The floating charge power supply is another power supply method, and the power supply capacity of the floating charge is compatible with the discharge capacity. But they all have a common problem, that is, the power supply of UHF RFID passive tags needs to balance supply and demand.
(1) Supply and demand balance power supply mode for burst communication
The current standard ISO/IEC18000-6 for UHF RFID passive tags is a burst communication system. For passive tags, no signal is sent during reception. Although the carrier is received during the response, it is equivalent to obtaining an oscillation source, so it can be regarded as simplex. the way. For this application, if the receiving time period is used as the charging time period of the energy storage capacitor, and the response time period is used as the discharging time period of the energy storage capacitor, the charging and discharging amounts are equal to maintain the power supply balance. Necessary conditions. According to the power supply mechanism of the UHF RFID passive tag described above, the power supply of the UHF RFID passive tag is neither a constant current source nor a constant voltage source. When the tag storage capacitor is charged to a voltage higher than the normal operating voltage of the circuit, the power supply will start; when the tag storage capacitor is discharged to a voltage lower than the normal operating voltage of the circuit, the power supply will stop.For burst communication (such as the UHF RFID air interface of passive tags), sufficient charge can be charged before the tag sends a response burst, which is sufficient to ensure that sufficient voltage can be maintained before the response is completed. Therefore, in addition to the strong enough radio frequency radiation that the tag can receive, the chip is also required to have a large enough on-chip capacitance and a long enough charging time. Tag response power consumption and response time must also be adjusted. Because the distance between the tag and the reader is different, the response time is also different, and the area of the energy storage capacitor is limited, it may be difficult to balance the supply and demand relationship through time division.(2) Floating power supply mode, continuous communication
For continuous communication, in order to maintain the uninterrupted power supply of the storage capacitor, it must be charged during discharge, and the charging speed is similar to the discharging speed, that is, the power capacity should be maintained before the end of charging. communication.Passive tags code division radio frequency identification and UHF RFID passive tags current standard ISO/IEC18000-6 have common features. The receiving state of the tag needs to be demodulated and decoded, and the response state needs to be modulated and sent. Therefore, the design should be based on continuous communication. Label chip power system. In order to make the charging speed close to the discharge speed, most of the energy received by the tag must be used for charging.