7.2 Layout Considerations

Keep all decoupling capacitors as close to the IC as possible, with the high-frequency decoupling capacitors (10 nF) closer than the low-frequency decoupling capacitors (2.2 µF).

Place ground vias as close as possible to the ground side of the capacitors and reader IC pins to minimize possible ground loops.

TI recommends not using any inductor sizes smaller than 0603, as the output power can be compromised. If smaller inductors are necessary, output performance must be confirmed in the final application.

Pay close attention to the required load capacitance of the crystal, and adjust the two external shunt capacitors accordingly. Follow the recommendations of the crystal manufacturer for those values.

There should be a common ground plane for the digital and analog sections. The multiple ground sections or islands should have vias that tie the different sections of the planes together.

Ensure that the exposed thermal pad at the center of the reader IC is properly laid out. It should be tied to ground to help dissipate any heat from the package.

All trace line lengths should be made as short as possible, particularly the RF output path, crystal connections, and control lines from the reader to the microprocessor. Proper placement of the TRF7964A, microprocessor, crystal, and RF connection or connector help facilitate this.

Avoid crossing of digital lines under RF signal lines. Also, avoid crossing of digital lines with other digital lines when possible. If the crossings are unavoidable, 90° crossings should be used to minimize coupling of the lines.

Depending on the production test plan, consider possible implementations of test pads or test vias for use during testing. The necessary pads or vias should be placed in accordance with the proposed test plan to enable easy access to those test points.

If the system implementation is complex (for example, if the RFID reader module is a subsystem of a greater system with other modules (microprocessors and clocks), special considerations should be taken to ensure that there is no noise coupling into the supply lines. If needed, special filtering or regulator considerations should be used to minimize or eliminate noise in these systems.

For more information/details on layout considerations, see the TRF796x HF-RFID Reader Layout Design Guide.