In addition to the layout guidelines already given, here are some additional comments for this specific layout example.
- The most critical part of the layout that the placement of the pull-up components (R19, R20, R21, and R22) is close to the pin for optimal output power.
- For this layout, all of the loop filter (C1LF, C2LF, C3LF, C4LF, R2LF, R3LF, and R4LF) are on the back side of the board. C4LF is located right underneath to the VTUNE pin. In the event that this C4LF capacitor would be open, it is recommended to move one of loop capacitors in this spot. For instance, if a 3rd order loop filter was used, technically C3LF would be non-zero and C4LF would be open. However, for this layout example that is designed for a 4th order loop filter, it would be optimal to make R3LF = 0 Ω, C3LF = open, and C4LF to be whatever C3LF would have been.