Wave transmission lines and networks – Coupling networks – Nonreciprocal gyromagnetic type
Reexamination Certificate
2001-03-13
2004-09-28
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Nonreciprocal gyromagnetic type
C333S105000, C333S262000, C333S017100, C200S181000, C310S309000
Reexamination Certificate
active
06798312
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrical isolators and in particular to a microelectromechanical system (MEMS) device providing electrical isolation in the transmission of analog electrical signals.
BACKGROUND OF THE INVENTION
Electrical isolators are used to provide electrical isolation between circuit elements for the purposes of voltage level shifting, electrical noise reduction, and high voltage and current protection.
Circuit elements may be considered electrically isolated if there is no path in which a direct current (DC) can flow between them. Isolation of this kind can be obtained by capacitive or inductive coupling. In capacitive coupling, an electrical input signal is applied to one plate of a capacitor to transmit an electrostatic signal across an insulating dielectric to a second plate at which an output signal is developed. In inductive coupling, an electrical input signal is applied to a first coil to transmit an electromagnetic field across an insulating gap to a second coil, which generates the isolated output signal. Both such isolators essentially block steady state or DC electrical signals.
Such isolators, although simple, block the communication of signals that have significant low frequency components. Further, these isolators can introduce significant frequency dependent attenuation and phase distortion in the transmitted signal. These features make such isolators unsuitable for many types of signals including many types of high-speed digital communications.
In addition, it is sometimes desirable to provide high voltage (>2 kV) isolation between two different portions of a system, while maintaining a communication path between these two portions. This is often true in industrial control applications where it is desirable to isolate the sensor/actuator portions from the control portions of the overall system. It is also applicable to medical instrumentation systems, where it is desirable to isolate the patient from the voltages and currents within the instrumentation.
The isolation of digital signals is frequently provided by optical isolators. In an optical isolator, an input signal drives a light source, typically a light emitting diode (LED) positioned to transmit its light to a photodiode or phototransistor through an insulating but transparent separator. Such a system will readily transmit a binary signal of arbitrary frequency without the distortion and attenuation introduced by capacitors and inductors. The optical isolator further provides an inherent signal limiting in the output through saturation of the light receiver, and signal thresholding in the input, by virtue of the intrinsic LED forward bias voltage.
Nevertheless, optical isolators have some disadvantages. They require a relatively expensive gallium arsenide (GaAs) substrate that is incompatible with other types of integrated circuitry and thus optical isolators often require separate packaging and assembly from the circuits they are protecting. The characteristics of the LED and photodetector can be difficult to control during fabrication, increasing the costs if unit-to-unit variation cannot be tolerated. The power requirements of the LED may require signal conditioning of the input signal before an optical isolator can be used, imposing yet an additional cost. While the forward bias voltage of the LED provides an inherent noise thresholding, the threshold generally cannot be adjusted but is fixed by chemical properties of the LED materials. Accordingly, if different thresholds are required, additional signal conditioning may be needed. Finally, the LED is a diode and thus limits the input signal to a single polarity unless multiple LEDs are used.
It is common to process analog electrical signals using digital circuitry such as microprocessors. In such situations, the analog signal may be periodically sampled and the samples converted into digital words input by an analog to digital converter (A/D) to and processed by the digital circuitry. Conversely, digital words produced by the digital circuitry may be converted into an analog signal through the use of a digital-to-analog converter (D/A) to provide a series of analog electrical values that may be filtered into a continuous analog signal. Isolation of such signals at the interface to the digital circuitry is often desired and may be performed by placing an optical isolator in series with the electrical signal representing each bit of the relevant digital word after the A/D converter and before the DIA converter. Particularly in the area of industrial controls where many isolated analog signals must be processed and output, a large number of optical isolators are required rendering the isolation very costly or impractical.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a mechanical isolator manufactured using MEMS techniques and suitable for transmitting analog signals without prior conversion to digital signals. A special fabrication process forms a microscopic beam whose ends are insulated from each other. One end of the beam is connected to a microscopic actuator, which receives an analog input signal to move the beam in proportion to a generated actuator force. The other isolated end of the beam is attached to a sensor detecting movement of the beam to provide a corresponding analog value. The small scale of the total device provides inexpensive, fast and reliable response.
Specifically, the present invention provides a microelectromechanical system (MEMS) analog isolator having a substrate and an element supported from the substrate for continuous movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other. An actuator attached to the first portion of the element receives an input electrical signal and exerts a force dependent on the input electrical signal urging the element toward the second position. A control device attached to the element to exert a force dependent on the displacement of the element toward the first position and a sensor assembly communicating with the second portion of the element provide an analog output electrical signal dependent on movement of the element between the first position and the second position.
It is one object of the invention to produce a simple mechanical isolation system using MEMS techniques suitable for direct isolation of an analog signal overcoming the need for many optical isolators and further avoiding many of the disadvantages of current optical isolators in costs, interdevice consistency, and incompatibility with other integrated circuit components. In addition, the present invention requires no preconditioning of the input signal. The input voltage, current, or mechanical displacement can be applied directly to the device with no pre-processing.
The control element may be a spring or its equivalent and the sensor assembly may include a sensor providing the analog output electrical signal based on the amount of movement of the element.
Thus another object of the invention is to provide the possibility of a simple open-loop analog isolator where the analog signal is transmitted over an insulated beam by motion of the beam.
Alternatively, the control element may be a second actuator attached to the element to receive a feedback electrical signal and exert a force dependent on the feedback electrical signal urging the element toward the first position. In this case, the sensor assembly may include a sensor indicating a location of the element with respect to a null position and an error detector receiving the output electrical signal to generate the feedback electrical signal so as to tend to restore the element to the null position. The output electrical signal is derived from the feedback signal.
Another object of the invention is thus to permit a more complex analog isolator using feedback techniques where the analog signal is trans
Dummermuth Ernst H.
Harris Richard D.
Knieser Michael J.
Kretschmann Robert J.
Glenn Kimberly
Pascal Robert
Quarles & Brady LLP
Rockwell Automation Technologies Inc.
Speroff R. Scott
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