Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Using a particular bridge circuit
Reexamination Certificate
1999-11-16
2001-12-11
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Using a particular bridge circuit
C073S001880, C073S708000, C073S721000, C374S143000, C324S706000, C324S721000
Reexamination Certificate
active
06329825
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sensing apparatus including a sensing bridge circuit for generating a sensor signal having the voltage level representing a detected physical quantity and a temperature detecting bridge circuit for correcting the temperature characteristics of the sensing bridge circuit.
For example, a conventional pressure sensing apparatus includes a diaphragm and a gauge resistor formed on a semiconductor chip. In this kind of conventional pressure sensing apparatus, the temperature compensation for adjusting the sensitivity or the offset is usually performed through an analog correcting circuit. Numerous operational amplifiers are required. In general, downsizing the operational amplifier is difficult. In other words, the conventional sensing apparatus relying on the operational amplifiers needs to prepare a semiconductor chip having a large chip area, and therefore cannot reduce the overall size.
Furthermore, due to the aging phenomenon which reduces the stress of the protective film covering the chip surface, the offset of each operational amplifier may deviate from its initial value or the pair ratio of resistors associated with each operational amplifier may also deviate from its initial value. In such cases, it is difficult to prevent the circuit constants of each section from variously changing or fluctuating. As a result, the sensing accuracy of the finally obtained pressure value is deteriorated.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a sensing apparatus which is capable of improving the sensing accuracy in this kind of sensing apparatus.
In order to accomplish this and other related objects, the present invention provides a sensing apparatus which comprises a sensing bridge circuit and a temperature detecting bridge circuit. The sensing bridge circuit includes a plurality of resistance elements for generating a sensor signal having the voltage level responsive to a detected physical quantity. The temperature detecting bridge circuit includes at least one temperature-sensing resistance element having a predetermined temperature coefficient and at least one reference resistance element having a temperature coefficient equal to or nearly equal to 0 for generating a temperature signal having the voltage level responsive to a temperature of the sensing bridge circuit. A signal selecting circuit is provided for selectively outputting the sensor signal and the temperature signal. And, an amplification circuit is provided for amplifying the signals successively outputted from the signal selecting circuit.
Furthermore, to improve the sensing accuracy, a variation width of the sensor signal in a physical quantity measuring range of the sensing bridge circuit is substantially equalized in advance with a variation width of the temperature signal in a temperature measuring range of the temperature detecting bridge circuit.
Preferably, the sensing bridge circuit and the temperature detecting bridge circuit are formed on a same semiconductor substrate.
Preferably, the variation width of the sensor signal in the physical quantity measuring range of the sensing bridge circuit is substantially equalized with the variation width of the temperature signal in the temperature measuring range of the temperature detecting bridge circuit by adjusting a design resistance value of at least one reference resistance element.
Preferably, the temperature detecting bridge circuit has at least one trimming resistor to adjust the variation width of the temperature signal produced from the temperature detecting bridge circuit.
Preferably, the sensing apparatus further comprises an A/D conversion circuit which converts the amplified signals of the amplification circuit into digital data corresponding to the sensor signal and the temperature signal. In this case, a signal processing means is provided for performing the digital calculating processing based on the digital data produced from the A/D conversion circuit to calculate the detected physical quantity corresponding to the sensor signal and correct the detected physical quantity in accordance with the temperature signal.
Preferably, the sensing apparatus further comprises 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 bridge circuit. The reference signal is selected by the signal selecting circuit and supplied to the amplification circuit. In this case, the A/D conversion circuit converts the amplified signals of the amplification circuit into digital data corresponding to the sensor signal, the temperature signal and the reference signal. A signal processing means is provided for performing the digital calculating processing based on the digital data produced from the A/D conversion circuit to calculate the detected physical quantity corresponding to the sensor signal and correct the detected physical quantity in accordance with the temperature signal and the reference signal.
Preferably, the A/D conversion 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 a power source voltage. Each of the amplified signals, 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, a zero-crossing point of the sensor signal in the physical quantity measuring range of the sensing bridge circuit is substantially equalized in advance with a zero-crossing point of the temperature signal in the temperature measuring range of the temperature detecting bridge circuit. In this case, the trimming resistor in the temperature detecting bridge circuit is used to adjust the zero-crossing point of the temperature signal produced from the temperature detecting bridge circuit.
Preferably, a power source for supplying electric power to the sensing apparatus is a battery.
Another aspect of the present invention provides a related method for adjusting temperature characteristics of the above sensing apparatus.
Namely, this method comprises the step of substantially equalizing the variation width of the sensor signal in the physical quantity measuring range of the sensing bridge circuit with the variation width of the temperature signal in the temperature measuring range of the temperature detecting bridge circuit.
The adjustment of the variation width of the output signal from the bridge circuit can be done by adequately determining a design resistance value of the at least one reference resistance element. The trimming resistor in the temperature detecting bridge circuit can be also used to adjust the variation width of the output signal from the bridge circuit.
Preferably, this method further comprises the step of substantially equalizing the zero-crossing point of the sensor signal in the physical quantity measuring range of the sensing bridge circuit with the zero-crossing point of the temperature signal in the temperature measuring range of the temperature detecting bridge circuit. The zero-point of the temperature signal produced from the temperature detecting bridge circuit is controlled by trimming at least one trimming resistor provided in the temperature detecting bridge circuit.
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patent:
Tanaka Hiroaki
Toyoda Inao
Denso Corporation
Nguyen Vinh P.
Patel Paresh
Pillsbury & Winthrop LLP
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