Gen 2 Tag Clock Rate — What You Need To Know

The EPCglobal™ Gen 2 specification mandates the functions that a tag must perform. The specific implementation and the tag's corresponding level of performance, though, are left to the tag designer. Not only are critical performance parameters not specified, they're not even evaluated as part of the certification process. Certification merely ensures that tags conform to the Gen 2 protocol. As a result, certified tags may still perform poorly if their designers made poor engineering choices.

The selection of a tag's clock frequency is one such engineering choice that is crucial to tag performance. Aim too low and the tag may decode reader commands incorrectly or may backscatter data to the reader at the wrong frequency. Aim too high and the tag will consume excessive power, shortening both read and write ranges.

Fortunately, the minimum clock frequency for a Gen 2 tag can be calculated from purely theoretical considerations. And that minimum value is 1.92 MHz. Unfortunately, some legacy RFID tags use a 1.28 MHz clock frequency. If a Gen 2 tag designer cuts corners and reuses one of their existing 1.28 MHz oscillators, then the tag's performance will be compromised. Worse yet, a tag designer is actually incentivized to use a 1.28 MHz clock, because the resulting longer tag range is easily demonstrated to an end user, whereas degraded command decoding and incorrect backscatter frequency can be conveniently blamed on the reader or on the "noisy environment."

Tag vendors generally don't tell their end customers which clock frequency they use, nor can end customers easily test a tag to uncover performance issues due to a poor clock-frequency choice. The purpose of this tech brief is to prove why 1.92 MHz is the right choice. Armed with this analysis, an end user can simply ask, "What clock frequency does your tag use?"