The purpose of decoupling is to provide clean, noise-free power supplies for SoC-internal power rails. Internal regulators are stabilized for a given capacitance and interaction between regulator modes relies on decoupling capacitors.
Power supply decoupling capacitors must be selected with care to ensure sufficient effective capacitance for the nRF power system, because insufficient capacitance can cause instability and malfunction in power system operation mode engine. The effective capacitance of chip capacitors may only be a small fraction of the marked nominal value. There are several factors that may reduce effective capacitance beyond the specified tolerance in operation conditions, the most common ones being temperature coefficient, DC bias, and AC bias.
Nonideal characteristics are most pronounced in small, low-profile, and therefore high-density multilayer ceramic capasitors (MLCC). In small footprint designs, where the area is restricted, extra care must be taken to attain proper decoupling for nRF power supplies.