JPH02311728A - Pressure-sensor driving circuit - Google Patents

Abstract

PURPOSE:To improve the sensitivity of a pressure sensor even if a power source voltage is low by providing a current setting means which supplies a current that is equal to a current flowing through one strain gage resistor through another strain gage resistor. CONSTITUTION:A current which is supplied to a pressure sensor through a constant current circuit 12 from a power source 11 passes through one strain gage resistor 13. A current which has the same value as that of said current flows through another strain gage resistor 14 by the action of a current setting means 15. Therefore, even if the power source voltage is low, a large current can be made to flow through the resistors 13 and 14 in comparison with a bridge constitution. It is possible to increase the sensitivity of the pressure sensor. Therefore, it is not necessary to connect a high-gain DC amplifier circuit to a rear stage, and the peripheral circuits of the sensor can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a drive circuit for a pressure sensor using, for example, a semiconductor strain gauge.

(Prior Art) For example, a semiconductor pressure sensor has four strain gauge resistors formed on a silicon diaphragm, which are bridge-connected to extract an output voltage proportional to pressure.

Drive methods for this pressure sensor include a constant voltage drive method and a constant current drive method, but the constant current drive method has better temperature characteristics of sensor sensitivity and is generally more commonly used.

FIG. 8 shows an example of a drive circuit for a conventional semiconductor pressure sensor using such a constant current drive method.

In the same figure, 1 is a power supply circuit, 2 is a constant current circuit, 3.4
．． 5.6 are strain gauge resistors. Among these strain gauge resistors, for example, two strain gauge resistors 3.5 increase in resistance value when pressure is applied, and the other two strain gauge resistors 4.6 is configured to decrease. Therefore, in this circuit, when pressure is applied to the diaphragm, the resistance value of each strain gauge resistor changes, and the voltage drop across that strain gauge resistor becomes VOU
Since it differs between T terminals 7a and 7b, the difference is expressed as V
The output voltage for pressure detection is taken out between the OUT terminals 7a and 7b.

However, originally, the change in resistance value of a strain gauge resistor due to pressure is minute, and the output voltage generated between the VOUT terminals is often on the order of several tens of mV at most. Therefore, in reality, the general method of use is to connect a DC amplifier circuit such as an instrumentation amplifier with high gain and excellent performance after this circuit.

Therefore, it is desired to increase the output of the pressure sensor, but to do so, it is necessary to increase the current supplied to the sensor or to increase the resistance value of each strain gauge resistor. Generally, the resistance value of the strain gauge resistor used is determined at the manufacturing stage, so to increase the output, the current supplied to the sensor must be increased.

However, in order to increase the current supplied to the sensor, it is necessary to increase the driving power supply voltage. Further, even when the resistance value of each strain gauge resistor is increased, it is necessary to increase the power supply voltage in order to flow the same current value as before increasing the resistance. However, it is not always easy to increase the power supply voltage due to the relationship with other circuits, cost, etc.

(Problems to be Solved by the Invention) The conventional pressure sensor drive circuit as described above has the following problems. That is, in these drive circuits, when the power supply voltage is low, sufficient current cannot flow through the pressure sensor, resulting in a decrease in sensitivity. Furthermore, a high gain is required for the DC amplifier circuit connected to the subsequent stage. High gain DC amplifier circuits generally tend to have poor characteristics, making it difficult to adjust the temperature characteristics, offset characteristics, etc. of the DC amplifier circuit. Alternatively, a highly accurate DC amplifier circuit may be used, but these are generally expensive.

The present invention has been made in view of the above-mentioned circumstances.
We have developed a pressure sensor drive circuit that can increase the sensitivity of the pressure sensor even when the gl' pressure is low, does not require a high-gain DC amplifier circuit in the subsequent stage, and can simplify the sensor peripheral circuit. The purpose is to provide.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the first invention provides a diaphragm that is formed on a diaphragm and whose resistance values have opposite change characteristics with respect to the detected pressure. and a pressure sensor drive circuit for driving the other strain gauge resistor, comprising current setting means for supplying a current equal to the current flowing through the one strain gauge resistor to the other strain gauge resistor. This is the summary.

The second invention also provides a first and second strain gauge resistor, each comprising a pair of strain gauge resistors formed on a diaphragm and having resistance values that change in reverse to each other with respect to the detected pressure.
A drive circuit for a pressure sensor that drives a second pair of strain gauge resistors, wherein a current proportional to a current flowing through one strain gauge resistor in the first pair of strain gauge resistors is supplied to the second strain gauge resistor. A first current setting means that supplies the other strain gauge resistor in the pair of gauge resistors, and a current that is proportional to the current flowing through the other strain gauge resistor in the first pair of strain gauge resistors at the same ratio as the constant ratio. a second strain gauge resistor supplied to one strain gauge resistor in the second strain gauge resistor pair;
The gist is that the current setting means is provided.

(Function) In the first invention, the current setting means can be constituted by, for example, a current mirror circuit that functions as an active load, and the voltage drop thereof is extremely low compared to the voltage drop occurring in the strain gauge resistor. Therefore, even when the power supply voltage is low, a larger current can be passed through one strain gauge resistor and the other strain gauge resistor than in the conventional bridge configuration, making it possible to increase the sensitivity of the pressure sensor. Therefore, it is not necessary to connect a high-gain DC amplifier circuit at the subsequent stage, and the sensor peripheral circuit can be simplified.

Further, the second invention is similar to the first invention, even when the power supply voltage is low, a larger current can be caused to flow through the first and second strain gauge resistor pair compared to the conventional bridge configuration. At the same time, the change in resistance value of one and the other strain gauge resistors in the first strain gauge resistor pair with respect to the detected pressure, and the detected pressure of one and the other strain gauge resistors in the second strain gauge resistor pair. The change in resistance value acts synergistically to further increase the sensitivity of the pressure sensor. Furthermore, in this invention, a current full of the power supply voltage is passed through the second pair of strain gauge resistors on the output side, and a current that is lower by a certain ratio than this is passed through the first pair of strain gauge resistors on the non-output side. This makes it possible to reduce the power consumption of the entire drive circuit even though the sensitivity is further increased as described above.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention.

In the figure, 11 is a power supply, 12 is a constant current circuit, 13.
Reference numeral 14 denotes one and the other strain gauge resistors formed on a diaphragm (not shown), and the strain gauge resistors 13 and 14 are constructed so that their resistance values change in opposite ways with respect to the pressure to be detected. ing. 15 is a current mirror circuit, and this current mirror circuit 15 constitutes a current setting means for supplying a current equal to the current flowing through one strain gauge resistor 13 to the other strain gauge resistor. 16a and 16b are VOUT terminals for taking out the sensor output.

Since the pressure sensor drive circuit of this embodiment is configured as described above, the current supplied from the power supply 11 to the pressure sensor via the constant current circuit 12 is transmitted through one strain gauge resistor 1.
3, and the other 1 by the action of the current mirror circuit 15.
A current of the same value flows through the real strain gauge resistor 14 as well.

In contrast, in the conventional example shown in FIG. 8, the current supplied to the bridge-configured pressure sensor flows from the power source through two strain gauge resistors, respectively, and to GND.

The voltage drop due to the current mirror circuit that functions as an active load is as low as Vf (0.6 to 0.7), so when the same current as in the conventional example with a bridge configuration is passed, the voltage drop in this example In this case, there is more margin in the power supply voltage than in the conventional example. Therefore, even if the power supply voltage is lowered by this margin, the sensitivity of this embodiment is equivalent to that of the bridge configuration. Furthermore, since the sensor itself is driven with a constant current, the sensitivity of the sensor can be the same as when driven with a constant current in a bridge configuration.

The superiority of this embodiment over the conventional example will be further explained using equations and FIG. 2.

Regarding the method of this embodiment and the method of the conventional example, the current flowing through the strain gauge resistor, the power supply voltage VsI of the method of this embodiment and the power supply voltage Vs2 of the conventional method, which are required at that time.
The relationships between the two are expressed by the following equations (1) and (2), respectively.

Vsl-1-R+ (2X0.6) -<1)
V s2 =2 ・IR+0. 6-(
2) Here, R is the value of the strain gauge resistance, and the voltage drop due to the constant current circuit and current mirror circuit was 0.6V. From the above equations (1) and (2), it can be seen that when trying to increase the drive current l, the power supply voltage can be increased by about half in the system of this embodiment compared to the conventional system.

FIG. 2 is a bluff showing these, where the turret axis represents the drive current and the vertical axis represents the power supply voltage required at that time.

Note that this graph assumes that the strain gauge resistance is IKΩ. From this graph, it can be seen that when driven with Sri and W pressures of 5V, the product of this example shown by the a characteristic line is b
Since it is possible to flow approximately 1.7 times as much current as in the conventional example shown by the characteristic line, the sensitivity of the sensor is also approximately 1.7 times as large.

Next, FIGS. 3 and 4 show a second embodiment of the present invention.

In FIG. 3, 21 is a power supply, 22 is a constant current circuit, and 23
．． 24.25.26 are strain gauge resistors, 23 and 25
The resistance change of one of the strain gauge resistors 24 and 26 is formed to have the same characteristic with respect to the detected pressure, and the resistance change of the other strain gauge resistor 24 and 26 has an opposite change characteristic. One strain gauge resistor 23 and the other strain gauge resistor 2
4 constitute a first strain gauge resistor pair, and similarly, one strain gauge resistor 25 and the other strain gauge resistor 26 constitute a second strain gauge resistor pair. And 23 and 26
A first current mirror circuit 27 is connected to one set of strain gauge resistors 24 and 25, and a second current mirror circuit 28 is connected to another set of strain gauge resistors 24 and 25. Current setting means for supplying, by the first current mirror circuit 27, a current equal to the current flowing through one strain gauge resistor 23 in the first strain gauge resistor pair to the other strain gauge resistor 26 in the second strain gauge resistor pair. is configured, and the second current mirror circuit 28 supplies a current equal to the current flowing through the other strain gauge resistor 24 in the first strain gauge resistor pair to one strain gauge resistor 25 in the second strain gauge resistor pair. A current setting means is configured.

29a and 29b are VOUT terminals for taking out the sensor output.

It is clear that the pressure sensor drive circuit of this embodiment, like that of the first embodiment, can obtain sensitivity equivalent to that of the bridge configuration even when the power supply voltage is lowered. Furthermore, in this embodiment, the change in resistance value of the two strain gauge resistors 23, 24 in the first strain gauge resistor pair with respect to the detected pressure, and the change in the resistance value of the two strain gauge resistors 25, 24 in the second strain gauge resistor pair. .26 The detection output synergistically acted on by the change in resistance value with respect to the detected pressure is -VO
Since it is taken out from the UT terminals 29a and 29b, it is possible to drive with higher sensitivity than in the first embodiment.

FIG. 4 shows a specific example of the configuration of the circuit shown in FIG.

In FIG. 4, 31 is an operational amplifier, 32 and 34 are resistors, 33 is a transistor, and VS is a reference voltage supply terminal, which constitute the constant current circuit 22.

Further, the first current mirror circuit 27 is configured by two transistors 35 and 38, and the other two transistors 35 and 38 constitute a first current mirror circuit 27.
6.37 constitutes a second current mirror circuit.

5 and 6 show a third embodiment of the present invention.

In addition, in FIGS. 5 and 6, the above-mentioned FIGS.
Components that are the same as or equivalent to equipment, circuit elements, etc. in the figures are indicated by the same reference numerals as above, and redundant explanation will be omitted.

In this embodiment, a resistor 39 is connected to the emitter of the primary transistor 35 in the first current mirror circuit 41, and a resistor with the same resistance value as the resistor 39 is connected to the emitter of the primary transistor 36 in the second current mirror circuit 42. 40 are connected. These resistances are 39.40
Therefore, in the first and second current mirror circuits 41.42, a current proportional to the current flowing to the negative side (transistor 35.36 side) at a constant ratio flows to the secondary side (transistor 35.36 side).
7.38 side).

Then, the first current mirror circuit 41 transfers a current proportional to the current flowing through one strain gauge resistor 23 in the first strain gauge resistor pair at a constant ratio to the other strain gauge resistor in the second strain gauge resistor pair. 26, and the second current mirror circuit 42 sets the current flowing through the other strain gauge resistor 24 in the first strain gauge resistor pair at the same ratio as the above-mentioned constant ratio. A second current setting means is configured to supply a current proportional to , to one strain gauge resistor 25 in the second strain gauge resistor pair.

In this embodiment, with the above configuration, the second strain gauge resistor pair 25 on the side from which the pressure of the pressure sensor is taken out
．． A current full of the power supply voltage is passed through 26, and the first strain gauge resistor pair 23.2 is connected to the side from which the output of the pressure sensor is not taken out.
4, it is possible to keep the total current consumption of the drive circuit small by flowing a current at a level lower by a certain ratio than this.

FIG. 7 shows the relationship between this drive current and power consumption, and the first and second current mirror circuits 41 and 42 provide
The characteristic when the ratio of the current flowing through the first strain gauge resistor pair 23.24 side and the current flowing through the second strain gauge resistor pair 25.26 side is set to 1=5 is shown by the C characteristic line. The characteristic as a comparative example when the same current ratio is set is shown by the d characteristic line. From both the c and d characteristic lines, the pressure sensor drive circuit of this embodiment can reduce current consumption by approximately 40% while maintaining high sensitivity.

In this embodiment, the setting of the current ratio consisting of a constant ratio in the first and second current mirror circuits 41.42 is performed by connecting both current mirror circuits 41.42 instead of connecting the resistor 39.40. Each transistor 3 in
This is possible by connecting other transistors in parallel to each of 7.38 and 7.38.

The pressure sensor drive circuit of each of the embodiments described above has a structure in which the sensor peripheral circuit is also integrated on the same chip, so that an increase in the number of elements has almost no effect, and the peripheral circuit is 5V.
Since there is a high possibility of driving with a voltage as low as 100%, each embodiment method has a large effect on improving sensitivity.

Furthermore, it is clear that similar actions and effects can be obtained even in a configuration in which the current mirror circuit is replaced with the power supply side and the pressure sensor is replaced with the GND side in the first to third embodiments.

[Effects of the Invention] As explained above, according to the first invention, the current setting means can use, for example, a current mirror circuit that functions as an active load, and the voltage drop is equal to the voltage drop occurring in the strain gauge resistance. can be made extremely low compared to Therefore, even when the power supply voltage is low, a larger current can be passed through the strain gauge resistors on one side and the other side than in the conventional bridge configuration, and the sensitivity of the pressure sensor can be increased. Therefore, it is not necessary to connect a high-gain DC amplifier circuit at the subsequent stage, and the sensor peripheral circuit can be simplified.

Further, according to the second invention, in addition to the effects of the first invention, a change in resistance value of one and the other strain gauge resistors in the first strain gauge resistor pair with respect to the detected pressure;
Changes in resistance values of one and the other strain gauge resistors in the second strain gauge resistor pair with respect to the detected pressure act synergistically to further increase the sensitivity of the pressure sensor. Also, a current full of the power supply voltage is passed through the second pair of strain gauge resistors on the output side, and a current at a level lower than this by a certain ratio is passed through the first pair of strain gauge resistors on the non-output side. This makes it possible to reduce the power consumption of the entire drive circuit even though the sensitivity is further increased.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the pressure sensor drive circuit according to the present invention, and FIG. 2 shows the relationship between the drive current and the necessary drive voltage in the first embodiment, together with a comparative example. 3 is a circuit diagram showing the second embodiment of the present invention, FIG. 4 is a circuit diagram showing the circuit configuration of the second embodiment in more detail, and FIG. 5 is a circuit diagram showing the third embodiment of the present invention. A circuit diagram showing an example, FIG. 6 is a circuit diagram showing the circuit configuration of the third embodiment of the same as above in more detail, and FIG. 7 shows the relationship between drive current and power consumption in the third embodiment of the same as above, together with a comparative example. Characteristic diagram, No. 8
The figure is a circuit diagram showing a drive circuit for a conventional semiconductor pressure sensor. 13.23.25 One strain gauge resistor, 14.24.
26: Other strain gauge resistor, 15: Current mirror circuit (current setting means), 41: First current mirror circuit (
42: second current mirror circuit (second current setting means). Eight Rijinfu! :±Hidekazu Miyoshi Figure 1 Dawn 11 Power 1 Threat Direct Current [llAkoWIJ2 ri! J Figure 3

Claims (2)

[Claims] (1) A drive circuit for a pressure sensor that drives one strain gauge resistor and the other strain gauge resistor formed on a diaphragm and whose resistance values have opposite change characteristics with respect to the detected pressure, wherein the one strain gauge resistor A drive circuit for a pressure sensor, comprising current setting means for supplying a current equal to the flowing current to the other strain gauge resistor. (2) Driving a first and second strain gauge resistor pair formed on a diaphragm and each having one and the other pair of strain gauge resistors whose resistance values change in opposite ways with respect to the detected pressure. A drive circuit for a pressure sensor, wherein a current proportional to a current flowing through one strain gauge resistor in the first pair of strain gauge resistors is passed through the other strain gauge resistor in the second pair of strain gauge resistors at a constant ratio. and a first current setting means for supplying a current to the second strain gauge resistor pair, which is proportional to the current flowing through the other strain gauge resistor in the first strain gauge resistor pair at the same ratio as the constant ratio. 1. A drive circuit for a pressure sensor, comprising: second current setting means for supplying one of the strain gauge resistors.