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An RFID tag is defined as active if a battery inside the tag housing provides power to the tag or the tag is connected to an external power source. A tag is defined as passive if it has no battery. In applications that use passive tags, RF energy from the interrogator powers tag circuits. The choice of active versus passive tags has consequences for overall system cost, initial tag cost, tag life, and battery life.
Passive tags have a lower overall cost due to low-cost tags and long tag life. The lifespan of passive tags is indefinite because the tag has no battery. The choice between active tags and passive tags is related to other system design issues. Active tags can support higher data rates and higher chip processing speeds, but passive tags also support data rates and chip processing speeds that are suitable for high-performance applications such as toll. Active tags can support user interfaces (lights and LEDs), but tag interfaces reduce battery life. A disadvantage of passive tags is that some countries do not allow sufficient interrogator power and suitable RF frequencies to support the range necessary for some high-performance applications.
Active tags have a higher overall cost if cost of ownership includes battery changes. Battery life is a primary concern for reliability and for cost of operation. In toll applications, for example, battery outages, which can cause RFID transactions to be processed as violations, are expensive and time-consuming both to users and toll road operators. Battery life depends on the battery capacity and the long-term average power drain. An overall view of tag cost must assess tag replacement costs for tags with fixed batteries or battery replacement costs for tags with user-replaceable batteries.
Tag/Reader Matrix [PDF]
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