Study On On-chip Electrochemical Sensing System

Following the development of integrated circuit technology and design, chemical analysis and biomedical research is based on microelectronics technology has become the mainstream of scientific research, and it is also expected for bring comprehensive development in chemical analysis and biological technology. Lab-on-a-Chip is a platform for micro total analysis system. It carried the lab which contains sample preparation, redox reaction and analysis on a single chip, and the chip is only a few square centimeters. The electrochemical analysis which contains micro-electrodes is a common component in Lab-on-a-Chip, and the potentiostat is the core of electrochemical analysis system. The electrochemical analysis system is based on three-electrode potentiostat has been studied in this paper, and it is the groundwork for the whole system of Lab-on-a-Chip in the future.On the study of microelectrode's principle and chemical reaction's characteristic, the appropriate equivalent circuit model of the micro electrode has been selected for the DC current signal which is generated by redox, and the signal is proportional to the concentration. For the weak current signal, the electrochemical measurement has been used. Comparing with the traditional three-electrode potentiostat, the potentiostat is based on the current mirror has been selected to hold the voltage which is between Working Electrode and Reference Electrode, and the structure senses the CE current. The circuit has simple structure, a wide range of current sensors (20pA ~ 20uA). Referencing to the input voltage of potentiostat, 10-bit DAC has been designed. DAC is a segmented structure, high six yards use a thermometer DAC, and the low four bits use binary code. In the high six yards, DAC use the two sets of 3-7 decoder for the rows of decoder (b9 ~ b7) and the column decoder (b7 ~ b4). In the switch of current source, DAC uses a buffer tube behind MOS switch to reduce the circuit glitch, and converts current to voltage in the output section. Under the Cadence simulation shows that: DAC has a good conversion from analog to digital, the output current is 0~10mA, the output range is 0.5~1.5V, Differential Nonlinearity (DNL) error and Integral Nonlinearity error (INL) were 0.7LSB and 0.8LSB, the settling time is about 2ns.Finally, layout of the entire system and DRC and LVS verification were carried out.