Research Of The Modeling, Parameters Extracting Of The On-chip Transformers

With the rapid developing of wireless communication technology, radio frequency integrated circuits(RFICs) have been driven to miniaturization, low power,low cost and higher integration. On-chip transformer as an important passive device have been widely applied such as low-noise amplifiers, voltage controlled oscillator,mixer,power amplifier, digital isolators and DC/DC converters to achieve impedance matching, the mutual conversion between single-end and differential signals,AC-coupling, bandwidth extension, digital signal and power isolation transmission etc.It has brought great difficulties to design and simulate circuits because most of the existing process does not provide a library on a common chip transformer model, thus it is necessary to establishing a transformer equivalent circuit model. At the same time,the on-chip transformer’s complex structures and various parasitic losses such as the skin effect or proximity effect of metal coils and the inductive or capacitive parasitic losses of substrate have increased the difficulty of modeling.In this paper, we study the modeling and parameter extraction method of on-chip transformer, and proposed a new T-model of planar spiral transformers and a new 2πmodel stacked spiral transformer. All the elements can be extracted.At first, we introduces some basic concepts of electromagnetism and electrical properties of the on-chip transformer, gives the definition of the parameters and formulas, analysis the reason of the on-chip transformer loss mechanism. Secondly,we summarize the current four common modeling methods, analyzes the strengths and weaknesses and scope of each of the modeling methods. The detailed derivation of rational approximation in parameter extraction is given. We also give the detailed steps to solve the poles, residues and other linear parameters.Finally, based on the summary and analysis of the previous results in terms of modeling and parameter extraction, the paper puts forward a new T-model of planar spiral transformer and a new 2π model of stacked spiral transformer combined with previous T-model and 2π model. It contains all the parasitic losses of metal coil and substrate. The new T-model uses an integrated circuit network to model substrate parasitic losses. Unlike conventional models, the new model uses a parallel L-R and L-R-C network to simulation Skin effect proximity effect and the substrate inductive parasitic. The new 2π model of stacked spiral transformer coupled with two single-πtopology, each single-π model were equivalent to the first and second coils. All theelements can be extracted using two port network analytical method and vector fitting.The proposed two models are verified by the measured data of L50 G 0.5μm CMOS process, and get a better result.