PCB circuit board layout and system test

The basic principles of high speed PCB circuit board layout are as follows:


1. Considering the circuit components in high frequency under the condition of the distribution parameters, all components should be double-sided circuit boards in uniform, neat, compact arrangement, reduce the length of the wire between the various components.

The analog circuit should be separated from the digital circuit. Eliminating the interference of digital signal to analog signal.


Reasonable arrangement of the position of the clock circuit.

The clock circuit and the signal line can not be directly connected, placed in the center of double-sided circuit board and grounding. The layout of the optical burst module circuit can be considered from the following 4 aspects:


The laser MAX3656 and connector position by the SFMSA specification set in advance, and as close as possible to drive laser.


The position of the limiting amplifier MAX3747 is as close as possible to the back end main amplifier chip MAX3748, which ensures the correct reception of the signal direction and the amplified signal, and reduces the interference to the maximum extent.


Clock and data recovery circuit MAX3872, should be placed in a central location and reliable grounding.


The MAX3654-47 ~ 870MHz analog CATV transimpedance amplifier as a function module area can consider consolidation.


First of all, to expand the package components library to meet the needs of the layout and wiring design; and then, using the relevant software directly call components package symbols, complete the circuit preliminary layout and wiring design. After the initial determination of the layout of the majority of components, it is usually carried out after the wiring and wiring of the simulation analysis. Front wiring simulation analysis is to determine key signal wire length, impedance matching, and so on, combined with the delay, reflection and noise affecting the signal integrity simulation analysis results were adjusted repeatedly, from the point of view of the system to do everything possible to ensure signal integrity, input signal relative delay can not exceed 0.2ns.


The design of EMI must meet the requirements of EMC in the design of high speed double sided circuit board. To measure the quality of the EMC design of the system, it is necessary to carry out a precise EMI test. Test, the frequency domain should be used as the basis of measuring instruments, test methods to strictly comply with all kinds of standards. Spectrum analyzer as a test equipment, the whole module can be a full range of components of the three-dimensional test, can show the overall status of electromagnetic radiation. According to the design size of the printed circuit board, the patch and welding assembly, the circuit board EMI debugging; the circuit board assembly into the light module of the small package shell; finally the light module test.


 

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