Linear capacitance measurement and touchless switch
First Claim
1. An apparatus for measuring relative changes in capacitances of at least one first capacitor (C1) and at least one second capacitor (C2), the apparatus comprising:
- at least one operational amplifier (A0, A1) operative to employ negative feedback to maintain the at least one first capacitor and the at least one second capacitor at substantially equal voltage potentials, each of the at least one first capacitor and the at least one second capacitor having one end connected to a common ground; and
at least one difference amplifier (A2) operative to provide an electrical signal (Vd), wherein a substantially linear relationship exists between the electrical signal and a specified arithmetic function of the capacitances of the at least one first capacitor and the at least one second capacitor, wherein one of the at least one operational amplifier (A1) is operative to provide an output (V1) directly or indirectly to an input of the at least one difference amplifier.
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Accused Products
Abstract
Capacitance measurement apparatus that enhances the sensitivity and accuracy of capacitive transducers, proximity sensors, and touchless switches. Each of two capacitors (C1, C2) under measurement has one end connected to ground and is kept at substantially the same voltage potential by operational amplifier (A1) or amplifiers (A0, A1) using negative feedback. The apparatus is driven by a periodic e.g. sinusoidal signal source (G1) or sources (G1, G2) and includes a difference amplifier (A2) operative to produce an electrical signal having a linear relationship with a specified arithmetic function of the capacitances of the two capacitors (C1, C2). A touchless switch is implemented using the capacitance measurement apparatus. The touchless switch includes two sensor electrodes (E1, E2) that correspond to the two capacitors (C1, C2) under measurement and in one embodiment has a front surface in the form of a container.
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Citations
53 Claims
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1. An apparatus for measuring relative changes in capacitances of at least one first capacitor (C1) and at least one second capacitor (C2), the apparatus comprising:
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at least one operational amplifier (A0, A1) operative to employ negative feedback to maintain the at least one first capacitor and the at least one second capacitor at substantially equal voltage potentials, each of the at least one first capacitor and the at least one second capacitor having one end connected to a common ground; and
at least one difference amplifier (A2) operative to provide an electrical signal (Vd), wherein a substantially linear relationship exists between the electrical signal and a specified arithmetic function of the capacitances of the at least one first capacitor and the at least one second capacitor, wherein one of the at least one operational amplifier (A1) is operative to provide an output (V1) directly or indirectly to an input of the at least one difference amplifier. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50)
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51. A capacitive sensing apparatus for generating at least one logical signal in response to proximity of a human appendage, the capacitive sensing apparatus comprising:
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a surface having a first side and a second side;
at least one first sensor electrode disposed on the first side of the surface;
a second sensor electrode disposed on one of the first and second sides of the surface, the second sensor electrode being adjacent to and at least partly surrounding the at least one first sensor electrode; and
an apparatus configured to maintain the at least one first sensor electrode and the second sensor electrode at substantially equal voltage potentials, and to measure relative changes in a first capacitance between the human appendage and the at least one first sensor electrode with respect to a second capacitance between the human appendage and the second sensor electrode, wherein the at least one logical signal is indicative of a status condition that the relative changes in the first and second capacitances exceed at least one preset threshold. - View Dependent Claims (52, 53)
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Specification