The Modeling And Verification Of LDO Based On VHDL-AMS

With the development of integrated circuit, EDA(Electronic Design Automation) technology becomes more and more essential. The complexity and running time of integrated circuit are increasing greatly along with the growth of the size of circuit, and EDA appears for the design of the integrated circuit providing a friendly method. Generally, integrated circuit can be divided as digital circuit and analog circuit. Therefore, the integrated circuit simulation also can be divided into the simulation of digital circuit and the simulation of the analog circuit, which can be designed by different methods. Now, it cannot meet the design requirements to simulate these two kinds of circuit respectively, so the digital and analog mixed-signal simulation arises at the moment. In this paper, the basic status of digital and analog mixed-signal system modeling methods and simulators are summarized and described. On this basis, LDO(Low Dropout Regulation) which provides power in analog circuit is modeled.In this thesis, firstly, the modeling methods of digital and analog mixed-signal system are introduced, which contain circuit level modeling, structural modeling method and behavioral modeling method. And these methods are explained for the digital circuit and analog circuit respectively. Then, the modeling language VHDL-AMS is introduced, which can model based on the thought of conservation laws and the thought of directed graph. Furthermore, this thesis points out the support of the simulation platform for VHDL-AMS language.LDO is modeled making use of the modeling method by the language of VHDL-AMS on the mixed signal simulation platform. And then, the basic structure of LDO is introduced, which is made up of four parts: pass Xsistor, error amplifier, sampling circuit and reference source. The basic structure of LDO is described to show the work process and principle of LDO, and the parameters of LDO are also analyzed.After understanding the basic structure of LDO, the mixed signal modeling methods are used to model it. According to the basic structure of LDO, the parts are connected to each other to make the LDO model perform correctly using the structure level modeling method.The error amplifier and reference source are modeled by the behavioral modeling method. The relationships of input and output are abstracted and the transfer functions are established. PMOS is chosen as the pass Xsistor, and according to the SPICE model of PMOS, the circuit level PMOS model is built. And then, these three models are verified separately and all of them are valid. For now, the basic structure model of LDO is set up, and the parameters of LDO are analyzed including the output voltage, dropout voltage, the maximum output current, the quiescent current, the noise, the line regulation and load regulation. These parameters of LDO can be adjusted by changing the parameters of the device in the basic structure of LDO. Experiments have been carried out to test the parameters, and the simulation results show that these parameters can be configured by the model.Now, the LDO model is complete, and the model can be connected into the circuit to verify. The output of the circuit is analyzed to prove the correctness and validity of the LDO model. Although, the LDO model is not a general model, it is also able to represent a class of LDO with MOS and it can describe the parameters of LDO perfectly. This model can be used for the simulation of LDO devices in some conditions.