Design Of Low-Voltage Low-Power CMOS Reference

Reference is an important module in the integrated circuits and widely used in various analog ICs,digital-analog mixed signal ICs and SoC. With the development of IC industry and manufactural technique of semiconductor, deep sub-micron standard digital CMOS process technology will be the main stream of SoC IC design. So it is a certain progress and representative to design a pure CMOS high precision voltage reference circuitry based on the sub-threshold MOSFETs with the SMIC 0.18μm standard CMOS process technique in this thesis.The main contents in this thesis include the following three aspects: the study of reference circuit model based on sub-threshold MOSFETs, the design of reference circuit based on MOSFETs operating in sub-threshold region and the correction of process divagation for reference circuit based on sub-threshold MOSFETs, respectively.Regarding with the study of the reference circuit model based on sub-threshold MOSFETs. Firstly, based on the CMOS device structure and factors affecting the MOSFET threshold voltage, the expression for MOSFET threshold voltage is concluded and then theoretically analyzed. From the quoted equation for the current between source and drain Ids of the sub-threshold MOSFET, the expression for the voltage between gate and source drain Vgs of the sub-threshold MOSFET is directly got and the temperature characteristic of Vgs is theoretically analyzed. The threshold voltage of MOSFET and the voltage between gate and source Vgs of MOSFET operating in sub-threshold region are simulated based on the SMIC 0.18μm standard CMOS process technology, and hence the theoretical foundations for design of the reference circuit based on sub-threshold MOSFET are received. Based on the design principle of traditional bandgap reference and the current-voltage characteristic for MOSFET operating in sub-threshold region, two reference circuit models based on sub-threshold MOSFET are proposed: voltage mode circuit model and current mode circuit model.The design of the sub-threshold MOSFET voltage reference is studied afterwards. Firstly, two simple MOSFET voltage references suitable for low voltage low power are designed which is based on the two models of the sub-threshold MOSFET reference circuit presented. Then, four low power sub-threshold MOSFET voltage reference circuits meeting the development of the senior consuming electronic chips and the communication electronic chips have been designed. While they mainly emphasize on the temperature coefficient and PSRR performance. Detailed deducing of circuit theory,analyzing of working principle are given to every kind of low voltage low power sub-threshold MOSFET voltage reference. Relative theoretical formulas and important design reference conclusions are given.The first kind current mode reference circuit based on sub-threshold MOSFET with the simple circuit arrangement is taken full advantage of the feedback technique to design. Its main virtue is that it has the very low temperature coefficient in a certain temperature range, and can work under 1V supply voltage with low power dissipation .However, the output reference voltage can't be modulated at will, and the power supply rejection ratio at low-frequency range is not too high.The second kind current mode reference circuit based on sub-threshold MOSFET is high-order curvature-compensated by the temperature coefficient difference of the varying kinds of integrated resistors. Its main virtue is that the reference current with low temperature coefficient in a wider frequency range. However, it is necessary for the circuit to use the low resistivity integrated resistance which will occupy more die area, and the power supply voltage is higher than 1 V.The third kind current mode reference circuit based on sub-threshold MOSFET is high-order curvature-compensated by the threshold voltage difference between the nMOSFET and pMOSFET. It can work under 1 V supply voltage because of the error amplifier designed with the low voltage designing technique.The fourth kind current mode reference circuit based on sub-threshold MOSFET mainly takes full advantage of the voltage regulation technique and the method to increase the PSRR of the operational amplifier to achieve a very high power supply voltage rejection ratio and the circuit's PSRR is about -127 dB at DC frequency.Finally, the correction of process divagation for reference circuit based sub-threshold MOSFET is presented in this thesis. Based upon the fuse and the laser trimming techniques respectively, two methods to correct the process divagation are presented, which are suitable to trim the reference circuit designed with the deep sub-micron standard CMOS process technology. Moreover, their shortcomings and virtues are given. The characteristics of each circuit presented in this thesis are also analyzed and the suitable trimming method to correct the process divagation is given consequently.