UHF RFID Passive Tag Chip Power Supply Mechanism

1. UHF RFID passive tag power supply characteristics

(1) Powered by Wireless Power Transfer

Wireless power transfer is the use of wireless electromagnetic radiation to transfer electrical energy from one place to another.  The working process is to convert electrical energy into radio frequency energy through radio frequency oscillation, and the radio frequency energy is converted into radio electromagnetic field energy through the transmitting antenna.

The UHF RFID system is based on the wireless power transmission mechanism. The passive tag does not have its own power supply. It needs to receive the radio frequency energy emitted by the reader and establish a DC power supply through voltage doubling rectification, that is, a Dickson charge pump.

(2) Power supply is implemented by charging and discharging of on-chip energy storage capacitor

Passive tags use wireless power transmission to obtain energy, convert it into DC voltage, charge the on-chip capacitor for energy storage, and then supply power to the load through discharge. Therefore, the power supply process of the passive tag is the capacitor charging and discharging process. The charging and discharging process of the capacitor is a pure charging process, and the power supply process is a discharging and supplementary charging process. The supplementary charging must start before the discharge voltage reaches the minimum supply voltage of the chip.

(3) Floating charging power supply

Floating charging power supply is another power supply method, and the floating charging power supply capacity is adapted to the discharging capacity. But they all have a common problem, that is, the power supply of UHF RFID passive tags needs to balance supply and demand.

2. Shared RF resources

Passive tags are not only used as the power source of the tags and postcards to the radio frequency energy from the readers, but more importantly, the instruction signal transmission from the reader to the tag and the response signal transmission from the tag to the reader are realized through wireless data transmission.

The radio frequency energy received by the tag should be divided into three parts, which are respectively used for the chip to establish the power supply, demodulate the signal (including the command signal and synchronization clock) and provide the response carrier.

When the tag enters the reader's radio frequency field and starts to build power, no matter what signal the reader sends at this time, the tag will provide all the received radio frequency energy to the voltage doubler rectifier circuit to charge the on-chip energy storage capacitor, thereby establishing the chip's power supply.

Wireless power transfer establishes the power supply for the tag, so it requires both sufficient voltage to drive the chip circuit, and sufficient power and continuous power supply capability.

3. Conclusion

Wireless power transfer establishes the power supply for the tag, so it requires both sufficient voltage to drive the chip circuit, and sufficient power and continuous power supply capability.