Passive Load Modulation (PLM)

Passive Load Modulation (PLM) is a fundamental technique used in passive NFC (Near Field Communitation) systems to enable communication between NFC tags and readers. In PLM, the NFC tag does not require an internal/external power source; instead, it utilizes the energy harvested from the RF signal emitted by the NFC reader.

Here's how Passive Load Modulation typically works:

Tag Activation

When the NFC reader emits an RF signal, it energizes the NFC tag's antenna through electromagnetic induction. This energy is used to power the tag's circuitry.


Once powered, the NFC tag modulates the RF signal by varying the load on its antenna. This modulation is achieved by selectively reflecting and absorbing portions of the RF signal.

Data Encoding

The modulation of the RF signal encodes data stored in the NFC tag's memory. The variations in the reflected RF signal represent the digital information stored in the tag.

Backscatter Communication

The modulated RF signal is backscattered (reflected) back to the NFC reader. The reader detects the changes in the RF signal's characteristics, such as amplitude or phase shifts, to extract the encoded data.

Low Power Consumption

Since passive NFC tags do not contain an internal power source, they consume minimal power and can operate for extended periods without needing battery replacements.


Passive RFID tags are relatively simple in design and construction, consisting of an antenna and a microchip. This simplicity reduces manufacturing costs and allows for smaller form factors.

Read Range

Typically, the passive NFC tags can achieve shorter read ranges compared to active NFC tags.


Passive RFID systems are generally more cost-effective than active RFID systems, making them suitable for large-scale deployments in applications such as inventory management, supply chain tracking, and asset tracking.

However, Passive Load Modulation also has limitations, including shorter read ranges compared to active NFC systems, susceptibility to interference. Despite these limitations, Passive Load Modulation remains a widely used and versatile technology for NFC applications where power efficiency and cost-effectiveness are paramount.

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