Capacitive pressure sensor with a symmetrical bridge circuit

Abstract

The invention relates to a capacitive pressure sensor (10) for capacitively measuring an ambient pressure in a sensor environment (22), comprising a sensor unit (12) with an electrical bridge circuit (18) to which an electrical first input potential (D1) and an electrical second input potential (D2) are applied and from which at least one electrical output potential (S) can be tapped off and which has at least one first measurement capacitance (M1), which can be changed depending on the ambient pressure, between a first electrode (24) and a first counter electrode (26), at least one first reference capacitance (R1), which cannot be changed with respect to the ambient pressure, between a first reference electrode (28) and a first reference counter electrode (30), a first input connection (34) which is at the first input potential (D1), a second input connection (36) which is at the second input potential (D2) and an output connection (38) which is at the output potential (S), the bridge circuit (18) being of symmetrical design at least with respect to a surface of the sensor unit (12) about an axis of symmetry (46) running through the output connection (38).

Description

[0001] Description

[0002] title

[0003] The invention relates to a capacitive pressure sensor according to the preamble of claim 1.

[0004] State of the art

[0005] DE 10 2020 214 757 A1 describes a capacitive pressure sensor comprising a diaphragm adjacent to a gas-tight internal volume within a housing component of the pressure sensor. The diaphragm can deform when there is a pressure difference between the internal and external pressures. A measuring electrode is attached to the diaphragm, the position of which changes due to the diaphragm's warping. This change in position leads to a change in the measuring capacitance, which consists of the measuring electrode and an associated measuring counter electrode. In addition, the sensor comprises at least one fixed reference capacitance with two reference electrodes that are firmly attached to the housing component and whose position does not change due to the diaphragm's warping.

[0006] Disclosure of the invention

[0007] According to the present invention, a capacitive pressure sensor with the features of claim 1 is proposed. This allows the impact of environmental influences on the detection of the ambient pressure to be reduced. The electrical influences resulting from the environmental influences can be passively compensated. Active compensation can be eliminated. The pressure sensor can be designed to be more robust against environmental influences. The pressure sensor can be an absolute pressure sensor, in particular a barometric pressure sensor, or a differential pressure sensor. The pressure sensor can be a microelectromechanical (MEMS) sensor.

[0008] The ambient pressure can be a fluid pressure, in particular a water pressure and / or air pressure, in the sensor's environment. The ambient pressure can be a sound pressure, which allows the pressure sensor to act as a microphone.

[0009] The sensor unit can comprise a sensor element. The first measuring capacitance and the first reference capacitance can be formed on the sensor element. The sensor unit can comprise an evaluation unit, in particular embodied as an ASIC. The sensor element can be arranged on the evaluation unit.

[0010] The sensor unit can be at least partially, in particular completely, covered by a protective layer, in particular a gel layer. This can increase the media robustness of the pressure sensor. The protective layer can be excluded with respect to the symmetry of the bridge circuit structure. The surface of the sensor unit can be formed by the surface of the sensor element and / or the evaluation unit. The protective layer can be applied to this surface.

[0011] The superficially symmetrical structure of the bridge circuit can be independent of designs of the bridge circuit below the surface, which can be asymmetrical with respect to the axis of symmetry. The bridge circuit can also be constructed symmetrically around the axis of symmetry below the surface of the sensor unit. The bridge circuit as a whole, i.e., on the surface of the sensor unit and as an embedded structure within the sensor unit, can be symmetrical around the axis of symmetry.

[0012] The symmetry in the design of the bridge circuit can relate to, and in particular be limited to, the electrically effective areas of the bridge circuit. For example, mechanical structures that are electrically insignificant can be designed asymmetrically. The axis of symmetry can run centrally through the output terminal, whereby the output terminal is also symmetrical with respect to the axis of symmetry. The axis of symmetry can run centrally or off-center with respect to the width of the sensor unit.

[0013] In a preferred embodiment of the invention, it is advantageous if the specificity of the input potential with respect to symmetry is irrelevant. The specificity of the input potential refers to the assignment from the first, second, or a further input potential. For example, the second input terminal can form the counterpart to the first input terminal with respect to the axis of symmetry.

[0014] The first input potential is preferably symmetrical to the second input potential with respect to an average of the first and second input potentials. The average may be zero. The first input potential may be sign-complementary to the second input potential.

[0015] In a preferred embodiment of the invention, it is advantageous if the function of the capacitances is irrelevant with regard to the symmetry. The function of the capacitances can relate to whether the capacitance is variable or fixed. In a specific embodiment of the invention, it is advantageous if the first measuring capacitance is arranged on one side of the axis of symmetry and the first reference capacitance, as a counterpart to the first measuring capacitance, is arranged on the other side of the axis of symmetry with regard to the axis of symmetry. The mechanical structure of the capacitances can be irrelevant with regard to the symmetry. The mechanical structure of the first measuring capacitance, for example with the deflectable first electrode, can differ from the mechanical structure of the first reference capacitance, for example with the rigid first reference electrode.The dimensions of the capacitances, which particularly influence the electrical function, can be the same to maintain symmetry around the symmetry axis.

[0016] In a specific embodiment of the invention, it is advantageous if the first input terminal is arranged on one side of the axis of symmetry and the second input terminal is arranged as a counterpart to the first input terminal with respect to the axis of symmetry on the other side of the axis of symmetry.

[0017] A preferred embodiment of the invention is advantageous in that the ambient pressure can be measured as a function of an electrical charge at the output terminal caused by at least one potential jump at the first and / or second input terminal via the first measuring capacitance and the first reference capacitance. A first potential jump at the first input terminal can be connected to a second potential jump of the same sign at the second input terminal.

[0018] The magnitude of the first and second potential jump can be the same.

[0019] In a specific embodiment of the invention, it is advantageous if the at least superficial structure of the bridge circuit, which is relevant for symmetry, comprises the design, arrangement, and connections of the first input terminal, the second input terminal, and the first output terminal and / or the first measuring capacitance and / or the first reference capacitance. However, the terminals corresponding to one another with respect to the axis of symmetry can also be identical with regard to the embedded structures, for example, the vias, the layer structure, and / or the material.

[0020] In a preferred embodiment of the invention, the bridge circuit comprises at least a second measuring capacitance between a second electrode and a second counter electrode, and a second reference capacitance between a second reference electrode and a second reference counter electrode. The second measuring capacitance can be electrically connected in series with the second reference capacitance. The first measuring capacitance and the first reference capacitance can be electrically connected in parallel with the second measuring capacitance and the second reference capacitance. The first measuring capacitance, the first reference capacitance, the second measuring capacitance, and the second reference capacitance can form a Wheatstone measuring bridge circuit.

[0021] In an advantageous embodiment of the invention, the bridge circuit comprises at least a third measuring capacitance between a third electrode and a third counter electrode, and a third reference capacitance between a third reference electrode and a third reference counter electrode. The third measuring capacitance can be electrically connected in series with the third reference capacitance. A third input potential can be applied to the third electrode, and a fourth input potential can be applied to the third reference electrode.

[0022] In a specific embodiment of the invention, it is advantageous if the first measuring capacitance and the second measuring capacitance are configured to measure the ambient pressure in a first pressure range, and the third measuring capacitance is configured to measure the ambient pressure in a second pressure range. The first measuring capacitance, the second measuring capacitance, the first reference capacitance, and the second reference capacitance can be electrically independent of the third measuring capacitance and the third reference capacitance. The first and second pressure ranges can at least partially overlap. The first pressure range can be above or below the second pressure range.

[0023] Further advantages and advantageous embodiments of the invention emerge from the description of the figures and the illustrations.

[0024] Character description

[0025] The invention is described in detail below with reference to the figures. They show in detail:

[0026] Figure 1: A plan view of a pressure sensor in a specific embodiment of the invention.

[0027] Figure 2: A circuit diagram of a bridge circuit of the pressure sensor from Figure 1.

[0028] Figure 3: A plan view of a pressure sensor in another specific embodiment of the invention.

[0029] Figure 4: A circuit diagram of a bridge circuit of the pressure sensor from Figure 3. Figure 5: A plan view of a pressure sensor in another specific embodiment of the invention.

[0030] Figure 6: A circuit diagram of a bridge circuit of the pressure sensor from Figure 5.

[0031] Figure 1 shows a top view of a pressure sensor in a specific embodiment of the invention. The pressure sensor 10 comprises a sensor unit 12 with a sensor element 14 and an evaluation unit 16, on which the sensor element 14 is arranged, and an electrical bridge circuit 18, to which a first electrical input potential D1 and a second electrical input potential D2 are applied and to which at least one electrical output potential S can be tapped. The bridge circuit 18 comprises a first measuring capacitance M1, which varies depending on an ambient pressure in a sensor environment 22 of the sensor unit 12, between a first electrode 24 and a first counter electrode 26, and a first reference capacitance R1, which is constant with respect to the ambient pressure, between a first reference electrode 28 and a first reference counter electrode 30.The sensor element 14 comprises a membrane 32 facing the sensor environment 22 and arranged on a surface 20 of the sensor unit 12, and deflectable depending on the ambient pressure. The first electrode 24 is deflectably connected to the membrane 32. As a result, a distance between the first electrode 24 and the first counter electrode 26, and thus the first measuring capacitance M1, depends on the deflection of the membrane 32 and consequently on the ambient pressure.

[0032] The first electrode 24 is arranged facing the sensor environment 22, and the first counter electrode 26 is arranged opposite it and facing away from the sensor environment 22. The first reference electrode 28 is arranged facing the sensor environment 22, and the first reference counter electrode 30 is arranged opposite it and facing away from the sensor environment 22.

[0033] Furthermore, a first input terminal 34 having the first input potential D1, a second input terminal 36 having the second input potential D2, and an output terminal 38 having the output potential S are arranged. The first input terminal 34 comprises a first connection area A1 on the evaluation unit 16 and a second connection area A2 on the sensor element 14, as well as a bonding wire 40 electrically connecting the first and second connection areas A1, A2 to one another. The second input terminal 36 comprises a third connection area A3 on the evaluation unit 16 and a fourth connection area A4 on the sensor element 14, as well as a bonding wire 40 electrically connecting the third and fourth connection areas A3, A4 to one another.The output connection 38 comprises a fifth connection area A5 on the evaluation unit 16 and a sixth connection area A6 on the sensor element 14, as well as a bonding wire 40 electrically connecting the fifth and sixth connection areas A5, A6 to one another. The bridge circuit 18 further comprises a first ground connection 42 with a seventh connection area A7 on the evaluation unit 16 and an eighth connection area A8 on the sensor element 14, as well as a bonding wire 40 electrically connecting the seventh and eighth connection areas A7, A8 to one another. The bridge circuit 18 further comprises a second ground connection 44 with a ninth connection area A9 on the evaluation unit 16 and a tenth connection area A10 on the sensor element 14, as well as a bonding wire 40 electrically connecting the ninth and tenth connection areas A9, A10 to one another.

[0034] The first electrode 24 is electrically connected to the first input terminal 34, and the first input potential D1 is applied to the first electrode 24. The first counter electrode 26 is electrically connected to the output terminal 38, and the output potential S is applied to the first counter electrode 26. The first reference electrode 28 is connected to the second input terminal 36, and the second input potential D2 is applied to the first reference electrode 28. The first reference counter electrode 30 is connected to the output terminal 38, and the output potential S is applied to the first reference counter electrode 30. Accordingly, the first electrode 24 is electrically directly connected to the first input terminal 34, the first counter electrode 26 is electrically directly connected to the output terminal 38, the first reference electrode 28 is electrically directly connected to the second input terminal 36, and the first reference electrode 28 is electrically directly connected to the output terminal 38.The bridge circuit 18 is constructed symmetrically about an axis of symmetry 46 running through the output terminal 38. The axis of symmetry 46 runs in particular centrally through the output terminal 38, as a result of which the output terminal 38 is also symmetrical with respect to the axis of symmetry 46. The specificity of the input potential D1, D2 and the function of the capacitances M1, R1 with respect to the symmetry are irrelevant. This means that the first measuring capacitance M1 is arranged on one side of the axis of symmetry 46 and the first reference capacitance R1 is arranged on the other side of the axis of symmetry 46 as a counterpart to the first measuring capacitance M1 with respect to the axis of symmetry 46. Furthermore, the first input terminal 34 is arranged on one side of the axis of symmetry 46 and the second input terminal 36 is arranged on the other side of the axis of symmetry 46 as a counterpart to the first input terminal 34 with respect to the axis of symmetry 46.

[0035] The structure of the bridge circuit 18 which is important for the symmetry comprises the design, the arrangement and the connections of the first input terminal 34, the second input terminal 36 and the first output terminal 38. This means in particular that for two corresponding terminals 34, 36, 38 the dimensions of the connection areas opposite one another with respect to the axis of symmetry 46 are the same, the distance to the axis of symmetry 46 is the same and the bond wires 40 are each arranged the same.

[0036] Figure 2 shows a circuit diagram of a bridge circuit of the pressure sensor from Figure 1. The bridge circuit 18 with the first measuring capacitance M1 and the first reference capacitance R1 comprises the first input terminal 34, to which the first input potential D1 is applied and which is electrically connected to the first electrode 24, the second input terminal 36, to which the second input potential D2 is applied and which is electrically connected to the first reference electrode 28, and the output terminal 38, which is electrically connected to the first counter electrode 26 and the first reference counter electrode 30. The first measuring capacitance M1 and the first reference capacitance R1 are electrically connected in series.

[0037] A first stray capacitance K1 and a first parasitic resistance P1 are connected in parallel to the first measuring capacitance M1. A second stray capacitance K2 and a second parasitic resistance P2 are connected in parallel to the first reference capacitance R1. The ambient pressure at the pressure sensor can be measured via the first measuring capacitance M1 as a function of an electrical charge q at the output terminal 38. The electrical charge q is determined by at least one first potential jump 48, in particular from 0 to V d at the first input terminal 34 and a sign-complementary second potential jump 50, in particular from 0 to —V dat the second input terminal 36 via the first measuring capacitance M1 and the first reference capacitance R1. The charge q at the output terminal 38 is thus dependent on the variable first measuring capacitance M1 and thus on the ambient pressure, omitting the stray capacitances K1, K2 and the parasitic resistances P1, P2, for example according to the relationship q = (M1 - RI) • Vd

[0038] Taking into account the first and second stray capacitance K1 , K2 and the first and second parasitic resistance P1 , P2 , the relationship

[0039] Due to the symmetrical design of the bridge circuit 18, the first and second stray capacitances K1, K2 are equal in magnitude, and the first and second parasitic resistances P1, P2 are equal in magnitude. The first and second stray capacitances K1, K2 and the first and second parasitic resistances P1, P2 thus compensate each other with respect to their influence on the charge q.

[0040] Figure 3 shows a plan view of a pressure sensor in a further specific embodiment of the invention. The pressure sensor 10 is similar to that in Figure 1 except for the following differences. The bridge circuit 18 further comprises a second measuring capacitance M2 between a second electrode 52 and a second counter electrode 54 and a second reference capacitance R2 between a second reference electrode 56 and a second reference counter electrode 58. The first counter electrode 26 is connected to a first output terminal 38, which has a first output potential S1, and the first reference counter electrode 30 is also connected to the first output terminal 38. However, the first output terminal 38 is divided into connection regions 60 arranged symmetrically about the axis of symmetry 46. The axis of symmetry 46 runs through a second output terminal 62, to which a second output potential S2 is applied.The second output terminal 62 is electrically connected to the second counter electrode 54 and the second reference counter electrode 58.

[0041] The first electrode 24 and the second reference electrode 56 are electrically connected to each other and to the first input terminal 34. The second electrode 52 and the first reference electrode 28 are electrically connected to each other and to the second input terminal 36.

[0042] Figure 4 shows a circuit diagram of a bridge circuit of the pressure sensor from Figure 3. The bridge circuit 18 is similar to that in Figure 2 except for the following additions. The first measuring capacitance M1 and the first reference capacitance R1 are electrically connected in series, and the second measuring capacitance M2 and the second reference capacitance R2 are electrically connected in series. The first measuring capacitance M1 and the first reference capacitance R1 are electrically connected in parallel with the second measuring capacitance M2 and the second reference capacitance R2.

[0043] The first stray capacitance K1 is connected in parallel with the first measuring capacitance M1, the second stray capacitance K2 is connected in parallel with the first reference capacitance R1, a third stray capacitance K3 is connected in parallel with the second measuring capacitance M2, and a fourth stray capacitance K4 is connected in parallel with the second reference capacitance R2. The parasitic resistances are omitted from this diagram.

[0044] Figure 5 shows a top view of a pressure sensor in another specific embodiment of the invention. The pressure sensor 10 is similar to that in Figure 3 except for the following differences. The bridge circuit 18 comprises at least a third measuring capacitance M3 between a third electrode 64 and a third counter electrode 66 and a third reference capacitance R3 between a third reference electrode 68 and a third reference counter electrode 70. The third electrode 64 is electrically connected to a third input terminal 72 having a third input potential D3. The third reference electrode 68 is electrically connected to a fourth input terminal 74 having a fourth input potential D4.

[0045] The second output terminal 62 is divided into two terminal regions 76, which are arranged symmetrically around the axis of symmetry 46. A third output terminal 78 is arranged centrally, and the third counter electrode 66 and the third reference counter electrode 70 are electrically connected to the third output terminal 78. The third output terminal 78 has a third output potential S3.

[0046] The third measuring capacitance M3 and the third reference capacitance R3 are electrically connected independently of the first and second measuring capacitances M1, M2 and the first and second reference capacitances R1, R2. The first measuring capacitance M1 and the second measuring capacitance M2 are configured to measure the ambient pressure in a first pressure range, and the third measuring capacitance M3 is configured to measure the ambient pressure in a second pressure range. This allows the pressure sensor 10 to measure the ambient pressure more accurately in two pressure ranges.

[0047] Figure 6 shows a circuit diagram of a bridge circuit of the pressure sensor from Figure 5. The bridge circuit 18 is similar to that in Figure 4 except for the following additions. The third measuring capacitance M3 is electrically connected in series with the third reference capacitance R3. The third input potential D3 is applied to the third electrode 64, and the fourth input potential D4 is applied to the third reference electrode 68. A fifth stray capacitance K5 is applied in parallel with the third measuring capacitance M3, and a sixth stray capacitance K6 is applied in parallel with the third reference capacitance R3. The parasitic resistances are omitted from this illustration.

[0048] The electrical charge q for measuring the ambient pressure in the second pressure range is determined by at least one third potential jump 80, in particular from 0 to V d at the third input terminal 72 and a sign-complementary fourth potential jump 82, in particular from 0 to —V dat the fourth input terminal 74 via the third measuring capacitance M3 and the third reference capacitance R3. The magnitude of the third and fourth potential jumps 80, 82 can be the same as or different from the magnitude of the first and second potential jumps 48, 50.

Claims

Patent claims 1. A capacitive pressure sensor (10) for capacitively measuring an ambient pressure in a sensor environment (22), comprising a sensor unit (12) with an electrical bridge circuit (18) to which an electrical first input potential (D1) and a second input potential (D2) are applied and at least one electrical output potential (S) can be tapped, and which has at least one first measuring capacitance (M1) that varies depending on the ambient pressure between a first electrode (24) and a first counter electrode (26), at least one first reference capacitance (R1) that is constant with respect to the ambient pressure between a first reference electrode (28) and a first reference counter electrode (30), a first input terminal (34) having the first input potential (D1), a second input terminal (36) having the second input potential (D2), and an output terminal (38) having the output potential (S), characterized in thatthat the bridge circuit (18) is constructed symmetrically at least with respect to a surface of the sensor unit (12) about an axis of symmetry (46) passing through the output terminal (38).

2. Capacitive pressure sensor (10) according to claim 1, characterized in that the specificity of the input potential (D1, D2) is irrelevant with respect to the symmetry.

3. Capacitive pressure sensor (10) according to claim 1 or 2, characterized in that the function of the capacitances (M1, R1) is irrelevant with regard to the symmetry.

4. Capacitive pressure sensor (10) according to one of the preceding claims, characterized in that the first measuring capacitance (M1) is arranged on one side of the axis of symmetry (46) and the first reference capacitance (R1) is arranged as a counterpart to the first measuring capacitance (M1) with respect to the axis of symmetry (46) on the other side of the axis of symmetry (46).

5. Capacitive pressure sensor (10) according to one of the preceding claims, characterized in that the first input terminal (34) is arranged on one side of the axis of symmetry (46) and the second input terminal (36) is arranged as a counterpart to the first input terminal (34) with respect to the axis of symmetry (46) on the other side of the axis of symmetry (46).

6. Capacitive pressure sensor (10) according to one of the preceding claims, characterized in that the ambient pressure can be measured as a function of an electrical charge (q) at the output terminal (38) resulting from at least one potential jump at the first and / or second input terminal (34, 36) via the first measuring capacitance (M1) and the first reference capacitance (R1).

7. Capacitive pressure sensor (10) according to one of the preceding claims, characterized in that the at least superficial structure of the bridge circuit (18) which is important for the symmetry comprises the design, the arrangement and the connections of the first input terminal (34), the second input terminal (36) and the first output terminal (38).

8. Capacitive pressure sensor (10) according to one of the preceding claims, characterized in that the bridge circuit (18) comprises at least a second measuring capacitance (M2) between a second electrode (52) and a second counter electrode (54) and a second reference capacitance (R2) between a second reference electrode (56) and a second reference counter electrode (58).

9. Capacitive pressure sensor (10) according to one of the preceding claims, characterized in that the bridge circuit (18) comprises at least a third measuring capacitance (M3) between a third electrode (64) and a third counter electrode (66) and a third reference capacitance (R3) between a third reference electrode (68) and a third reference counter electrode (70).

10. Capacitive pressure sensor (10) according to claim 8 and 9, characterized in that the first measuring capacitance (M1) and the second measuring capacitance (M2) are configured to measure the ambient pressure in a first pressure range and the third measuring capacitance (M3) is configured to measure the ambient pressure in a second pressure range.

Images