Patent US5148126A successfully refreshed from Google Patents.
US5148126A
Expired / Lapsed
US
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Capacitance sensor circuit and method for measuring capacitance and small changes in capacitance
Assignee: Sentech Corp
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Filing: 1991-12-13
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Granted: 1992-09-15
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Expires: 2011-12-13
Abstract
Abstract An improved oscillator circuit and method for measuring capacitance and small changes in capacitance is described. The circuit provides a digital output signal that has a frequency inversely proportional to the capacitance being measured, is substantially immune to stray capacitance, has low sensitivity to noise and temperature variations, is relatively simple and inexpensive to implement and provides a high precision measurement. One embodiment of the oscillator includes a capacitor to be measured, an integrator, an inverting amplifier, a comparator, a summing amplifier and a digital output circuit. A second embodiment of the oscillator further provides compensation for the non-linear response of a parallel plate capacitive transducer.
Inventors
- 👤 Mark E. Spencer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 21:00
CPC Classifications
G; G01; G01R; G01R27/00; G01R27/02; G01R27/26; G01R27/2605; H; H03; H03B; H03B5/00; H03B5/20; H03B5/26; H03B5/02; H03B5/04
Claims Analysis
Total Claims: 40
Claim 1
Independent Claim
120 words
An oscillator circuit for measuring capacitance and small changes in capacitance comprising, in combination: a capacitor having a capacitance to be measured; means for generating an output signal that is proportional to the integral over time of an exponential current flowing through said capacitor; means coupled to said generating means for inverting said output signal; means coupled to said inverting means for switching a bistable signal at a frequency that is inversely proportional to said capacitance to thereby provide an indication of the value of said capacitance; and means coupled to said switching means, coupled to said inverting means and coupled to said generating means for summing an output of said switching means and an output of said inverting means.
Claim 2
Dependent Claim
120 words
An oscillator circuit for measuring capacitance and small changes in capacitance comprising, in combination: a capacitor having a capacitance to be measured; means for generating an output signal that is proportional to the integral over time of an exponential current flowing through said capacitor; means coupled to said generating means for inverting said output signal; means coupled to said inverting means for switching a bistable signal at a frequency that is inversely proportional to said capacitance to thereby provide an indication of the value of said capacitance; and means coupled to said switching means, coupled to said inverting means and coupled to said generating means for summing an output of said switching means and an output of said inverting means.
Claim 3
Dependent Claim
36 words
The oscillator circuit of claim 1 wherein said generating means comprises an amplifier having an input coupled to a first terminal of said capacitor and having an output coupled to a second terminal of said capacitor.
Claim 4
Dependent Claim
83 words
The oscillator circuit of claim 1 wherein said generating means comprises: a resistor having a first terminal coupled to the input of said generating means and having a second terminal coupled to a first terminal of said capacitor; and an operational amplifier having an inverting input coupled to said first terminal of said capacitor, having a non-inverting input coupled to circuit ground and having an output coupled to a second terminal of said capacitor and coupled to the output of said generating means.
Claim 5
Dependent Claim
34 words
The oscillator circuit of claim 1 wherein said inverting means comprises an inverting amplifier having an input coupled to said output of said generating means and having an output coupled to said summing means.
Claim 6
Dependent Claim
89 words
The oscillator circuit of claim 4 wherein said inverting means comprises: a first resistor having a first terminal coupled to the input of said inverting means and having a second terminal; a second resistor having a first terminal coupled to said second terminal of said first resistor and having a second terminal; and an operational amplifier having an inverting input coupled to said second terminal of said first resistor, having a non-inverting input coupled to circuit ground and having an output coupled to the output of said inverting means.
Claim 7
Dependent Claim
50 words
The oscillator circuit of claim 1 wherein said switching means comprises a bistable circuit having a first input coupled to an output of said summing means, having a second input coupled to an output of said inverting means and having an output coupled to an input of said summing means.
Claim 8
Dependent Claim
50 words
The oscillator circuit of claim 6 wherein said bistable circuit comprises a voltage comparator having an inverting input coupled to an output of said summing means, having a non-inverting input coupled to an output of said inverting means and having an output coupled to an input of said summing means.
Claim 9
Dependent Claim
50 words
The oscillator circuit of claim 6 wherein said bistable circuit comprises a voltage comparator having a non-inverting input coupled to an output of said summing means, having an inverting input coupled to an output of said inverting means and having an output coupled to an input of said summing means.
Claim 10
Dependent Claim
50 words
The oscillator circuit of claim 1 wherein said summing means comprises a summing amplifier having a first input coupled to said output of said switching means, having a second input coupled to an output of said inverting means and having an output coupled to an input of said switching means.
Claim 11
Dependent Claim
120 words
The oscillator circuit of claim 9 wherein said summing amplifier comprises: a first resistor having a first terminal coupled to the first input of said summing amplifier and having a second terminal; a second resistor having a first terminal coupled to the second input of said summing amplifier and having a second terminal coupled to said second terminal of said first resistor; a third resistor having a first terminal coupled to said second terminal of said first resistor and having a second terminal; and an operational amplifier having an inverting input coupled to said second terminal of said first resistor, having a non-inverting input coupled to circuit ground and having an output coupled to the output of said summing amplifier.
Claim 12
Dependent Claim
34 words
The oscillator circuit of claim 1 wherein said capacitor to be measured comprises a parallel plate capacitive transducer for measuring a physical parameter that is a function of a separation of the parallel plates.
Claim 13
Dependent Claim
69 words
The oscillator circuit of claim 1 wherein said capacitor to be measured comprises a capacitive proximeter for measuring distance or vibration having an electrically conductive sensing plate and having an electrical connection to a conductive object whose distance from said sensing plate or whose vibration is to be measured, with said capacitance of said capacitor to be measured being the capacitance between said sensing plate and said conductive object.
Claim 14
Dependent Claim
42 words
The oscillator circuit of claim 12 further comprising compensation means for linearizing the normally non-linear frequency vs. distance response obtained when the distance from said sensing plate to said conductive object is large relative to the physical size of said sensing plate.
Claim 15
Dependent Claim
49 words
The oscillator circuit of claim 13 wherein said compensation means comprises: an amplifier having an input coupled to said output of said switching means; and a second capacitor having a first terminal coupled to said output of said amplifier and having a second terminal coupled to said sensing plate.
Claim 16
Dependent Claim
82 words
The oscillator circuit of claim 14 wherein said amplifier comprises: a first resistor having a first terminal electrically coupled to said output of said switching means and having a second terminal; a second resistor having a first terminal electrically coupled to said second terminal of said first resistor and having a second terminal; and an operational amplifier having an inverting input coupled to said second terminal of said first resistor, having a non-inverting input coupled to circuit ground and having an output.
Claim 17
Dependent Claim
31 words
The oscillator circuit of claim 15 wherein one of said first or said second resistor comprises a potentiometer configured as a variable resistor to allow external adjustment of said compensation means.
Claim 18
Dependent Claim
45 words
The oscillator circuit of claim 13 further comprising: a third capacitor coupled to said inverting means to induce a lowpass frequency response in said inverting means; and a fourth capacitor coupled to said summing means to induce a lowpass frequency response in said summing means.
Claim 19
Dependent Claim
51 words
The oscillator circuit of claim 1 further comprising means coupled to said switching means for converting an output of said switching means to a digital output signal having a frequency inversely proportional to said capacitance and suitable for processing by external digital circuits to thereby indicate the value of said capacitance.
Claim 20
Dependent Claim
27 words
The oscillator circuit of claim 18 wherein said converting means comprises a transistor switch having an open-collector output coupled to a digital supply voltage through a resistor.
Claim 21
Independent Claim
125 words
A method for measuring capacitance and small changes in capacitance comprising the steps of: providing a capacitor having a capacitance to be measured; providing means for generating an output signal that is proportional to the integral over time of an exponential current flowing through said capacitor; providing means coupled to said generating means for inverting said output signal; providing means coupled to said inverting means for switching a bistable signal at a frequency that is inversely proportional to said capacitance to thereby provide an indication of the value of said capacitance; and providing means coupled to said switching means, coupled to said inverting means and coupled to said generating means for summing an output of said switching means and an output of said inverting means.
Claim 22
Independent Claim
125 words
A method for measuring capacitance and small changes in capacitance comprising the steps of: providing a capacitor having a capacitance to be measured; providing means for generating an output signal that is proportional to the integral over time of an exponential current flowing through said capacitor; providing means coupled to said generating means for inverting said output signal; providing means coupled to said inverting means for switching a bistable signal at a frequency that is inversely proportional to said capacitance to thereby provide an indication of the value of said capacitance; and providing means coupled to said switching means, coupled to said inverting means and coupled to said generating means for summing an output of said switching means and an output of said inverting means.
Claim 23
Dependent Claim
35 words
The method of claim 20 wherein said generating means comprises an amplifier having an input coupled to a first terminal of said capacitor and having an output coupled to a second terminal of said capacitor.
Claim 24
Dependent Claim
82 words
The method of claim 20 wherein said generating means comprises: a resistor having a first terminal coupled to the input of said generating means and having a second terminal coupled to a first terminal of said capacitor; and an operational amplifier having an inverting input coupled to said first terminal of said capacitor, having a non-inverting input coupled to circuit ground and having an output coupled to a second terminal of said capacitor and coupled to the output of said generating means.
Claim 25
Dependent Claim
33 words
The method of claim 20 wherein said inverting means comprises an inverting amplifier having an input coupled to said output of said generating means and having an output coupled to said summing means.
Claim 26
Dependent Claim
88 words
The method of claim 23 wherein said inverting means comprises: a first resistor having a first terminal coupled to the input of said inverting means and having a second terminal; a second resistor having a first terminal coupled to said second terminal of said first resistor and having a second terminal; and an operational amplifier having an inverting input coupled to said second terminal of said first resistor, having a non-inverting input coupled to circuit ground and having an output coupled to the output of said inverting means.
Claim 27
Dependent Claim
49 words
The method of claim 20 wherein said switching means comprises a bistable circuit having a first input coupled to an output of said summing means, having a second input coupled to an output of said inverting means and having an output coupled to an input of said summing means.
Claim 28
Dependent Claim
49 words
The method of claim 25 wherein said bistable circuit comprises a voltage comparator having an inverting input coupled to an output of said summing means, having a non-inverting input coupled to an output of said inverting means and having an output coupled to an input of said summing means.
Claim 29
Dependent Claim
49 words
The method of claim 25 wherein said bistable circuit comprises a voltage comparator having a non-inverting input coupled to an output of said summing means, having an inverting input coupled to an output of said inverting means and having an output coupled to an input of said summing means.
Claim 30
Dependent Claim
49 words
The method of claim 20 wherein said summing means comprises a summing amplifier having a first input coupled to said output of said switching means, having a second input coupled to an output of said inverting means and having an output coupled to an input of said switching means.
Claim 31
Dependent Claim
119 words
The method of claim 28 wherein said summing amplifier comprises: a first resistor having a first terminal coupled to the first input of said summing amplifier and having a second terminal; a second resistor having a first terminal coupled to the second input of said summing amplifier and having a second terminal coupled to said second terminal of said first resistor; a third resistor having a first terminal coupled to said second terminal of said first resistor and having a second terminal; and an operational amplifier having an inverting input coupled to said second terminal of said first resistor, having a non-inverting input coupled to circuit ground and having an output coupled to the output of said summing amplifier.
Claim 32
Dependent Claim
32 words
The method of claim 20 wherein said capacitor to be measured comprises a parallel plate capacitive transducer for measuring a physical parameter that a function of a separation of the parallel plates.
Claim 33
Dependent Claim
68 words
The method of claim 20 wherein said capacitor to be measured comprises a capacitive proximeter for measuring distance or vibration having an electrically conductive sensing plate and having an electrical connection to a conductive object whose distance from said sensing plate or whose vibration is to be measured, with said capacitance of said capacitor to be measured being the capacitance between said sensing plate and said conductive object.
Claim 34
Dependent Claim
45 words
The method of claim 31 further including the step of providing compensation means for linearizing the normally non-linear frequency vs. distance response obtained when the distance from said sensing plate to said conductive object is large relative to the physical size of said sensing plate.
Claim 35
Dependent Claim
48 words
The method of claim 32 wherein said compensation means comprises: an amplifier having an input coupled to said output of said switching means; and a second capacitor having a first terminal coupled to said output of said amplifier and having a second terminal coupled to said sensing plate.
Claim 36
Dependent Claim
81 words
The method of claim 33 wherein said amplifier comprises: a first resistor having a first terminal electrically coupled to said output of said switching means and having a second terminal; a second resistor having a first terminal electrically coupled to said second terminal of said first resistor and having a second terminal; and an operational amplifier having an inverting input coupled to said second terminal of said first resistor, having a non-inverting input coupled to circuit ground and having an output.
Claim 37
Dependent Claim
30 words
The method of claim 34 wherein one of said first or said second resistor comprises a potentiometer configured as a variable resistor to allow external adjustment of said compensation means.
Claim 38
Dependent Claim
48 words
The method of claim 32 further including the step of providing: a third capacitor coupled to said inverting means to induce a lowpass frequency response in said inverting means; and a fourth capacitor coupled to said summing means to induce a lowpass frequency response in said summing means.
Claim 39
Dependent Claim
54 words
The method of claim 20 further including the step of providing means coupled to said switching means for converting an output of said switching means to a digital output signal having a frequency inversely proportional to said capacitance and suitable for processing by external digital circuits to thereby indicate the value of said capacitance.
Claim 40
Dependent Claim
26 words
The method of claim 37 wherein said converting means comprises a transistor switch having an open-collector output coupled to a digital supply voltage through a resistor.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1995-09-15 | 1996-03-16 | 1996-09-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1999-09-15 | 2000-03-16 | 2000-09-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2003-09-15 | 2004-03-16 | 2004-09-15 | $7700.00 | Window Closed / Lapsed |