Tag Sensitivity

Tag Sensitivity

Tag sensitivity is the minimum RF power level, measured in dBm at the tag antenna input, that a Tag IC requires to activate, demodulate the reader's commands, and generate a backscatter response. It is the single most important specification determining the maximum read range of a passive RFID system.

Understanding the Metric

Tag sensitivity is expressed as a negative dBm value -- the more negative, the more sensitive (better). A tag with -22 dBm sensitivity requires less power to wake up than one with -18 dBm, and will therefore achieve a longer read range given identical reader power and antenna configurations.

Each 3 dB improvement in sensitivity doubles the power budget, translating to approximately a 40% increase in read range under free-space conditions.

Factors Affecting Effective Sensitivity

The datasheet sensitivity value assumes ideal conditions. Real-world performance is degraded by:

• Material detuning -- metals, liquids, and the human body shift the tag antenna's resonant frequency away from its design centre, reducing energy capture.
• Orientation sensitivity -- misalignment between reader and tag antenna polarisation planes causes polarisation loss.
• Inlay design -- the antenna's efficiency and matching to the IC directly affect how much received RF energy reaches the chip.
• Temperature -- IC sensitivity can vary 1-3 dB across the -40 C to +85 C operating range.

Link Budget Relationship

Tag sensitivity is one term in the link budget equation. The forward link (reader to tag) is almost always the range-limiting direction for passive systems because the tag must receive enough power to activate its IC. The return link (tag to reader) is typically 10-15 dB more favourable because the reader has a sensitive receiver with low noise figure.

See also: Link Budget | Read Range | Tag IC