Showing papers on "Capacitive sensing published in 1992"

Driven shielding capacitive proximity sensor

Abstract: A capacitive proximity sensing element, backed by a reflector driven at the same voltage as and in phase with the sensor, is used to reflect the field lines away from a grounded robot arm towards an intruding object, thus dramatically increasing the sensor's range and sensitivity.

Surface micromachined, digitally force-balanced accelerometer with integrated CMOS detection circuitry

Abstract: The authors have described a surface micromachined accelerometer with digital electrostatic feedback using Sigma - Delta modulation technique, fabricated in a modular CMOS/microstructure process. Detection circuits have been tested successfully. The unity gain buffer with low input capacitance can also be used for other capacitive detection applications. The accelerometer has been characterized in the self-testing mode and has demonstrated the functionality of the device. >

Circuit architectures for high linearity monolithic continuous-time filtering

Abstract: Circuit architectures for high-linearity monolithic continuous-time filters are described based on the use of integrated passive components in active RC structures. Tunability of the frequency response is achieved by arranging either resistive or capacitive elements in programmable arrays. The array value is then set using a digital code produced by an on-chip calibration circuit. The advantages and disadvantages of possible configurations are analyzed, indicating the limits of usefulness. Different filter architectures are considered, and design equations for determining basic cell specifications are given. The analyses are compared with results of experimental integrated filter designs, confirming that both very high linearity (-90 dB) and reasonable tuning accuracy (around +or-5%) are achievable. >

A low-cost, smart capacitive position sensor

Abstract: A high-performance, low-cost, capacitive position-measuring system is described. By using a highly linear oscillator, shielding and a three-signal approach, most of the errors are eliminated. The accuracy amounts to 1 mu m over a 1 mm range. Since the output of the oscillator can directly be connected to a microcontroller, an A/D converter is not needed. >

Automatic calibration of a capacitive touch screen used with a fixed element flat screen display panel

Abstract: A touch screen display is automatically calibrated during periods of active use or extended periods of non-use. Calibration contacts are cemented or embedded to the surface of a touch sensitive panel, and electrically connected to a reference during calibration. The reference is either electrical ground or a resistive, capacitive, or inductive load.

Micropower gate charge pump for power MOSFETS

Abstract: A power efficient circuit for charging the gate of a transistor switch to a charge-pumped voltage level in excess of a supply rail voltage is provided. The circuit includes a current-controlled oscillator which generates an oscillating waveform that drives a capacitive charge-pump circuit. The circuit monitors the gate voltage of the transistor switch and reduces the frequency of the oscillating waveform, thereby reducing power consumption, when the gate voltage exceeds a frequency switching value indicating that the transistor switch has been sufficiently turned so as to allow the circuit to enter a micropower mode.

In situ method for forming a capacitive PCB

Abstract: An in situ method for forming a bypass capacitor element internally within a PCB comprising the steps of arranging one or more uncured dielectric sheets with conductive foils on opposite sides thereof and laminating the conductive foils to the dielectric sheet simultaneously as the PCB is formed by a final lamination step, the conductive foils preferably being laminated to another layer of the PCB prior to their arrangement adjacent the dielectric sheet or sheets, the dielectric foils even more preferably being initially laminated to additional dielectric sheets in order to form multiple bypass capacitive elements as a compound subassembly within the PCB.

Planar ferro-electric phase shifter

Abstract: A planar ferro-electric phase shifter which is compatible with commonly-u microwave transmission media to include microstrip, inverted microstrip, and slot line. The ferro-electric material, Bax Sr1-x TiO3, which has a high dielectric-constant, is the phase shifting element. In the microstrip embodiment, the microstrip circuit consists of a ferro-electric element interposed between a conductor line and a ground plane. A DC voltage is applied between the conductor line and the ground plane, thereby controlling the dielectric constant of the ferro-electric material. The dielectric constant of the ferro-electric element in turn controls the speed of the microwave signal, which causes a phase shift. Microwave energy is prevented from entering the DC supply by either a high-impedance, low pass filter, or by an inductive coil. DC voltage is blocked from traveling through the microstrip circuit by a capacitive high-voltage DC bias blocking circuit in the ground plane.

A latching accelerometer fabricated by the anisotropic etching of (110) oriented silicon wafers

Abstract: The anisotropic etching of (110) oriented silicon wafers is used to fabricate a simple latching accelerometer for moderate and high-g applications. This accelerometer consists of two cantilever beams that interlock at a set threshold acceleration which is determined by their design. The accelerometer is robust, fairly easy to fabricate and can be mass produced. Two units designed to latch at 85 g and 600 g were tested on a centrifuge and the error between the calculated latching acceleration and the experimental result was less than 15%. Arrays of accelerometers can be easily fabricated on the same silicon wafer to bracket the true acceleration. Readout schemes could include either capacitive or optical techniques. The structure can be easily designed for a wide range of acceleration ranging from a few g to several thousand g.

Method and apparatus for simulating a microelectric interconnect circuit

Abstract: A method and apparatus for simulating a microelectronic circuit or system includes the storing of a microelectronic circuit or system representation in a computer and then transforming the representation into an equivalent DC circuit containing resistive, capacitive and inductive elements. Then, a directed graph of the DC equivalent circuit is generated and a spanning tree is constructed therefrom. The spanning tree is then actually or virtually traversed to obtain multiple generations of circuit moments. The moments are then used to calculate the poles and residues for a given node and generate an approximate model of the circuit's transient response at that node. Moment shifting is used to provide for a stable approximate model. The actual residues corresponding to the coefficients of the time domain representation for the model can be calculated using the first q-1 moments. This constitutes a partial-Pade approximation.

Fabrication of high frequency two-dimensional nanoactuators for scanned probe devices

Abstract: The authors have developed an integrated silicon process that uses suspended single crystal silicon (SCS) structures to fabricate x-y capacitive translators and high aspect ratio conical tips for scanned probe devices. The integrated nanomechanical device design and the process sequence include methods to form integrated tunneling tip pairs and to produce electrical isolation, contacts, and conductors. Each device occupies a nominal area of 40 mu m*40 mu m. These devices include a novel self-aligned tip-above-a-tip tunneling structure and capacitive x-y translators defined by electron beam lithography and the thermal oxidation of silicon. The x-y translators produce a maximum x-y displacement of +or-200 nm for an applied voltage of 55 V. The low mass (2*10/sup -13/ kg), rigid structure has a measured fundamental mechanical resonant frequency of 5 MHz. >

Self-testing capacitive pressure transducer and method

Abstract: A high-performance switched-capacitor circuit for electronic read-out of a pressure sensor-based ultrasensitive microflow transducer. The microflow transducer uses a differential capacitive pressure sensor to measure flow. Read-out electronics associated with the transducer feature a clocking speed of 100 KHz and drive loads up to 35 pF. The read-out electronics include a high DC gain that nulls out stray input capacitance, which is beneficial for the multichip realization of the microflow transducer disclosed herein. The uncompensated linearity of the overall read-out electronics is 10 bits, and the pressure/flow resolution is 12 bits. An ultrasensitive membrane associated with the pressure sensor does not respond to a pulsed waveform for frequencies above 50 KHz. But for lower frequencies, it deflects in response to the time-average voltage applied across the capacitor plates of the pressure sensor. A self-test mode is provided which employs an extremely long pre-charge pulse. An integrated flowmeter package including transducer and circuitry, and a second circuit for extending the range of the microflowmeter circuitry are also disclosed.

Micromachined atomic force I microprobe with integrated I I capacitive read-out I

Abstract: . We developed a micromachining process for the fabrication of highly sensitive capacitor probes to be used for displacement measurement of an atomic force cantilever. The capacitive structure consists of two adjacent single-crystal silicon beams, one carrying a sharp tip for the force interaction, the other being the counter-electrode. The air gap of 1.5 pm separating the two electrodes is obtained by removal of the oxide in between by selective etching. The capacitance has a typical value of -0.2 pF. Forces acting on the tip induce a bending of the cantilever and change the caDacitance which can be detected bv electronic circuits. 1. Introduction Using capacitive variation to sense physical displace- ments represents an interesting alternative to optical, tunneling or piezoresistive methods. Sensors that use single-crystal silicon as highly elastic material and capacitance change as the readout principle are known to be reliable and accurate [I]. Additionally, thermal silicon dioxide provides good electrical insulation and allows, in combination with highly doped silicon, the

Phase discriminating capacitive array sensor system

Abstract: A phase discriminating capacitive sensor array system which provides multiple sensor elements which are maintained at a phase and amplitude based on a frequency reference provided by a single frequency stabilized oscillator. Sensor signals provided by the multiple sensor elements are controlled by multiple phase control units, which correspond to the multiple sensor elements, to adjust the sensor signals from the multiple sensor elements based on the frequency reference. The adjustment made to the sensor signals is indicated by output signals which indicate the proximity of the object. The output signals may also indicate the closing speed of the object based on the rate of change of the adjustment made, and the edges of the object based on a sudden decrease in the adjustment made.

A capacitive tactile sensor for shear and normal force measurements

Abstract: This paper describes a new capacitive tactile sensor for shear and normal force measurements. The spatial sampling principle has been applied to measure the capacitance values efficiently and to transfer the spatial capacitance distribution into the time domain. The shear and normal forces are determined by measuring variations in the phase and amplitude of the output signal, respectively. A first experimental model of the sensor shows a resolution of 0.05 N over the range of 10 N for both shear and normal force measurements.

Data input device with a pressure-sensitive input surface

Abstract: The data input device (11) comprises, above a resistive layer arrangement (2), an arrangement (4) of deformable layers consisting at least partially of dielectric material. This material is elastically deformable so that, when pressure is applied onto the input surface, the distance between the input surface and the resistive layer arrangement (2) is reduced at the pressure point. On the side of the deformable layer arrangement (4) facing away from the resistive layer arrangement (2), there is arranged an electrode which preferably is formed as a conductive layer (1). Thus results in a change of the capacitive properties of the deformable layer arrangement (4) at the pressure point since the thickness of the deformable layer arrangement (4) is reduced on this site. This capacitive measurement is used for detection of the pressing force, while the position of the pressing point within the input surface is detected in two mutually orthogonal directions on the basis of the voltage divider forming in the resistive layer arrangement (2).

Electrical interconnect device with interwoven power and ground lines and capacitive vias

Abstract: The invention relates to an electrical interconnect device with power and ground lines interwoven about signal line layers and capacitive vias between signal layers so as to make efficient use of otherwise undedicated area between signal lines and signal layers and to reduce or eliminate the need for separate power and ground layers while providing decoupling capacitance within the wiring structure.

Micromachined subminiature condenser microphones in silicon

Abstract: Silicon subminiature microphones can be manufactured with the methods of micromachining technology. Several condenser-type microphones have been designed and fabricated at our institute. Capacitive microphones are described, which have a structured back electrode and a membrane of silicon nitride. A smooth frequency response up to 30 kHz with a maximum open-circuit sensitivity of 10 mV/Pa is obtained. A special design of a capacitive sensor has been realized with the FET microphone. The drain current of a field-effect transistor with a suspended gate is modulated by the vibrations of the membrane. This design represents the first suspended-gate sensor, the drain current of which is deflection controlled. Design, construction and experimental results of sensitivity and frequency response are given.

Anodic bonding for integrated capacitive sensors

Abstract: Anodic bonding of silicon to Pyrex glass was studied from the viewpoint of its application to integrated capacitive sensors. Equipment that was developed to allow substrate bonding in atmosphere and in vacuum is described. Vertical and lateral electrical feedthrough structures, which have excellent electrical properties and airtight performance, were developed. The vertical feedthrough structures were applied to capacitive sensors. Other bonding-related problems that were studied, such as wafer distortion, circuit damage, and metallization are noted. >

Steering capaciflector sensor

Abstract: A capacitive type proximity sensor having substantial range and sensitivity between a machine and an intruding object in the immediate vicinity of the machine and having a steerable sensing field has an outer electrical conductor on the machine forming one electrode of a sensor capacitor, the other electrode is the object. The outer conductor is a thin sheet of conductive material with a pair (or more) of intermediate electrical conductors located between the outer conductor and the machine. The pair of intermediate electrical conductors are in close proximity to each other and together form a surface having a size substantially larger than the outer conductor to act as a shield for reducing the parasitic capacitance between the outer conductor and the machine and to steer the sensor field. The pair of intermediate conductors are thin sheets of conductive material substantially wider than the first conductor. The outer and pair of intermediate conductors are attached to a surface on the machine in electrical isolation and with no gaps between the conductors and no gap between the surface and the pair of intermediate conductors. The outer and pair of intermediate conductors are also in conformance with each other and the surface of the machine, and the surface of the machine acts as a ground plane. Variable gain voltage follower circuits are used for coupling, in phase, the instantaneous voltage at the outer electrical conductor to the pair of intermediate electrical conductors and a signal generator is coupled to the outer conductor and is responsive to the capacitance of the sensor capacitor for generating a control signal to the machine.

Micromachined atomic force microprobe with integrated capacitive read-out

Abstract: The authors developed a micromachining process for the fabrication of highly sensitive capacitor probes to be used for displacement measurement of an atomic force cantilever. The capacitive structure consists of two adjacent single-crystal silicon beams, one carrying a sharp tip for the force interaction, the other being the counter-electrode. The air gap of 1.5 mu m separating the two electrodes is obtained by removal of the oxide in between by selective etching. The capacitance has a typical value of approximately=0.2 pF. Forces acting on the tip induce a bending of the cantilever and change the capacitance which can be detected by electronic circuits.

Capacitive melt pressure measurement with center-mounted electrode post

Abstract: A melt pressure measurement probe for insertion through wall of melt-containing vessel has a pressure-deflectable end portion for contact with pressurized melt. Pressure-resistant securing means fixes the end surface in a non-flow obstruction relationship. A seal surface on the probe prevents exposure of the melt to the securing means. Pressure detection means internal of the probe, responsive to deflection of the probe end surface to detect melt pressure, comprises a temperature-compensated capacitive sensor, one capacitor plate defined by the end portion and an opposite capacitor plate in the probe with a capacitive gap in-between. Electronic circuitry remote from the melt-exposed end, including circuitry within the probe to generate a signal proportional to the capacitance, compensates for change of temperature of the capacitor to generate an output signal proportional to melt pressure.

Electrical surface perturbation of a piezoelectric acoustic plate mode by a conductive liquid loading

Abstract: Surface loading of a piezoelectric crystal supporting acoustic plate modes (APMs) by a dilute conductive liquid is analyzed using a perturbation theory. The formulation of the problem is such that only the electrical loading is relevant, and the mass loading and viscous entrainment caused by the solute are ignored. The perturbation in the propagation characteristics is then obtained relative to the solvent and is described in terms of the coupling coefficient, the capacitive loading, and the conductivity of the liquid. The results are compared to measurements made on Z-cut X-propagating LiNbO/sub 3/ APM device loaded with various conductive liquids of different concentrations. While an interpretation of the results can be given on the use of the APM device as a detector of the liquid properties, it is shown that a conductive liquid loading of the piezoelectric surface can be used as a means of assessing the electromechanical coupling coefficient of APMs. >

Amplifier for driving large capacitive loads

Abstract: An amplifier design for a capacitive load reduces power supply requirements by recovering, during the discharge of the capacitive load, a substantial amount of the stored energy without causing noise signals to be created. The recovered energy is stored in novel series-connected capacitors to be reused during the subsequent load charge cycle. The stack becomes an effective multiple power supply source. The capacitors are successively switched and thus sequentially harnessed to the load capacitor so that the voltage across the load capacitor is increased by selected step increments instead of by one large voltage jump which causes circuit noise. By using MOSFET devices for the switches, the voltage increase during charging and decrease during discharging is continuous, thus eliminating the step function which causes much of the deleterious noise. The amplifier is especially useful as a driver for an actuator in an active control system for quieting noise-causing vibrations in buildings and other structures, which can be a health hazard.

Personal-care apparatus comprising a capacitive on/off switch

Abstract: A personal-care apparatus comprises a load (LD) and a switch (SW), which load (LD) and which switch (SW) are coupled in series between a first (1) and a second (2) supply terminal for receiving an alternating voltage, the personal-care apparatus further comprising a rectifying circuit (RC) for converting the alternating voltage into a direct voltage, and a safety circuit (SC), which is coupled between a third (3) and a fourth (4) supply terminal for receiving the direct voltage and which comprises a capacitive sensor (CS) for the detection of the presence of a part of a human body in the proximity of the personal-care apparatus, the safety circuit being adapted to control the switch (SW) in response to said detection.

Apparatus and method for in situ evaluation of capacitive type pressure transducers in a nuclear power plant

Abstract: An apparatus and method to facilitate the in situ detection of small leaks in fluid-filled, capacitive type pressure transducers by remotely and non-intrusively inducing a brief time varying transient signal, and then analyzing the frequency response of the transducer to such excitation in order to detect the presence and effects of a fluid leak. The adverse effect of this induced transient signal on the process control circuitry is insignificant, while providing for an accurate and sensitive method for detecting the extent of fluid loss in the transducer when evaluated according to the present invention. As a consequence of such transducer evaluation techniques, frequency responsive characteristics of such devices may be recorded and self-correlated over long periods of time. Such self-correlation provides an accurate, transducer-specific historical profile which may be used as a means for detecting malfunction anomalies in the output of the pressure sensing transducer device and predicting when the device will fail due to loss of internal dielectric fluid.

System and method of measuring high-speed electrical waveforms using force microscopy and offset sampling frequencies

Abstract: A potentiometry apparatus for measuring a periodic electrical waveform existing proximate the surface of a sample such as a semiconductor wafer is disclosed herein. The potentiometry apparatus includes a pulse generator for generating a sequence of electrical pulses at a pulse frequency offset from the frequency of the surface waveform by a mixing frequency. A cantilever coupled to the pulse generator serves to carry the electrical pulses to a position proximate the surface of the sample. In a capacitive displacement mode the cantilever is mechanically displaced so as to generate a time-expanded representation of the electrical surface waveform having a repetition frequency equal to the mixing frequency. During displacement mode operation an optical detection circuit may be employed to monitor deflection of the cantilever. In a tunneling current mode the cantilever is again employed to carry the electrical pulses to a position proximate the surface of the sample. In this mode a tunneling current propagating through the cantilever at the mixing frequency provides a time-expanded representation of the electrical surface waveform.

Micromachined sensor structures with linear capacitive response

Abstract: Capacitive membrane-type pressure sensors normally have nonlinear pressure-capacitance relationships, implying the need for sophisticated electronics. Various capacitive pressure sensor structures with improved linearity are suggested in this article. These include membranes that touch the bottom of the cavity, corrugated or thinned membrane edges with stiffened membrane centers, as well as a sensor structure with a double-comb design. The design possibilities increase with these methods. Most work was carried out with the help of finite element analysis (FEA). Pressure sensors have been manufactured based on the FEA simulations, and the experiments verify the calculations. The results show very promising linearity properties, with nonlinearities less than 1%, and sensitivities around 10 pF/bar. Weaknesses introduced in the membrane can improve performance if they are located correctly.

High Resolution CMOS Current Comparators

Abstract: A 2?m CMOS current comparator prototype is presented with an input current comparison range of 140dB and virtual zero offset(≪10pA). The circuit uses capacitive sensing for high resolution and nonlinear feedback to achieve small input voltage variations in the complete input current range. Operation speed for low current is abot two orders of magnitude larger than for conventional circuits. Simplified modeling issues are used to compare alternative comparator architectures.

A highly symmetrical capacitive micro-accelerometer with single degree-of-freedom response

Abstract: A high-performance acceleration sensor concept is presented, which combines multiple wafer bonding and differential capacitance measurement into a fully symmetrical design. The main device characteristics are an exclusive response to a translational acceleration component in a single axis, a maximized sensitivity for a given chip area and a substantially improved linearity by suppression of error sources as fringing fields, stray capacitances, leakage resistances and electrostatic pressure. Modifiable damping characteristics and hence adjustable bandwidth is an additional device feature. The general concept, the main design considerations, the fabrication procedure and the performance of this new solid state acceleration sensor are discussed. The particular problem of gas flow damping at low pressures is addressed via SPICE simulation of electrical equivalent networks. Damping-relate distortion effects on dynamic range and bandwidth are demonstrated quantitatively.