PCB miscellaneous mail

A brief description of the signal and signal integrity ：

In any type of PCB When the design , Obviously , You will send from the input to the desired region of interest via copper wire . The signal you will send can be a digital signal , It can also be an analog signal .

digital signal

• Also called a square signal , It is output , You will always encounter any digital signals that exist on this planet .
• Unlike analog signals with random numbers everywhere , The digital signal has a well-organized result system , By high and low or 1 and 0 Express , Some even call them close and open .
• Let's look at the following digital signals .

analog signal

• This type of signal has random output points , Consists of negative and positive values .
• Different from digital signals with open and close points , Analog signals have random results , These results are defined by frequency and signal strength .
• The following are the outputs that should be expected when using analog signals .

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The main problem with these signals is that they are susceptible to interference , This is where we introduce signal integrity , Because whenever the signal is affected by the environment , There will be some problems .

Let's take a look at the following example .

Suppose you have a circuit that is sending a signal from PCB In plate 1 Point is transmitted to the 2 spot . spot 1 Can be classified as a transmitter , spot 2 Can be classified as a receiver . When the signal goes from point 1 Move to point 2 when , The signal may be affected by different factors , for example ;

1. The signal rings ; When the current or voltage is shifted unnecessarily , That's what happens , This will result in the flow of additional current in the trace , So as to delay the arrival of the signal .

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1. 1. Signal reflection ; This is when your signal is in coper Flow in the track , But when the whole signal cannot reach the destination , Because some of these signals are reflected back to the origin .

• Signal noise ; When there is random signal fluctuation in the circuit board , That's what happens , This in turn will affect the signal close to it . Fluctuation may eventually damage the signal data transmitted in the circuit board .

• Signal timing ; Sometimes , When you send a signal over copper wire , They will not reach that goal in time , So it can match the clock signal . When that happens , The signal may be interpreted as zero , And in reality , It's for 1. This is called signal timing .
• Signal crosstalk ; When you place two copper wires too close to each other , That's what happens , Because the wiring carries different signals . Electromagnetic radiation emitted from one signal may affect another signal , So as to affect the data flowing in it .

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Design rules and challenges of high-speed design .

Just like any engineering work , When we deal with high speed PCB When the design , Some rules must be observed . Let's delve into some of these challenges ; Let's look at some of these challenges .

Adjust the trace length

ad locum , If you are using a high-speed interface , The length of the trace must be signal adjusted , In order to synchronize the signal propagation . If you miss the synchronization , Then your interface will fail at a very high frequency , It doesn't even work . therefore , In high-speed design , Tuning is a very important aspect .

• In any high-speed design , There should be two types of interference , Parallel and serial interfaces .
• The parallel interface will only involve the length of the routing tuning , For the serial interface , The signals are combined into several differential pairs .

• Tuned differential pairs

• The following is the tuning length of the track ;

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