Microsemi IGLOO2 - DC Blocking Capacitors; Connectors; Figure 53 Via-To-Via Pitch; Figure 54 GND Via or Return Via

Layout Guidelines for SmartFusion2- and IGLOO2-Based Board Design
AC393 Application Note Revision 14.0 58
Figure 53 • Via-to-Via Pitch
• Symmetrical ground vias (return vias) should be used to reduce discontinuity for Common mode
signal component, as shown in the following figure. Common mode of part of the signal requires
continuous return path RX to TX and GND. Return vias help in maintaining the continuity.
Figure 54 • GND Via or Return Via
3.8.3 DC Blocking Capacitors
The plane underneath the pads of DC blocking capacitors should be removed (as shown in the following
figure) to match the impedance of the pad to 50 Ω. This has to be done only on immediate reference
plane, not on all planes.
Figure 55 • Capacitor Pad Reference Plane
3.8.4 Connectors
The plane keep-out clearance should be optimized from the pin to get 50 Ω impedance when through
hole SMAs or connectors are used. This reduces the reflection loss.
NO!
Wide
Placement
Vias are narrowly
spaced
GOOD!