GTY Transceiver Breakout Use Case

Diamond Jog BGA Breakout Geometries (WP538)

Document ID
WP538
Release Date
2022-09-14
Revision
1.0 English

The following example shows a typical GTY transceiver breakout of a small form-factor plugable (SFP) data bus on a Virtex® UltraScale+™ device (VU23P). In the image, the RX signals are routed on layer 3 (dark pink) and the TX signals are routed on layer 5 (light pink).

Figure 1. GTY Transceiver Breakout

The following image shows the opposite end of the differential pair trace terminating at an SFP SMT connector. The ideal entry for a non-via in pad is marked by the orange arrow. The yellow arrows show a sub-optimal entry.

Figure 2. Differential Pair Trace Terminating at an SFP SMT Connector

The SFP entry is compromised because there are routing loopbacks on entry, that effects the P-N skew and influences signal fidelity. By performing P&N swaps at the FPGA end, we can reduce the SFP entry to two loopbacks. However, it will make the proximity issue worse, and via to pad distances will be reduced to a critical distance because the jog via is moved closer to the adjacent GTY transceiver breakout pair. This is shown in the following image.

Figure 3. Comparing Standard with P&N Swapped Diagonal Via Breakouts

The following image shows the proposed new breakout. It offers maximum distance pad to via, no cross routing at via structures, and reduces loopback occurrences to just one from four. By mixing via structure breakouts, we can maximize the distance between via and pad and remove all instances of trace proximity. The diamond breakout allows the P&N swap to remove loopback at the DSFP connector end. In this image:

  • Diamond jog breakout is circled in orange
  • Southeast diagonal jog breakout is circled in yellow
Figure 4. Proposed Breakouts to Reduce Loopback Occurrences