Massimo Merenda

Fully-integrated wireless temperature sensor with on-chip antenna

This paper presents two new wireless temperature sensors made with a standard CMOS process exhibiting an on-chip antenna. The realized chips include a 3-stage ring oscillator structure which transforms the silicon substrate temperature variation into a frequency modulation. The first device works at a frequency of about 750 MHz @ 30degC. The signal is transmitted by a small loop antenna structure which is realized by aluminium deposition on the top surface of the chip. The electronic design of the ring oscillator has been carefully tuned to get a linear dependence of frequency vs. temperature. However, a bias voltage dependence is observed. An improvement of this design involves the implementation of a technique, based on a mathematical procedure between two different signals, that allows the extraction of reliable information on temperature, regardless of the bias voltage variation, and without recurring to power consuming voltage regulators. This concept is implemented using two 3-stage ring oscillators with slightly different frequency-vs-temperature characteristics, both close however to 2.4 GHz, switched alternatively on for a few milliseconds. Each ring-oscillator has its own antenna and the device is realized with a standard 0.35 mum process, improving the antenna efficiency with respect the first one.

Dynamic impedance matching network for RF energy harvesting systems

In this paper, an RF energy harvesting system with an improved dynamic impedance matching network (DyIMN) is proposed. With this solution, the minimum RF input power required for circuit operation is -10 dBm, allowing a working distance of 1.5 m from an RF energy source of 30dBm. The system was fabricated on an FR4 substrate using off-the-shelf discrete components and it is able to convert RF energy to regulated DC voltage in order to power general-purpose electronic devices. The experimental results demonstrate the capability of the system to obtain an optimum impedance matching with a received RF power in the range -10 - +5dBm.

Battery-less smart RFID tag with sensor capabilities

The pervasiveness of RFID technology in novel application fields, such as agriculture and food chain integrated management, is related to the addition of sensor and computational capabilities to the systems, and as a consequence, their powering becomes a challenge. Passively powered devices, such as inductively coupled passive HF RFID systems, utilize an external electromagnetic field to operate without an internal power source. This paper presents a battery-less RFID sensor useful to establish a safer and more manageable food supply chain of perishable comestibles.

A Monolithic Multisensor Microchip with Complete On-Chip RF Front-End

In this paper, a new wireless sensor, designed for a 0.35 µm CMOS technology, is presented. The microchip was designed to be placed on an object for the continuous remote monitoring of its temperature and illumination state. The temperature sensor is based on the temperature dependence of the I-V characteristics of bipolar transistors available in CMOS technology, while the illumination sensor is an integrated p-n junction photodiode. An on-chip 2.5 GHz transmitter, coupled to a mm-sized dipole radiating element fabricated on the same microchip and made in the top metal layer of the same die, sends the collected data wirelessly to a radio receiver using an On-Off Keying (OOK) modulation pattern.

An autonomous and energy efficient Smart Sensor Platform

A novel Wireless Smart Sensor Platform compatible with EPCglobal Class-1 Gen2 readers was developed. The platform is comprised of a five stage Dickson voltage multiplier, a dynamic impedance matching network (DyIMN), an XLP microcontroller (MCU) and an RFID tag IC with an embedded temperature sensor. Device range operations have been assessed up to a distance of 1.5 m from the RF source, corresponding to a minimum RF input power of -10 dBm. Firmware optimization leads to a reduction of power dissipation below 500nW in sleep mode, allowing an optimal energy harvesting and storage from the RF source. The harvested power enable logical operations to be completed from MCU, thus enabling sensing and storing of temperature measurements directly into the user memory of an RFID tag. Also the efficiency of the energy harvester is calculated from the MCU, hence tuning the DyIMN dynamically to respond over a wide range of input power and load impedance. The experiments demonstrate the feasibility of the system to operate autonomously within the reading range of a standard RFID reader, that acts both as RF power source and receiver of the data stored in the tag user memory.

Modulation speed improvement in a Fabry-Perot thermo-optical modulator through a driving signal optimization technique

A three-power-level method for obtaining efficient thermo- optical modulation in an all-silicon waveguide-integrated Fabry-Perot thermo-optic modulator is discussed by means of a thermo-optical ana- lytical model and demonstrated. The thermal system is represented as a two-pole model where, at every time, the temperature in the waveguide core is modified by means of a heater. This temperature is calculated and used in turn for calculating the refractive index. In this way, the impact of the driving signal shape on the device speed performance is assessed. Results clearly indicate that the application of a thermal bias holding the modulator at a higher average temperature with respect to the substrate heat sink allows increasing the modulator speed. An application-specific integrated circuit has been designed and developed in order to test the new modulation logic. The systems electronics is implemented in a 0.8 m, 5 V, CMOS process. The experimental results of this new three-power-level driver method are reported, showing the shortening of the characteristic transient times.

Performance assessment of an enhanced RFID sensor tag for long-run sensing applications

In this paper we present a battery-less RFID sensor tag, operating at 868 MHz, characterized by a novel impedance matching, guaranteeing improvements in terms of wireless energy transfer efficiency. A more efficient energy transfer is of high interest for several applications and, in particular, for a reduced recharging time of the embedded capacitor. This represents a fundamental step to enlarge the range of applications usually limited to classic wireless sensor networks, such as data logging or environmental sensing in large spaces. Challenges related to energy replenishment and data collection should be taken into account to enable an effective deployment of large networks. In particular, we investigate on the number of mobile readers moving around a sensing network to gather data and transfer energy, such that all nodes are kept alive and all data is collected. The improvements introduced by the new RFID sensor tag for this application will be evaluated with respect to state-of-the-art devices.

Remotely Powered Smart RFID Tag for Food Chain Monitoring

The pervasiveness of RFID technology in novel application fields, such as agriculture and food chain integrated management, is related to the addition of sensor and computational capabilities to the systems, and as a consequence, their powering become a challenge. Passively powered devices, such as inductively coupled passive HF RFID systems, utilize an external electromagnetic field to operate without an internal power source. This paper presents a battery-less RFID sensor useful to create a safer and more manageable food supply chain of perishable comestibles.

CMOS fully integrated 2.5GHz active RFID tag with on-chip antenna

This paper presents a fully integrated active RFID tag, realized in a 3.3V 0.35µm CMOS process, which exploits an on-chip loop antenna for short-range communications. This solution eliminates the need of a post-process assembled external antenna thus allowing to obtain a low-cost system for RFID applications. The implemented chip uses a 2.5GHz complementary cross-coupled LC oscillator based OOK transmitter. The system is duty cycled for reducing the power consumption. For the transmission of the stored 32bit indentifying code at 5kbit/s data rate, the average power consumption is 160µW. The integrated loop antenna radiates sufficient power for 1m communication range.

Design and implementation of high resolution, high linearity temperature sensor in CMOS process

An high-resolution CMOS temperature sensor with high linearity in the range from 20°C to 90°C is presented. The circuit uses substrate bipolars as temperature transducers. The temperature sensor consists of two building blocks: a Proportional To Absolute Temperature (PTAT) voltage generator and a differential amplifier. The second block is necessary to obtain reasonable voltage level that can be either read with a simple setup using it as analog input for an ADC. The simulation predictions are confirmed with experimental data resulting from the IC fabricated in a standard 0.35μm CMOS technology.