PCB layout and system test

1. Consider the distribution parameters of circuit components under high-frequency operating conditions. All components should be arranged evenly, neatly, and compactly on double-sided circuit boards to minimize and shorten the lead length between components.

2. Analog circuits should be separated from digital circuits. Eliminate the interference of digital signals with analog signals.

3. Reasonably arrange the position of the clock circuit.

The clock circuit cannot be directly connected to the signal line, 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 four aspects:

1. The location of the 1 laser MAX3656 and the connector is pre-set by the SFMSA specification, with the laser and driver as close as possible.

2. The position of the limiting amplifier MAX3747 is as close as possible to the MAX3748 back-end amplifier chip to ensure proper signal reception and amplified signals, and to minimize interference.

3. The clock and data recovery circuit MAX3872 should be placed in the center and grounded reliably.

4. MAX3654-47 ~ 870MHz analog CATV transimpedance amplifier as a functional module area can be considered combined processing.

First of all, the expansion of the package library to meet the needs of layout and wiring design; then, use the relevant software directly call the component package symbol to complete the circuit layout and layout design. After a preliminary determination of the layout of most of the components, simulations are usually performed before and after wiring. The simulation analysis before wiring is mainly to determine the length of the traces of the key signals, impedance matching or not, etc., and it is repeatedly adjusted in combination with the delay, reflection, and noise, etc., which affect the signal integrity simulation analysis results, and as far as possible from the system perspective. For signal integrity, the relative delay of the input signal cannot exceed 0.2 ns.

The design of EMI in high-speed double-sided circuit board design must comply with EMC's design requirements. To measure the EMC design quality of a system, you must first perform accurate EMI testing. In the test, measurement instruments should be used based on the frequency domain, and the test methods should strictly comply with various standards. As a test device, the spectrum analyzer can perform a full range of three-dimensional tests on the components on the entire module and can display the overall status of electromagnetic radiation. According to the design size processed into a printed circuit board, patch and welding assembly, the circuit board EMI debugging; the circuit board is assembled into the small package of the optical module; Finally, the optical module is tested.