MOSFET Characterization Method For Ultra-low Voltage RF Low Noise Design

Modeling of high frequency noise in MOSFET is the basis of its application in wireless communication.For low power,mixed signal and high frequency applications,the best high frequency characteristics of short channel COMS technology have been transferred from low to medium inversion region to weak inversion region.Compared with long channel devices,the noise characteristics of devices have also changed significantly,and the characterization of noise models is more complex.Noise modeling of nano-MOSFET is mainly based on the measurement of four noise parameters and scattering parameters of the device.Through the analysis of two-port noise network,the original data of the two-port equivalent noise current model of the device are extracted,and the mathematical and physical model of the device equivalent noise current source is established by combining the small signal equivalent noise circuit analysis of the device.The accuracy of mathematical and physical modeling of device noise depends on the depth of understanding of device process characteristics and the accuracy of measurement system.The mathematical representation of the precise physical model of short channel MOSFET noise is very complicated.In order to make the existing mathematical and physical model of short channel MOSFET high frequency noise available for engineering design,the expression of its concise model is studied in this paper,and the application experiments are carried out to verify it.The work of this paper includes the following three aspects:Firstly,the dual-port equivalent noise current high frequency physical model of 40nano-MOSFET and its original data are defined.The ADS simulation model of its small signal equivalent noise circuit and the original data of its four noise parameters are determined.The effectiveness and accuracy of the high frequency noise physical model determined in this paper are verified by the simulation of scattering parameters and four noise parameters based on ADS2008 software.Secondly,in order to make the complex nano-MOSFET high-frequency noise physical model available for engineering design,the expression of its concise model is studied in this paper.The complex noise physical model is simplified by transforming and analyzing the two-port correlation noise matrix of the device.The concise model not only expresses the non-quasi-static effect of the device with high accuracy,but also can be directly embedded into the ADS simulation design tool by Verilog-A language in the form of four nodes,thus ensuring the accuracy and greatly reducing the design complexity.The experimental results show that the proposed model is more accurate in both strong and weak inversion regions than the existing three-node model.Finally,based on the engineering practice that the ultra-low voltage RF low noise design concentrates on the weak and medium-inversion region of MOSFET,a characterization method based on inversion coefficient(IC)is proposed,and an example of component parameters with bias dependence is given to prove that this characterization method has clearer and easier identification of the characteristics of MOSFET working at ultra-low voltage when characterizing the weak inversion region.The reversibility and validity of the method are illustrated by the conversion back to VGS and the comparison with the original data.Designers can select the best operating point through the MOSFET characteristic curve characterized by inverse coefficients,indirectly select the physical bias voltage value,and then use the simple model established in this paper to simulate,which can make the design more accurate and effective.