PCB not only plays a role in current conduction in electronic products, but also plays a role in signal transmission. The high frequency and high speed of electronic products require that the circuit performance provided by PCB must ensure that the signal does not reflect during

PCB not only plays a role in current conduction in electronic products, but also plays a role in signal transmission; the high frequency and high speed of

electronic products require that the circuit performance provided by the PCB must ensure that the signal is not reflected during transmission, and the signal is kept intact and not distorted; characteristic impedance is the core of solving the problem of signal integrity;

electronic devices (such as computers, communication switches, etc.) operate, the signals sent by the drive element (Driver) must reach the receiving element (Receiver) through the PCB signal line. To ensure signal integrity, the characteristic impedance (Z0) of the PCB signal line must match the "electronic impedance" of the head and tail element; when the transmission line ≥1/3 of the rise time, the signal will be reflected, and the characteristic impedance must be considered.

If there is no impedance control, it will cause considerable signal reflection and signal distortion, resulting in design failure. Common signals, such as PCI bus , PCI-E bus , USB, Ethernet, DDR memory, LVDS signals, etc., all require impedance control. Impedance control ultimately needs to be implemented through PCB design, which also puts forward higher requirements for the PCB board process. After communication with the PCB factory and combined with the use of EDA software, the impedance of the trace is controlled according to the signal integrity requirements. What are the impedance types of

?

(1) Characteristic impedance

In computers, wireless communication and other electronic information products, the energy transmitted in the PCB line is a square wave signal composed of voltage and time (square wave signal, called pulse pulse), and the resistance it encounters is called characteristic impedance.

(2) Differential impedance

drive end input two identical signal waveforms with opposite polarity, respectively transmitted by two differential lines, and the two differential signals at the receiving end are reduced. The differential impedance is the impedance Zdiff between two lines.

(3) odd mode impedance

The impedance Zoo of one line to the ground in the two lines, the impedance values ​​of the two lines are the same.

(4) Even mode impedance

The driver inputs two identical signal waveforms with the same polarity, and the impedance Zcom when connecting the two wires together.

(5) Common mode impedance

The impedance Zoe of one line to ground in the two lines. The impedance values ​​of the two lines are the same, which is usually larger than the odd mode impedance.

How to calculate PCB impedance? What is the formula?

characteristic impedance formula

microstrip line (microstrip)

　　Z={87/[sqrt(Er+1.41)]}ln[5.98H/(0.8W+T)] where W is the line width, T is the copper skin thickness of the trace, H is the distance from the trace to the reference plane, and Er is the dielectric constant of the PCB board material. This formula must be applied at 0.1(W/H)2.0 and 1(Er)15.

stripline

Z=[60/sqrt(Er)]ln{4H/[0.67π(0.8W+T)]} where H is the distance between the two reference planes, and the trace is located in the middle of the two reference planes. This formula must be used in W/H0.35 and T/H0.25 before

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customization process find board

1. Supports small and medium batch orders from 1 to 14 layers, and consult customer service for more layers;

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6. Supports copper thickness of 10oz and 35μm of copper hole;

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9. Copper on the edge of the board, two-color ink, plug-in hole, countersunk hole, square groove, step hole, step groove, nickel palladium and other special processes;

10. PCBA set stickers, single and double sides can be sticked;