Patent Publication Number: US-8981798-B2

Title: Electronic system comprising a sensor structure and an analog interface connected thereto with sensor independent operating range

Description:
BACKGROUND 
     1. Technical Field 
     Generally, the present disclosure relates to smart electronic systems including a sensor structure, such as a temperature sensor, in combination with a dedicated integrated circuit that is connected to the sensor structure and that is configured to control power supply, data processing and the like of the entire electronic system. 
     2. Description of the Related Art 
     Immense progress has been made in the field of electronics due to the fact that sophisticated manufacturing techniques in the field of semiconductor industry allow the fabrication of circuit elements, such as transistors, having extremely small critical dimensions, thereby also providing for extremely high packing density in sophisticated semiconductor devices. As a consequence of the progress made in the semiconductor technologies circuit functions can be implemented into a single carrier material, such as a silicon substrate, so that entire circuit systems can be fabricated on a single semiconductor die. Similar progress has been made in the field of semiconductor-based sensor structures, since many of the manufacturing techniques used and developed in the semiconductor industry may also advantageously be applied to the fabrication of semiconductor-based sensors. Moreover, in a further attempt to reduce the overall volume of complex electronic systems different carrier substrate may be combined into a single package, thereby increasing the overall volume density of an electronic system with respect to the volume of a dedicated device package or substrate. Since very complex circuit portions and sensor structures can be fabricated on the basis of volume production techniques, the total cost per individual device has been significantly reduced in the past, thereby allowing the application of complex electronic systems in a wide variety of technical fields and circumstances. The low production costs may even enable the fabrication of disposable electronic systems, which may have a very limited time of usage while on the other hand producing valuable data and information with respect to a plurality of applications, however, without significantly contributing to the overall cost of ownership of specific applications. 
     Generally, a corresponding smart system may comprise one or more sensors, which can generate an output signal whose variation depends on parameters to be monitored, such as temperature, pressure, magnetic field, humidity, and the like, wherein dedicated electronic circuitry receives the sensor signal and provides the resources to at least preprocess the sensor signal so as to obtain information or data that is stored in the smart system or that is frequently communicated to an external device for further usage or processing. 
       FIG. 1   a  schematically illustrates a top view of a smart electronic system  100 , which comprises one or more sensors  110  that are operatively connected with a dedicated integrated circuit  130  via any appropriate connection  102 . The integrated circuit  130  is typically referred to as an ASIC (application specific integrated circuit) and provides for the interface capabilities for connecting to the one or more sensors  110  and has also implemented therein functions for the entire electronic system  100  in order to generate the desired data and information. Typically, the integrated circuit  130  comprises an energy management unit  170  that provides energy for operating the system  100 . To this end, the circuit portion  170  may comprise any appropriate transducers, energy storage elements, and the like in order to convert externally applied energy, such as mechanical energy, heat, radiation energy, and the like, into electric energy, while in other cases in addition to or alternatively to energy converters also appropriate energy storage elements, such as batteries, and the like may be provided so as to power the electronic system  100 . Moreover, a circuit portion  150  is implemented so as to act as an analog interface, also referred to as analog front end (AFE), in which an appropriate analog signal processing is accomplished on signals received from the sensor  110  via the connection  102 . Furthermore, the electronic circuit  130  comprises a control unit  140 , typically implemented by digital logic possibly in combination with a memory area, analog/digital and digital/analog converters, and the like, for performing the overall function of the electronic system  100 . Furthermore, the control unit  140  is typically configured to control operation of the various circuit portions the electronic circuit  130 . Moreover, a communication channel is frequently provided for instance in the form of a radio frequency (RF) transmitter/receiver  160 , which is connected to an antenna  180  via any appropriate connection  103 , thereby establishing a wireless communication channel. Consequently, the electronic system  100  can communicate with any external device by means of the wireless communication channel, thereby offering superior flexibility for using the electronic system  100  in various applications. It should be appreciated, however, that a communication channel to a peripheral device may be implemented in addition to or alternatively to the wireless communication path on the basis of a wired communication channel, if considered appropriate. In other cases the electronic system  100  may be provided without any communication resources for communicating with peripheral devices, when, for instance, the system  100  itself is appropriately configured to respond to any sensor signals obtained from the sensor  110  by using appropriate circuit portions (not shown), which may comprise electromechanical actuators, power electronics, and the like. 
     In many applications the electronic system  100  is developed for very restricted conditions, for instance as a disposable system in healthcare applications, in applications, in which compact organic substrates are used in combination with an electronic system, wherein frequently the electronic system, such as the system  100 , is to be operated on the basis of a reduced power consumption order to enhance overall flexibility, reduce cost of ownership and provide for a desired long usable lifetime, for instance when used as a stand-alone system for specific monitoring applications, such as monitoring environmental conditions, and the like. For this reason, the electronic circuit  130  is typically designed in view of low power consumption, while at the same time providing for a desired degree of noise immunity, accuracy with respect to signal and data processing, and the like. To this end a plurality of highly sophisticated semiconductor manufacturing technologies are available. Similarly, the one or more sensors  110  may also significantly contribute to the overall power consumption of the system  100 , thereby making desirable dedicated sensor structures in order to achieve the desired sensitivity, without unduly increasing the overall power consumption of the electronic system  100 . Since resistive sensor structures may readily be implemented into a semiconductor-based carrier material, a Wheatstone bridge-like sensor structure is one of the most frequently used type of sensors in integrated semiconductor devices, such as the electronic system  100 . 
       FIGS. 1   b  to  1   e  schematically illustrate circuit diagrams of different Wheatstone bridge architectures and the resulting output voltages for a given supply voltage V B  of the resistive bridge. 
       FIG. 1   b  schematically illustrates the case in which three of the four bridge resistors are non-varying resistors, while a fourth resistor is considered as a varying resistor, whose resistance value is influenced by a certain parameter, such as temperature, length distortion, and the like. 
       FIG. 1   c  schematically illustrates the bridge architecture in which two resistors of oppositely arranged bridge legs are considered as varying resistors, while the remaining resistors have a substantially constant resistance value. As shown, in this case the resulting output voltage is twice the output voltage of the architecture having one varying resistor. 
       FIG. 1   d  schematically illustrates the architecture, in which also two resistors are varying resistors that are arranged within the same bridge leg and that is an opposite sign of the change of resistance value when exposed to the same influencing parameter. Also in this case the output voltage is higher compared to the case, in which only one varying resistor is provided. 
       FIG. 1   e  schematically illustrates the architecture, in which the resistance values of the four bridge resistors vary in such a way that the resistance values of two oppositely arranged resistors vary in opposite direction, thereby obtaining an output voltage that is basically four times the output voltage obtained from the bridge having only one varying resistor. 
     Generally, in the present application a “varying resistor” is to be understood, compared to a non-varying resistor, as a resistor having a resistance value that changes under the influence of the certain environmental parameter, such as temperature, and the like, by at least twice the magnitude compared to the non-varying resistor. For example, in a resistive structure in which the change of the resistance value of one of the resistors is to be induced by generating a length distortion, for instance by positioning the resistor on a flexible membrane, this resistor is considered as a varying resistor compared to another resistor, which is formed on a more rigid portion of the substrate material so that upon any mechanical influence on their flexible membrane the resulting distortion and thus resistance change of the “varying” resistor is at least twice the change of the non-varying resistor. Similar criteria also apply to other influencing parameters, such as temperature, and the like. 
       FIG. 1   f  schematically illustrates a bridge circuit comprising the resistors R 1 , R 2 , R 3  and R 4 , which results in an output voltage as indicated in equations (1): 
     
       
         
           
             
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     Consequently, at balance, i.e., for an output voltage V 0 =0, the condition as described by equation (2) is to be met. 
     
       
         
           
             
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     If, for instance, a substantially temperature independent output voltage is to be obtained from the bridge of  FIG. 1F , a variation of the resistance value of any of the bridge resistors is determined by a certain parameter of interest, while the temperature induced variation is identical for each of the bridge resistors R 1 , . . . , R 4 . For example, in a linear approximation the temperature dependence of the resistance values can be described by equation (3):
 
 R=f ( T )→ R ( T )= Ro[ 1+( a/ 1 e 6)( T−To )]
         a=Temperature Coefficient of Resistance (TCR, ppm/K),
 
so that the same temperature coefficient has to be implemented in each resistor of the bridge to obtain a temperature independent sensor signal with respect to the varying parameter of interest, which may be caused by, for instance, a deformation of one or more of the resistors R 1 , . . . , R 4 . On the other hand, when using the bridge as a temperature sensor, a different temperature sensitivity has to be implemented for at least one of the resistors in order to obtain a temperature dependent sensor signal, since then the temperature dependency as described in equation 3 results in an appropriate output signal, as long as the variation of at least one of the resistors is sufficiently different from one or more of the other resistors. For example, frequently two resistors of the bridge are implemented so as to have a negative temperature coefficient compared to the remaining two resistors, thereby obtaining a maximum difference in the resistance value and thus the output voltage for a given change in temperature.
       

     Typically, a certain resolution over a desired operating range of the sensor is desirable in order to obtain a precise measurement within the specified operating range. As can be seen from the above cited equations, however, the resolution, i.e., the change in voltage of the bridge relative to a certain change of the parameter of interest, depends on the ratio of the change of resistance and the total resistance so that the output voltage is reduced for a high total resistance of the bridge for a given delta of the resistance value as caused by a variation of the parameter of interest. Since the change of the resistance value may be moderately small for a given change of a parameter to be monitored, a relatively small total resistance value of the bridge sensor is desirable. On the other hand, with regard to low power consumption, however, the current across the bridge is to be reduced for a given bridge voltage, which can be achieved by employing moderately high resistance values of the bridge resistors. Consequently, in low power applications typically a compromise is to be made between the resolution and thus low intrinsic noise level and the power consumed by the sensor structure. Therefore, frequently low-power sensor structures are not sufficiently sensitive for certain applications, for instance for temperature in a very limited temperature range, for instance between 30 and 45° C. for typical temperature coefficients associated with typical semiconductor-based materials as are used for the fabrication of semiconductor bridge sensors. Also in other cases moderately high resistance values may generally restrict the applicability of such low-power sensor structures in many monitoring applications. 
     For these reasons it has been proposed to implement a further amplification chain into the circuit portion  150  (cf.  FIG. 1   a ) which may thus increase the resulting output voltage. On the other hand, implementing an additional amplification chain may introduce additional flicker noise, thereby eventually reducing the entire sensor resolution. Furthermore, any mismatches of the resistance values of the bridge resistors may result in an offset, which in turn can saturate the amplifier chain of the circuit or may at least increase the power supply rejection ratio (PSRR) of the amplifier. 
       FIG. 1   g  schematically illustrates a circuit diagram of a typical bridge architecture, in which the bridge  110  is connected to an amplifier  151  within the circuit portion  150 , thereby providing an amplified output signal, wherein the gain of the amplifier  151  may be adjusted on the basis of a gain resistor  152 , while an offset correction may be achieved on the basis of an adjustable voltage source  153 . 
       FIG. 1   h  schematically illustrates a typical configuration of the electronic system  100  including the sensor  110  and their connection  102  so as to connect the circuit portion  150 , which in turn comprises the amplifier  151  as explained above with reference to  FIG. 1G . Moreover, the output signal of the circuit portion  150 , i.e., the output signal of the amplifier  151 , may be supplied to the circuit portion  140  of the circuit  130 , wherein the circuit portion  140  is illustrated in the form of a microprocessor. In the circuit portion  140  an appropriate data processing is performed, as is also previously discussed, and the results of the processing may be communicated by a communication channel, as is also discussed above with reference to  FIG. 1A , while in the example shown information or data can be displayed on a display unit  135  depending on the overall configuration and the application of the electronic system  100 . As discussed above, however, the amplifier  151  may represent itself an additional source of noise and may also require a specific adaptation of the circuit portion  150  i.e., of the analog front end of the circuit portion  130 , to the specific sensor structure  110 . That is, the output voltage of the amplifier  151  depends on the gain of the amplifier  151  and the bridge resistance, and also depends on the adjustable offset voltage provided by the voltage source  153 . Consequently, upon designing electronic systems for different applications, which may require different types of sensor structures  110 , a redesign of the circuit portion  130  is required in order to take into account the specific configuration of the sensor structure to be used for a specific application. 
     Therefore active bridges have been developed, in which a preprocessed signal is provided so as to avoid the adaptation of the analog front end interface of the ASIC. That is, the signal conditioning is implemented into the bridge structure in order to provide a standardized output signal, which is received by the ASIC without requiring any modification of the design of the ASIC upon changing the sensor structure. Consequently, for different types of sensor structures the same ASIC can be used. 
       FIG. 1   i  schematically illustrates a typical configuration of a basic active bridge circuit, wherein one bridge leg includes between a first reference resistor, a first variable resistor, a p-channel transistor T 3 , and an n-channel transistor T 4 , respectively, connected in series, while the other bridge leg includes a p-channel transistor T 1  and an n-channel transistor T 2  between a second variable resistor and a second reference resistor. Moreover, a programmable offset current source may also be connected to the power inputs of the p-channel transistors T 1  and T 3 , i.e., to the source terminals of these transistors. Consequently, upon a variation of the variable resistors a shift of the output voltage is obtained, which may further be processed as required. Seen from another point of view, the active circuitry of the bridge structure may be considered as a first current mirror formed by the p-channel transistors T 1  and T 3 , wherein the first current mirror is connected in series to a second current mirror formed by the n-channel transistors T 2  and T 4  so that a corresponding change of the resistance value and thus of the current results in a corresponding shift of the output voltage at the output node of the bridge configuration. 
     Although the basic configuration as shown in  FIG. 1   i  provides for superior flexibility in combining different types of sensor configurations with the same ASIC design, however, the overall gain of the active bridge depends on the resistance values of the sensor resistors thereby requiring a specific adaptation the active circuitry in view of the sensor structure to be used. More, the transistors of the active bridge circuit have to be implemented in the same carrier material as is used for forming the bridge resistance. Additionally, the overall current consumption of the active sensor structure may be moderately high, depending on the specific values of the bridge resistors. 
     BRIEF SUMMARY 
     One embodiment of the present disclosure is an electronic system including a sensor structure, wherein superior operating characteristics and a high degree of flexibility in combining a given design of an electronic circuit with various sensor structures may be achieved. 
     According to one aspect of the present disclosure there is provided an electronic system the electronic system comprises a sensor structure that includes a plurality of resistors, at least one of which is a variable resistor. The electronic system further comprises an electronic portion that includes an analog interface connected to the sensor structure, wherein the analog interface comprises a current amplifier supplied by an adjustable current source. The current amplifier is configured to receive first and second input current from the sensor structure and to provide an output signal indicated of an amplified difference of the first and second input currents. 
     The sensor structure, i.e., at least some of the plurality of resistors, is used as a voltage/current converter in order to provide the first and second input currents for the current amplifier, which in turn is supplied, i.e., powered, by the adjustable current source so that the operating range of the current amplifier can be adjusted on the basis of the adjustable current source irrespective of the characteristics of the sensor structure. Hence, the same analog interface can be used in combination with different sensor structures, since the operating range of the current amplifier can be adjusted within a wide window of input currents, while the current amplifier at the same time ensures high resolution at low power consumption. 
     In a further preferred embodiment the electronic system further comprises a control unit in the circuit portion, the control unit being configured to control the current source so as to maintain a valid operating range of the current amplifier. In this manner the circuit portion itself enables an adaptation to different sensor structures or varying operating conditions of the same sensor structure for a fixed configuration of the electronic portion. 
     In a further advantageous embodiment the electronic system comprises a flexible substrate carrying the sensor structure and the circuit portion. By using their flexible substrate and due to the superior flexibility in combining the same design of the circuit portion with different sensor structures, a wide variety of low cost and low power applications may be covered by the inventive smart electronic system. For instance, in the field of healthcare applications, in which basically the device is to be provided in a resilient package in order to enable the incorporation of the smart electronic system into flexible products, such as clothes, bandages, and the like so as to obtain valuable information with respect to the status of a person. It should be appreciated, however, that due to the resiliency of the electronic system many other applications are available, in which high accuracy, low power consumption and low cost for producing the electronic system for various monitoring applications are of great importance. 
     In a further advantageous embodiment the electronic system further comprises a first carrier material, in and above which is formed the sensor structure, and the electronic system further comprises a second carrier material, in and above which is formed in the electronic portion wherein the first and second carrier materials are separated from each other. While many applications of the inventive electronic system may be based on the concept that at least a portion of the analog interface is incorporated in the same carrier material as is used for providing the sensor structure, in this embodiment a further increased degree of flexibility respect to applicability and the manufacturing process, since the sensor structure may be formed in and above any appropriate carrier material on the basis of any desired process technology, while independently there from the circuit portion may be formed in a separate carrier material without requiring a redesign of the analog interface when different versions of the electronic systems are to be fabricated by using different types of sensor structures. For example, the sensor structure may be provided in the form of a passive resistive structure, which comprises an appropriate interconnection system so as to enable accessibility of the various resistors in the sensor structure. On the other hand, the active circuit components, i.e., the current amplifier, may be implemented into the circuit portion on the basis of any appropriate header material and process technology so that the sensor structure and the circuit portion are finally packaged on the basis of any appropriate package or substrate material. 
     In one illustrative embodiment the current amplifier is composed of transistors of the same conductivity type. In this manner, any desired and well established manufacturing technology may be applied upon forming the current amplifier such as MOS technology, bipolar technology, combined MOS technology and bipolar technology, and the like, wherein the conductivity type of the transistors may be selected on the basis of criteria such as deduced area consumption in the semiconductor substrate, overall production cost, and the like. For example, by providing the transistors in the form of field effect transistors, the selection of n-channel transistors may result in a highly space efficient implementation. 
     In other illustrative embodiments transistors of inverse conductivity type may be used for implementing the current amplifier, for instance on the basis of CMOS technology, thereby enhancing overall performance in terms of gain and power consumption of the current amplifier. 
     In a further illustrative embodiment, the current amplifier comprises a first current mirror and a second current mirror, which may have any appropriate design, for instance comprising two transistors, three transistors or more per each current mirror so as to specifically adapt the characteristics of the current amplifier in view of the overall design and performance specifications. 
     In a further illustrative embodiment the electronic system further comprises a chopper stage connected between the sensor structure and the current amplifier. In this manner, DC noise compensation can be enhanced by alternatingly connecting the bridge legs with a different current path of the current amplifier. 
     The electronic system may be provided with a sensor structure that is sensitive to temperature and/or pressure and/or magnetic field and/or humidity. In some illustrative embodiments the electronic system comprises the sensor structure as a temperature sensor with high sensitivity my wherein in some particular embodiments, a pronounced sensitivity is obtained with a temperature range of approximately 30° to 45° C., thereby making the inventive electronic system particularly useful in healthcare applications. 
     According to a further aspect of the present disclosure an electronic system is provided which comprises a resistive sensor structure that is formed above a flexible substrate material and that is responsive to at least one external influence. The electronic system further comprises an interface circuit connected to the resistive sensor structure and being formed above the flexible substrate material. The interface circuit comprises an adjustable current amplifier configured to receive an input current and to output signal indicative of the response of the resistive sensor structure to the at least one external influence. Hence, also in this case the resistive sensor structure provides a current input signal and thus acts as a voltage/current converter, wherein the input signal is appropriately amplified by the current amplifier so as to generate an appropriate output voltage. Moreover, due to the fact that these components are provided above the flexible substrate material and a superior flexibility is obtained with respect to combining the interface circuit with different types of resistive sensor structures, a wide variety of applications can be covered by the inventive electronic system, while at the same time superior performance at low power consumption may be provided by the electronic system with respect to sensor signal processing. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Further illustrative embodiments of the present disclosure are defined in the appended claims and the present disclosure will now be described in more detail with reference to the attached drawings, in which: 
         FIG. 1   a  schematically illustrates a top view of a conventional smart electronic system that comprises a sensor structure, 
         FIGS. 1   b  to  1   e  schematically illustrate circuit diagrams of various resistive bridge configurations, 
         FIG. 1   f  schematically illustrates a circuit diagram of a Wheatstone bridge configuration, which may be used as a temperature sensor, 
         FIG. 1   g  schematically illustrates a circuit diagram of an amplifier chain connected to a passive bridge configuration according to conventional strategies, 
         FIG. 1   h  schematically illustrates a smart electronic system including the amplifier chain as shown in  FIG. 1   g,    
         FIG. 1   i  schematically illustrates a circuit diagram of active bridge circuitry as is frequently used in conventional circuit designs, 
         FIG. 2   a  schematically illustrates a cross-sectional view of an electronic system of the present disclosure comprising a sensor structure and an interface circuit formed on the basis of a current amplifier by using a voltage to current conversion mechanism provided by the sensor structure, 
         FIG. 2   b  schematically illustrates a more detailed you of the electronic system, i.e., of the sensor structure and an electronic portion including the interface circuit, 
         FIG. 2   c  schematically illustrates a circuit diagram of an actual implementation of the adjustable current amplifier used in the interface circuit according to illustrative embodiments of the present disclosure, 
         FIGS. 2   d  and  2   e  schematically illustrate simulation results obtained from the inventive current amplifier on the basis of input currents supplied by the resistive sensor structure ( FIG. 2   d ) in comparison to a passive bridge circuit having the same resistance values ( FIG. 2   e ), 
         FIGS. 2   f ,  2   g  and  2   h  schematically illustrate circuit diagrams of further implementations of the adjustable current amplifier or portions thereof and 
         FIG. 2   i  schematically illustrates a circuit diagram of a further embodiment, in which a couple stage is implemented in order to reduce noise in DC measurement. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2   a  schematically illustrates a cross-sectional view of an electronic system  200  comprising a substrate  201 , which in the embodiment shown, is a flexible substrate material above which are formed various components of the electronic system  270 . A sensor structure  210  is formed in and above an appropriate carrier material  211  and is in the form of a resistive sensor structure, as will be explained in more detail below, wherein the carrier material  211  may be a semiconductor material, and the like. It should be appreciated, as discussed above, that various technologies and base materials may be used for implementing a resistive sensor structure, for instance in the form of temperature sensitive resistors, pressure sensitive resistors, and the like. Moreover, the electronic system  200  comprises a circuit portion  230 , which in turn comprises an analog interface circuit  250  so as to connect to the resistive sensor structure  210  by using any appropriate interconnection system, as is for instance also explained above with reference to the electronic system  100 . In the embodiment shown the interface circuit  250  is formed in and above a carrier material  231 , in which also other circuitry of the circuit portion  230  is implemented, wherein the carrier material  231  is separated from the carrier material  211  which both are mechanically combined via the substrate material  201 . It should be appreciated, however, that in other illustrative embodiments (not shown) the sensor structure  210  and the interface circuit  250  or at least a portion thereof may be formed in and above one and the same carrier material. Moreover, the electronic system  200  may comprise a further component  280 , such as an antenna, power circuitry, electromechanical actuators and the like, which may be formed on a separate carrier material  281 , such as a semiconductor material, and the like. In some cases, the further component  280  may also be formed in and above the carrier material  231  if compatible with the circuitry in the circuit portion  230 . 
     In some illustrative embodiments, in which the substrate material  201  is provided as a flexible material, the electronic system  200  is thus resilient to a certain degree and may thus incorporated into or attached to deformable materials and products as for instance required in a plurality of healthcare applications, and the like. 
       FIG. 2   b  schematically illustrates the resistive sensor structure  210  in more detail according to one illustrative embodiment, in which resistors  212 A, . . . ,  212 D are provided so as to have respective resistance values R 1 , . . . , R 4 . Moreover, in the embodiment shown corresponding terminals  213 A, . . . ,  213 D are arranged so as to allow access to the individual resistors of the structure  210 , while also respective two of the resistors are commonly connected to a corresponding supply voltage line. For example, the resistors  212 B,  212 D are connected to one supply voltage line, while the resistors  212 A,  212 C are connected to the other supply voltage line. The sensor structure  210  is connected to the interface circuit  250  by any appropriate interconnection structure  202 , wherein the interface circuit  250  is a part of the circuit portion  230 , as discussed above. The interface circuit  250  comprises a current amplifier  252 , which receives its supply current from the first adjustable current source  253 A and from a second adjustable current source  253 B. That is, the adjustable current amplifier  252  is powered by the adjustable current sources  253 A,  253 B. The current amplifier  252  is connected so as to receive at a first input node  254 A a first input current supplied by the sensor structure  210  and to receive at a second input node  254 B a second input current supplied by the sensor structure  210 . In the present embodiment, the resistors  212 B,  212 D connected to the supply voltage Vdd function as voltage/current converters that provide the first and second input currents. 
     Consequently, upon operating the circuit portion  230  and the sensor structure  210 , when the circuit portion  230  and thus the current amplifier  252  and the adjustable current sources  253 A,  253 B are connected to an appropriate supply voltage and also the sensor structure  210  is connected to an appropriate supply voltage, which do not need to be identical, the sensor structure  210  provides the input currents at the nodes  254 A,  254 B, the difference of which is amplified and provided as an output signal at an output node  255 . The magnitude of the input currents depends on the supply voltage of the structure  210  and on the resistance values. Irrespective of the configuration of the sensor structure  210 , the operating range of the current amplifier  252  is adjusted using the adjustable current sources  253 A,  253 B, thereby enabling an appropriate adaptation of the operating range of the amplifier  252  with respect to a wide variety of different configurations of resistive sensor structures, i.e., for different resistance values and thus input currents. Consequently, the same configuration of the circuit  230  and thus of the analog interface circuit  250  may be used in combination with different sensor structures  210  or varying operating conditions, such as a re-adjusted operating voltage of the sensor structure  210 , and the like. To this end, in some embodiments, the sensor structure  210  and the circuit portion  230  including the interface circuit  250  may be formed on separate carrier materials, as discussed above, so that a high degree of flexibility is achieved for the fabrication of the electronic system  200 . At the same time, the overall production cost can be maintained at a very low level, since the same design of the circuit  230  may be used in combination with different configurations of the sensor structure  210 , depending on the specific application of a corresponding combined electronic system  200 . 
       FIG. 2   c  schematically illustrates a circuit diagram of an actual implementation of the current amplifier  252 . As shown, the current amplifier  252  comprises a first current mirror  256 A, which in the embodiment shown is implemented in the form of a simple current mirror including transistors  257 A,  258 A. The transistors  257 A,  258  are shown as field effect transistors, although bipolar transistors, and the like, could be employed depending on the process technology to be used for implementing the current amplifier in the circuit  230 . The first current mirror  256 A is supplied by the adjustable current sources  253 A,  253 B, i.e., in the case of n-channel field effect transistors the current supplied by the sources  253 A,  253 B are fed into the respective drain terminals of the transistors  257 A,  258 A, respectively. It should be appreciated that in other illustrative embodiments the transistors  257 A,  258 A could be in the form of p-channel transistors or as PNP transistors, if a bipolar transistor technology is considered. Moreover, the “power outputs” of the first current mirror  256 A, i.e., the source terminals of these transistors, are connected to the input nodes  254 A,  254 B, respectively, which also receive the input currents Iin 1 , Iin 2  of the sensor structure  210 . First current mirror  256 A is connected to a “power input” of a second current mirror  256 B i.e., the drain terminals of transistors  257 B,  258 B are connected to the input nodes and thus to the source terminals of the transistors  257 A,  258 A. On the other hand, the power outputs of the second current mirror  256 B, i.e., the source terminals of the transistors  257 B,  258 B, are connected to the sensor structure  210 , i.e., to the resistors  212 A,  212 C, respectively. The output voltage at the output node  255  may be referenced to the supply voltage Vss or to a reference voltage node  255 R depending on the further signal processing. 
     For example, for a typical bridge configuration the resistors  212 B,  212 D may have the same basic resistance value, and similarly the resistors  212 A,  212 C may also have a common resistance value, wherein the resistance values of these resistive pairs may differ from each other. In order to implement a temperature sensitive configuration in the structure  210 , the temperature coefficients of the resistors  212 B,  212 D on the one hand are selected to be substantially identical. Similarly, the temperature coefficients of the resistors  212 A,  212 C on the other hand are also selected to be substantially identical, however, with an inverse sign compared to the temperature coefficients of the resistors  212 B,  212 D. In this manner, a desired temperature dependent variation of the input currents at the nodes  254 A,  254 B and thus a corresponding temperature varying output voltage at the node  255  is obtained that corresponds to an amplified difference of the input currents. On the other hand, gain and offset of the current amplifier  252  are adjusted on the basis of the programmable or adjustable current sources  253 A,  253 B, thereby allowing an adaptation to the specific configuration of the sensor structure  210  without requiring a modification of the hardware configuration of the amplifier  252 . That is, since a different sensor structure may provide different input currents due to its different voltage/current conversion characteristic for a given supply voltage of the sensor structure the amplifier characteristics, such as gain, offset and generally calibration can be appropriately adjusted by programming the current sources  253 A and/or  253 B which can be achieved for a wide variety of input currents with the same circuit configuration of the amplifier  252 . 
       FIG. 2   d  schematically illustrates simulation results when operating the amplifier  252  and the resistive sensor structure  210 . In the simulation the resistance values of the resistors  212 B,  212 D (CF  FIG. 2C ), indicated as R 2  and R 4 , are 100 kΩ, while the resistance values R 1 , R 3  corresponding to the resistors  212 A,  212 C (CF  FIG. 2   c ) are selected as 10 kΩ. Furthermore, in the simulation the sum of currents driven through the amplifier  252  by the adjustable current sources are the same and are, in one example, approximately 100 μA, while in a further example 65 μA are used. Furthermore, the temperature coefficient is selected as 0.003 with different sign for the resistance values R 1 , R 3  on the one hand and R 2  and R 4  on the other hand. In this case for a temperature range of 30° C. to 45° C. a change of the output voltage of greater than 2.3V for a bridge supply voltage of 5 V is obtained. In a further example a reduction of the supply voltage to 2.5 V with the current through the amplifier  252  reduced to 65 μA produces a change of the output voltage across the above specified temperature range of greater than 0.9 V. 
       FIG. 2   e  schematically illustrates the simulation results when using a passive sensor bridge  210 P, wherein the same resistance values and supply voltages are used as in the active circuit shown in  FIG. 2   d . For example, curve A represents the results of the simulation for the passive bridge configuration, in which the resistance values R 1 , R 4  are 10 kΩ with a negative temperature coefficient, while the resistance values R 2 , R 3  are 100 kΩ with a positive temperature coefficient. In this case, the current driven through the bridge  210 P is approximately 100 μA for a supply voltage of 5 V. Under these conditions the change of the output voltage for the above specified temperature range is approximately 0.007 V. Similarly, curve B represents the results of a simulation for a configuration, in which the resistance values R 2 , R 4  are 100 kΩ the resistance values R 1 , R 3  are 10 kΩ with the latter resistors having a negative temperature coefficient. Also in this case the change of the output voltage is 0.007 V. As is evident from the simulation results, the total power consumption in the active circuitry may be comparable or even less compared to the passive circuit configuration, while the change and thus the resolution of the output voltage of the active circuitry is significantly greater across the specified temperature range compared to the small voltage variation obtained from the passive circuit. For example, a total current of approximately 65 μA, i.e., a power consumption of approximately 163 mW, and the voltage change of greater than 0.9 V compares to a total current of approximately 100 μA, i.e., a power consumption of approximately 500 mW, and a change of output voltage of 0.007 V. 
       FIG. 2   f  schematically illustrates the interface circuit  250  including the current amplifier  252  in the configuration in which the sensor structure  210  is composed of the resistors  212 B,  212 D that provide the input currents for the amplifier  252 , as discussed above. In this case, the resistance values of the resistors  212 A,  212 C (CF  FIG. 2   c ) may be assumed to be negligible compared to the resistance values of the resistors  212 B,  212 D. Also in this case, the adjustable current sources  253 A,  253 B can be programmed or adjusted so as to obtain appropriate operating conditions for the amplifier  252 , i.e., gain and offset are appropriately adjusted so as to obtain a desired swing of the output voltage for a given temperature range. The current sources  253 A,  253 B may be implemented in the form of any appropriate current mirror configuration, for instance in the form of a simple current mirror having a structure similar to the structural as shown for the current mirrors  256 A,  256 B (CF  FIG. 2   c ), wherein the ratio of the currents in the sources  253 A,  253 B may readily be adjusted by selecting appropriate transistor characteristics, as is well known in the art. Similarly, other mirror configurations may be used, such as a Wilson mirror, a Cascode mirror and the like. 
     It should be appreciated that an appropriate control of the operating range of the amplifier  252  may be implemented on the basis of a feedback control, for instance with respect to the current source  253 A, wherein the feedback control loop may be established by using a control unit  240  that may represent a part of the circuit portion  230  (CF  FIG. 2   a ) and that may perform other control functions with respect to power management, signal processing, communication, and the like, as is for instance also described above with reference to the electronic system  100  when referring to the control unit  140 . 
       FIG. 2   g  schematically illustrates an alternative implementation of, for instance, the current mirror  256 A (CF  FIG. 2   c ), and which more than two transistors are incorporated, for example in a cascode configuration, wherein additional transistors  257 K,  258 K are provided so as to be connected in series to the transistors  257 A,  258 A, respectively. It should be appreciated that the corresponding configuration may also be applied to the second current mirror  256 B (CF  FIG. 2   c ). It should be appreciated, however, that any other appropriate current mirror structure can be implemented, for instance in the form of a Wilson mirror, and the like. That is, at least one additional transistor may typically be provided in the first and/or second current mirrors  256 A,  256 B so as to enhance overall performance, if considered appropriate. 
       FIG. 2   h  schematically illustrates the first and second current mirrors  256 A,  256 B according to an embodiment, in which transistors of inverse conductivity type are provided in order to enhance overall performance in terms of gain and current consumption of the current amplifier composed of the first and second current mirrors  256 A,  256 B. For example, in the embodiment shown the transistors  257 A,  258 A of the first current mirror  256 A are provided in the form of p-channel transistors, while the transistors of the second current mirror  256 B are implemented as n-channel transistors. To this end, well-established CMOS technologies can be used, while in other cases, other technologies may be applied, in which transistors of different conductivity type can be implemented, such as bipolar transistors of inverse conductivity type. 
       FIG. 2   i  schematically illustrates the interface circuit  250  according to a further illustrative embodiment, in which a chopper stage  220  is incorporated and connected between the sensor structure  210 , which may for instance comprise the resistors  212 A, . . . ,  212 D (CF  FIG. 2   c ), and the current amplifier  252 . The chopper stage  220  is appropriately configured so as to alternatingly connect the two bridge legs with the two current paths of the amplifier  252 . The resistors  212 B,  212 D, which act as voltage/current converters, are alternatively connected to the input nodes  254 A,  254 B, respectively, under the control of a control signal  221  received by the chopper stage  220 , while at the same time also the resistors  212 A,  212 C are alternatively connected to the source terminals of the two transistors of the second current mirror  256 B. Thus, during a certain phase of the control signal  221 , a certain configuration of the sensor structure  210  is connected to the amplifier  252 , while in a subsequent phase of the control signal  221  the first configuration of the sensor structure  210 , i.e., the first configuration of the bridge legs, is connected to the amplifier  252 . In this manner, a significant reduction of noise in DC measurements can be accomplished. It should be appreciated that the chopper stage  220  may have any other configuration so as to provide for corresponding switches in order to perform the above described function of the chopper stage  220 . 
     As a result, the present disclosure provides an electronic system including a resistive sensor structure and an analog interface circuit, which performs signal conditioning to an output current provided by the resistive sensor structure. To this end, the resistive sensor structure is used as a voltage/current converter in order to provide input signals for a current amplifier, which in turn amplify the difference of the input currents so as to provide an amplified output voltage. The current amplifier is supplied, i.e., “powered”, by adjustable or programmable current sources and adjustment of gain and offset of the amplifier without being affected by the characteristics of the sensor structure. In this manner the same electronic circuit portion of the electronic system can be combined with resistive sensor structures of different configuration without requiring a re-design of the electronic components of the electronic system. Moreover, the electronic system can respond to a wide variety of different operating conditions, thereby ensuring enhance flexibility for various environmental conditions and applications for a given sensor structure. Consequently, the present disclosure enables enhanced flexibility in designing and producing low-cost and low-power electronic systems with superior performance, wherein the electronic systems may be used as disposable systems even for sophisticated applications, such as healthcare applications, and the like. In some illustrative embodiments, the superior flexibility with respect to design and manufacture of the electronic system may even further be enhanced by providing flexible substrate materials, which may thus enable attachment or incorporation in resilience products or materials, thereby even further increasing the overall applicability of the inventive electronic systems. Furthermore, due to the possibility of using the same design of the electronic circuit in combination with different sensor structures, the overall manufacturing process may be enhanced, in particular when the sensor structure is formed on a dedicated separate carrier material. For example, very cost efficient yet accurate and sensitive temperature sensor structures may be used in the inventive electronic systems on the basis of a given design of the electronic circuit, wherein a high sensitivity is obtained in a limited temperature range as is highly advantageous in the context of healthcare applications. It should be appreciated that other resistive sensor structures may efficiently be incorporated into the electronic system of the present disclosure in order to provide sensitivity to various environmental influences, such as pressure, humidity, magnetic field, and the like, wherein typically the corresponding environmental influence is “converted” into gate information of one or more of the resistive elements in the resistive sensor structure, thereby obtaining a change of the resistance value. 
     The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.