Capacitive sensing device

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,
• wherein said signal processing circuit is a differential arithmetic circuit including an up-down counter, which circuit calculates a difference between a number of pulses of said reference pulse signal delivered to said up-down counter in a predetermined time interval and a number of pulses of said measuring pulse signal delivered to said up-down counter in said predetermined time interval and provides a value according to said difference as a detected value of said force.

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,
• wherein said measuring capacitor comprises:
• a pressure-sensitive diaphragm formed on a semiconductor substrate and capable of being deformed by pressured applied to said diaphragm,
• an upper substrate joined to said semiconductor substrate so as to form a first mating surfaces together with said pressure-sensitive diaphragm so that the interval between said first mating surfaces changes when pressure is applied to said diaphragm,
• a first electrode formed on said first mating surface of said pressure-sensitive diaphragm, and
• a second electrode formed on said first mating surface of said upper substrate;
• and wherein said reference capacitor comprises:
• second mating surfaces formed respectively on a rigid portion of said semiconductor substrate and said upper substrate and having an interval therebetween which is not changed by said pressure applied to said pressure-sensitive diaphragm,
• a first correction electrode formed on said second mating surface of said semiconductor substrate, and
• a second correction electrode formed on said second mating surface of said upper substrate.

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,
• wherein said signal processing circuit comprises means for calculating 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.