Rules that should be followed in PCB design
1) Ground circuit rules:
The loop minimum rule means that the loop area formed by the signal line and its loop should be as small as possible. The smaller the loop area is, the less external radiation is and the less external interference is received. According to this rule, the distribution of ground plane and important signal routing should be taken into account during ground plane segmentation to avoid problems caused by ground plane grooving. In double plate design, in the case of leave enough space for the power supply, should be part of the filled with reference to the left, and add some necessary holes, connect double-sided signals efficiently, to some of the key signal adopting the ground as far as possible, to the design of some high frequency, special consideration should be to plane problem of signal circuit, recommended sandwich plate is advisable.
2) Tampering control
CrossTalk refers to the mutual interference between different networks on a PCB due to long parallel wiring, mainly due to distributed capacitance and distributed inductance between parallel lines. The main measures to overcome crosstalk are:
Increase the spacing of parallel cabling and follow the 3W rule.
Insert grounded isolators between parallel lines.
Reduce the distance between the wiring layer and the ground plane.
3) Shielding protection
Do not allow one end to float.
The main purpose is to avoid the “antenna effect” and to reduce unnecessary interference with radiation and reception, which might otherwise bring unpredictable results.
6) Impedance matching inspection rules:
In high-speed digital circuit, more than when the delay time of PCB wiring signal rise time (or down) a quarter, the wiring is as a transmission line, in order to ensure that the signal of input and output impedance matching with the impedance of the transmission lines correctly, you can use a variety of forms of matching method, the choice of matching method and the network connection and wiring topology structure.
A. For point-to-point connections (one output corresponds to one input), you can choose starting series matching or terminal parallel matching. The former has simple structure, low cost, but large delay. The latter has good matching effect, but complex structure and high cost.
B. For point-to-multipoint connections (one output corresponds to multiple outputs), if the topology structure of the network is Daisy chain, parallel terminal matching should be selected. When the network is a star structure, refer to the point-to-point structure.
Star and Daisy chain are two basic topological structures, and the other structures can be regarded as the deformation of the basic structure, and some flexible measures can be taken to match. In practice, cost, power consumption and performance should be taken into account. In general, perfect matching is not pursued, as long as the reflection and other interference caused by mismatching is limited to an acceptable range.