How do you route a PCIe signal?

How do you route a PCIe signal?

Motherboards with PCIe card slots normally route all signals on the same layer (Rx and Tx on opposite board sides), so you should leave enough room on the board for routing your lanes without layer transitions (more on vias below).

How do you route a high-speed signal?

11 Best High-Speed PCB Routing Practices

1. Route high-speed signals over a solid ground plane.
2. Avoid hot spots by placing vias in a grid.
3. Keep trace bends at 135⁰ instead of 90⁰ avoid acute angles.
4. Increase the spacing between traces to avoid crosstalk.
5. Avoid long stub traces by implementing daisy chain routing.

What is high-speed routing?

“High-speed routing” is an abbreviated description of routing copper traces on a printed circuit board in ways that minimize the undesirable parasitic effects that can occur with high-speed signals.

How to route differential signals?

Route the Diff Pairs Together

1. Avoid using vias if possible.
2. Inner layer routing is preferable to minimize crosstalk, but that means transitioning through the layers with vias.
3. Keep the diff pairs isolated from other traces.
4. If possible, consider broadside diff pair routing on adjacent signal layers.

How does PCIe protocol work?

The PCI Express protocol consists of a Transaction Layer, a Link Layer, and a Physical Layer. The Physical Layer consists of the Logical and Electrical Sublayers. The Logical Sublayer of the PHY contains a Physical Coding Sublayer (PCS), which encodes/decodes each 8-bit data-byte to a 10-bit code.

What is Perst in PCIe?

> The PERST# signal is used to indicate when the power supply is within its specified voltage tolerance and is stable. It also initializes a component’s state machines and other logic once power supplies stabilize.

What are the routing specifications for PCIe Gen 1?

The exact routing specifications depend on which PCIe generation you are using for your design. Trace lengths in Gen 1 and Gen 2 both allow RX and TX signal traces to reach up to 21 inches in length, while Gen 3 only allows trace lengths up to 14 inches on these signal trace PCIe lanes.

Where are signals routed on a PCIe motherboard?

Motherboards with PCIe card slots normally route all signals on the same layer (Rx and Tx on opposite board sides), so you should leave enough room on the board for routing your lanes without layer transitions (more on vias below).

How are the lanes in a PCIe card routed?

Communication is bidirectional with groups of Rx and Tx lanes. PCIe lanes are routed point-to-point as differential pairs, so standard rules on length matching and skew should be in place. The PCIe standards define up to 16 available lanes, which also define the size of standardized PCIe card slots.

What’s the maximum trace length for PCIe Gen 1?

For traces on a COM Express carrier board sent to a PCIe slot, Gen 1 and Gen 2 both allow maximum trace lengths up to 9 inches. The differential impedance of signal lines depends on the bus used to connect to your PCIe board. Standard PCBs with differential pair routing typically use 100 Ohm differential impedance.