Analysis Of Signal Integrity And PCB Design For High-speed Digital-analog Hybrid Circuit

Modern electronic products are towards higher speed, higher integration and higher reliability. The bandwidth of high-speed amplifiers and analog-to-digital converters is above hundreds MHz, even GHz.These high-speed analog devices are more and more widely used in video signal processing, signal acquisition and real-time detecting circuits. The high-speed digital devices with edge rate up to ps level are quite common. Accordingly, High-speed digital-analog hybrid circuit PCB become the new trend of PCB,which has new features. The traditional design methods can not meet the demands. The design of high-speed hybrid circuit PCB is facing new challenges. It's necessary to take new design methods and steps to ensure the first product successful.Signal integrity refers to the signal quality in interconnecting lines. In a high-speed interconnected system, signal flows through chip's internal wires, chip's packages, PCB wires, pads, via stubs. Any transmitting paths maybe produce signal integrity problems. The paper mainly focuses on the problems in interconnecting lines. The interconnection among high-speed signal is no longer unblocked and transparent. Its influence can not be neglected. The signal integrity problems could make system instable or malfunctioned. It is a key performance index for any successful high-speed PCB design to properly deal with the problems such as reflection, crosstalk, synchronous switching noise, and electromagnetic interference. A sound signal integrity design should run through all phases of the whole project, and the potential problems should be solved at early stage as soon as possible.Based on high-frequency effect,transmission line theory and electromagnetic interference theory,the signal integrity problems are analyzed thoroughly in the paper,which include reflection, crosstalk, synchronous switching noise, and electromagnetic interference. Various corresponding solutions for these problems are discussed. The author analyzed signal integrity of an high-speed data sampling and signal processing mainboard in an analytical instrument and designed the printed circuit board.Mainly through improving the PCB signal integrity of high-speed digital circuits and high-speed analog circuits,the noise between digital circuits and analog circuits was reduced and the whole board's quality was ensured. Signal integrity design process with the software of Cadence Allegro PCB SI and Ansoft SIwave/Designer SI were also introduced. In order to optimize EMI sources and coupling paths,the simulations for key nets and the whole board contained termination strategy, crosstalk, resonance of the power and ground planes, synchronous switching noise,conduction and radiation analysis. The results of simulation are helpful to establish relevant design constraints for PCB layout and routing. Post-simulation is employed to verify signal integrity and effective measures can be adopted to improve the PCB performance in design phase and to achieve better quality. This further indicates it is indispensable to adopt emulational analysis in high-speed PCB design.The high-speed hybrid PCB design method and process based on emulational analysis for signal integrity given in this paper can improve design quality, reduce the risk of failure or repeated design, shorten design period and cut down costs. This also perfects the concepts, steps and means of the high-speed hybrid PCB design.