KR101455815B1 - Pressure Sensor - Google Patents

Abstract

According to the present invention, disclosed is a temperature sensor. A pressure sensor according to a desirable embodiment of the present invention is formed to have a pressure sensor circuit so that an output value of the pressure sensor can be linearly proportional to the pressure applied to the sensor, using a variable capacitor whose capacitance varies according to pressure. Therefore, the pressure sensor can accurately measure pressure, using an inexpensive variable capacitor without using an expensive resistive element. Also, according to another desirable embodiment of the present invention, the pressure sensor is formed to include a temperature compensation capacitor in order to remove parasitic capacitance which change according to a temperature. Therefore, pressure can be accurately measured when an ambient temperature changes.

Description

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor, and more particularly, to a pressure sensor in which a value is output linearly according to a pressure.

Generally, a pressure sensor includes a sensor for measuring a pressure using a change in capacitance according to a pressure, and a sensor for measuring a pressure by measuring a resistance value varying with a change in pressure.

A sensor for measuring a change in capacitance measures a pressure by measuring a change in capacitance as a distance between both ends of a capacitor changes as a pressure is applied.

의 수식에 따라서, 커패시터 양단의 면적(A)에 비례하고, 앙단간의 간격(d)에 반비례한다. 즉, 커패시터 양단의 면적(A)이 고정된 경우, 양단 간격(d)이 커지면 커패시턴스를 감소하고, 양단 간격(d)이 작아지면 커패시턴스는 커진다.In general, the capacitance of a capacitor is

, It is proportional to the area A at both ends of the capacitor and is inversely proportional to the interval d between the bottom ends. That is, in the case where the area A at both ends of the capacitor is fixed, the capacitance is decreased when the both end d is increased, and when the both ends d are smaller, the capacitance is larger.

On the other hand, as the pressure of the sensor increases, the gap between both ends decreases. When the pressure decreases, the gap between both ends increases. Therefore, the relationship between the pressure and the capacity of the capacitor can be expressed by the following equation (1).

In Equation (1), p represents the amount by which the distance between both ends of the capacitor decreases according to the pressure, and is proportional to the applied pressure.

As can be seen from Equation (1), when the pressure increases, the denominator decreases and the capacitance increases. However, when the pressure decreases, the denominator increases and the capacitance decreases. As a result, it can be determined that the capacitance is directly proportional to the pressure.

However, since the capacitance C is proportional to -1 / (p-d) in Equation (1), the capacitance C is not linearly proportional to the pressure, so that it is not possible to measure the pressure accurately by simply measuring the capacitance.

FIG. 1 shows a graph according to Equation 1. FIG. 1, the change of the capacitance C due to the change of the pressure p is indicated by a solid line, and the capacitance C is proportional to the pressure p but the linearity is severely damaged as shown in Fig. 1, It can be known that measuring the value alone will not yield the correct pressure value.

In addition, parasitic capacitance inevitably occurs in the case of a capacitor circuit, and accurate pressure measurement is impossible when the influence of such a parasitic capacitance is not taken into consideration.

Various schemes have been proposed to compensate for this linearity. U.S. Patent No. 3,869,676 discloses a pressure sensor that couples a variable capacitor to a bridge circuit, the capacitance of which varies with pressure.

However, even in the case of the above-mentioned U.S. patent, it has been confirmed that an error of about 4% or more occurs in the relation between the input voltage and the output voltage according to the pressure change.

As described above, in the case of a pressure sensor using a capacitor, the capacitor itself is simple to implement, but a circuit for compensating for the linearity is complicated. Recently, a resistance element A pressure sensor using a pressure sensor is mainly used.

However, the pressure sensor using such a resistance element has a problem in that the entire circuit configuration is simple, but the production of the resistance element itself is difficult and the cost is increased.

A problem to be solved by the present invention is to provide a pressure sensor that exhibits an output value linearly changing with respect to a pressure change simply without a complicated circuit configuration.

Pressure sensor according to an embodiment of the present invention for solving the above problems, one end connected to the first node and the other end is connected to a first switching gain power by parts (V _gain) or a driving power source (V _DD) A reference capacitor; A variable capacitor having one end connected to the first node and the other end connected to a second node or a bias power supply ( _Vbias ) through a second switching unit, the capacitance of which varies according to the pressure; A linear compensation capacitor having one end connected to the first node and the other end connected to the bias power supply or the third node through a third switching unit; An operational amplifier having a first input terminal connected to the first node, a second input terminal grounded, and an output terminal connected to the second node; And a sample and hold circuit in which an input terminal is connected to a second node through a fourth switching unit and an output terminal is connected to the third node.

The first switching unit may connect the gain power supply to the reference capacitor according to a first switching control signal and the second switching unit may connect the bias power supply to the variable capacitor in accordance with a first switching control signal, 3 switching unit may connect the output of the sample and hold circuit to the linear compensation capacitor in accordance with the first switching control signal.

The pressure sensor according to a preferred embodiment of the present invention may further include a fifth switching unit for connecting the first node and the second node according to the first switching control signal.

The first switching unit couples the gain power supply to the reference capacitor according to a second switching control signal and the second switching unit couples the bias power supply to the variable capacitor in accordance with a second switching control signal, 3 switching unit may connect the output of the sample and hold circuit to the linear compensation capacitor in accordance with a second switching control signal.

The sample-and-hold circuit may further include an operational amplifier having a non-inverting input terminal connected to the second node through the fourth switching section and an inverting input terminal connected to the third node, And a ground capacitor to which the other end is grounded.

, 상기 수학식에서 C_REF는 상기 기준 커패시터의 커패시턴스값이고, 상기 C_LIN은 상기 선형 보상 커패시터의 커패시턴스값이며, 상기 C_VAR 은 압력에 따라서 변화하는 상기 가변 커패시터의 커패시턴스값일 수 있다.Also, the pressure measurement value of the pressure sensor according to the preferred embodiment of the present invention is output as the voltage value (V _O ) of the third node, the output value of the third node is calculated by the following equation,

Where C _REF is a capacitance value of the reference capacitor, C _LIN is a capacitance value of the linear compensation capacitor, and C _VAR is a capacitance value of the variable capacitor varying with a pressure.

The pressure sensor according to the preferred embodiment of the present invention may further include a temperature compensation unit having one end connected to the first node and the other end connected to a gain power supply V _gain or a driving power supply V _DD through a sixth switching unit And may further include a capacitor.

, 상기 수학식에서 C_REF는 상기 기준 커패시터의 커패시턴스값이고, 상기 C_LIN은 상기 선형 보상 커패시터의 커패시턴스값이며, 상기 C_VAR 은 압력에 따라서 변화하는 상기 가변 커패시터의 커패시턴스값이고, 상기 C_TMP 는 온도 보상 커패시터의 커패시턴스값일 수 있다.
Also, in the pressure sensor according to the preferred embodiment of the present invention, the pressure measurement value of the sensor is output as the voltage value (V _O ) of the third node, and the output value of the third node is calculated by the following equation ,

Wherein C _REF is a capacitance value of the reference capacitor, C _LIN is a capacitance value of the linear compensation capacitor, C _VAR is a capacitance value of the variable capacitor varying with a pressure, and C _TMP is a temperature May be the capacitance value of the compensation capacitor.

A pressure sensor according to a preferred embodiment of the present invention uses a variable capacitor whose capacitance varies according to a pressure and constitutes a pressure sensor circuit so that the output value of the pressure sensor is linearly proportional to the pressure applied to the sensor, Accurate pressure measurement is possible by using low cost variable capacitor without device.

In addition, another preferred embodiment of the present invention further comprises a temperature compensating capacitor for eliminating parasitic capacitance which varies with temperature, so that a pressure sensor can be constituted so that accurate pressure measurement is possible even with changes in ambient temperature.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the change in capacitance according to pressure in a pressure sensor of the prior art. Fig.
2 is a circuit diagram showing a configuration of a pressure sensor according to a first preferred embodiment of the present invention.
FIG. 3A is a circuit diagram showing the configuration of the pressure sensor circuit according to the first embodiment of the present invention when the first switching control signal is outputted, and FIG. 3B is a circuit diagram showing the configuration of the pressure sensor circuit according to the present invention 1 is a circuit diagram showing a configuration of a pressure sensor circuit according to an embodiment.
4 is a circuit diagram showing a configuration of a pressure sensor according to a second preferred embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

2 is a circuit diagram of a pressure sensor according to a first preferred embodiment of the present invention.

2, the pressure sensor according to the first preferred embodiment of the present invention includes a reference capacitor 210, a variable capacitor 230, a linear compensation capacitor 220, an operational amplifier 240, and a sample and hold circuit 250).

One end of the reference capacitor 210 (C _REF ) is connected to the first node and the other end is connected to the gain power supply V _gain or the driving power supply V _DD through the first switching unit 271.

One end of variable capacitor 230 (C _VAR) is exposed to the outside, the distance of the capacitor between both ends changes in accordance with the pressure as a capacitor, which capacitance is changed according to the pressure, the variable capacitor 230 is connected to the first node, And the other end is connected to the second node or the bias power supply ( _Vbias ) through the second switching unit 272. [

The linear compensation capacitor 220 (C _LIN ) is a capacitor provided to eliminate the parasitic capacitance of the variable capacitor 230, and its capacitance value is set by the user's setting. In addition, the linear compensation capacitor 220 has one end connected to the first node and the other end connected to the bias power supply or the third node through the third switching unit 273.

The operational amplifier 240 has a first input terminal connected to the first node, a second input terminal grounded, and an output terminal connected to the second node. Here, the first input terminal is an inverting input terminal, and the second input terminal is a non-inverting input terminal.

The sample-and-hold circuit 250 is a circuit for holding an output value for a predetermined time, and includes an operational amplifier 240 and a grounding capacitor 253.

First, in the case of the operational amplifier 251 of the sample-and-hold circuit 250, the second node and the non-inverting input terminal are connected through the fourth switching unit 274, and the ground capacitor 253 are installed.

The inverting input terminal of the operational amplifier 251 of the sample and hold circuit 250 is connected to the output terminal of the operational amplifier 251 and the output terminal of the operational amplifier 251 is connected to the output terminal of the operational amplifier 251 through the third switching unit 273, And the point where the output terminal and the inverting input terminal of the operational amplifier 240 are connected to the linear compensation capacitor 220 constitute the third node.

In addition to the first to third switching units 271 to 274, the fifth switching unit 275, which is provided between the first node and the second node and directly connects the two nodes in the switched ON state, .

Each of the first to third switching units 271 to 273 includes a first switch ck1 and a second switch ck2. The first switch ck1 is connected to the first switching control signal And the second switch ck2 is turned ON only while the second switching control signal is input.

The fourth switching unit 274 is implemented as a second switch ck2 that is turned on only while the second switching control signal is input. The fifth switching unit 275 is implemented only when the first switching control signal is input The first switch ck1 is turned on.

In addition, the first switching control signal and the second switching control signal are alternately outputted at mutually different time intervals with different phases.

Fig. 3A is a circuit diagram showing the configuration of the pressure sensor circuit when the first switching control signal is outputted, and Fig. 3B is a circuit diagram showing the configuration of the pressure sensor circuit when the second switching control signal is outputted. The operation of the pressure sensor according to the first preferred embodiment of the present invention will be described with reference to FIGS. 3A and 3B.

First, referring to FIG. 3A, since the non-inverting terminal of the operational amplifier 240 is grounded, the potential of the first node is set to zero. When the first switching control signal is outputted, the first switch ck1 of the first switching unit 271 is turned on so that the gain power supply is connected to the reference capacitor 210 so that the reference capacitor 210 is charged with the gain power supply, The first switch ck1 of the second switching unit 272 is turned on so that the bias power is connected to the variable capacitor 230 so that the variable capacitor 230 is charged with the bias power.

The first switch ck1 of the third switching unit 273 is turned on so that the linear compensation capacitor 220 is charged to the output power supply V _o of the sample and hold circuit 250, Is turned on and the second node, which is the output terminal of the operational amplifier 240, is connected to the first node connected to the inverting input terminal and is set to zero potential.

In this case, the amount of charge charged in the entire pressure sensor circuit is expressed by Equation 2 below.

On the other hand, when the second switching control signal is outputted, the first switch ck1 of the first switching unit 271 to the third switching unit 273 is opened, the second switch ck2 is turned on, The portion 274 is turned ON, and the pressure sensor circuit is configured as shown in Fig. 3B.

In the circuit shown in FIG. 3B, the second switch ck2 of the first switching unit 271 is turned on, and the driving power is connected to the reference capacitor 210, so that the reference capacitor 210 is charged with the driving power. The second switch ck2 of the second switching unit 272 is turned on and the fourth switching unit 274 is turned on so that the variable capacitor 230 is connected to the second node and the output of the sample and hold circuit 250 Is charged to the voltage (V _O ). In addition, the linear compensation capacitor 220 is charged with a bias power supply.

In this case, the amount of charge charged in the entire pressure sensor circuit is expressed by Equation (3) below.

On the other hand, since the first switching control signal and the second switching control signal described above are alternated in a very short period of time, the charges accumulated in the circuit do not flow out to the outside, and charge transfer occurs to each other inside. Therefore, Q _T1 and Q _T2 are equal to each other (Q _T1 = Q _T2 ). The output voltage V _O can be summarized as Equation (4) below.

Referring to Equation (4), the offset value of the output value V _O of the pressure sensor is adjusted by V _bias .

In addition, CREF and VDD are fixed values, Vgain is a gain value adjustable by the user, and the parasitic capacitance of the variable capacitor 230 is removed by (C _VAR -C _LIN ) Is reflected in the output.

Consequently, as described in Equation (4), the capacitance of the variable capacitor 230, which changes in accordance with the pressure, is proportional to the reciprocal of the pressure applied to the pressure sensor, and the output V _O of the pressure sensor is proportional to the reciprocal of the capacitance Therefore, it can be seen that the output V _O of the pressure sensor is directly proportional to the pressure, and therefore, the pressure sensor according to the first preferred embodiment of the present invention can ensure 100% linearity.

4 is a view showing a pressure sensor according to a second preferred embodiment of the present invention. Referring to FIG. 4, the pressure sensor according to the second embodiment of the present invention further includes a temperature compensation capacitor 260 for correcting not only linear errors but also temperature-dependent errors.

In general, the temperature characteristics of both capacitors are almost the same because the pressure sensor generally manufactures the variable capacitor 230 responsive to the pressure and the reference capacitor 210 not reactive with pressure in the same process. Therefore, if the temperature coefficients of the variable capacitors 230 and the reference capacitor 210 are the same, the following equation (5) is obtained.

Therefore, when the transfer function of the pressure sensor circuit becomes C _REF / C _VAR type as shown in Equation (4), the temperature term is _weakened , and C _REF0 / C _VAR0 remains on the transfer function.

However, as described above, the parasitic capacitance of the variable capacitor 230 can be eliminated by the linear compensation capacitor 220 to compensate for the linearity error, but the parasitic capacitance of the reference capacitor 210 is not removed, .

Accordingly, in the second preferred embodiment of the present invention, the temperature compensating capacitor 260 (C _TMP ) is connected to the first terminal of the variable capacitor 230 as shown in FIG. 4, as the linear compensation capacitor 220 serves to remove the parasitic capacitance of the variable capacitor 230. The parasitic capacitance of the reference capacitor 210 can be removed to realize a complete temperature compensation.

First, one end of the temperature compensating capacitor 260 is connected to the first node, and the other end is connected to the gain power source or the driving power source through the sixth switching unit 276. The sixth switch 276 is turned on in response to the first switching control signal to turn on the first switch ck1 for connecting the driving power to the temperature compensating capacitor 260 and the second switching control signal to turn on the gain power, And a second switch (ck2) for connecting to the capacitor (260).

The method of calculating the total charge amount when the first switching control signal is outputted is calculated in the same manner as the method described with reference to the above-mentioned Equation (2), and expressed as Equation (6) below.

Similarly, the method for calculating the total charge amount when the second switching control signal is output is measured in the same manner as described with reference to Equation (3) and expressed as Equation (7) below.

As in the first embodiment, the first switching control signal and the second switching control signal alternate with each other for a very short period of time, so that the charges accumulated in the circuit do not flow out to the outside, and charge transfer is generated internally. Therefore, Q _T1 and Q _T2 are equal to each other (Q _T1 = Q _T2 ). The output voltage V _O can be summarized as Equation 8 below.

As can be seen from Equation (8), the pressure sensor according to the second preferred embodiment of the present invention is capable of eliminating the influence of the parasitic capacitance of the reference capacitor 210 by the temperature compensating capacitor 260 Therefore, if the temperature coefficients of the reference capacitor 210 and the variable capacitor 230 except for the parasitic capacitance are the same, the temperature characteristic is completely independent of the temperature.

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

210 Reference capacitor (C _REF )
220 Linear compensation capacitor (C _LIN )
230 variable capacitor (C _VAR )
240 operational amplifier
250 sample and hold circuit
251 operational amplifier
253 Grounding capacitors
260 Temperature Compensation Capacitor (C _TMP )
271 to 276 First to sixth switching units

Claims (8)

A reference capacitor having one end connected to the first node and the other end connected to the gain power supply (V _gain ) or the driving power supply (V _DD ) through the first switching unit;
A variable capacitor having one end connected to the first node and the other end connected to a second node or a bias power supply ( _Vbias ) through a second switching unit, the capacitance of which varies according to the pressure;
A linear compensation capacitor having one end connected to the first node and the other end connected to the bias power supply or the third node through a third switching unit;
An operational amplifier having a first input terminal connected to the first node, a second input terminal grounded, and an output terminal connected to the second node; And
And a sample and hold circuit in which an input terminal is connected to a second node through a fourth switching unit and an output terminal is connected to the third node. The method according to claim 1,
In accordance with the first switching control signal,
The first switching unit connects the gain power supply to the reference capacitor,
The second switching unit connects the bias power source to the variable capacitor,
And the third switching unit connects the output of the sample and hold circuit to the linear compensation capacitor. 3. The method of claim 2,
And a fifth switching unit for connecting the first node and the second node according to the first switching control signal. 3. The method of claim 2,
According to the second switching control signal,
The first switching unit connects the gain power supply to the reference capacitor,
The second switching unit connects the bias power source to the variable capacitor,
And the third switching unit connects the output of the sample and hold circuit to the linear compensation capacitor. 2. The circuit of claim 1, wherein the sample and hold circuit
An operational amplifier having a non-inverting input terminal connected to the second node through the fourth switching unit and an inverting input terminal connected to the third node;
And a ground capacitor having one end connected to the non-inverting input terminal and the other end grounded. The method according to claim 1,
The pressure measurement value of the sensor is output as the voltage value (V _O ) of the third node,
The output value of the third node is calculated by the following equation,

Wherein C _REF is a capacitance value of the reference capacitor, C _LIN is a capacitance value of the linear compensation capacitor, and C _VAR is a capacitance value of the variable capacitor varying with a pressure. The method according to claim 1,
And a temperature compensation capacitor having one end connected to the first node and the other end connected to a gain power supply (V _gain ) or a driving power supply (V _DD ) through a sixth switching unit. 8. The method of claim 7,
The pressure measurement value of the sensor is output as the voltage value (V _O ) of the third node,
The output value of the third node is calculated by the following equation,

Wherein C _REF is a capacitance value of the reference capacitor, C _LIN is a capacitance value of the linear compensation capacitor, C _VAR is a capacitance value of the variable capacitor varying with a pressure, and C _TMP is a temperature compensation Wherein the capacitance of the capacitor is a capacitance value of the capacitor.

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