In the layout design of the double sided, the unit of the should be analyzed, and the layout design should be carried out according to the function of the . The following principles should be followed in the layout of all the components of the circuit:
1.The location of each functional circuit unit is arranged according to the circuit flow, so that the layout is convenient for the signal circulation and the signal keeps the same direction.
2.The core components of each functional unit are centered on it. Components should be uniform. And it compactly arranged on the PCB. It minimizes the connections between components.
3.The distribution parameters between components should be considered in the circuit operating at high frequency. General circuits should be arranged in parallel as far as possible, which is not only easy to mass product but also easy to solder，and it is beautiful.
Pay attention to the following points when designing the specific layout of PCB:
(1)The line length is as short as possible in order to minimize the lead inductance. In low frequency circuits, multipoint grounding is avoided because the ground of all circuits flows through common grounding impedance or grounding plane.
(2) The common ground wire should be arranged at the edge of theas much as possible. The should keep as much copper foil as the ground wire, which can enhance the shielding ability.
(3)The double-layer board can use a ground plane. The purpose of the ground plane is to provide a low-impedance ground.
In multilayer, grounding layer can be set, and the grounding layer is designed as a mesh. The spacing of the earth grid can not be too large because one of the main functions of the earth wire is to provide the signal return path. If the spacing of the grid is too large the signal loop area will be formed. Large loop area can cause radiation and sensitivity problems. In addition, the signal reflux actually takes the path of small loop area; other ground lines do not play a role.