Pressure sensor

Details Pressure sensor Pressure sensor

2001-11-06

2003-12-23

Bui, Bryan (Department: 2863)

Data processing: measuring, calibrating, or testing

Measurement system

Pressure

C702S098000

Reexamination Certificate

active

06668238

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure sensor, and in particular, to one suitable for automotive use or the like.
2. Description of the Related Art
FIG. 11
is a block diagram illustrating an example of the construction of a known semiconductor pressure sensor. An element portion
1
for detecting pressure is, for example, formed on a diaphragm D which is adapted to be deformed by an external force to be measured and acting thereon as shown in
FIG. 12
, and the element portion
1
is comprised of a bridge circuit including semiconductor gauge resistors RA-RD (a resistor RD is arranged at a side opposite a resistor RA) whose resistances change due to distortions thereof caused by the deformation of the diaphragm D. Note that a symbol R
1
designates a temperature characteristic compensation resistor, and a symbol T designates a constant current circuit.
In
FIG. 11
, the known pressure sensor includes the element portion
1
for detecting the above-mentioned pressure, and a circuit portion
2
having a signal processing function. The circuit portion
2
includes a first integrated circuit (IC)
3
and a second integrated circuit (IC)
4
for storing bit data
22
to adjust and compensate for the initial variation and temperature dependency of a bridge circuit output
41
of the element portion
1
. The second IC
4
includes an analog processing section
21
which operates to receive the bridge circuit output
41
of the element portion
1
and generates an analog output corresponding to the pressure applied to the diaphragm D, a characteristic adjustment and compensation section
23
for adjusting and compensating for the initial variation and temperature dependency of the bridge circuit output
41
of the element portion
1
based on the above-mentioned bit data
22
, and an interface section
24
optimized to interface with external wiring.
Now, the operation of the known pressure sensor as illustrated in
FIG. 11
will be described below in detail. When the diaphragm D (see
FIG. 12
) arranged at the element portion
1
receives an external force to be measured and is deformed thereby, the resistances of the semiconductor gauge resistors RA-RD, which are formed on the diaphragm D and whose resistances change in accordance with the distortion of the diaphragm D, change, thus resulting in a change in the output
41
of the bridge circuit comprised of the semiconductor gauge resistors RA-RD illustrated in FIG.
13
. This change is amplified by the analog processing section
21
incorporated in the second IC
4
to provide a desired output SPAN.
The bridge circuit output
41
from the element portion
1
changing in accordance with the pressure applied to the diaphragm D usually varies depending upon individual elements. This is due to differences in the element detection sensitivities of the individual elements. At this time, in order to easily obtain the desired output SPAN for different element detection sensitivities varying in accordance with the individual elements, there is employed a technique or the like for controlling the amount of current supplied to the bridge circuit, as disclosed in Japanese Patent Application Laid-Open No. 9-218118 for instance.
According to this current amount controlling technique, the magnitude of the voltage to be supplied to resistors, which determine the amount of current flowing in the constant current circuit, is changed by giving the voltage in terms of bit data
22
stored in the first IC
3
. The bit data is given via a communications channel
42
to the characteristic adjustment and compensation section
23
, which is incorporated in the second IC
4
for adjusting and compensating for the initial variation and temperature dependency of the bridge circuit output
41
of the element portion
1
.
With the above arrangement, it is possible to compensate for the element detection sensitivities, which change depending on the temperature for instance, by changing the bit data to be used depending on the temperature. The signal thus obtained according to the above operation is output as an analog signal
32
through the interface section
24
optimized to interface with external wiring.
The environments around motor vehicles in recent years have been greatly changed, and hence, system environments such as a surrounding environment of securing the tolerance to electromagnetic waves of very high frequencies, an environment in which sensor signals can be commonly used for various kinds of systems, in particular such a system environment in which sensor signals can be freely read in at timing as required by systems, have come to be demanded even in the field of motor vehicles.
A method of materializing this is a vehicle mounted LAN, and for instance there is a CAN or the like as such a method. This CAN method handles voltage information, which has usually been handled as an analog signal, by digitizing and converting it into a serial signal represented by bits. This has a merit in that there can be easily realized such a system environment in which the tolerance to noise such as electromagnetic waves can be greatly improved, and in which a sensor signal can be freely read in at timing as required by the above-mentioned system.
On the other hand, inexpensive sensors having a minimum function come to be demanded even more than before, and hence there is a problem with these contradictory demands in that the known pressure sensor configuration as illustrated in
FIG. 11
is particularly difficult to adapt to the CAN method. In order to adapt the known sensor to the CAN system, it is at least necessary to add a CAN driver for interfacing with a bus line, a digital processing section for arithmetically processing and controlling a serial signal output in conformance with the CAN requirements, and an encoding section for digitally encoding an analog signal of the sensor. However, there arises another problem that the number of component members to be added for this purpose is not desirable or suitable for achieving miniaturization and cost reduction of the sensor for automotive use.
SUMMARY OF THE INVENTION
The present invention is intended to obviate the problems as referred to above, and has for its object to provide a pressure sensor which has greatly improved tolerance to noise such as electromagnetic waves, is configured such that a system environment is able to be easily selected in which a sensor signal can be freely read in at timing as required by the above-mentioned system, and is able to realize reduction in the size and cost thereof suitable for automotive use.
Bearing the above object in mind, according to one aspect of the present invention, there is provided a pressure sensor including an element portion for detecting pressure and a circuit portion having a signal processing function, both of which are integrally accommodated in the same package. The circuit portion comprises: a first section for performing analog processing of a detection signal from the element portion; a second section for storing bit data for characteristic adjustment and compensation and performing characteristic adjustment and compensation of the detection signal from the element portion based on the bit data; an interface section optimized to interface with external wiring; an A/D conversion section for digitally encoding the analog processed detection signal; and a digital processing section for converting the digitized signal into a desired serial signal.
Preferably, the pressure sensor includes an analog signal output and a digital signal output which are selectable between two output forms inclusive of an analog processed detection signal and a digital processed detection signal.
Preferably, the A/D conversion section and the digital processing section are incorporated in a first IC, whereas the interface section is incorporated in a second IC different from the first IC.
Preferably, the first IC comprises a section for storing the bit data, an A/D conversion section for digitally encoding the anal

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