High frequency circuit wiring technique in PCB circuit board
High frequency circuits are often highly integrated and have high wiring density.In PCB Layout stage, reasonable choice of a certain layer printed circuit board size, the middle tier can be fully used to set the shielding, better implement nearby ground, and effectively reduce the parasitic inductance and shorten the length of the transmission of signals, but also can greatly reduce the cross interference of signals etc., all of these methods are good for the reliability of the high frequency circuit.With the same material, the noise of four layers is 20dB lower than that of double panels.However, there is also a problem: the higher the number of layers of PCB, the more complex the manufacturing process, and the higher the unit cost. Therefore, in the process of PCB Layout, in addition to selecting the appropriate number of layers of PCB, reasonable component Layout planning should be carried out and proper wiring rules should be adopted to complete the design.
1. The less alternating lead layer between the pins of high-frequency circuit devices, the better
The so-called “less interlaminar alternation of leads is better” means that the fewer Via used in the connection of components, the better.A single through-hole can bring about a distribution capacitance of about 0.5pF, reducing the through-hole number can significantly improve the speed and reduce the possibility of data error.
2. The shorter the lead, the better
The radiation intensity of the signal is directly proportional to the routing length of the signal line. The longer the high-frequency signal leads, the more easily they can be coupled to components close to the signal. Therefore, the shorter the signal line is, the better.
3. The less bend between the pins of high-speed electronic devices, the better
It is better to use full straight line to lead the wiring of high-frequency circuit, which needs to be turned, and can be broken by 45 degrees or circular arc. This requirement is only used to improve the bonding strength of copper foil in low-frequency circuits, while in high frequency circuits, meeting this requirement can reduce the external emission and mutual coupling of high-frequency signals.
4. Pay attention to the “crosstalk” introduced by the signal line parallel to close distance.
5. The ground line of high-frequency digital signal and the ground line of analog signal are isolated
6. The power pin of integrated circuit block increases the capacitance of high frequency withdrawal
The power pins of each IC block add a high frequency demultiplexing capacitance nearby.Increasing the capacitance of the power supply pin can effectively suppress the interference of the high frequency harmonic on the power supply pin.
7. Avoid the loop formed by routing
All kinds of high frequency signals should not form a loop as far as possible, if unavoidable, should make the loop area as small as possible.
8. Good signal impedance matching must be ensured
During the transmission process, when the impedance does not match, the signal will be reflected in the transmission channel, which will make the synthetic signal overshoot, causing the signal to fluctuate near the logical threshold.high frequency circuit
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