AN3433 datasheet(23/34 Pages) STMICROELECTRONICS

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AN3433

Tag detection principle

Doc ID 019046 Rev 2

23/34

Figure 8.

Tag detection principle (levels of antenna current)

A.1

Tag detection sequence

Several parameters of the tag detection sequence can be managed to optimize the wakeup

time or power budget.

By adjusting the inactivity time (tINACTIVE), the time between two tag detection RF bursts, the

power consumption can be modified through the WuPeriod parameter in the Idle command

(usually set to

0x20).

tINACTIVE = (WuPeriod+1)*tREF

The user can choose to limit number of tag detection trials by adjusting the MaxSleep value.

This MaxSleep value is validated only when the correct Wakeup condition is set (Bit 0 of the

Wakeup condition register). Otherwise, the tag detection sequence is repeated continuously

until a wakeup event occurs.

A minimum duration of 3 ms must be set for the DAC and HFO setup times to obtain a good

accuracy of measure. This phase is a high consumption period, so we recommend keeping

it short. These setup times (DacStart and OscStart, respectively) are defined in the Idle

command and are both usually set to

0x60.

The RF burst length (SwingCnt) corresponds to the acquisition time necessary for the DAC.

It must be sufficient to obtain a reproducible measurement, but it means turning on the RF

driver which consumes the most energy. The SwingCnt parameter value is defined in the

Idle command and is usually set to

0x3F.

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