Sensor circuit with compensation resistor for compensating for a temperature coefficient of a bridge circuit

Abstract

The present disclosure relates to a sensor circuit (300; 600; 800) comprising a first terminal (110), a second terminal (120), and a bridge circuit (130) connected between the first terminal (110) and the second terminal (120), the bridge circuit having a plurality of bridge resistors, each with a temperature coefficient. The bridge circuit has a measurement sensitivity and a temperature coefficient of the measurement sensitivity, and a bridge offset with a temperature coefficient of the bridge offset. The sensor circuit further comprises at least one compensation resistor (140) connected between the first terminal (110) and the second terminal (120), the compensation resistor having a temperature coefficient that differs from that of the bridge resistors.

Description

Technical area

[0001] The present disclosure relates to sensor circuits having at least one compensation resistor for compensating temperature coefficients of a (measuring) bridge circuit. background

[0002] Physical quantities to be measured can, for example, be measured using measuring bridge circuits (sensor bridges). Half-bridges and full bridges are known in measuring bridge circuits. A half-bridge comprises two (bridge) resistors connected as a voltage divider between a first terminal (e.g. supply terminal) and a second terminal (e.g. ground terminal), at least one of which is dependent on a physical quantity to be measured (e.g. magnetic field). If the physical quantity to be measured (measured quantity) changes, the voltage division ratio of the (measurement) bridge resistors also changes. A full bridge (e.g. Wheatstone bridge) comprises two half-bridges connected in parallel between the supply terminal and ground terminal. Here, a differential output signal can be output between the two half-bridges depending on the measured quantity.

[0003] Measuring bridge circuits are supplied with either a constant voltage or a constant current as a supply signal. In both cases, the difference between the two half-bridge output voltages can usually be used as a sensor output signal in a full bridge. A measured value-dependent (measuring) bridge resistance and its measuring sensitivity can change over temperature according to the respective temperature coefficients. In the case of tunnel magnetoresistive (TMR) resistors, the temperature coefficient TC R the bridge resistance and the temperature coefficient TC SB_TMR the measurement sensitivity has a negative sign. This means that with increasing temperature, resistance and measurement sensitivity may decrease.

[0004] In the case of a magnetic field sensor, the measuring sensitivity S B_Br the sensor bridge (e.g. full bridge) can be defined as the change ΔV outthe bridge output voltage when the applied magnetic field changes ΔB: SB_Br:=(ΔVout) / ΔB

[0005] Instead of the magnetic field, other physical measurement quantities can of course also be considered.

[0006] The output voltage V out However, the sensor bridge is dependent on a voltage across the entire Wheatstone bridge V Br dependent. The measuring sensitivity S B0 the sensor bridge is therefore proportional to V Br : SB0∼VBr

[0007] With a negative temperature coefficient (TCs B_TMR < 0) of the measuring sensitivity of the bridge resistors, also has a temperature coefficient TC SB_B , the measuring sensitivity of the sensor bridge has a negative sign. With a negative temperature coefficient (TC R< 0) of the individual bridge resistances, the total resistance of the sensor bridge between the supply terminals also has a negative temperature coefficient TC R_Br on.

[0008] If the sensor bridge is supplied with a constant current as a supply signal, as may be required in certain applications, the temperature coefficient TC R_Br of the total resistance of the sensor bridge the bridge voltage V Br , because VBr=RBr⋅IDD, where I DD is the constant supply current.

[0009] The temperature coefficient TC SB_B , the measuring sensitivity of a sensor bridge supplied with a constant current is therefore: TCSB0_Br=TCSB_TMR+TCR_Br

[0010] Since these two temperature coefficients are usually negative, their effects add up and the temperature behavior of a current-fed sensor becomes worse overall than that of a voltage-fed sensor bridge.

[0011] If an operating B field of the sensor is not at B = 0mT (ie at B OP + / - B Range with B OP ≠ 0), the output voltage (ie the offset at B = B OP ) depends on the measuring sensitivity of the bridge resistors. Consequently, a change / shift in the measuring sensitivity over temperature (ie a TC SB_TMR ) also directly to a temperature coefficient TC Off the offset of the sensor bridge.

[0012] Thus, there is a need for concepts for temperature compensation of the measurement sensitivity and the offset voltage in sensors (e.g. magnetic field sensors) with resistance bridge circuits. Summary

[0013] This need is met by the devices and methods of the independent patent claims. Advantageous further developments are the subject of the dependent patent claims.

[0014] According to a first aspect of the present disclosure, a sensor circuit is proposed. According to some embodiments, it may, for example, be a magnetic field sensor circuit. The sensor circuit comprises a first terminal (e.g., supply terminal), a second terminal (e.g., ground terminal), and a (measuring) bridge circuit connected between the first and second terminals, having a measuring sensitivity. According to some embodiments, the bridge circuit may be a half-bridge with a first and a second resistor, at least one of which is dependent on a physical quantity to be measured (e.g., magnetic field), or a full bridge with two half-bridges. The bridge circuit has a temperature coefficient of the measuring sensitivity (measuring sensitivity temperature coefficient). The sensor circuit further comprises at least one between the first terminal (e.g.,A compensation resistor connected between the first terminal (supply terminal) and the second terminal (e.g., ground terminal) is designed to at least partially compensate the temperature coefficient of the measurement sensitivity (measurement sensitivity temperature coefficient) of the bridge circuit. Therefore, if the bridge circuit has a negative measurement sensitivity temperature coefficient, the compensation resistor can make the measurement sensitivity temperature coefficient more positive (ideally zero). If the bridge circuit has a positive measurement sensitivity temperature coefficient, the compensation resistor can make the measurement sensitivity temperature coefficient more negative (ideally zero).

[0015] Another aspect of the present disclosure is a sensor circuit comprising a first terminal (e.g., supply terminal) and a second terminal (e.g., ground terminal). The sensor circuit further comprises a bridge circuit connected between the first terminal (e.g., supply terminal) and the second terminal (e.g., ground terminal). The bridge circuit has a plurality of bridge resistors with a respective temperature coefficient of resistance. The sensor circuit also comprises at least one compensation resistor connected between the first terminal (e.g., supply terminal) and the second terminal (e.g., ground terminal), said compensation resistor having a temperature coefficient of resistance that differs from the temperature coefficient(s) of the bridge resistors.The different temperature coefficient of the compensation resistor can compensate for temperature-related changes in the measurement sensitivity and / or the offset of the bridge circuit.

[0016] The compensation resistor can be connected directly or indirectly between the first terminal (e.g., supply terminal) and the second terminal (e.g., ground terminal). "Directly" means that the compensation resistor is connected directly to the first terminal (e.g., supply terminal) and the second terminal (e.g., ground terminal), for example, in parallel with the bridge circuit. "Indirectly" means that the compensation resistor can be connected in series with other circuit components between the first terminal (e.g., supply terminal) and the second terminal (e.g., ground terminal). For example, the compensation resistor can be arranged in series with the bridge circuit or, within the measuring bridge circuit, in series with bridge resistors.

[0017] According to some embodiments, the compensation resistance is independent of the measured variable. This means that the compensation resistance does not change depending on the measured variable (e.g., magnetic field).

[0018] According to some embodiments, the compensation resistor has a different (resistance) temperature coefficient than one or more bridge resistors of the bridge circuit. The at least partial compensation can be achieved through the different (resistance) temperature coefficient.

[0019] According to some embodiments, the compensation resistor is connected in parallel with the bridge circuit. This can be useful, for example, when a constant current is used as the supply signal.

[0020] According to some embodiments, the compensation resistor or another compensation resistor within the bridge circuit is connected in series with the first and second resistors. This can also be useful, for example, with a constant current as the supply signal or to compensate for the temperature dependence of the offset voltage.

[0021] According to some embodiments, the compensation resistor or the additional compensation resistor is connected between an output signal terminal of the bridge circuit and the second terminal (e.g., ground terminal). In other embodiments, the compensation resistor or the additional compensation resistor can also be connected between an output signal terminal of the bridge circuit and the first terminal (e.g., supply terminal).

[0022] According to some embodiments, the temperature coefficient of the measurement sensitivity (sensitivity) of the bridge circuit is negative (TC SBO_TMR < 0), a temperature coefficient of the bridge resistances negative (TC R < 0) and a temperature coefficient of the compensation resistor positive (TC R,comp > 0).

[0023] According to some embodiments, the temperature coefficient of the measurement sensitivity of the bridge circuit is positive (TC SBO_TMR > 0), the temperature coefficient of the bridge resistances is negative (TC R < 0) and the temperature coefficient of the compensation resistor is more negative than the temperature coefficient of the bridge resistors (TC R,comp < TC R ).

[0024] According to some embodiments, the temperature coefficient of the measurement sensitivity of the bridge circuit is negative (TC SBO_TMR < 0), the temperature coefficient of the bridge resistances is positive (TC R> 0) and the temperature coefficient of the compensation resistor is more positive than the temperature coefficient of the bridge resistors (TC R,comp > TC R ).

[0025] According to some embodiments, the temperature coefficient of the measurement sensitivity of the bridge circuit is positive (TC SBO_TMR > 0), the temperature coefficient of the bridge resistances is positive (TC R > 0) and the temperature coefficient of the compensation resistor is negative (TC R,comp < 0).

[0026] According to some embodiments, the compensation resistor is connected between the first terminal (e.g., supply terminal) and the bridge circuit. According to other embodiments, the compensation resistor is connected between the second terminal (e.g., ground terminal) and the bridge circuit. This can be useful, for example, when a constant voltage is used as the supply signal.

[0027] According to some embodiments, the temperature coefficient of the measurement sensitivity of the bridge circuit is negative (TC SBO_TMR < 0). The compensation resistor is independent of the measured value and has a smaller temperature coefficient than the temperature coefficient of the bridge resistors (TC R,comp < TC R ).

[0028] According to some embodiments, the temperature coefficient of the measurement sensitivity of the bridge circuit is positive (TC SBO_TMR > 0) The compensation resistor is independent of the measured value and has a larger temperature coefficient than the temperature coefficient of the bridge resistors (TC R,comp > TC R ).

[0029] According to some embodiments, the resistors of the bridge circuit are designed as magnetoresistive resistors. Magnetoresistance is a physical phenomenon in which the electrical resistance of a material is influenced by an external magnetic field. There are several types of magnetoresistance that can occur in different materials and applications. In anisotropic magnetoresistance (AMR), the electrical resistance of a material changes depending on the direction of the external magnetic field. This phenomenon occurs in some materials that exhibit magnetic anisotropy, meaning they are preferentially magnetized in a certain direction. Giant magnetoresistance (GMR) occurs in thin layer structures consisting of alternating ferromagnetic and non-magnetic layers. The resistance of these structures changes with the orientation of the magnetic regions in the layers.GMR is used in magnetoresistive sensor technology (MR sensors) and has important applications in hard drives, magnetic field sensors, and data transmission technology. Colossal magnetoresistance (CMR) is a phenomenon that occurs in certain types of compounds, such as manganese oxides (manganates). At very low temperatures and in the presence of an external magnetic field, the electrical resistance of these materials can decrease dramatically. This phenomenon is being investigated in materials science and potentially in the development of new electronic components. Tunneling magnetoresistance (TMR) occurs in thin insulator layers between two ferromagnetic electrodes. The electrical resistance changes dramatically when the orientation of the magnetic moments in the electrodes varies. This technology is used in the development of magnetic field sensors and non-volatile magnetic field memories.Extraordinary magnetoresistance (EMR) is a very rare and special phenomenon observed in certain exotic materials. This is an extremely large magnetoresistive effect that has been observed in some high-energy materials. EMR has potential applications in spintronics and the development of ultrafast electronic components. The various magnetoresistances can be summarized under the term "xMR."

[0030] According to some embodiments, the resistors of the bridge circuit are designed as TMR resistors.

[0031] According to a further aspect of the present disclosure, a sensor circuit is proposed. The sensor circuit comprises a constant current source, a ground terminal, and a bridge circuit connected between the constant current source and the ground terminal, which bridge circuit has a negative temperature coefficient of measurement sensitivity (measurement sensitivity temperature coefficient). The bridge circuit comprises at least one half-bridge with a first and a second xMR resistor, each of which has a negative temperature coefficient (resistance temperature coefficient).

[0032] The sensor circuit further comprises at least one compensation resistor connected between the constant current source and the ground terminal, which shows essentially no magnetic field sensitivity (i.e. is not magnetoresistive) and has a positive temperature coefficient of resistance (resistance temperature coefficient).

[0033] According to some embodiments, the compensation resistor is connected between the constant current source and the ground terminal and in parallel to the bridge circuit.

[0034] According to some embodiments, the compensation resistor or another compensation resistor in the half-bridge is connected in series with the first and second xMR resistors.

[0035] According to a further aspect of the present disclosure, a sensor circuit is proposed. The sensor circuit comprises a constant voltage source, a ground terminal, and a bridge circuit having a negative temperature coefficient of measurement sensitivity (measurement sensitivity temperature coefficient). The bridge circuit comprises at least one half-bridge with a first and a second xMR resistor, each having a negative temperature coefficient of resistance (resistance temperature coefficient). The sensor circuit further comprises at least one compensation resistor that exhibits essentially no magnetic field sensitivity (i.e., is non-magnetoresistive) and has a negative temperature coefficient of resistance (resistance temperature coefficient).The compensation resistor is connected between the constant voltage source and the bridge circuit, and the bridge circuit is connected between the compensation resistor and the ground terminal. Alternatively, the compensation resistor is connected between the bridge circuit and the ground terminal, and the bridge circuit is connected between the constant voltage source and the compensation resistor.

[0036] According to some embodiments, the temperature coefficient of resistance of the compensation resistor is smaller than the temperature coefficient of resistance of the first or second xMR resistor.

[0037] According to some embodiments, a further compensation resistor within the half-bridge is connected in series with the first and second xMR resistors, and the sensor circuit comprises a second parallel half-bridge between the compensation resistor and the ground terminal.

[0038] With embodiments of the present disclosure, a measurement sensitivity temperature coefficient (TC SBO_Br ) of a sensor bridge can be reduced in magnitude. For a discrete sensor bridge supplied with a constant current, for example, a parallel resistor with a resistance temperature coefficient that has an opposite sign compared to the resistance temperature coefficient of the sensor bridge can trim a bridge supply voltage and make the measurement sensitivity more stable over temperature. For a discrete sensor bridge supplied with a constant voltage, a series resistor can have the same effect. With a negative measurement sensitivity temperature coefficient of the sensor bridge (TC SBO_ < 0) a compensation resistor with a resistance temperature coefficient TC RComp < TC R_Br(resistance temperature coefficient of the sensor bridge). With a positive measuring sensitivity temperature coefficient of the sensor bridge (TC SBO_ > 0) a compensation resistor with a resistance temperature coefficient TC Rcomp > TC R_Br To reduce the temperature dependence of the offset voltage, resistors with defined resistance and temperature coefficients can be placed in the bridge paths. Short character description

[0039] Some examples of devices and / or methods are explained in more detail below with reference to the accompanying figures. They show: Fig. 1 a conventional sensor bridge circuit; Fig. 2 a relationship between measurement sensitivity temperature coefficient and offset drift; Fig. 3 shows a sensor circuit with a compensation resistor according to a first embodiment; Fig. 4 a ratio V Br (ΔT) / V Br (ΔT=0) and a ratio S B0 (ΔT) / S B0 (ΔT=0) for different temperature differences ΔT relative to a reference temperature and for different compensation resistors; Fig. 5 a ratio V Br (ΔT) / V Br (ΔT=0) and a ratio S B0 (ΔT) / S B0 (ΔT=0) for different temperature differences ΔT relative to a reference temperature and for different compensation resistors; Fig. 6 a sensor circuit with compensation resistor according to another embodiment; Fig. 7 a ratio V Br (ΔT) / V Br (ΔT=0) and a ratio S B0 (ΔT) / S B0(ΔT=0) for different temperature differences ΔT relative to a reference temperature and for different compensation resistors; Fig. 8 shows a sensor circuit with a compensation resistor according to a further embodiment; Fig. 9 Effects of the compensation resistor according to Fig. 8 to an output voltage offset; Fig. 10 a sensor circuit according to another embodiment; and Fig. 11 further sensor circuits according to embodiments. Description

[0040] Some examples will now be described in more detail with reference to the accompanying figures. However, other possible examples are not limited to the features of these detailed embodiments. These may include modifications of the features, as well as equivalents and alternatives to the features. Furthermore, the terminology used herein to describe specific examples is not intended to be limiting of other possible examples.

[0041] Throughout the description of the figures, identical or similar reference numerals refer to identical or similar elements or features, which may be implemented identically or in a modified form while providing the same or a similar function. Furthermore, the thickness of lines, layers, and / or regions in the figures may be exaggerated for clarity.

[0042] When two elements A and B are combined using "or," this is to be understood as disclosing all possible combinations, i.e., only A, only B, and both A and B, unless explicitly defined otherwise in the individual case. Alternative wording for the same combinations may be "at least one of A and B" or "A and / or B." This applies equivalently to combinations of more than two elements.

[0043] If a singular form is used, such as "a," "an," and "the," and the use of only a single element is neither explicitly nor implicitly defined as mandatory, further examples may also use multiple elements to implement the same function. If a function is described below as being implemented using multiple elements, further examples may implement the same function using a single element or a single processing entity.It is further understood that the terms "comprises", "comprising", "has" and / or "having" when used herein describe the presence of the specified features, integers, steps, operations, processes, elements, components and / or a group thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components and / or a group thereof.

[0044] The Fig. Figure 1 shows an example of a sensor circuit 100. Sensor circuit 100 can measure a physical quantity. For example, sensor circuit 100 can be a magnetic field sensor circuit for measuring an external magnetic field.

[0045] The sensor circuit 100 comprises a supply terminal 110, a ground terminal 120 and a measuring bridge circuit 130 connected between the supply terminal 110 and the ground terminal 120. The measuring bridge circuit 130 comprises a first half-bridge connected between the supply terminal 110 and the ground terminal 120 and having a series circuit of measured-variable resistors R1 and R2 and, in parallel thereto, a second half-bridge connected between the supply terminal 110 and the ground terminal 120 and having a series circuit of measured-variable resistors R3 and R4. In the embodiment shown, the resistors R1 to R4 are magnetoresistive resistors, in particular TMR resistors with the values ​​shown in Fig. 1 shows the different reference magnetizations of the two half-bridges.

[0046] Between the resistors R1 and R2 of the first half-bridge there is a first output signal terminal V out1. Between the resistors R3 and R4 of the second half-bridge there is a second output signal terminal V out2 . A differential voltage between the two output signal terminals V out1 and V out2 provides a measured variable dependent (e.g. magnetic field dependent) bridge output voltage V out the sensor circuit 100.

[0047] A measurement sensitivity S B_Br the measuring bridge circuit 130 can be defined as a change ΔV out the bridge output voltage V out with a change ΔB of an applied external magnetic field (measured quantity): SB_Br:=(ΔVout) / ΔB

[0048] The bridge output voltage V out is of a voltage V Br between supply terminal 110 and ground terminal 120 across the entire (measuring) bridge circuit 130. The measuring sensitivity S B_Br the bridge circuit 130 is therefore proportional to V Br : SB_Br∼VBr

[0049] In case of a supply with constant supply current I DD is the voltage VBr=IDD⋅RBr, where R Br the total resistance of the bridge circuit 130 means, with RBr=(R1+R2)⋅(R3+R4)(R1+R2)+(R3+R4)⋅

[0050] If the bridge circuit 130 is operated with a constant current I DD as a supply signal, as may be required in certain applications, the temperature coefficient TC influences R_Br of the total resistance R Br the bridge voltage V Br . The temperature coefficient TC R_Br of the total resistance is in turn dependent on the temperature coefficients TC R the individual measurement-dependent bridge resistors R1 to R4.

[0051] With a negative temperature coefficient (TCs B_TMR< 0) of the measuring sensitivity of the bridge resistors R1 to R4, also has a temperature coefficient TC SB_Br the measuring sensitivity of the bridge circuit 130 has a negative sign. With a negative temperature coefficient (TC R < 0) of the individual bridge resistors R1 to R4, the total resistance R Br the bridge circuit 130 between the supply terminals 110, 120 also has a negative temperature coefficient TC R_Br < 0.

[0052] The temperature coefficient TC SB_B , the measuring sensitivity of a sensor bridge supplied with a constant current is therefore: TCSB_Br=TCSB_TMR+TCR_Br

[0053] Since these two temperature coefficients TC SB_TMR and TC R_B, are usually negative for TMR bridge resistances, their effects add up and the temperature behavior of a current-fed sensor becomes worse overall than that of a voltage-fed sensor bridge.

[0054] Furthermore, TC shifts SB_TMR also a magnetic field B OP , where the output voltages V out1 , V out2 of the two half-bridges (with different reference magnetizations) are identical, V out1 = V out2 , and thus the differential bridge output voltage V out = 0. In case of a change in the intrinsic measurement sensitivity (SB TMR ) of the bridge circuit, V out1 = V out2 to B ≠ B OP . At B OP This results in a non-vanishing bridge output voltage V out ≠ 0, i.e. an offset drift. Consequently, the temperature coefficient of the measurement sensitivity TC SB_TMRthe bridge circuit 130 also directly to a temperature coefficient of the offset TC Off the bridge circuit 130. This relationship is in Fig. 2 shown.

[0055] Embodiments of the present disclosure aim to determine the temperature coefficient of measurement sensitivity TC SB_TMR of the sensor bridge circuit 130 and thus obtain a sensor circuit with an ideally vanishing (at least reduced in magnitude) temperature coefficient of the measurement sensitivity. Various embodiments are described below.

[0056] The Fig. The sensor circuit 300 shown in Fig. 3 is supplied via the supply terminal 110 with a constant current I DD (constant current source) and further comprises a compensation resistor 140 (R comp ). The compensation resistor Rcomp is designed to measure the temperature coefficient of measurement sensitivity (measurement sensitivity temperature coefficient) TC SB_Br of the bridge circuit 130. For this purpose, the compensation resistor R comp Ideally independent of the measured value (e.g. independent of the magnetic field), in the case of magnetoresistive bridge resistors R1 to R4, for example, it is not magnetoresistive. Furthermore, the compensation resistor R comp a different temperature coefficient of the compensation resistor TC Rcomp than the temperature coefficient TC R the bridge resistors R1 to R4, ie, TC Rcomp ≠ TC R Depending on the application or requirement, TC Rcomp greater or less than TC R be.

[0057] In the example shown, the resistance temperature coefficient TC Rof the bridge resistors R1 to R4 is negative (here: -800 ppm / K). This also results in a negative resistance temperature coefficient TC R_Br of the total resistance R Br the bridge circuit 130. Furthermore, in the example shown, the measurement sensitivity temperature coefficient TC SB_Br the bridge circuit 130 negative (TC SB_Br < 0).

[0058] In the sensor circuit 300 of the Fig. 3 is the compensation resistor R comp between the supply signal terminal 110 and the ground terminal 120 and connected in parallel to the bridge circuit 130. At a constant supply current I DD the voltage drop V Br across the bridge circuit 130 decreases with increasing temperature. If the compensation resistor R comp with positive resistance temperature coefficient TC Rcomp (TC Rcomp > 0), the negative TC R_Brthe bridge circuit 130 by the parallel connection of the compensation resistor R comp at least partially or completely compensated. The compensation resistor R comp can therefore be used in a bridge circuit 130 with negative TC R_Br be designed as a resistor with a positive temperature coefficient (PTC resistor). This allows the bridge voltage V Br and the output voltage V out stabilized over temperature. A stabilized output voltage V out This in turn leads to a temperature-stabilized measurement sensitivity S B_Br the bridge circuit 130 according to TCSB_Br=TCSB_TMR+TCR_Overall, where TC R_Overall the resistance temperature coefficient of the parallel circuit of bridge circuit 130 and compensation resistor R comp means.

[0059] The compensation resistor R compAccording to some embodiments, the compensation resistor R can be selected in the order of magnitude of the bridge resistors R1 to R4. For example, if the bridge resistors R1 to R4 are each 4 kΩ, the compensation resistor R comp for example in a range of 1 kΩ < R comp < 10 kΩ. Possible materials for the compensation resistor R comp are metals, PTC thermistors, PTC thermistors (thermistors), polymer PTC resistors, or (highly doped) polysilicon.

[0060] The Fig. 4 (above) shows for different temperature differences ΔT relative to a reference temperature the resulting ratio V Br (ΔT) / V Br (ΔT=0). The Fig. 4 (below) shows for different temperature differences ΔT the resulting ratio S B0 (ΔT) / S B0 (ΔT=0). For example, R1 = R2 = R3 = R4 = 4 kΩ was assumed. For R comp = 2 kΩ and TC Rcomp= +800 ppm / K, the best stabilization of the bridge voltage V Br and the measuring sensitivity of the sensor bridge. Even for TC Rcomp = 0 were used for R comp = 2 kΩ and R comp = 4 kΩ better stabilization is achieved than without compensation resistor R comp . It is also possible to imagine embodiments in which TC Rcomp < 0, but TC Rcomp > TC R , where the resistance temperature coefficient TC R the bridge resistors R1 to R4 negative (TC R < 0), the measuring sensitivity temperature coefficient of the bridge circuit 130 is negative (TC SB_B , < 0) and the resistance temperature coefficient of the compensation resistor is negative (TC Rcomp < 0) but greater than TC R (TC Rcomp > TC R ) is.

[0061] The Fig. 5 shows similar curves as the Fig. 4 for R comp = 2 kΩ or 4 kΩ and TCRcomp = 0 ppm / K or TC Rcomp = +3000 ppm / K.

[0062] In the case of measurement-dependent bridge resistors R1 to R4 with a positive resistance temperature coefficient TC R Embodiments of the sensor circuit 300 are also conceivable in which the resistance temperature coefficient TC R the bridge resistors R1 to R4 positive (TC R > 0), the measuring sensitivity temperature coefficient of the bridge circuit 130 is positive (TCs B_B , > 0) and the resistance temperature coefficient of the compensation resistor is negative (TC Rcomp < 0). Furthermore, embodiments are conceivable in which the resistance temperature coefficient TC R the bridge resistors R1 to R4 positive (TC R > 0), the measuring sensitivity temperature coefficient of the bridge circuit 130 is positive (TCs B_B , > 0) and the resistance temperature coefficient of the compensation resistor is positive (TC R-comp> 0) but smaller than TC R is (TC Rcomp < TC R 0).

[0063] Furthermore, embodiments of the sensor circuit 300 are also conceivable in which the measurement sensitivity temperature coefficient of the bridge circuit 130 is positive (TC SB_B , > 0), the resistance temperature coefficient TC R the bridge resistors R1 to R4 negative (TC R < 0) and the resistance temperature coefficient of the compensation resistor is smaller than the resistance temperature coefficient of the bridge resistors (TC Rcomp < TC R ). Furthermore, embodiments are conceivable in which the measurement sensitivity temperature coefficient of the bridge circuit is negative (TC SB_B , < 0), the resistance temperature coefficient of the bridge resistors is positive (TC R > 0) and the resistance temperature coefficient of the compensation resistor is greater than the resistance temperature coefficient of the bridge resistors (TC Rcomp > TCR ).

[0064] For a constant current I DD fed sensor bridge circuit 130, an additional resistor R comp connected in parallel to the sensor bridge circuit 130. The constant supply current I DD is connected between the additional compensation resistor R comp and the sensor bridge circuit 130. If the temperature coefficient TC Rcomp of the compensation resistor is greater than the temperature coefficient TC R_Br of the total bridge resistance, the temperature coefficient of the entire circuit is 300 greater than without compensation resistor R comp , resulting in a more stable bridge voltage V out above the temperature. With a large positive TC Rcomp of the compensation resistor R compA positive temperature coefficient for the overall system resistance can also be achieved, resulting in an increasing bridge voltage over temperature. This can be used to compensate for the negative temperature coefficient of the measurement sensitivity observed at constant bridge voltage.

[0065] The Fig. The sensor circuit 600 shown in Figure 6 is driven by a constant supply voltage V DD fed (constant voltage source) and comprises a compensation resistor 140 (R comp ). The compensation resistor R comp is also connected between supply terminal 110 and ground terminal 120 - but as a series resistor instead of a parallel resistor. The compensation resistor R compis also designed here to determine the temperature coefficient of the measuring sensitivity (measuring sensitivity temperature coefficient) TC SB_Br of the bridge circuit 130. For this purpose, the compensation resistor R comp Ideally independent of the measured value (e.g. independent of the magnetic field), i.e. not magnetoresistive. Furthermore, compensation resistance R comp a different temperature coefficient of the compensation resistor TC Rcomp than the temperature coefficient TC R the bridge resistors R1 to R4, ie, TC Rcomp ≠ TC R .

[0066] In the Fig. In the example shown in Figure 6, the resistance temperature coefficient TC R of the bridge resistors R1 to R4 is negative (here: -800 ppm / K). This also results in a negative resistance temperature coefficient TC R_Br of the total resistance R Brthe bridge circuit 130. Furthermore, in the example shown, the measurement sensitivity temperature coefficient TC SB_B , the bridge circuit 130 is also negative (TC SB_Br < 0).

[0067] In the sensor circuit 600 of the Fig. 6 is the measurement-independent compensation resistance R comp connected between the supply signal terminal 110 and the bridge circuit 130 and has a resistance temperature coefficient TC Rcomp which is smaller (more negative) than the resistance temperature coefficient TC R the bridge resistors R1 to R4 (TC Rcomp < TC R ). According to Fig. 6 is the measurement sensitivity temperature coefficient TC SB_Br the bridge circuit 130 is negative, the compensation resistor is essentially independent of the measured value and has a smaller resistance temperature coefficient TC R-comp than the resistance temperature coefficient TC Rof the bridge resistances. As a result, at a constant supply voltage V DD the voltage drop across the compensation resistor R comp more than the voltage drop across the bridge circuit 130. At constant supply voltage V DD thus the voltage drop V Br across the bridge circuit 130 increases with increasing temperature. This is shown in Fig. 7 (above), which shows the resulting ratio V for different temperature differences ΔT Br (ΔT) / V Br (ΔT=0). The Fig. 7 (below) shows the resulting measurement sensitivity ratio S for different temperature differences ΔT B0 (ΔT) / S B0 (ΔT=0). The different curves of the Fig. 7 concern different R comp from 0 kΩ to 8 kΩ and TC Rcomp = 0 ppm / K or TC Rcomp = -1600 ppm / K.

[0068] If the compensation resistor R compwith resistance temperature coefficient TC Rcomp < TC R selected, the negative TC R_Br the bridge circuit 130 can be at least partially or completely compensated. Due to the bridge voltage V increasing with ΔT > 0 Br the output voltage V out despite decreasing bridge resistances R1 to R4 over temperature. A stabilized output voltage V out This in turn leads to a temperature-stabilized measurement sensitivity S B_Br the bridge circuit 130 (see Fig. 7 (below)).

[0069] In the case of measurement-dependent bridge resistors R1 - R4 with positive resistance temperature coefficient TC R Embodiments of the sensor circuit 600 are also conceivable in which the measurement sensitivity temperature coefficient TC SB_Br the bridge circuit 130 is positive (TC SB_Br > 0), the compensation resistor R compis independent of the measured value and has a larger resistance temperature coefficient TC Rcomp than the resistance temperature coefficient TC R the bridge resistors (TC Rcomp > TC R ).

[0070] If the bridge 130 is connected to a constant supply voltage V DD supplied, a serial compensation resistor R comp with defined temperature coefficient TC Rcomp for trimming the bridge voltage V Br be used. With suitable values ​​for resistance R comp and temperature coefficient TC Rcomp This series resistance can determine the temperature coefficient of sensitivity TC SB_TMR compensate.

[0071] The Fig. The sensor circuit 800 shown in Figure 8 is supplied at the supply terminal 110 by a constant supply current I DD and includes a compensation resistor 140 (R2,series ). The compensation resistor R 2,series is therefore connected in series with the first resistor R1 and the second resistor R2 in the bridge circuit 130. In the example shown, the compensation resistor R 2,series between the first output signal terminal V out1 and the bridge resistor R2. Other arrangements of the compensation resistor within the first half-bridge are also conceivable. Likewise, the compensation resistor R 2,series in the second half-bridge R3, R4.

[0072] The compensation resistor R 2,series is therefore also connected between supply terminal 110 and ground terminal 120. Furthermore, the compensation resistor R 2,series also designed here to measure the sensitivity temperature coefficient TC SB_Br of the bridge circuit 130. For this purpose, the compensation resistor R 2,seriesIdeally independent of the measured value (e.g. independent of the magnetic field), i.e. not magnetoresistive. Furthermore, the compensation resistor R 2,series a different temperature coefficient TC R2_series than the temperature coefficient TC R the bridge resistors R1 to R4, ie, TC R2_series ≠ TC R .

[0073] In Fig. 9 are the output voltages V out1 , V out2 of the half-bridge branches as a function of the B-field for the two cases with and without the additional compensation resistor R 2,series At room temperature (thin lines), V out1 and V out2 at B=B OP identical, ie the bridge offset is zero. For the case with the additional compensation resistor R 2,series the measurement-dependent bridge resistance R2 must be adjusted to ensure that even when B = B OP to have the offset = 0. The thick curves correspond to the output voltages Vout1 , V out2 at high temperature (HT). With a negative temperature coefficient of the bridge resistances, the total bridge resistance decreases and the bridge voltage also decreases at constant supply current. Consequently, the output voltages V out1 and V out2 reduced. A typically negative TC of sensitivity TC SB_TMR leads to a flatter V OUT vs. B behavior, resulting in a shift of the zero-offset B field to higher values. As a result, the bridge offset at B OP no longer zero, ie there is one from TC SB_TMR originating TC Off The straight, bold lines indicate the V OUT1 / 2 for the case without the additional compensation resistor R 2,series .

[0074] If an additional compensation resistor R 2,series with a positive resistance temperature coefficient TC R2,seriesis connected in series with the bridge resistor R2, the decrease in the total resistance of the bridge 130 and thus also the decrease in V out1 / 2 at higher temperatures, as in Fig. 9 (dashed bold lines). In addition, the resistance of the half-bridge, in which the additional compensation resistor R 2,series a smaller decrease in V OUT1 on (line 902) as the other half-bridge V OUT2 (Line 904). This means that the B field, in which V out1 and V out2 cross, is not shifted as much to higher values ​​than without the additional compensation resistor R 2,series (Lines 906, 908). As a result, the offset shift is reduced over temperature and thus also the TC Off . Out of Fig. 9 it can be seen that the additional compensation resistor R 2,series the effect of the TC SB_TMR(partially) compensated. It is also possible to overcompensate to avoid a change in the sign of the TC Off by using the additional compensation resistor R 2,series and chooses its temperature coefficient accordingly.

[0075] The same effect could be achieved by using instead of the additional compensation resistor R 2,series an additional compensation resistor R 1,series connected in series with the bridge resistor R1, which then has a negative resistance temperature coefficient. Alternatively, an additional compensation resistor R 3,series with a positive temperature coefficient of resistance can also be connected in series with R3. Then the drop in V OUT2 at higher temperatures, resulting in a smaller shift in the offset and thus a lower TC Off leads.

[0076] In general, the proposed principle also works in the case that the bridge 130 is supplied with a constant supply voltage V DD is supplied or that the TC SB_TMR is positive. In the latter case, the resistance temperature coefficient of the implemented series resistor must also have the opposite sign.

[0077] In general, there are several possibilities for arranging the series or parallel resistors in the bridge circuit to achieve temperature compensation of sensitivity and offset. A combination of the Fig. 3 and Fig. 8 described embodiments is in Fig. 10, where the parallel connected compensation resistor R comp with reference number 140 and the series compensation resistor R connected in the half-bridge R1, R2 2,series designated by reference numeral 140'. The Fig. 6 and Fig. The embodiments described in Figure 8 can be combined with one another to create a sensor circuit comprising a constant voltage source, a ground terminal 120, and a bridge circuit 130 comprising at least one half-bridge with a first and a second xMR resistor, each of which has a negative temperature coefficient. The combined sensor circuit comprises at least one compensation resistor 140 with a negative temperature coefficient that is smaller than the temperature coefficient of the first or second xMR resistor. The compensation resistor 140 is connected between the constant voltage source and the bridge circuit 130, and the bridge circuit 130 is connected between the compensation resistor (140) and the ground terminal.Alternatively, the compensation resistor 140 is connected between the bridge circuit 130 and the ground terminal (120), and the bridge circuit 130 is connected between the constant voltage source and the compensation resistor 140. Another compensation resistor R. 2,series is connected in series with the first and second xMR resistors R1, R2 within the half-bridge (R1, R2). The combined sensor circuit also includes a second parallel half-bridge (R3, R3) between the compensation resistor 140 and the ground terminal 120.

[0078] Two further examples are in Fig. 11. In the left circuit, each bridge resistor R 11 to R 22 a respective series compensation resistor. In the circuit on the right, each bridge resistor R 11 to R 22 an associated parallel compensation resistor.

[0079] In semiconductor devices, resistors with a positive temperature coefficient can be realized using materials such as metal or highly doped (poly)silicon. Resistors with a negative temperature coefficient can be achieved, for example, using less doped (poly)silicon.

[0080] The proposed sensor circuits with compensation resistors can achieve more stable characteristics over temperature without the cost and additional space required for active temperature compensation.

[0081] The aspects and features described in connection with a particular one of the previous examples may also be combined with one or more of the further examples to replace an identical or similar feature of that further example or to additionally introduce the feature into the further example.

[0082] It is further understood that the disclosure of multiple steps, processes, operations, or functions disclosed in the specification or claims should not be construed as necessarily being in the described order, unless explicitly stated in the individual case or technically required. Therefore, the foregoing description does not limit the performance of multiple steps or functions to any particular order. Furthermore, in further examples, a single step, function, process, or operation may include and / or be broken down into multiple sub-steps, functions, processes, or operations.

[0083] If some aspects in the preceding sections were described in connection with a device or system, these aspects are also to be understood as a description of the corresponding method. For example, a block, a device, or a functional aspect of the device or system can correspond to a feature, such as a method step, of the corresponding method. Accordingly, aspects described in connection with a method are also to be understood as a description of a corresponding block, a corresponding element, a property, or a functional feature of a corresponding device or system.

[0084] The following claims are hereby incorporated into the Detailed Description, each claim being understood to stand on its own as a separate example. It should also be noted that although a dependent claim in the claims refers to a particular combination with one or more other claims, other examples may include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are hereby explicitly contemplated unless it is specifically stated that a particular combination is not intended. Furthermore, features of a claim for any other independent claim are also intended to be included, even if that claim is not directly defined as dependent on that other independent claim.

Claims

[1] Sensor circuit (300; 600; 800), comprising a first terminal (110); a second terminal (120); a bridge circuit (130) connected between the first terminal (110) and the second terminal (120) with a plurality of bridge resistors with a respective temperature coefficient, wherein the bridge circuit has a measuring sensitivity with a temperature coefficient of the measuring sensitivity and a bridge offset with a temperature coefficient of the bridge offset; and at least one compensation resistor (140) connected between the first terminal (110) and the second terminal (120) with a temperature coefficient that differs from the temperature coefficient of the bridge resistors. [2] Sensor circuit (300; 600; 800) according to claim 1, wherein the compensation resistor (140) is independent of the measured variable. [3] Sensor circuit (300; 600; 800) according to one of the preceding claims, wherein the compensation resistor (140) is connected between the first terminal (110) and the second terminal (120) and in parallel with the bridge circuit (130). [4] Sensor circuit (300; 600; 800) according to claim 3, wherein a further compensation resistor (140') in the bridge circuit (130) is connected in series with a bridge resistor. [5] Sensor circuit (300; 600; 800) according to one of the preceding claims, wherein the temperature coefficient of the measuring sensitivity of the bridge circuit (130) is negative, the temperature coefficient of the bridge resistors is negative and the temperature coefficient of the compensation resistor (140) is positive. [6] Sensor circuit (300; 600; 800) according to one of claims 1 to 4, wherein the temperature coefficient of the measuring sensitivity of the bridge circuit (130) is positive, the temperature coefficient of the bridge resistors is negative and the temperature coefficient of the compensation resistor (140) is smaller than the temperature coefficient of the bridge resistors. [7] Sensor circuit (300; 600; 800) according to one of claims 1 to 4, wherein the temperature coefficient of the measuring sensitivity of the bridge circuit (130) is negative, the temperature coefficient of the bridge resistors is positive and the temperature coefficient of the compensation resistor (140) is greater than the temperature coefficient of the bridge resistors. [8] Sensor circuit (300; 600; 800) according to one of claims 1 to 4, wherein the temperature coefficient of the measuring sensitivity of the bridge circuit (130) is positive, a temperature coefficient of the bridge resistors is positive and the temperature coefficient of the compensation resistor (140) is negative. [9] Sensor circuit (300; 600; 800) according to one of claims 1 or 2, wherein the compensation resistor (140) in the bridge circuit (130) is connected in series with a bridge resistor. [10] Sensor circuit (300; 600; 800) according to one of claims 1 or 2, wherein the compensation resistor (140) is connected in series to the bridge circuit (130). [11] Sensor circuit (300; 600; 800) according to claim 10, wherein a further compensation resistor in the bridge circuit (130) is connected in series with a bridge resistor. [12] Sensor circuit (300; 600; 800) according to claim 11, wherein the further compensation resistor is connected between an output signal terminal of the bridge circuit (130) and one of the first or second terminals (110; 120). [13] Sensor circuit (300; 600; 800) according to one of claims 10 to 12, wherein the temperature coefficient of the measuring sensitivity of the bridge circuit (130) is negative and the compensation resistor (140) has a smaller temperature coefficient than a temperature coefficient of the bridge resistors. [14] Sensor circuit (300; 600; 800) according to one of claims 10 to 12, wherein the temperature coefficient of the measuring sensitivity of the bridge circuit (130) is positive and the compensation resistor has a larger temperature coefficient than a temperature coefficient of the bridge resistors [15] Sensor circuit (300; 600; 800) according to one of the preceding claims, wherein the bridge circuit (130) comprises a first half-bridge and a parallel second half-bridge. [16] Sensor circuit (300; 600; 800) according to one of the preceding claims, wherein bridge resistors of the bridge circuit (130) are designed as xMR resistors. [17] Sensor circuit (300; 600; 800) according to claim 16, wherein the bridge resistors are designed as TMR resistors. [18] Sensor circuit (300), comprising a constant current source; a ground connection (120); a bridge circuit (130) connected between the constant current source and the ground terminal (120), comprising at least one half-bridge with a first and a second xMR resistor, each having a negative temperature coefficient; and at least one compensation resistor (140) with a positive temperature coefficient connected between the constant current source and the ground connection (120) and in parallel with the bridge circuit. [19] The sensor circuit (300; 600; 800) of claim 18, wherein a further compensation resistor in the half-bridge is connected in series with the first and second xMR resistors, the further compensation resistor having a temperature coefficient that differs from the temperature coefficient of the xMR resistors. [20] Sensor circuit according to claim 18 or 19, wherein the bridge circuit (130) further comprises a second half-bridge in parallel with the half-bridge. [21] Sensor circuit (600), comprising a constant voltage source; a ground connection (120); a bridge circuit (130) comprising at least one half-bridge with a first and a second xMR resistor, each having a negative temperature coefficient; and at least one compensation resistor (140) with a negative temperature coefficient, wherein the temperature coefficient of the compensation resistor (140) is smaller than the temperature coefficient of the first or second xMR resistor, wherein the compensation resistor (140) is connected between the constant voltage source and the bridge circuit (130) and the bridge circuit (130) is connected between the compensation resistor (140) and the ground terminal, or wherein the compensation resistor (140) is connected between the bridge circuit (130) and the ground terminal (120) and the bridge circuit (130) is connected between the constant voltage source and the compensation resistor (140). [22] The sensor circuit (300; 600; 800) of claim 21, wherein a further compensation resistor in the half-bridge is connected in series with the first and second xMR resistors, the further compensation resistor having a temperature coefficient that differs from the temperature coefficient of the xMR resistors. [23] Sensor circuit according to claim 21 or 22, wherein the bridge circuit (130) further comprises a second half-bridge in parallel with the half-bridge.

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