Electricity: measuring and testing – Testing potential in specific environment
Reexamination Certificate
2001-12-05
2003-12-02
Hirshfeld, Andrew H. (Department: 2854)
Electricity: measuring and testing
Testing potential in specific environment
C324S071100, C324S522000, C324S537000, C324S678000, C324S548000, C340S660000
Reexamination Certificate
active
06657423
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a physical quantity detection device for generating a physical quantity detection signal.
2. Description of the Prior Art
Generally, pressure sensors for vehicles operate with a single power supply of 5 V, and the output range is from 0.5 to 4.5 V. Outside this range within 0 to 5 V, there are error detection ranges from 0 to 0.3 V and from 4.7 to 5V as shown in FIG.
9
.
FIG. 9
is a graphical diagram illustrating an output range and error detection ranges in a prior art pressure sensor. If the pressure sensor generates its output at the error detection range, a diagnostic function provided to a control system for the pressure sensor or the like detects the error only by comparing the detected voltage with reference voltages, i.e., 0.3 V and 4.7 V.
FIGS. 6 and 7
show interconnections when the pressure sensor is used in a vehicle in the prior art pressure sensors. The difference between
FIGS. 6 and 7
is that in
FIG. 6
, a pull-up resistor
108
is provided, on the other hand, in
FIG. 7
, a pull-down resistor
105
is provided. Connector assembly
101
, which includes connectors
100
a
,
100
b
, and
100
c
, and connector assembly
102
provide interconnections between pressure sensor
100
and system control circuit
104
. These interconnections between the pressure sensors
100
and the system control circuits
104
provide disconnection detection.
For example, in
FIG. 7
, the pressure sensor
100
is connected to the system control circuit
104
with a wire cable
103
a
for power supply, a wire cable
103
b
for outputting the detection signal, and a wire cable
103
c
for grounding, wherein the line connected to the output signal wire cable in the system control circuit
104
is connected to the ground through a pull-down resistor
105
. Then, if the wire cable
103
a
or its connector
100
a
or the wire cable
103
b
or its connector
100
b
is disconnected, the detected voltage at the wire cable
103
b
becomes zero volts. If the ground line
103
c
or its connector
100
c
is disconnected, the detected voltage on the wire cable
103
b
becomes higher than 4.7 V due to voltage dividing with the internal resistance of the pressure sensor
100
and the pull-down resistor
105
. A CPU
107
detects this voltage as an error signal through an A/D converter
106
. Then, the CPU
107
judges that there is disconnection between the pressure sensor
100
and the system control circuit
104
.
In the circuit structure shown in
FIG. 6
, the disconnection condition is detected in the similar manner.
FIG. 8
is a schematic circuit diagram of a prior art pressure sensor. This prior art pressure sensor includes resistors Ra, Rb, Rc, and Rd as strain gages which are formed in a diaphragm arranged at a middle of an Si chip. When a pressure on the diaphragm increases, the resistances of the resistors Ra and Rd decreases. On the other hand, resistances of the resistors Rb and Rc increase. Thus, these resistors Ra, Rb, Rc, and Rd form a Wheatstone bridge.
Resistors R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
71
, R
72
, R
81
, R
82
, R
9
, R
10
, R
11
, and R
12
other than the resistors Ra, Rb, Rc, and Rd comprise thin film resistors such as CrSi films of which temperature coefficients of resistance TCRs are almost zero.
The resistors R
1
and R
2
divide the supply voltage Vcc to generate a middle voltage at the junction point between these resistors which is used as a reference voltage for operational amplifiers OP
10
and OP
40
.
The operational amplifier OP
10
and the resistors R
1
, R
2
, and R
5
form a constant current source for driving the Wheatstone bridge. This constant current source keeps the constant current supply irrespective of temperature variation because the temperature coefficient of resistance of the resistor R
5
is almost zero.
The strain gages operate such that if they are driven with a constant current, the sensitivity in pressure is temperature-compensated. That is because the strain gages are formed of p type diffused resistors including impurity at a concentration of about 10
20
cm
−3
. This fact is well known. Moreover, the resistors R
71
, R
72
, R
81
, and R
82
are used for zero point adjustment of the Wheatstone bridge by trimming the resistors R
71
, R
72
, R
81
, and R
82
with laser. The resistor R
6
is connected in parallel with the Wheatstone bridge for fine adjustment of temperature characteristic in sensitivity.
The operational amplifiers OP
20
and OP
30
are provided as voltage follower circuits supplied with the voltages at the junction points of the Wheatstone brides. More specifically, an output of the operational amplifier OP
20
is connected to a transistor T
1
which is connected to a transistor T
2
with Darlington connection. The operational amplifier OP
40
operates as an amplifier and an adder. The gain of the operational amplifier for the pressure signal is R
12
/R
9
. The inverting input of the operational amplifier OP
40
is connected to the supply power V
CC1
through the resistor R
11
, so that zero point of the sensor output V
O1
is adjusted by trimming the resistor R
11
. The resistors R
10
, R
3
, and R
4
are used for temperature compensation of the zero point by trimming the resistor R
3
or the resistor R
4
. Here, the resistor R
10
has a larger resistance than the resistors R
3
and R
4
.
This circuit operates with reference to the above-mentioned reference voltage generated by dividing the supply voltage V
CC1
. Thus, if the supply voltage V
CC1
varies within an allowable range, the output voltage V
O1
varies in proportion to the variation of the supply voltage V
CC1
. More specifically, the supply voltage V
CC1
is commonly used between the A/D converter
106
in the system control circuit
104
and the reference voltage generation portion in the pressure sensor. This suppresses the error in the pressure detection signal (V
O1
) with respect to variation in supply voltages.
FIG. 9
is a graphical drawing of voltage ranges for error detection in the prior art pressure sensor.
FIG. 10
is an interconnection diagram of the prior art pressure sensor for a vehicle. The pressure sensor
110
is connected to the system control circuit
111
through the cables and connectors because the pressure sensor
110
is located remote from the system control circuit
111
. In this interconnection, if a contact resistance in a connector increases, the output voltage may become an intermediate voltage outside the error detection range shown in FIG.
9
.
This condition could not be detected with the pull-down resistor or the pull-up resistor.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a superior physical quantity detection device.
According to the present invention, a first aspect of the present invention provides a physical quantity detection device supplied with a supply voltage from a system control circuit having a function for varying said supply voltage, comprising: a sensor circuit for generating a detection signal corresponding to a physical quantity to be measured; and an output circuit for outputting said detection signal when said supply voltage is within a predetermined voltage range and for generating and outputting a predetermined voltage which is irrespective of said physical quantity when said supply voltage is outside said predetermined voltage range.
According to the present invention, a second aspect of the present invention provides a physical quantity detection device on the basis of the first aspect, wherein said sensor circuit comprises: a bridge circuit for generating said detection signal corresponding to said physical quantity; and wherein said outputting circuit comprising: a voltage follower circuit coupled to said bridge circuit; and control means for controlling an output of said voltage follower circuit such that said voltage follower circuit outputs said detection signal when said supply voltage is within said predetermined voltage range, and said voltage follower circuit generates said
Denso Corporation
Hamdan Wasseem H.
Hirshfeld Andrew H.
Posz & Bethards, PLC
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