| With the increasing demand for communication and radar systems,radio frequency(RF)chips based on CMOS technology are evolving towards higher frequencies and greater integration.For complex systems,it is crucial to fully assess system performance and validate algorithms during the design phase to ensure system efficiency and development cycle.Circuit-level simulations use analytical expressions of physical or empirical bases to characterize the current-voltage relationship of the device,which can provide very accurate simulation results,but such simulations take a long time and the simulation results may not converge.For example,for the vehicle-mounted millimeter-wave FMCW radar,where it works at 77 GHz and the intermediate frequency does not exceed 20 MHz,a difference of 3-4 orders of magnitude,it is basically impossible to achieve a complete sweep process using circuit-level simulation.Behavioral models serve as high-level abstract models that describe and simulate the functional and behavioral characteristics of RF modules without delving into physical or circuit details.These models are typically implemented through mathematical equations or algorithms to accurately simulate module behaviors such as nonlinear responses,signal distortion,noise,etc.,thus predicting system performance during the design phase and guiding system design and optimization.The significance of these models lies in their ability to facilitate system-level design and optimization without the need for actual hardware,significantly reducing development costs and cycle time while helping designers understand and predict system performance in real operational environments.However,its accuracy,reliability,and efficiency all affect the final simulation results.Therefore,the behavior-level modeling technology to improve the accuracy and efficiency of the behavior-level model of RF modules is a key technology in the process of complex system design.In this dissertation,the behavioral models for frequency source which is based on event-driven model,phase shifter which is based on filter banks model,frequency multiplier which is based on Hammerstein model and mixer based on simplified multi-box models,are modeled.Then,a behavioral model for FMCW radar is developed through that of above-mentioned modules.This model incorporates the physical characteristics of frequency sources and mixers,making it closer to the actual device situation and providing a more accurate data source for algorithm validation.The research mainly comprises the following four parts:1.Research on frequency source modeling based on the event-driven and bandpass sampling.In response to the requirements for accuracy and simulation efficiency in the behavioral model of a charge pump phase-locked loop(CP-PLL)with mixed analog and digital modules,this dissertation proposes an event-driven model with a renewal process combined with a time domain model that incorporates bandpass sampling.The equivalent third-order loop filter model is used in the event-driven model,so that the output voltage has an explicit expression,and the phase explicit expression can still be obtained when the VCO sensitivity function is nonlinear,which improves the efficiency.At the same time,the modeling process considers an ideal clock and retains the state parameters at the moment of the clock’s arrival,thereby enabling uniform sampling of the control voltage,which can characterize the dispersion and noise of the frequency source.Simulation results show that when implementing a fourth-order CP-PLL to generate a 50μs FMCW waveform,the simulation time of this model is around 4 seconds,which is several orders of magnitude faster than circuit simulation.Based on the event-driven model,a time domain modeling method based on bandpass sampling is proposed.This modeling method combines the accuracy of the event-driven model with the efficiency of bandpass sampling,providing an accurate signal source input for the system’s time domain simulation.2.Research on the linear model of the phase shifter.An iterative complex domain least squares method is proposed to fit the filters with arbitrary gain and phase response,and then the frequency response fitting of Hybrid and VGA is realized by starting from the vector synthesis phase shifter.The relationship between the control voltage,gain and phase of VGA is fitted by using the hyperbolic tangent function,and the coefficient matrix is obtained.Compared with the circuit-level simulation results,the phase and amplitude errors of the model simulation results are less than 1° and 1d B,respectively.So this model can be applied to the system instead of circuit-level simulation to verify the influence of the phase shifter on the overall system.According to the simulation results and test results of the phase shifter as a whole,a phase shifter model based on look-up table is proposed.The model uses the layout data and the measured data of a65 nm CMOS phase shifter chip as inputs,and realizes the phase shifter modeling based on the look-up table,in which the maximum difference between the model and the measured data in the relative phase shift is 1.5°,and the average error is 0.4°.The correctness of the model is verified by using FMCW signals through two models with different phase-shifting values and comparing them with the theoretical values.The model is applied to the simulation of the beamforming of the array,which reflects the actual beam performance more realistically,compared with the model with only quantization error.Finally,the model is used to analyze the influence of the wideband signal in the communication system when it passes through the phase shifter.3.Research on the multi-box model of the mixer and Hammerstein model of the multiplier.The modeling method of the mixer is studied,and a simplified multi-box model of the mixer is proposed.This model equates the local oscillator and RF input to two nonlinear modules,and uses polynomial fitting to fit the nonlinear characterization of the mixer,while the coefficients of the polynomial use exponential fitting.When extracting parameters,the QPSS simulation results of a single-tone signal input are used as the data source.Then,the QPSS simulation results of a dual-tone input are used as verification,and the spectrum of the intermediate frequency output of the model is compared to verify the correctness of the model.For the quadruplier,the Hammerstein method is used to model the nonlinearity,and the IIR filter equivalent method is used to fit the frequency response.By comparing with the simulation data,the amplitude error in the passband is less than 2d B,which can be used in system behavior-level simulation.4.Research on the behavioral-level model of the FMCW radar system.A behavioral-level model of the FMCW radar system based on the time-domain model is proposed.In this model,the local oscillator signal and multi-channel echo signal are generated by using the frequency source time-domain model based on bandpass sampling,and then decimation filter is carried out through a mixer with nonlinear characteristics to obtain the intermediate frequency signal.The model includes the physical characteristics of the signal source,such as the spurs of the Delta-Sigma modulator(DSM),as well as the nonlinear characteristics of the mixer and frequency multiplier,so the output results contain more information,which provides support for the verification of the performance of the system and the verification of the algorithm. |
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