been studied. According to the reaction principle of the microelectrodes, a proper circuit model of the sensor is built.Secondly, a potentiostat current integration unit is used to the readout circuit; it could transducer the signal of micro electrodes to the CMOS readout circuit and separating the readout circuit and the 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, five 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, and the stability of the circuit can be ensured. The unit is simulation verified with Spectre simulator. CDS is a widespread noise reduction method for discrete-time output signal. A new CDS circuit is designed and simulation verified.Thirdly, we use a successive approximation (SAR) ADC to convert analog signals into digital signals for readout circuit, to achieve bio-sensor digital signal. It's a medium-speed, low power ADC that is suitable for micro arrays biosensor readout circuit. The high speed comparator is used the structure of three-tier cascade operational amplifier; and DAC is realized of a portfolio optimization program, the MSB is used charge scaling DAC and LSB is used voltage scaling DAC.Finally, the whole digital readout circuit is simulation verified with Spectre simulator, and the layout of digital readout circuit is designed with 0.6μm DPDM N-well CMOS process.The simulation results are follows.①Compared with other literatures, the output changed by almost synchronizes to the input signals. CDS holding circuit has a good responsiveness to integral voltage.②the output transfer voltage of micro biosensor readout circuit presents a good linear relationship at the range of 0 to 50nA of biological current, a wide dynamic response range and an output swing of greater than 3V are also obtained.③the ADC has a good performance to complete analog to digital conversion, its maximum integral nonlinearity error (INL) is -1LSB, in the sample voltage is 3V, the sampling rate of 50Ksps circumstances, the power consumption of ADC is only 0.93mW.④the digital readout circuit presents a good linear relationship for biosensor micro arrays signal.