US 7,323,886 B2Granted

Linear capacitance measurement and touchless switch

OwnerYing Lau Leeinventor

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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.

Claims50

Dependent claims

An apparatus for detecting relative changes in capacitances of at least one first capacitor and at least one second capacitor, each of the at least one first capacitor and the at least one second capacitor having a first end and a second end, the apparatus comprising:

at least one power source operative to produce at least one periodic output signal at at least one corresponding power source output;
electrical circuitry including at least one operational amplifier and at least one difference amplifier, the electrical circuitry being coupled to the first ends of the at least one first capacitor and the at least one second capacitor, the second ends of the at least one first capacitor and the at least one second capacitor being electrically connected at the same time to a common ground,
wherein the at least one power source output is operative to charge the at least one first capacitor and the at least one second capacitor,
wherein the at least one operational amplifier is configured to employ negative feedback to maintain the first ends of the at least one first capacitor and the at least one second capacitor at substantially equal voltage potentials with respect to the common ground while the at least one first capacitor and the at least one second capacitor are being charged responsive to the at least one power source output,
wherein the at least one difference amplifier is operative to provide at least one electrical signal, and
wherein a substantially linear relationship exists between the at least one electrical signal and a specified arithmetic function involving one of a ratio of the capacitances of the at least one first capacitor and the at least one second capacitor and a difference between the capacitance of the at least one first capacitor multiplied by a first constant factor and the capacitance of the at least one second capacitor multiplied by a second constant factor.

3 more elements

An apparatus for detecting relative changes in capacitances of at least one first capacitor and at least one second capacitor, the apparatus comprising:

at least one operational amplifier 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 operative to provide at least one electrical signal,
wherein a substantially linear relationship exists between the at least one 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 is operative to provide an output directly or indirectly to an input of the at least one difference amplifier,
wherein the at least one operational amplifier includes first and second operational amplifiers, and
wherein the apparatus further includes:
at least one power source comprising a periodic varying voltage source operative to provide an output voltage to a non-inverting input of the first operational amplifier and a non-inverting input of the second operational amplifier;
a first resistor connected between an output of the first operational amplifier and the first capacitor at a first node,
wherein a voltage potential at the first node is provided to an inverting input of the first operational amplifier, whereby a feedback current flowing through the first resistor maintains the voltage potential at the first node substantially equal to a voltage potential of the output voltage of the periodic varying voltage source;
and
a second resistor connected between an output of the second operational amplifier and the second capacitor at a second node,
wherein a voltage, potential at the second node is provided to an inverting input of the second operational amplifier, whereby a feedback current flowing through the second resistor maintains the voltage potential at the second node substantially equal to the voltage potential of the output voltage of the periodic varying voltage source,
wherein the output of the first operational amplifier is provided to a first differential input of the difference amplifier, and the output of the second operational amplifier is provided to a second differential input of the difference amplifier, and
wherein at steady state, the at least one electrical signal provided by the difference amplifier is substantially proportional to a signal representing a time derivative of the output voltage of the periodic varying voltage source which is a periodic function of time being modulated by a value r1*c1−r2*c2, wherein c1 is the capacitance of the first capacitor, c2 is the capacitance of the second capacitor, r1 is the resistance of the first resistor, and r2 is the resistance of the second resistor.

12 more elements

Dependencies are inferred from the claim text.

Facts

Application: 11/202,486Filed 12 Aug 2005 · us provisional application
Priority: 16 Aug 2004
Published: US 2006/0033508 A116 Feb 2006
Granted: 29 Jan 2008
Term ends: Not estimatedThe source records don’t support an estimate.

Classification11 codes

H03F 3/68
Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements: combinations of amplifiers, e.g. multi-channel…
G01R 27/2605
Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric…:…
H03F 1/34
Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements:…
H03F 3/45475
Characterised by the way of implementation of the active amplifying circuit in the differential amplifier: using IC blocks as the active…

Family

Application60/601,610Us provisional application · filed 16 Aug 2004
Application60/619,697Us provisional application · filed 19 Oct 2004
Application60/662,378Us provisional application · filed 17 Mar 2005
Application60/690,486Us provisional application · filed 15 Jun 2005
US 2006/0033508 A1Pre-grant publication · published 16 Feb 2006
US 7,323,886 B2This patent

From the US filing history. Foreign family members aren’t listed.