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Reference GND/PWR for high speed signals
miguelangel.alfonso , 09-22-2023, 01:11 AM
Hello,
Currently, I am working in a design with different high speed signals (RGMII, DDR3, eMMC...) and I have a doubt about the reference planes for this signals.
In my previous designs, with this signals I made a "sandwich" between the GND and the power plane of that particular signal. For instance, 1V5 and GND for DDR3 or 1V8 and GND for RGMII (see pictures).
I do that because I understand that with high-speed signals, the power plane and the GND plane are almost the same reference and I don't want that any signal of the DDR3 bus cross a power plane split or to be under a voltage different from its voltage reference.
My question is, if I have the signals in a layer between the GND plane and the PWR plane, do I need to do that sandwich or the power plane is independent since I have the GND plane as reference? If only the GND reference is needed, does it depend on the proximity to the planes? I mean, you need to put closer (thinner prepeg/core) the reference plane you want to use.
Thank you very much in advance.
Currently, I am working in a design with different high speed signals (RGMII, DDR3, eMMC...) and I have a doubt about the reference planes for this signals.
In my previous designs, with this signals I made a "sandwich" between the GND and the power plane of that particular signal. For instance, 1V5 and GND for DDR3 or 1V8 and GND for RGMII (see pictures).
I do that because I understand that with high-speed signals, the power plane and the GND plane are almost the same reference and I don't want that any signal of the DDR3 bus cross a power plane split or to be under a voltage different from its voltage reference.
My question is, if I have the signals in a layer between the GND plane and the PWR plane, do I need to do that sandwich or the power plane is independent since I have the GND plane as reference? If only the GND reference is needed, does it depend on the proximity to the planes? I mean, you need to put closer (thinner prepeg/core) the reference plane you want to use.
Thank you very much in advance.
miguelangel.alfonso , 09-22-2023, 02:26 AM
Hello again,
Sorry, but I have just seen the Lesson 5 for this course and in that video there is an explanation that it is better not to route critical signals under this power plane, since you are crossing several power planes.
So, I assume that it is a good practice to do the sandwich shown in my previous post but, if you can't do that, rout the signals between 2 GND layers.
Everything is clear now.
Sorry, but I have just seen the Lesson 5 for this course and in that video there is an explanation that it is better not to route critical signals under this power plane, since you are crossing several power planes.
So, I assume that it is a good practice to do the sandwich shown in my previous post but, if you can't do that, rout the signals between 2 GND layers.
Everything is clear now.
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