A New Modeling Method Of Microwave Nonlinear Circuit Based On Scattering Function

As a sub-topic named"Research of microwave nonlinear circuit modeling method", this paper is derived from the project of"Basic research of microwave and millimeter wave test equipment".With the wide use in communication, radar, electronics and instrumentation,how to accurately design and high-performance analyze microwave semiconductor circuits is very important. Models of semiconductor devices are the main factor to affect the accuracy of the circuit design. Larger the circuit , higher the frequency, to the higher requirements of the device models. It is critical of the accurate device models to improve the design of RF and microwave millimeter-wave circuit and shorten the development cycle. According to the working conditions of microwave circuits, which are often working in high-power and large-signal, the circuit is in a strongly nonlinear. Traditional characterization and modeling methods of S parameters at small-signal can not represent them accurately, while the large-signal device model is not easy to obtain. Volterra series, power series and the equivalent circuit approach is often used in a weak non-linear state of the circuit, to the strong non-linear circuits it can not be an accurate representation.Based on the traditional large-signal circuit characterization, measurement and modeling methods, it is analyzed that the application, characteristics, advantages and disadvantages of a variety of methods. General steps of microwave circuits modeling are summarized. As some problems of traditional modeling methods, the frequency domain black-box model of nonlinear scattering function is introduced.First, the research is focused on the linearization of nonlinear scattering function model, introduction of the upper and lower standard labeling methods, analysis and description of the physical meaning to the element of nonlinear scattering function and the interchangeable of the traditional S parameters. Secondly, it is concluded that other description of the nonlinear network functions, the relationship between nonlinear scattering function and other nonlinear network function and the relationship between nonlinear network function of the network link and the sub-network. The results of them have laid a theoretical basis for the proper use of this model.Then, it is developed the extraction system of nonlinear scattering function based on the digital oscilloscope and the calibration methods of system errors. This system provided the experiment conditions to the extraction of nonlinear scattering function model of power devices. Nonlinear scattering function of power FETs and diodes can be tested and the results accurately reflected the nonlinear variation with the increase of input power to the power devices.Links and differences of the model of nonlinear scattering function and the model of parameters X are proposed by Agilent recently are analyzed. Through the comparison of the description,characteristic,extraction methods and the applications between them, it provides a useful reference and comparison to the study and application of nonlinear scattering function.Based on the test data of nonlinear scattering function of power devices, the new machine learning method of support vector machine is used to predict the model of nonlinear scattering function and the good predict accuracy is got. Then, it is summarized that the affection to the modeling accuracy from the selection of the support vector machine, kernel function and other parameters.Last, the model of nonlinear scattering function of FETs and Schottky barrier diodes are used to design the microwave power amplifier and frequency multiplier. It is verified that the applicability of the large-signal model.Compare with the traditional large-signal model, the advantages of this black-box model can be generalized. The first is the compatibility with the parameters S at small signal. Through this, the unified microwave circuit model can be established between the working conditions of large-signal and small-signal. Different from the foreign NNMS(Nonlinear network measurement system), the second is the time domain measurement method based on the digital oscilloscope. This method is simple and convenient. Adopting the common test fixture, a unified method can be used to exact the nonlinear scattering function model. The last, the model is frequency-domain black-box model, it can be extracted which is not needed to know the structure of microwave semiconductor devices and circuits in advance. The model not only contains some of the intrinsic part, and the affection of parasitic parameters is included in this model. It can be used in the design of microwave circuits conveniently and accurately.It can be proved that this new large-signal model of microwave devices can improve the design efficiency, improve design accuracy and performance effectively.In addition ,some problems, such as how to improve the consistency problem to the phase of nonlinear scattering function; modeling accuracy is not high to the part of nonlinear scattering function using support vector machine and how to design a unified large signal CAD(Computer aided design) model with the model of nonlinear scattering function, still requires in-depth study and explore.