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Advanced circuit board prototype: circuit board layout and system test

Release Date:2020-02-21

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

① Considering the distribution parameters of circuit components under high-frequency operating conditions, all components should be arranged uniformly, neatly and compactly on a double-sided circuit board to minimize and shorten the lead length between components.
② Analog circuits should be separated from digital circuits. Eliminate the easy interference of digital signals to analog signals.
③ Reasonably arrange the position of the clock circuit.

The clock circuit cannot be directly connected to the signal line. It should be placed in the center of the double-sided circuit board and grounded. The layout of the optical burst module circuit can be considered from the following 4 aspects:

① The position of the laser MAX3656 and the connector is set in advance by the SFMSA specification, and the laser and the driver are as close as possible.
② The position of the limiting amplifier MAX3747 is as close as possible to the back-end main amplification chip MAX3748, ensuring the correct reception of the signal direction and the amplified signal, and minimizing interference.
③ The clock and data recovery circuit MAX3872 should be placed in the center and reliably grounded.

④ MAX3654-47 ~ 870MHz analog CATV mutual resistance amplifier can be considered as a function module area for combined processing.


First, the package component library is expanded to meet the needs of layout design. Then, the related software is used to directly call the component package symbols to complete the preliminary layout design of the circuit. After the layout of most components is initially determined, simulation analysis before and after wiring is usually performed. The pre-wiring simulation analysis is mainly to determine the length of the key signal traces, impedance matching, etc., and to repeatedly adjust the simulation analysis results that affect signal integrity, such as delay, reflection, and noise, to ensure as much as possible from a system perspective Signal integrity, the relative delay of the input signal cannot exceed 0.2ns.

The design of EMI in high-speed double-sided circuit board design must meet EMC design requirements.

To measure the EMC design quality of a system, an accurate EMI test must first be performed. In the test, the measurement instrument should be used on the basis of the frequency domain, and the test method should strictly comply with various standards. As a test device, the spectrum analyzer can perform all-dimensional three-dimensional testing on the components on the entire module, and can display the overall status of electromagnetic radiation. The printed circuit board is processed according to the design size, and the patch and solder assembly are performed to debug the EMI of the circuit board; the circuit board is assembled into a small package shell of the optical module; and finally, the optical module is tested.

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