The basic principle of the high-speed circuit -sided circuit board layout is as follows :
① consider distributed parameter circuit components at high frequency working conditions , all components should be double-sided circuit board in a uniform , neat, compact arrangement , minimize and shorten lead lengths between the various components .
② analog circuits and digital circuits to be separated. Bridging the digital signal to analog signal interference Yi.
③ reasonable arrangements clock circuit position.
Clock circuitry and signal lines can not be directly connected , double-sided circuit board placed in the center and grounded. Optical burst module circuit layout can be obtained from the following four aspects to be considered : ① laser MAX3656 and connector position preset by SFMSA specification , lasers and drive as close as possible . ② position as the limiter amplifier amplifying the MAX3747 and MAX3748 close to the rear end of the main chip to ensure that the signal is correctly received and amplified signal, and minimizes interference. ③ clock and data recovery circuit MAX3872, should be placed in a central location and a reliable ground . ④ MAX3654-47 ~ 870MHz Analog CATV Transimpedance Amplifier module area can be considered as a function of the consolidation .
First, the packaging components library expanded to meet the needs of layout design ; Then, using the relevant software package components directly call sign , complete the preliminary circuit layout designs. After most of the layout initially identified components , wiring and cabling simulation after the former usually also carried . Simulation analysis is to determine the wiring length in front of the main key signal traces , impedance matching or not , combined with the delay , reflecting the impact of signal integrity and noise simulation results were repeated adjustments , from the perspective of the system to ensure as much as possible signal integrity , the relative delay of the input signal must not exceed 0.2ns.
EMI design of high-speed double-sided circuit board design must comply with EMC design requirements. EMC designed to measure the quality of the system , it must first be precise EMI testing. Tests should be based on the frequency domain using measuring instruments , test methods must be strictly complied with various standards . Spectrum analyzer as test equipment, the components of the entire module on a full range of three-dimensional test shows overall status of electromagnetic radiation. According to the design process into a printed circuit board size , placement and welding assembly carried on board EMI debugging ; circuit board assembly into a small package optical module housing ; finally light module for testing.
