Daniel Brenk

Local positioning with passive UHF RFID transponders

This paper describes the theory of distance measurements with passive UHF transponders using the principle of modulated backscattering. The method was evaluated with the analogue frontend of a passive RFID chip for the UHF range. The chip was designed in a 0.14µm CMOS technology.

The Roots, Rules, and Rise of RFID

This article has offered a brief excerpt of the basic requirements and current development trends in (passive) RFID systems in different application areas. Even after reaching a sophisticated state of development, RFID technology is still dependent on sufficient acceptance at the market. Conventional bar code systems lack programmability, have low storage capability, and need a line-of-sight connection to the reader. If the fall in prices for low-cost tags continues, barcodes could be largely replaced in some years. In this case, additional features like positioning or sensing will become even more attractive for commercial and industrial application fields.

A multistandard HF/ UHF-RFID-tag with integrated sensor interface and localization capability

This paper presents a passive multistandard HF/ UHF-RFID-tag implemented in a 0.13μm bulk CMOS process. The RFID-tag consists of a multistandard HF/ UHF frontend for both frequency bands at 13.56 MHz and around 900 MHz. The tag is enhanced with additional functionality for sensing and localization. The integrated sensor interface consists of a multiplexer, a temperature sensor and an ultra-low power SAR analog-to-digital converter, which features a sampling rate of 100 kHz at a power consumption of less than 700 nW. Additionally the tag supports its localization through an FMCW-radar working at 2.45 GHz.

A highly efficient UHF RFID frontend approach

The passive radio frequency identification (RFID) presents a key technology for unattended wireless networks. To achieve a higher reading range and to improve the operational reliability of passive RFID tags, the design of integrated circuits with an ultra low power consumption and novel concepts for high-efficiency energy harvesting are required. This paper presents a highly efficient analog frontend for passive UHF RFID transponders. This frontend includes a multistage Schottky rectifier, a backscatter modulator, an ASK demodulator, a current reference source, and power limiting circuits. These building blocks are implemented in a 0.14 µm CMOS technology. The measured overall RF-to-DC conversion efficiency of the analog frontend for a DC output power of 10 µW (1V and 10 µA) is about 20%. The DC power consumption of the analog building blocks is about 1 µW for a supply voltage of 1V.

Ultra low power oscillator for UHF RFID transponder

This paper presents a realization of an ultra low power ring oscillator in 0.14 mum bulk CMOS technology. The application field for this oscillator is the clock generation for a baseband processor of a passive ultra high frequency (UHF) radio frequency identification (RFID) transponder. This technology will play an important role in the field of automatic identification. The paper contains simulation and measurement results for tuning range, cycle to cycle jitter and power consumption with regarding to the control current and supply voltage. The circuit was designed and fabricated by using 0.14 mum bulk CMOS technology.

Highly efficient multistandard RFIDs enabling passive wireless sensing

This paper presents a highly efficient analog multistandard frontend for passive sensor-enabled RFID transponders. The CMOS only frontend is implemented in a 0.13 µm CMOS technology. The measured overall RF-to-DC power conversion efficiency of the analog frontend for a DC output power of 10 µW is about 7% and the maximum efficiency is about 15% at UHF. An implemented sensor interface consumes 1.4 µA at 1V supply. This interface contains an ultra low-power successive approximation ADC that uses the capacitive charge redistribution technique for its integrated DAC.

Ultra low-power techniques for sensor-enhanced RFID tags

This paper gives an overview on current design techniques for ultra low-power applications in passive UHF RFID tags. Specialized sensor data acquisition methods are discussed as well as generic sensor interfaces and their building blocks. Analog to digital converters working in ranges of less than 100 fJ/conversion-step are presented which can be applied as data converters for generic interfaces. Example calculations and simulations on single circuits are made to prove operability at UHF RFID conditions of only several µA available at 1 V supply voltage.

Energy-Efficient Wireless Sensing Using a Generic ADC Sensor Interface Within a Passive Multi-Standard RFID Transponder

A successive approximation analog-to-digital converter (ADC) is presented, whose components make use of effective ultralow-power techniques to enable wireless sensing with passive and semi-passive sensor nodes. Compared with prior publications, new layout enhancements were applied to the capacitive array of the integrated digital-to-analog converter (DAC) to achieve less distortion caused by mismatch. In addition, it is shown that the digital circuit parts consume most of the available energy. Therefore, digital near-threshold operation is proposed to minimize their consumption. The applicability of the ADC is demonstrated in a UHF RFID system. Within this system, it is applied as a core of a sensor interface integrated into a passive multistandard RFID transponder. The EPC protocol used for communication ensures the compatibility with standard UHF RFID readers while the sensor data is acquired using custom commands. Single sensor readings are demonstrated as well as continuous sensor data transmission without further interaction of the reader device. A stable transponder reading distance of 6.5 m is achieved. The integrated ADC consumes only 525 nA at 40 kSps and 0.9-V supply voltage. Under these conditions, an ENOB of 7.23 is achieved and thus a FOM of 79 fJ/conversion-step.

Wireless sensing by means of passive multistandard RFID tags

This paper presents a generic sensor interface built in a 0.13 µm CMOS process capable of being applied in passive HF & UHF RFID Tags without any additional power supply. The sensor interface contains an ultra low-power successive approximation ADC that uses the capacitive charge redistribution technique for its integrated DAC. An on-chip temperature sensor and up to three additional sensor signals can be applied to the ADC. A conversion rate of 100 kSps is reached while consuming less than 1.5 µA at 0.9 Volt supply voltage.

Low voltage reference cells for UHF transponders with advanced features

In this paper a low voltage RC oscillator for standard RFID applications and local positioning is presented. Its bias current is provided by a current-mode bandgap whose reference voltage can also be used for enhanced transponder applications like sensing. The chip is designed in a 0.13 µm CMOS technology with p substrate. It was developed at the Institute for Electronics Engineering within the scope of a research project supported by the Bavarian Research Foundation.