Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Reexamination Certificate
1999-10-04
2001-10-23
JeanPierre, Peguy (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
C702S006000, C702S130000
Reexamination Certificate
active
06307496
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sensing apparatus including an A/D conversion circuit for converting an analog sensing signal detected by a sensing circuit into digital data and a signal processing circuit for processing the digital data.
The Unexamined Patent Application No. 9-113310 or No. 10-281912 discloses a sensing apparatus comprising a selector for selectively outputting a pressure signal (i.e., sensor signal), a temperature signal, and a reference signal. Furthermore, the sensing apparatus comprises two oscillation circuits for detecting a time difference between two signals for A/D conversion based on the time A/D processing. In this case, the A/D conversion time is determined in accordance with a signal to be A/D converted, while a constant power source voltage is applied to the A/D conversion circuit.
However, according to such a conventional sensing apparatus, the circuit scale is enlarged due to provision of two oscillation circuits which are associated with capacitors and dividers.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a sensing apparatus which is capable of converting an analog sensor signal into digital data without using the oscillation circuits.
In order to accomplish this and other related objects, the present invention provides a first sensing apparatus comprising a sensing circuit for generating a sensor signal having a voltage level responsive to a detected physical quantity, a temperature detecting circuit for generating a temperature signal having a voltage level responsive to a temperature of the sensing circuit, and a reference voltage generating circuit for generating a reference signal having a constant voltage level irrespective of the detected physical quantity and the temperature of the sensing circuit. An analog multiplexer is provided for selectively outputting the sensor signal, the temperature signal, and the reference signal. An amplification means is provided for amplifying a signal successively produced from the analog multiplexer. An A/D conversion circuit receives an amplified signal produced from the amplification means as a power source voltage and converts the amplification signal into digital data as an A/D conversion value during a predetermined time. And, a signal processing means is provided for performing calculations based on the obtained digital data in such a manner that the physical quantity corresponding to the sensor signal is corrected with reference to the temperature signal and the reference signal.
Namely, the first sensing apparatus uses the analog multiplexer for time division processing the sensor signal, the temperature signal, and the reference signal. The digital data corresponding to respective signals are obtained through the common amplification means and the common A/D conversion means, so that the temperature compensation is performed with respect to the sensitivity. The correcting calculation (digital calculation) is performed based on the digital data thus obtained, thereby enabling a reliable physical quantity detection.
The A/D conversion receives the amplified signal produced from the amplification means as a power source voltage and converts the amplified signal into digital data as an A/D conversion value during a predetermined time interval. With this arrangement, the A/D conversion is feasible based on only one signal supplied from the amplification means. There is no necessity of using two oscillation circuits.
According to the first sensing apparatus, it is not necessary to provide numerous operational amplifiers and amplification circuits. The overall size of the circuit can be reduced.
As the common analog circuit (i.e., the analog multiplexer, the amplification means, the A/D conversion circuit) is used to process the sensor signal, the temperature signal, and the reference signal, it becomes possible to cancel the drift components of respective signals derived from the variation of circuit constants in the signal transmitting path. In other words, it becomes possible to eliminate adverse effect of the aging deterioration. The sensing accuracy can be maintained adequately for a long time.
Preferably, the A/D converting circuit includes a ring-gate delay circuit comprising a plurality of inverting circuits connected in a ring pattern and having an inverting operation time varying in accordance with the power source voltage. Each of the sensor signal, the temperature signal, and the reference signal, when serving as the power source voltage of the ring-gate delay circuit, is converted into digital data based on a pulse signal circulation frequency when a pulse signal is entered into the ring-gate delay circuit.
Preferably, the physical quantity to be detected by the sensing circuit is pressure. In this case, the signal processing means is for calculating a pressure P applied to the sensing circuit according to the following equation
P={(T/A−b)×(−e/a)+D/A−f}/{(T/A−b)×c/a+d}
where D, T and A are digital data respectively representing pressure information, temperature information, and reference information converted by the A/D converting circuit, “c” represents a temperature coefficient in the sensitivity of the sensing circuit, “d” represents a room temperature sensitivity of the sensing circuit, “e” represents a temperature coefficient of an offset of a detected pressure value, “f” represents a room temperature offset value of the detected pressure value, “a” represents a temperature coefficient of a detected temperature value, and “b” represents a room temperature offset value of the detected temperature value.
It is preferable that the first sensing apparatus further comprises a power source circuit which is operative to supply a constant voltage to the sensing circuit, the temperature detecting circuit, the reference voltage generating circuit, the analog multiplexer, and the amplification means. And, a control means is provided for stopping an operation of the power source circuit when the A/D converting circuit has completed the operation for converting the sensor signal, the temperature signal, and the reference signal into digital data.
It is also preferable that the first sensing apparatus further comprises a constant voltage power source for maintaining the amplified signal of the amplification means at a predetermined voltage level.
Furthermore, the present invention provides a second sensing apparatus comprising a sensing circuit for generating a sensor signal having a voltage level responsive to a detected physical quantity, a temperature detecting circuit for generating a temperature signal having a voltage level responsive to a temperature of the sensing circuit, and a reference voltage generating circuit for generating a reference signal having a constant voltage level irrespective of the detected physical quantity and the temperature of the sensing circuit. The A/D conversion circuit of the second sensing apparatus includes a ring-gate delay circuit comprising a plurality of inverting circuits connected in a ring pattern and having an inverting operation time varying in accordance with the power source voltage, for converting each of the sensor signal, the temperature signal, and the reference signal, when serving as a power source voltage of the ring-gate delay circuit, into binary data based on a pulse signal circulation frequency when a pulse signal is entered into the ring-gate delay circuit. A signal processing means is provided for performing calculations based on the digital data in such a manner that the physical quantity corresponding to the sensor signal is corrected with reference to the temperature signal and the reference signal. And, a compensating means is provided for compensating the power source voltage applied to the ring-gate delay circuit in the A/D conversion circuit.
The second sensing apparatus is characterized in that the compensating means includes memory means for storing correction voltage data corresponding to offs
Endo Noboru
Ikuta Toshio
Watanabe Takamoto
Denso Corporation
Jean-Pierre Peguy
Jeanglaude Jean Bruner
Pillsbury & Winthrop LLP
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