When designing with an RF amplifier operating in the frequency range 3.3 GHz to 3.8 GHz with relatively high gain, certain board layout precautions must be taken to ensure stability and optimum performance. TI recommends that the LMH9235 board be multi-layered to improve thermal performance, grounding, and power-supply decoupling. Figure 10-1 shows a good layout example. In this figure, only the top signal layer is shown.

• Excellent electrical connection from the thermal pad to the board ground is essential. Use the recommended footprint, solder the pad to the board, and do not include a solder mask under the pad.
• Connect the pad ground to the device terminal ground on the top board layer.
• Ensure that ground planes on the top and any internal layers are well stitched with vias.
• Design the input and output RF traces for appropriate impedance. TI recommends grounded coplanar waveguide (GCPW) type transmission lines for the RF traces. Use a PCB trace width calculator tool to design the transmission lines.
• Avoid routing clocks and digital control lines near RF signal lines.
• Do not route RF or DC signal lines over noisy power planes.
• Place supply decoupling caps close to the device.
• The differential output traces must be symmetrical in order to achieve the best differential balance and linearity performance.

See the LMH9235 Evaluation Module user's guide for more details on board layout and design.