EP0520352A2
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EP
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Capacitive sensing device
Assignee: Toyoda Koki KK
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Filing: 1992-06-22
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Granted: —
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Expires: 2012-06-22
Abstract
Abstract A digital capacitive sensing device comprises: a reference capacitor having a reference capacitance unaffected by a force to be measured; a reference pulse signal generating circuit which generates a reference pulse signal of a frequency corresponding to the reference capacitance ; a sensing capacitor having capacitance variable according to the magnitude of the force ; a measuring pulse signal generating circuit having a construction similar to that of the reference pulse signal generating circuit and capable of generating a measuring pulse signal of a frequency corresponding to the capacitance of the sensing capacitor; and a differential arithmetic circuit which adds the number of pulses of the reference pulse signal in a predetermined time interval to a set value and subtracts the number of pulses of the measuring pulse signal in a predetermined time interval from the set value. The reference pulse signal generating circuit is capable of compensating a zero point temperature characteristic of a detection value, and the measuring pulse signal generating circuit is capable of compensating a detection sensitivity temperature characteristic.
Inventors
- 👤 Shizuki Sakurai
- 👤 Tomio Nagata
- 👤 Shiro Kuwahara
- 👤 Osamu Tabata
- 👤 Susumu Sugiyama
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 16:45
CPC Classifications
G; G01; G01L; G01L9/00; G01L9/0041; G01L9/0072; G01L9/0073; G01D; G01D3/00; G01D3/028; G01D3/036; G01D3/0365; G01D5/00; G01D5/12; G01D5/14; G01D5/24; G01D5/241; G01D5/2417; G01L9/12; G01L9/125; G01P; G01P15/00; G01P15/02; G01P15/08; G01P15/125; G01R; G01R27/00; G01R27/02; G01R27/26; G01R27/2605
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
128 words
A capacitive sensing device comprising: a sensing capacitor having capacitance variable according to a variation of a force to be measured; a measuring pulse signal generating circuit connected to said sensing capacitor for generating a measuring pulse signal with a frequency in accordance with capacitance of said sensing capacitor; a reference capacitor having a reference capacitance that is not affected by said force; a reference pulse signal generating circuit connected to said reference capacitor, having a construction similar to that of said measuring pulse signal generating circuit and capable of generating a reference pulse signal with a frequency in accordance with said reference capacitance; and a signal processing circuit for calculating a value of said force from frequencies of said reference pulse signal and said measuring pulse signal.
Claim 2
Dependent Claim
147 words
A capacitive sensing device according to claim 1, wherein said measuring pulse signal generating circuit and said reference pulse signal generating circuit have oscillation circuits that provide said measuring pulse signal and said reference pulse signal, respectively, ratios of frequency deviations of said measuring pulse signal and said reference pulse signal to temperature deviations being controlled by varying input voltages applied to said measuring pulse signal generating circuit and said reference pulse signal generating circuit, respectively; an input voltage applied to said measuring pulse signal generating circuit is adjusted so that a detection sensitivity is nearly constant for a temperature variation; and an input voltage applied to said reference pulse signal generating circuit is adjusted so that a ratio of a deviation of a frequency difference between said measuring pulse signal and said reference pulse signal to a temperature deviation is nearly constant for a temperature variation.
Claim 3
Dependent Claim
67 words
A capacitive sensing device according to claim 1, wherein said signal processing circuit is a differential arithmetic circuit which calculates a difference between a number of pulses of said reference pulse signal in a predetermined time interval and a number of pulses of said measuring pulse signal in said predetermined time interval and provides a value according to said difference as a detected value of said force.
Claim 4
Dependent Claim
47 words
A capacitive sensity device according to claim 1, wherein said signal processing circuit calculates a ratio of a frequency of said reference pulse signal to a frequency of said measuring pulse signal and outputs a value of said ratio as a detected value of a said force.
Claim 5
Dependent Claim
107 words
A capacitive sensity device according to claim 4, wherein a frequency of one of said reference pulse signal and said measuring pulse signal is higher than two times a frequency of the other signal; said signal processing circuit generates a duty ratio signal which has a period equal to a period of a signal with a lower frequency of said two pulse signals and has a high or low level period equal to a period of a signal with a higher frequency of said two pulse signals, and calculates said detected value of said force on the basis of a duty ratio of said duty ratio signal.
Claim 6
Dependent Claim
70 words
A capacitive sensing device according to claim 2, wherein Each of said measuring pulse signal generating circuit and said reference pulse signal generating circuit comprises a constant-current power circuit having a transistor which charges and discharges said sensing capacitor or said reference capacitor between two predetermined voltage levels, and a circuit having a transistor which changes a temperature characteristic of a charging and discharging current according to said input voltage.
Claim 7
Dependent Claim
13 words
A capacitive sensing device according to claim 1, wherein said force is pressure.
Claim 8
Dependent Claim
182 words
A capacitive sensing device according to claim 1, wherein said measuring capacitor comprises: a pressure-sensitive diaphragm formed on a semiconductor substrate and capable of being deformed by pressure applied to said diaphragm, an upper substrate joined to said semiconductor substrate so as to form a sealed reference pressure chamber over said pressure-sensitive diaphragm so that a volume thereof changes when pressure is applied to said diaphragm, a first electrode formed on a surface of said pressure-sensitive diaphragm exposed to said reference pressure chamber, and a second electrode formed on a surface of said upper substrate exposed to said reference pressure chamber; said reference capacitor comprises: a sealed sub-reference pressure chamber formed between a rigid portion of said semiconductor substrate and said upper substrate and having a volume which is not changed by said pressure applied to said pressure-sensitive diaphragm, a first correction electrode formed on a portion of said surface of said semiconductor substrate exposed to said sub-reference pressure chamber, and a second correction electrode formed on a portion of said surface of said upper substrate exposed to said sub-reference pressure chamber.
Claim 9
Dependent Claim
27 words
A capacitive sensing device according to claim 8, wherein said first electrode and said first correction electrode are formed integrally on said surface of said semiconductor substrate.
Claim 10
Dependent Claim
134 words
A capacitive sensing device according to claim 3, wherein said signal processing circuit comprises: a reference clock generating circuit for generating a clock signal, a first counter which receives said clock signal and provides an output signal specifying said time interval in which a number of pulses of said reference pulse signal and a number of pulses of said measuring pulse signal are counted; a switching circuit for alternately passing said reference pulse signal and said measuring pulse signal according to said output signal of said first counter; an up-down counter having an up-terminal for receiving said reference pulse signal through said switching circuit and a down-terminal for receiving said measuring pulse signal through said switching circuit; and a latch circuit which latches a count value of said up-down counter at a predetermined moment.
References Cited (Backward Citations)
No citation records indexed.
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