AN4409 STMICROELECTRONICS | Alldatasheet
Document overview
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Technical content
Table 1 lists the products concerned by this application note. Table 1. Applicable products
Antenna tuning frequency and performance AN4409
1 Antenna tuning frequency and performance
M24LRXXE-R and M24SRXX-Y ICs are passive RFID memories powered by the RF magnetic field generated by the reader. Tag to reader communication is achieved by mean of M24SRXX-R and M24SRXX-Y impedance modulation mechanism, called load modulation or backscattering. Maximizing the tag operating distance requires maximizing the powering distance but also the tag to reader link. To achieve these requirements, STMicroelectronics recommends a tuning frequency:
- 13.56MHz and 14MHz for RFID tags based on M24LRXXE-R family,
- 14MHz and 14.4MHz for RFID tags based on M24SRXX-R family.
2 Tuning capacitance dependency for using the same
mounted on a loop antenna in the presence of a sinusoidal magnetic field. Figure 1. M24LRXXE-R or M24SRXX-R tag equivalent Circuit magnetic field strength, the antenna size and number of turns.
Tuning capacitance dependency for using the same antenna design AN4409 Equation 2 Equation 3 Dividing Equation 2 by Equation 3 leads to: Equation 4 or, after simplification, to Equation 5: Equation 5 Respecting the tuning frequencies defined in section 1) leads to the following relationship: The M24SRXX-Y and M24LRXXE-R internal tuning capacitance has been designed following this rule offering to customers a simple way to use the M24LRXXE-R or M24SRXX-Y Dual Interface EEPROMs in their application without changing their antenna design. ftunf M24LR 2π LA CSM24LR ftun M24SR 2π LA CSM24SR ftun M24LR ftun M24SR 2π LA CSM24SR 2π LA CSM24LR CSM24SR CSM24LR CSM24SR CSM24LR ftun M24LR ftun M24SR ⎛⎞ 2 CSM24SR CSM24LR ⎛⎞ 2 0.94≅=
3 Tuning capacitance specification vs tuning reference
Figure 2. Typical tuning capacitance variation of M24LRXXE-R and M24SRXX-Y
tuning” that discusses this point in details for the M24LR series. Table 2. Tuning parameters for M24LRXXE-R and M24SRXX-R
4 Revision history
Table 3. Document revision history 19-Dec-2013 1 Initial release.