High-Sensitive Demodulator with Built-in Negative Offset Comparator for Passive UHF RFID Tags

The need for reliable detection of ASK-modulated RF signals in passive RFID tags, especially under varying power levels and low modulation depths, drives the design of a highly sensitive demodulator. One of the major factors in increasing the sensitivity is the comparator's ability to detect the small voltage differences. This paper presents the design and implementation of a high sensitivity voltage mode demodulator for passive RFID tags. Compared to the weighted average demodulator, it eliminates the need for a calibration circuit to increase the difference between the input voltages of the comparator. A rail-to-rail input comparator with built-in negative offset is proposed, which enhances the sensitivity by increasing the input voltage difference of the comparator, providing reliable detection across a wide range of power levels and data rates. The design is implemented in commercially available 0.18-µm CMOS technology and operates from a 1.2V supply. The demodulator can demodulate the minimum input power of −9dBm and modulation depth of 10% at a power consumption of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.04\mu\mathrm{W}$</tex>