Mitigating Board Noise Desense in Cellular Hardware Radiators
Mitigating board noise desense requires unbroken ground planes, filtered switching stages, and RF shielding cans to preserve receiver sensitivity margins.
RF Choke
Meaning
Inductive component designed to block high frequency alternating current while allowing direct current to pass ensures the separation of power and signal paths in wireless hardware. An rf choke presents a high impedance to radio frequency signals, preventing them from leaking into the power supply lines where they could cause instability. This device defines the limit where high frequency signals are isolated from DC rails, preventing noise from corrupting other sensitive circuits.
Component Operation
High impedance at high frequencies is achieved by utilizing the self inductance of the coil. The component allows direct current to flow to the active devices with minimal resistive loss. This dual function makes the coil essential for biasing active devices such as power amplifiers and low noise receiver amplifiers.
Selection Parameter
Self resonant frequency is the primary factor that dictates the useful operating range of the inductor. At the self resonant frequency, the parasitic capacitance of the windings cancels the inductance, which causes the component to act as a high impedance resistor. Above this frequency, the component becomes capacitive and loses its ability to block high frequency signals, meaning that designers must select a component with a resonant frequency well above the highest operating frequency of the system.
Placement Practice
Physical positioning of the inductor on the circuit board is critical to prevent unwanted radiative coupling. Placing the component close to the active device minimizes trace lengths and reduces parasitic capacitance. Shielded inductors are preferred in compact multi radio systems to contain the electromagnetic fields within the component body.