Yiannos Manoli

A continuous-time /spl Sigma//spl Delta/ Modulator with reduced sensitivity to clock jitter through SCR feedback

This paper presents a means to overcome the high sensitivity of continuous-time sigma-delta (/spl Sigma//spl Delta/) modulators to clock jitter by using a modified switched-capacitor structure with resistive element in the continuous-time feedback digital-analog converter (DAC). The reduced sensitivity to jitter is both simulated and proven by measured results from two implemented third-order modulators. Additionally, the nonideal behavior is analyzed analytically and by simulations.

A Comparative Study on Excess-Loop-Delay Compensation Techniques for Continuous-Time Sigma–Delta Modulators

Excess loop delay (ELD) is well known for its detrimental effect on the performance and stability of continuous-time sigma-delta modulators. A detailed analysis on the most recently published compensation techniques for single-stage modulators is performed in this paper, thus enabling their application to an arbitrary modulator. Based on different characteristics such as circuit complexity, achievable dynamic range, or requirements on the operational amplifiers, their advantages and disadvantages are investigated. Subsequently, the analysis is extended to cascaded modulators. Contrary to intuition, the results indicate that a compensation of ELD in every stage of the cascade is insufficient for optimal performance. Although not configured in a feedback configuration and as such not suffering from stability problems, each coupling network between two stages must additionally be compensated for ELD.

Fabrication, characterization and modelling of electrostatic micro-generators

This paper presents an electrostatic energy-harvesting device for electrical energy extraction from vibrations. We successfully fabricated prototypes of completely packaged micro-generators with a chip size of 5 mm by 6 mm. This was achieved using a modified SOI technology developed for inertial sensors at HSG-IMIT. Micro-generators produce a maximum rms power of 3.5 µW when they are excited at their resonance frequency with an input excitation of 13 g. During a long-term experiment over a period of 2 h, the electrostatic energy harvester generated a total net energy of 13.38 mJ corresponding to an average power of 1.58 µW. The effect of mechanical stoppers and the bias voltage on the generated power is also evaluated. In order to get a more profound understanding of the dynamic behaviour of the micro-generator, we have developed a signal-flow model for numerical simulation of the electrostatic transducer on system level. This model includes a mechanical and an electrical domain which are coupled by electrostatic forces. The limited displacement of the proof mass is also considered using an elastic stopper model. We show that the numerical model is capable of providing good predictions of the device behaviour.

Compensation of finite gain-bandwidth induced errors in continuous-time sigma-delta modulators

This paper introduces a possible compensation for finite gain-bandwidth (GBW) induced errors in continuous-time sigma-delta modulators. Therefore, a novel model is derived which reduces the effect of a finite GBW to a corresponding integrator gain-error and feedback loop delays. Thus, previously published methods for the compensation of these errors can be adopted with some modification. The results are confirmed analytically and by simulations and show a possible GBW reduction of about one order of magnitude compared to current designs.

Surface micromachined pressure sensors with integrated CMOS read-out electronics

Abstract In this paper a single chip pressure and tenperature sensor system with on chip electronics is presented. The capacitive pressure sensor is fabricated using a CMOS process with additional surface micromachining steps to form a membranes. The membrane dimensions have been optimized for a pressure range of 2, 3.5, 10 and 35 bars, respectively. The temperature sensor shows a straight linear output signal in a temperature range of 0 to 70 °C. For the signal processing switched capacitor circuits are used. The sensor signals are converted to a pulse width modulated output signal. The silicon chip has an active area of 3.5 mm 2 . Between 0 and 80 °C a temperature dependence of the pressure segnal of less than 200 ppm/°C referring to full scale was found.

A closed-loop wide-range tunable mechanical resonator for energy harvesting systems

This paper presents a novel electrically tunable structure which can be used as a resonator for vibration-based energy harvesters. The adjustment of the resonance frequency is provided by mechanical stiffening of the structure using piezoelectric actuators. This concept can easily be stand-alone integrated to realize an autonomous, tunable harvester. The resonator was simulated using ANSYS to find the optimum operation point concerning tuning range. The scalability of this tuning concept is also investigated in this work. A phase shift control circuit was developed for very efficient autonomous closed-loop control of the resonance frequency. Prototypes of the resonators were fabricated and measured with and without the control circuit. The tuning voltage can be kept as low as ±5 V leading to a measured resonance shift of ±15% for the larger resonator (40 mm) and around ±8% for the smaller resonator (27 mm). This tuning range can be simply enhanced by increasing the tuning voltage.

A CMOS integrated voltage and power efficient AC/DC converter for energy harvesting applications

In this paper, a fully CMOS integrated active AC/DC converter for energy harvesting applications is presented. The rectifier is realized in a standard 0.35 µm CMOS process without special process options. It works as a full wave rectifier and can be separated into two stages—one passive and one active. The active part is powered from the storage capacitor and consumes about 600 nA at 2 V supply. The input voltage amplitude range is between 1.25 and 3.75 V, and the operating frequency range is from 1 Hz to as much as several 100 kHz. The series voltage drop over the rectifier is less than 20 mV. Measurements in combination with an electromagnetic harvester show a significant increase in the achievable output voltage and power compared to a common, discrete Schottky diode rectifier. The measured efficiency of the rectifier is over 95%. Measurements show a negligible temperature influence on the output voltage between −40 °C and +125 °C.

A Sub-500 mV Highly Efficient Active Rectifier for Energy Harvesting Applications

This paper presents a highly efficient, ultra-low-voltage active full wave rectifier. A two-stage concept is used including a first passive stage and only one active diode as second stage. A bulk-input comparator working in the subthreshold region is used to drive the switch of the active diode. The voltage drop over the rectifier is some tens of millivolt, which results in voltage and power efficiencies of over 90%. The design was successfully implemented in an 0.35 μm CMOS technology. The measured power consumption of the comparator is 266 nW@500 mV and the minimum operating voltage is 380 mV. Input voltages with frequencies up to 10 kHz can be rectified.

Energy harvesting from human motion: exploiting swing and shock excitations

Modern compact and low power sensors and systems are leading towards increasingly integrated wearable systems. One key bottleneck of this technology is the power supply. The use of energy harvesting techniques offers a way of supplying sensor systems without the need for batteries and maintenance. In this work we present the development and characterization of two inductive energy harvesters which exploit different characteristics of the human gait. A multi-coil topology harvester is presented which uses the swing motion of the foot. The second device is a shock-type harvester which is excited into resonance upon heel strike. Both devices were modeled and designed with the key constraint of device height in mind, in order to facilitate the integration into the shoe sole. The devices were characterized under different motion speeds and with two test subjects on a treadmill. An average power output of up to 0.84 mW is achieved with the swing harvester. With a total device volume including the housing of 21 cm3 a power density of 40 μW cm−3 results. The shock harvester generates an average power output of up to 4.13 mW. The power density amounts to 86 μW cm−3 for the total device volume of 48 cm3. Difficulties and potential improvements are discussed briefly.

A 62 mV 0.13

Sub-threshold circuits have recently gained attention mainly due to the possibility of operating at the minimum energy per operation point [1]. There are applications where a supply voltage reduction below this point is advantageous though, even at the cost of increasing active energy per operation. Always-on circuits, e.g. wake-up circuitry for chips sleeping at ultra-low supply voltages, reduce power consumption with decreasing supply. Furthermore, energy-harvesting applications are often limited by the very low output voltages of the harvesting devices, thus the minimum VDD of the electronic circuits dictates when active operation can start (e.g. thermoelectric harvesters [2]).