| With the rapid development of integrated circuit technology,the digitization of electronic systems has become the trend of future.Wireless software is the ultimate goal of digitization in fields of radio such as communications and radar.Its main content is to place ADCs or DACs as close to the antenna as possible,replace analog circuits with digital ones as much as possible,build common and open hardware platforms and use software to implement the functions of each module.It should also have the characteristics of programmable and upgradeable features.As an important part of the radar,the multi-channel receiver and its modularization,miniaturization and digitization are also the future development trends.The general approach to digitizing radar receivers is to use ADCs to sample at intermediate or higher frequencies,and then transfer information to FPGAs for down mixing and signal processing.Compared with the traditional analog receiver,its main advantages includes high resolution,stability,reliability,and strong anti-interference ability.This thesis focuses on the integration of the intermediate frequency circuit and the parallel sampling circuit after mixing.The parallel sampling circuit converts the analog signal in intermediate frequency after mixing and IQ intermodulation into high-precision digital signals through sampling,and completes subsequent packet transmission of the output data.This article introduces the basic theory related to the IF sampling circuit of the receiver,such as the sampling theorem,etc.The classification and principle of the ADC are briefly described and compared.The relevant theory of signal integrity is introduced,mainly the transmission line theory and differential pairs.According to the equivalent circuit model of the transmission line,a quantitative analysis was performed to obtain the key physical parameters of the transmission line,such as characteristic impedance and transmission delay.Subsequently,a brief analysis of the reflection and crosstalk mechanisms of the transmission line was made,an equivalent model was given,and two equivalent models of common crosstalk were given.The simulation of a single transmission line reflection was performed,and differential analysis was performed.Crosstalk with a transmission line was simulated and analyzed,and the effects of reflection and crosstalk on the transmission line were intuitively obtained.Then,the differential pair circuits commonly used in high-speed and ultra-high-speed circuits are introduced.The impedance of the differential pair is analyzed and calculated,and the structure of the terminal impedance matching circuit of the commonly used differential pair is given.Microstrip-via-taper-via-microstrip line structures based on common four-layer PCBs are modeled and electromagnetically simulated in HFSS,taking full account of pads and anti-pads in real PCBs.The S-parameter simulation results of the differential mode signal was obtained and the relevant theory was demonstrated.According to the technical specifications of the receiver system,the design scheme of the intermediate frequency circuit is proposed,and the circuit design is completed.The PCB Editor tool in Cadence 16.6 is used to realize the layout and wiring of the entire circuit structure,and the high-speed serial digital signal integrity analysis is completed.The main method is to use the SI tools in Cadence to extract the high-speed serial signal ADC,and combined with the IBIS model of the ADC to obtain the output signal waveform curve and eye diagram for analysis.The key signal path and wiring scheme is verified.On the other hand,the layout is simulated.The specific operation method is to extract the layout of the high-speed SERDOUT differential signal line from Cadence,import it into ADS,perform simulation,and finally obtain the S-parameter of the output signal.Through the simulation of the layout after wiring,the performance of the high-speed differential signal transmission line was verified and the design requirements were achieved. |
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