Abstract
Battery-less passive sensor tags based on RFID or NFC technology have achieved much popularity in recent times. Passive tags are widely used for various applications like inventory control or in biotelemetry. In this paper, we present a new RFID/NFC frontend IC (integrated circuit) for 13.56 MHz passive tag applications. The design of the frontend IC is compatible with the standard ISO 15693/NFC 5. The paper discusses the analog design part in details with a brief overview of the digital interface and some of the critical measured parameters. A novel approach is adopted for the demodulator design, to demodulate the 10% ASK (amplitude shift keying) signal. The demodulator circuit consists of a comparator designed with a preset offset voltage. The comparator circuit design is discussed in detail. The power consumption of the bandgap reference circuit is used as the load for the envelope detection of the ASK modulated signal. The sub-threshold operation and low-supply-voltage are used extensively in the analog design—to keep the power consumption low. The IC was fabricated using 0.18 m CMOS technology in a die area of 1.5 mm × 1.5 mm and an effective area of 0.7 . The minimum supply voltage desired is 1.2 V, for which the total power consumption is 107 W. The analog part of the design consumes only 36 W, which is low in comparison to other contemporary passive tags ICs. Eventually, a passive tag is developed using the frontend IC, a microcontroller, a temperature and a pressure sensor. A smart NFC device is used to readout the sensor data from the tag employing an Android-based application software. The measurement results demonstrate the full passive operational capability. The IC is suitable for low-power and low-cost industrial or biomedical battery-less sensor applications. A figure-of-merit (FOM) is proposed in this paper which is taken as a reference for comparison with other related state-of-the-art researches.
Highlights
RFID technology has been widely employed for the design of the remotely powered telemetry systems since the 1950s
A typical RFID/NFC system consists of a reader device and a tag consisting of a frontend IC and a microcontroller as described in [36]
The proposed frontend IC was fabricated in 0.18 μm one-poly and six-metal CMOS technology with a total die area of 1.5 mm × 1.5 mm and an effective area of 0.7 mm2
Summary
RFID (radio frequency identification) technology has been widely employed for the design of the remotely powered telemetry systems since the 1950s. A commercial ISO 15693 RFID reader or an NFC capable smart device can be employed to communicate with the tag designed with the proposed IC. Some of the examples in recent years are - dual carrier NFC based WPT (wireless power transfer) meant for small sized biomedical sensor applications [27], intraocular pressure measurement for monitoring glaucoma [28], wearable healthcare system including an ECG (electrocardiograph) processor and Instantaneous Heart Rate (IHR) monitor [29], and wireless fluorimeter for fully implantable biosensing applications [30]. A few years later, a passive tag IC compatible with the ISO-14443 type-B standard was presented in [33], which had an IC area of 1.1 mm and a total power consumption of 360 μW. The NFC tag IC proposed in [3] had a moderate analog power consumption of 67.7 μW and an IC die area of 0.68 mm.
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