Low modulation index RF signal detection for a passive UHF RFID transponder

Abstract

In a typical RFID system the reader transmits modulated RF power to provide both data and energy for the passive transponder. Low modulation index RF energy is preferable for an adequate tag power supply and increase in communication range but gives rise to difficulties for near-field conventional demodulation. Therefore, a novel ASK demodulator for minimum 20% modulation index RF signal detection over a range of 23 dB is presented. Thanks to the proposed innovative divisional linear conversion from the power into voltage signal, the detection sensitivity is ensured over a wide power range with low power consumption of 8.6 μW. The chip is implemented in UMC 0.18 μm mix-mode CMOS technology, and the chip area is 0.06 mm2.

Electromagnetic Models for Passive Tag-to-Tag Communications

“…The most critical configurations are the collinear tags ( in the example with 3 3 grid) and the true possibility to establish the link will depend on the minimum modulation depth really required by the RFID chip to decode the information. It is worth noticing that in [13] there is the indication of a custom chip front-end able to respond to as low as 20% modulation index of the incoming signal. Even in this optimistic condition, the communication among collinear dipoles looks however rather challenging and it is therefore better displacing tags so that they are facing, at least partially, as in the case of circular alignment.…”