A voltage multiplier is an electrical circuit that converts AC electrical power from a lower voltage to a higher DC voltage, typically using a network of capacitors and diodes. Voltage multipliers can be used to generate a few volts for electronic appliances, to millions of volts for purposes such as high-energy physics experiments and lightning safety testing. The most common type of voltage multiplier is the half-wave series multiplier, also called the Villard cascade (but actually invented by Heinrich Greinacher). Operation Assuming that the peak voltage of the AC source is +Us, and that the C values are sufficiently high to allow, when charged, that a current flows with no significant change in voltage, then the (simplified) working of the cascade is as follows:

going from positive peak (+Us) to negative peak (−Us): The C1 capacitor is charged through diode D1 to Us V (potential difference between left and right plate of the capacitor is Us).

going from negat

Analysis and optimization of passive UHF RFID systems

Jari-Pascal Curty

Radio Frequency IDentification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. An RFID tag is a small object that can be attached to or incorporated into a product, animal or person. RFID tag contains antenna to enable it to receive and respond to Radio-Frequency (RF) queries from an RFID reader or interrogator. Passive tags require no internal power source, whereas active tags require a power source. As of today (2005), the ubiquitous computing and ambient intelligence ideas are making their way. In order for these to become a reality, a number of key technologies are required. Briefly, these technologies need to be sensitive, responsive, interconnected, contextualised, transparent and intelligent. RFID is such a technology and more particularly passive RFID tags. But, in order to deliver the necessary characteristics that could trigger ambient intelligence, there are some challenges that need to be addressed. Remote powering of the tags is probably the most important. Issues concerning the antenna-tag interface, as well as the rectifier design, that allows the RF signal to be converted to Direct Current (DC) are in pole position. Secondly, the communication link and the reader should be optimized. The RF signal that contains the tag data suffers from a power of four decay with the distance between tag and reader. As a result, both the reader sensitivity and the tag backscattered power efficiency have to be maximized. Long-range powering, as well as sufficient communication quality, are the guidelines of this work. This research project proposes a linear two-port model for an N-stage modified-Greinacher full wave rectifier. It predicts the overall conversion efficiency at low power levels where the diodes are operating near their threshold voltage. The output electrical behavior of the rectifier is calculated as a function of the received power and the antenna parameters. Moreover, the two-port parameters values are computed for particular input voltages and output currents for the complete N-stage rectifier circuit using only the measured I-V and C-V characteristics of a single diode. Also presented in this work is an experimental procedure to measure how the impedance modulation at the tag side affects the signal at the reader. The method allows the tag designer to efficiently predict the effect of modulator design at system level and gives an useful instrument to choose the most appropriate impedances. Finally, the design of a fully integrated remotely powered and addressable RFID tag working at 2.45 GHz is described. The achieved operating range at 4 W Effective Isotropically Radiated Power (EIRP) reader transmit power is 12 m. The Integrated Circuit (IC) is implemented in a 0.5 μm silicon-on-sapphire technology. A state of the art rectifier design achieving 37% of global efficiency is embedded to supply energy to the transponder. Inductive matching and a folded-dipole antenna are key elements to achieve these performances. The necessary input power to operate the transponder is about 2.7 μW.

EPFL2006

A Sub-Threshold Passive Step-Up Rectifier for Vibration Energy Scavengers

Alexis Boegli, Danick Briand, Nico de Rooij, Pierre-André Farine, Don Isarakorn, Pattanaphong Janphuang, Christian Robert, Jaskaranjeet Singh

This paper reports on the design and experimental verifications of a passive step-up rectifier for MEMS piezoelectric energy scavengers. The purpose of the proposed circuit is to improve system startup for vibration micro-generators without the need of an external source of energy. The design chosen is based on a voltage multiplier where conventional diodes are replaced by PMOS low-VT transistors. The circuit is produced in 1.8V 0.18μm UMC CMOS technology. Test and verifications were performed using a real piezo scavenger providing an AC voltage of 0 to 350mVpeak at a frequency of around 2.4 kHz. Up to 2V DC was measured at the output of the rectifier.

Cell Bench Research Center, KAIST2011

Analysis and optimization of passive UHF RFID systems

Jari-Pascal Curty

EPFL2006