Karti Mayaram

Efficient Far-Field Radio Frequency Energy Harvesting for Passively Powered Sensor Networks

An RF-DC power conversion system is designed to efficiently convert far-field RF energy to DC voltages at very low received power and voltages. Passive rectifier circuits are designed in a 0.25 mum CMOS technology using floating gate transistors as rectifying diodes. The 36-stage rectifier can rectify input voltages as low as 50 mV with a voltage gain of 6.4 and operates with received power as low as 5.5 muW(22.6 dBm). Optimized for far field, the circuit operates at a distance of 44 m from a 4 W EIRP source. The high voltage range achieved at low load current make it ideal for use in passively powered sensor networks.

Piezoelectric micro-power generation interface circuits

New power conversion circuits to interface to a piezoelectric micro-power generator have been fabricated and tested. Circuit designs and measurement results are presented for a half-wave synchronous rectifier with voltage doubler, a full-wave synchronous rectifier and a passive full-wave rectifier circuit connected to the piezoelectric micro-power generator. The measured power efficiency of the synchronous rectifier and voltage doubler circuit fabricated in a 0.35-/spl mu/m CMOS process is 88% and the output power exceeds 2.5 /spl mu/W with a 100-k/spl Omega/, 100-nF load. The two full-wave rectifiers (passive and synchronous) were fabricated in a 0.25-/spl mu/m CMOS process. The measured peak power efficiency for the passive full-wave rectifier circuit is 66% with a 220-k/spl Omega/ load and supplies a peak output power of 16 /spl mu/W with a 68-k/spl Omega/ load. Although the active full-wave synchronous rectifier requires quiescent current for operation, it has a higher peak efficiency of 86% with an 82-k/spl Omega/ load, and also exhibits a higher peak power of 22 /spl mu/W with a 68-k/spl Omega/ load which is 37% higher than the passive full-wave rectifier.

Novel power conditioning circuits for piezoelectric micropower generators

Low power devices promote the development of micropower generators (MPGs). This paper presents a novel power conditioning circuit (PCC) that enables maximum power extraction from a piezoelectric MPG. Synchronous rectification (SR) is employed to improve the PCC efficiency. A simplified model of the piezoelectric generator is developed for simulation. Performance of the proposed PCC is verified by PSpice simulation and experimental results. A maximum output power of 18.8 /spl mu/W has been extracted from a single piezoelectric MPG. Arbitrary waveform generator representation (AWGR) of the flexing piezoelectric membrane is also presented. The hardware AWGR enables research on the PCC without the need for the actual MPG heat engine or bulge tester used to flex the piezoelectric membrane, and also demonstrates the feasibility of cascading many MPGs to extract additional power.

A comprehensive geometry-dependent macromodel for substrate noise coupling in heavily doped CMOS processes

An accurate substrate noise coupling macromodel for heavily doped CMOS processes is presented. The model is based on Z parameters that are scalable with contact separation and size. Extensive experimental validations of the model have demonstrated that the modeled Z parameters are most often accurate to within 2-8%.

Spectral analysis of time-domain phase jitter measurements

A simplified overview of time-domain jitter measurements is presented in this paper. The relationship between the time-domain jitter measurements and the power spectrum of the phase jitter is described using fundamental Fourier properties and basic random variables analysis. This leads to a unifying analysis and the results are in agreement with commonly accepted understanding of jitter accumulation in oscillators. The presented analysis also provides the basis for comparing different jitter measurements.

The effect of supply and substrate noise on jitter in ring oscillators

Measurements, simulations and equations show that differential and single-ended ring oscillators have comparable performance when subjected to the same deterministic noise sources. Both topologies are shown to have a much greater sensitivity to supply noise than substrate noise. It is also shown that symmetrical/asymmetrical noise injection must be considered. The measured results are compared to predictive jitter equations and Spectre/spl reg/ time domain simulations. It is shown that the measurements are in agreement with the simulations and equations.

The effect of power supply noise on ring oscillator phase noise

Low phase noise monolithic oscillators are in high demand in this age of wireless communications. Although LC oscillators generally have better phase noise performance, there is motivation to design ring oscillators with comparable phase noise compared to LC oscillators. The advantages of ring oscillators include significantly less die area and generally wider tuning range. Ring oscillator phase noise analysis and simulation, however, often ignore power supply noise, which is a major and possibly dominant contributor of phase noise. This paper presents a method of determining a given oscillators sensitivity to both intrinsic and power supply noise sources and provides a means for comparing different oscillator architectures based on this information.

A noise-reducing 0.48 nJ/bit interference-robust non-coherent energy detection IR-UWB receiver for wireless sensor networks

A non-coherent interference-tolerant energy detection (ED) IR-UWB receiver with a front-end noise reduction technique is presented. By relaxing the LNA noise requirement, a reduction in power consumption is achieved without sacrificing performance. The fabricated prototype in a 130 nm CMOS process operating with a supply voltage of 1.2 V, achieves the best energy efficiency of 0.48 nJ/bit for ED receivers reported to date. This energy efficiency is maintained across a wide data rate range of 0.1-25 Mb/s. In-band and out-of-band narrowband interferers as strong as -61 dBm and -42 dBm, respectively, can be tolerated to achieve a BER of 10-3. The measured sensitivity is -82 dBm.