Active Load Modulation (ALM) is a technique used in radio frequency (RF) communication systems, particularly in NFC (Near Field Communitation) technology. It is employed to improve the efficiency and reliability of data transmission between NFC tags and readers.
In NFC systems, there are typically two main components: the NFC tag and the NFC reader. The tag contains a microchip and an antenna, while the reader emits RF signals to power the tag and communicate with it. When the reader's RF signal interacts with the tag, the tag's microchip modulates the signal to transmit data back to the reader. This principle is known as the Passive Modulation.
Traditional passive NFC tags rely solely on backscatter modulation to communicate with the reader. In this process, the tag reflects a portion of the reader's RF signal back to the reader with modulated data encoded in the signal. However, this method has limitations, especially in terms of communication range and reliability, particularly in environments with interference or weak RF signals.
Active Load Modulation addresses these limitations by incorporating an active component into the NFC tag. ALM-enabled tags actively modulate their response. This modulation is used to encode data, allowing for more reliable and efficient communication between the tag and the reader.
The ALM is typically generated by a push pull MOS-FET driver
See the typically ALM pattern below:
Green - Active Load Modulation generated by NFC Reader in Card Mode (Captured on the TX pins)
Yellow - RF Field
The key advantages of Active Load Modulation include:
1. Improved communication range
ALM enables NFC systems to achieve greater communication distances compared to traditional passive NFC tags. However the device using ALM requires a power supply.
2. Enhanced reliability
By actively modulating, the ALM reduces the susceptibility to interference and noise, resulting in more reliable data transmission. If the NFC system is supposed to be used in some NFC "unfriendly" environments e.g., metal, or if the space for the antenna is very limited. Then the Active Load Modulation is a great choice.
3. Flexibility
ALM technology provides greater flexibility in designing NFC systems, as it can adapt to different environmental conditions and communication requirements. Especially for metal enviroments or when the space for the antenna is limited.
Overall, Active Load Modulation is a promising technology that enhances the performance and capabilities of NFC systems, making them more suitable for a wide range of applications, including inventory management, supply chain tracking, and asset tracking.
The NFC Readers typically use the ALM in Card Emulation mode. There are also couple of NFC Tags using the ALM as e.g., NTAG 5 Boost from NXP.