Research Into CMOS Weak Current Readout Circuit For Biochemical Sensor System On Chip

Biochemical sensor SOC is an important cross-disciplinary research area over both biochemical field and microelectronic field. It has been also attracting much attention of the SOC design community from the start of this century. This dissertation presents a thorough study on the weak current readout circuit as well as on the integration of A/D conversion used for amperometric biosensors, thus forming some foundation for monolithic integration of biosensors.Aiming at the amperometric immunosensor, 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 for use in the whole chip simulation. The consistency of the signals between the front-end sensor and the back-end circuits and hence the yield of the chip design are also effectively increased.Based on the method of charging and discharging a small capacitance, this dissertation introduces several innovative techniques such as auto-delay-charging feedback, positive discharging feedback, and source voltage shifting, and construction of a whole weak current readout system. Besides, there is also a digital logic block employed to directly deliver a 10-bit digital output signal, which avoids the waste of space and power by using an extra A/D converter on the chip. The readout system can efficiently reduce the influences from leakage current, input offset, process parameter instability, and other causes. The value of input weak current signal can be obtained simply through demarcation.A brand new method of further enhancing the readout circuit performance is put forward in this dissertation, which steadies the input weak current signal, so that it cannot be much affected by any sudden change of the charge/discharge-switch signal. This effectively improves the measuring accuracy of the weak current less than 3pA, and leads to a deviation of only 0.086 for 1pA measuring result.The sensor chip is fabricated in a standard 0.35μm CMOS process (Chartered Semiconductor, Singapore) and operates at 3.3V. Finally, with the readout system, DC...