High Speed PCB

[alican.ozpay]

Hello everyone,

I want to learn something about High Speed PCB. I have listed my questions below.

1- How many MHZ after routing lenght tuning should ı do ?

2- I saw so much routing like snake. What is it ? Can ı do differential pair all at high MHZ ?

3- What is your purpose for high speed PCB ?

Best regards,

[robertferanec]

1) Usually I have seen the "waves" from 500MHz and above.

Important is to know the timing - for example, even if you have a slow bus and you make CLK very very very short and data very very very long, then your interface may not work. However, generally for frequencies bellow 500MHz, if you route signals on your PCB, usually the length will be in tolerance even if you do not do length matching (because for slower signals the tolerance in length between signals can be for example 30mm, however for high speed signals the tolerans is often in range below 1 mm).

Note: For negative and positive signals in differential pairs you would like to generally keep length almost same.

2) I am not sure if by "snake" you mean like "waves", but if yes, then the waves add additional length so signal through that traces travels longer and it then arrives within tolerance - together with other signals to the receiver (chip).

3) Some of the things why you may need to be careful when designing high speed PCB: if PCB layout is not done properly, your high speed interface may not work or may not work reliably (eg. if memory layout is not done properly, you may be losing some bits and your board will be crashing or freezing), possibly you may have a lot of problems passing EMC / EMI tests (means your product will not be approved), etc