It is recommended to categorize and prioritize connections between nRF9151 and application components based on their criticality.
The main principle in placing nRF9151 is to optimize the routings of the highest priority connections. Additionally, it is important to ensure good thermal and mechanical contact with the application board and to avoid placing nRF9151 near noisy components like buck regulators or high-frequency signals.
RF routings are the most critical for nRF9151's performance due to the mandatory impedance control and their noticeable impact on user experience. Ensuring sufficient power supply routings are also important for optimal operation. In addition, the Subscriber Identity Module (SIM) and MIPI RF Front-End Control Interface (RFFE) interfaces are sensitive and should be given priority in the layout.
It is recommended to categorize application components according to which ones can be adjacent to one another on the PCB. For example, sensitive antennas should not be placed next to noisy buck regulators or LEDs. Two antennas, such as Global Navigation Satellite System (GNSS) and Long-Term Evolution (LTE), should never be adjacent to each other due to the risk of mutual load effect between two nearby radiators. This interference can significantly deteriorate antenna efficiency and radiation pattern, severely impacting the overall performance of the end product.
Some components, such as the LTE antenna and SIM holder, should be placed close to nRF9151 to minimize the negative effects of long PCB routing, but they should not be near each other. These components should not be too far from nRF9151, but their mutual distance should be maximized. If possible, it is recommended to place these components on the opposite sides of the PCB.
Based on connections and component categorization, you can begin the layout and component placement mockup. Start the layout work from the most critical routings. For a best practice design, each signal layer should have an adjacent metal layer, that is, ground plane, which is dedicated to signal return currents. This metal layer also serves as the main path for thermal dissipation and power relief for nRF9151 and other active components on the application board.
A small form factor PCB sets constraints for component placement, especially for the antenna and its ground layer. Optimal placement for antennas is important and helps guarantee radiated performance and a good user experience for the end product. Therefore, it is recommended to use EM simulation tools to estimate the impact of different antenna locations and grounding on the PCB. Antenna design and simulation services are provided by various design houses globally.
Antenna vendors often provide design and measurement services, but these are typically for their own products. If the end product includes antennas from multiple vendors, it is important to ensure that all antennas are verified to perform as expected when used together in the end product.