Description
RF limiters are used in systems to prevent damage to sensitive circuitry caused by excessive power at the input of a system. Components in the receive chain of a wireless system are extremely sensitive, as they are typically designed to accept only small signal levels which are then amplified. RF limiters reduce high power inputs to low levels that can be tolerated by the next component in the Rx chain.
Limiter parameters
Insertion loss is the total RF power transmission loss resulting from the insertion of a device in a transmission line.
Flat leakage is the designed RF output power level limit for a given limiter. For example, if the maximum power an LNA can handle is 20 dBm, a limiter with flat leakage of less than 20 dBm should be selected.
Maximum input power (CW) is the maximum input power (CW) that a limiter can handle during normal operation of a system.
Maximum input power (peak) is the maximum input peak power that a limiter can handle without getting damaged. This is not continuous power; it is the maximum surge in power that a limiter can handle.
Turn-on time of a limiter is crucial. It tells how long it takes for the limiter to start limiting the input signal. So the shorter the turn-on time the better.
Spike leakage occurs if the RF input pulse rises faster that the turn-on time of the limiter. It is the spike in RF power that gets through the limiter before it turns on. If the turn-on time is shorter than the rise time of the RF input signal, there will be no spike leakage. Spike leakage is often represented in units of energy, not power.
Limiter types
Conventional PIN diode limiters protect sensitive circuit elements by reducing high power inputs to low levels that can be tolerated by the next component.
Feedback limiters have lower threshold and leakage levels than standard limiters to protect more sensitive components.
High power limiters protect sensitive receiver circuits from nearby, high power signals.
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