# Load modulation

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**Load Modulation** is a method of sharing information from one device to another by means of [modulating](/source/Modulation) the load that the transmitting device imposes on a signal provided by the receiving device.

This is used, for example, to allow [ISO/IEC 14443](/source/ISO/IEC_14443) and [ISO/IEC 15693](/source/ISO/IEC_15693) NFC cards to reply to the reading device without the need for the NFC card to contain a power source. Instead, it is powered by the magnetic field provided by the reader, conveying its data back to the reader by switching a resistor or capacitor in and out of its antenna circuit, thus modulating the load that the card imposes upon the reader's field.[1][2]

## References

1. ["Understanding the Requirements of ISO/IEC 14443 for Type B Proximity Contactless Identification Cards"](https://ww1.microchip.com/downloads/en/devicedoc/doc2056.pdf)

1. Klaus Finkenzeller, Giesecke & Devrient GmbH. ["Battery powered tags for ISO/IEC 14443, actively emulating load modulation"](http://www.rfid-handbook.de/downloads/Active-load-modulation_Finkenzeller_20110413_final.pdf)

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Adapted from the Wikipedia article [Load modulation](https://en.wikipedia.org/wiki/Load_modulation) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Load_modulation?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.