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How to calculate trace length tolerances in a high speed PCB design?
I heard that there are matched trace length tolerances depending on frequency so that it will not damage the signal acquisition by the destination. My question is how to calculate trace length tolerances in a High Speed PCB design? (in differential pair routing and high speed data bus routing)
How to calculate the trace length of a data bus?
I have to interface a video format converter with a ADC IC, which converters RGB analog data to digital. The connection between this ADC and Converter is a 20 bit data bus which clocks at about 170MHz. Since I have the PCB area constraints I cannot perfectly match the trace length of this data bus.
How many entries can a message trace display?
The message trace can display a maximum of 500 entries. By default, the user interface displays 50 entries per page, and you can navigate through the pages. You can also change the entry size of each page up to 500.
What’s the propagation time for a top layer trace?
Propagation time for a top layer trace, a microstrip is about 150ps/in. So a 1 inch difference will skew a data signal from clock +/- 150ps. That’s really not bad at all considering your 5.882ns clock period. In fact 170Mhz is really not that fast.
What happens if you forget to match PCB trace lengths?
You shouldn’t freak out just yet, just because you’ve forgotten to match data buses or differential pairs. Depending on the difference between the PCB trace lengths and the speed of the traveling pulse, you’ll be able to estimate if there are going to be any issues with signal integrity.
How to calculate trace length on FR4 PCB?
In the absence of a specification for the bus standard or the receiver timing, you can apply a rule of thumb such as keeping the skew to less than 5% of the clock period. Signals on an FR4 PCB travel at approx half the speed of light, so you’d want to make your longest trace no more than 44 mm longer than the shortest trace. Not too tricky.
What are differential pairs and trace tuning in PCB?
Differential Pairs: This is a rule tied to a routing feature that allows the user to route the two nets of a differential pair tightly together. Trace Tuning: For those traces that require more length, this is another rule tied to a function that will create serpentine routing to achieve their target length.