JP2012252008A - Method and device for calculating measurement value of chemical sensitivity field effect transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a method of calculating a measurement value of a chemical sensitivity field effect transistor.SOLUTION: A method of calculating a measurement value of a chemical sensitivity field effect transistor (110) includes: a preparation step (402) of preparing a first signal and a second signal, and amplifying at least the first signal by a certain amplification factor; a supply step (404) of supplying the first signal to the chemical sensitivity field effect transistor (110) to which measurement fluid is applied to acquire output information, and supplying the second signal to a transistor (114) for reference in a reference environment to acquire reference information; a comparison step (406) of comparing the output information with the reference information, and adapting the amplification factor in accordance with the result of comparison; and an evaluation step (408) of evaluating the amplification factor in order to obtain the measurement value.

Description

Prior Art The present invention relates to a method for determining a measured value of a chemically sensitive field effect transistor, an apparatus for determining a measured value of a chemically sensitive field effect transistor, and a corresponding computer program product.

  In a sensor that senses a chemical substance, the output signal depends on the concentration of the chemical substance contained in the sample or the medium to be analyzed. However, the signal output by the sensor that senses this chemical is not an absolute signal representing concentration, but rather a change or drift in the signal that is both persistent and insignificant. To accommodate such changes or drift, another sensor can be used as a reference sensor. Ideally, the aging process and environmental effects that occur on this reference sensor are the same as the aging process and environmental effects that occur on the sensor, so the change or drift of the reference sensor is the same as the sensor. It is. The concentration of the chemical substance in the sample can be estimated from the sensor signal and the reference signal.

  US Pat. No. 6,703,241 B1 describes a method for reducing signal drift in an artificial olfactory device having a plurality of sensor components.

US6703241B1

  Against the background of the above-mentioned prior art, the object of the present invention is to improve the method for determining the measured value of a chemically sensitive field effect transistor.

  The present invention discloses a method for obtaining a measured value of a chemically sensitive field effect transistor described in an independent claim, and further obtains a measured value of a chemically sensitive field effect transistor described in an independent claim. And finally a corresponding computer program product is disclosed. Advantageous embodiments can be derived from the respective dependent claims and the following description of the specification.

It is a circuit diagram of the apparatus for calculating | requiring the measured value of the chemical sensitivity field effect transistor of the Example of this invention. It is a circuit diagram of the apparatus for calculating | requiring the measured value of the chemical sensitivity field effect transistor of the Example of this invention. It is a circuit diagram of the apparatus for calculating | requiring the measured value of the chemical sensitivity field effect transistor of the Example of this invention. 4 is a flowchart of a method for obtaining a measured value of a chemically sensitive field effect transistor according to an embodiment of the present invention. It is a block circuit diagram of the apparatus for calculating | requiring the measured value of the chemical sensitivity field effect transistor of the Example of this invention.

  By using a sensor and a reference sensor to measure a substance in a sample, an uncertain signal is output. The uncertainty of this signal is determined by using the control circuit and the control circuit. The recognition that it can be compensated by using the signal output from the controller is the basis of the present invention. This signal contains noise, and so-called 1 / f noise is dominant, especially at low frequencies. Furthermore, changes in the signal caused by changes in the concentration of the substance to be measured are often minimal as compared to the overall signal level. Therefore, it is advantageous to use an indirect parameter to determine the measurement result, for example by estimating the actual measurement result by using a controlled feedback value directly related to the signal. Can do. By appropriately selecting the controller parameters, the feedback value can be expressed with a negligible deviation of the signal with high accuracy. In addition, the voltage range of the feedback value can be completely used, and thus the concentration can be expressed with high measurement accuracy.

  The measurement sensitivity of a chemically sensitive field effect transistor type chemical sensor can be improved at low cost by the means of the present invention to improve the signal to noise ratio and reduce ambient effects.

  A chemical sensor can be composed of two chemically sensitive field effect transistors (ChemFETs) and a circuit of the present invention for performing a differential measurement that is timing synchronized with the output of the ChemFETs. Advantageously, the fundamental problem in measuring the signal of a ChemFET type chemical sensor can be solved with one simple circuit. According to the present invention, it is possible to easily solve the problem that the change in the channel current that is the original measurement signal is on the order of smaller than the channel current that is the background signal. Furthermore, the signal to noise ratio can be improved by reducing the measurement bandwidth. The circuit of the present invention can be used in conjunction with “switched biasing” noise suppression.

The present invention discloses a method for determining a measured value of a chemically sensitive field effect transistor, which method comprises the following steps:
A preparation step of preparing a first signal and a second signal and amplifying at least the first signal with a certain amplification factor.
Output information is obtained by supplying the first signal to the chemically sensitive field effect transistor to which the measurement fluid is supplied, and reference information is supplied by supplying the second signal to a reference transistor in a reference environment. Can be obtained supply step.
A comparison step of comparing the output information with the reference information and adapting the amplification factor according to the comparison result.
An evaluation step of evaluating the amplification factor to obtain the measured value.

The present invention further discloses an apparatus for determining a measured value of a chemically sensitive field effect transistor, the apparatus having the following configuration:
A preparation device for preparing the first signal and the second signal. At least the first signal is amplified with a certain amplification factor.
In order to obtain output information, the first signal is supplied to the chemically sensitive field effect transistor to which a measurement fluid is supplied, and a second reference transistor in the reference environment is obtained to obtain reference information. A supply device for supplying the signal.
A comparison device for comparing the output information with the reference information and adapting the amplification factor according to a result of the comparison.
An evaluation device for evaluating the amplification factor in order to obtain the measurement value.

  The embodiment of the present invention can solve the problem underlying the present invention quickly and efficiently even as an apparatus.

  The measured value can mean a value representing the concentration of a substance to be measured in the measurement fluid. For example, the measured value can be a current or a voltage. In this case, the current or voltage value represents the concentration. The measurement value may be a data word. At that time, a column of values (bits) represents the density. A chemically sensitive field effect transistor can be a semiconductor element, for example, a chemically sensitive field effect transistor can have a source contact, a drain contact, and a gate electrode, the gate electrode having special electrochemical characteristics. And / or an electrode having catalytic properties. As a result, the equilibrium state between the molecule or atom to be detected of the substance to be measured in the measurement fluid and the molecule or atom of the substance to be measured adsorbed to the gate electrode is The potential can be affected. The potential at the gate electrode can also be changed by applying a voltage. The potential at the gate electrode can affect the channel current between the source contact and the drain contact. This channel current can represent the concentration of the substance to be measured in the measurement fluid. This channel current can include a component that does not depend on a change in potential. The first signal can be a voltage and the second signal can be a voltage. The supply of the first signal or a signal derived from the first signal can be performed at least by the gate electrode of the chemically sensitive field effect transistor, and the second signal or the second signal can be supplied. The signal to be derived can also be supplied at least by the gate electrode of the reference transistor. The supply of the first signal can also be performed at the drain contact of the chemically sensitive field effect transistor, and the supply of the second signal can also be performed at the drain contact of the reference transistor. The amplification factor can affect the voltage level of the first signal. The second signal can be amplified with a different amplification factor. The another amplification factor may be an amplification factor that is inverted with respect to the amplification factor with reference to a reference potential. In this case, for example, the amplitude of the first signal can be made larger and the amplitude of the second signal can be made smaller. The output information can represent the channel current, for example, the output information can be a voltage drop across a measurement resistor, such as a shunt resistor.

  The reference transistor can be a semiconductor element, for example, the reference transistor can be a field effect transistor having a source contact, a drain contact and a gate electrode, the gate electrode having special electrochemical characteristics and It can also be an electrode having catalytic properties. If the reference transistor does not have electrochemical and / or catalytic properties, the measurement fluid can also be supplied to the reference transistor as a reference environment and / or the chemically sensitive field effect transistor The reference transistor can be placed on the same support member in order to be exposed to the same environmental conditions to which it is exposed. With this configuration, the reference information does not change due to a change in concentration in the measurement fluid. For example, the reference transistor may have a passivation layer. That is, if the reference transistor is, for example, passivated, it can be placed in the same measurement environment. This is because the reference layer is separated from the measurement environment by the passivation layer. If the reference transistor has electrochemical and / or catalytic properties, for example, the reference transistor can be exposed to a reference fluid that is a reference environment. The reference fluid may include a substance to be measured having a known concentration. When the environmental conditions are the same or similar, the reference signal represents the concentration of the fluid to be measured in the reference fluid. The evaluation can be a calculation using a known algorithm, or the evaluation can be obtained using a stored table for obtaining a measurement value.

  Here, the apparatus can include an electronic device that processes a sensor signal and outputs a control signal depending on the processed sensor signal. The device may have an interface, which may be comprised of hardware and / or software. If implemented in hardware, the interface can for example be part of a so-called system ASIC containing the various functions of the device. However, the interface can be an independent integrated circuit or at least partially composed of discrete elements. When configured by software, the above-described interface can be, for example, a software module provided in parallel with another software module on the microcontroller.

  Furthermore, in the comparison step, the amplification factor can be adapted so that the output information and the reference information are angled. In this amplification factor adaptation, at least the first signal can be adapted so that the output information corresponds to the reference information. In that case, the amplification factor can be regarded as a measurement value representing the concentration of the substance to be measured in the measurement fluid. As a result, it is possible to remove components that do not originate in the density from the output information.

  Further, the method of the present invention can include a calibration step. In this calibration step, the chemically sensitive field effect transistor and the reference transistor are placed in a calibration environment. The calibration environment can have a known environmental condition, at which the at least one expected value of the output signal or the expected value of the output signal and the reference signal can be stored. For example, the concentration of the substance to be measured can be known. Further, for example, the substance to be measured is not included in the calibration environment. Further, the ratio of the substance to be measured in the calibration environment can be made known. Thereby, the amplification factor can be adjusted so that the output signal and the reference signal correspond to the at least one expected value. The calibration can ensure a measurement of the chemically sensitive field effect transistor at at least one operating point.

  Further, in the preparing step, the amplitude of the first signal can be an alternating amplitude, and the second signal can be prepared as a signal inverted with respect to the first signal with reference potential as a reference. In the step, the output information and the reference information can be compared using the first signal or the second signal. Amplitude can refer to the actual value of the signal, for example the voltage value of the signal. The alternating amplitude allows the chemically sensitive field effect transistor and the reference transistor to operate at a plurality of different operating points. In order to properly evaluate the output information and the reference information, the first signal or the second signal can be used as an auxiliary parameter or as a timing signal. If the second signal is an inverted signal of the first signal, the reference transistor can measure the amount if the chemically sensitive field effect transistor does not measure the amount, The reverse is also possible.

  Furthermore, in the supplying step, when the first signal has a first amplitude, the output information can represent a concentration of at least one substance in the measurement fluid, and the first signal is If it has the second amplitude, the potential of the gate electrode of the chemically sensitive field effect transistor is changed and / or the channel is inverted. In this case, the first amplitude may be different from the second amplitude. For example, when a low voltage is applied to the gate electrode, a hole is formed in the semiconductor substrate of the chemically sensitive field effect transistor. Can be played. In particular, when the first signal and the second signal are inverted with respect to a reference potential, the chemosensitive field effect transistor can be regenerated while the reference transistor is measuring. it can.

  Furthermore, the method of the present invention may include an integration step of generating overall information including the output information and the reference information, and in this case, in the comparison step, a first part representing the output information; The whole information can be separated into a second part representing the reference information. During the regeneration of the chemically sensitive field effect transistor, the output information does not include measurement related components. The overall information can be, for example, the sum of the output information and the reference information. Further, the overall information can alternately represent the output information and the reference information. In that case, the output information and the reference information can be switched in response to a timing signal. Thereby, a separate transmission line for transmitting the reference information can be reduced, and a transmission line for transmitting the output information can be shared. In that case, a plurality of components in the whole signal can be easily separated in response to the timing signal in the comparison step.

  Furthermore, in an embodiment of the present invention, it is advantageous if the amplification factor is influenced according to amplification information in the evaluation step. The amplification information can be, for example, a signal from a (external) control device. Influencing the amplification factor may change the amplification factor after the amplification factor is adapted in the comparison step. This can affect the chemically sensitive field effect transistor, for example, to change the sensitivity of the chemically sensitive field effect transistor for measurement in another measurement region.

  The preparation device includes a timing generator configured to output the first signal and the second signal, and at least one amplifier configured to amplify the first signal at the amplification factor. Can be included. Furthermore, the supply device may be configured to apply the first signal or a signal derived from the first signal at at least one gate electrode and / or source electrode of the chemically sensitive field effect transistor. it can. The supply device may be configured to apply the second signal or a signal derived from the second signal to at least one gate electrode and / or source electrode of the reference transistor. Further, the output information can represent a current flowing between the drain contact and the source contact of the chemically sensitive field effect transistor, and the reference information flows between the drain contact and the source contact of the reference transistor. Current can be represented. Further, the comparison device can include a controller. The timing generator can be configured to output periodic timing. In this case, the timing signal can be output in the form of a square wave signal, for example, in a binary system. The timing signal may be a signal that oscillates between a minimum value and a maximum value. Individual components can also be used to quickly and efficiently solve the problems underlying the present invention.

  Also advantageous is a computer program product comprising the program code of the program used to implement the above-described embodiments of the method of the invention when the program is executed on a device corresponding to a computer. The computer program product can be stored on a machine-readable carrier, such as a semiconductor memory, hard disk storage device or optical storage device.

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

  In describing the preferred embodiments of the present invention below, elements that are shown in different figures and that have similar functions have the same or similar reference numerals, and that the description of such elements is not repeated. Omitted.

  Chemosensitive field effect transistors (ChemFETs) are a new technique for measuring gas phase or liquid phase analytes. In this chemically sensitive field-effect transistor, the potential of the gate electrode is usually changed by supplying the species to be detected to the transistor gate, and the channel current of the transistor is changed by the change in the potential of the gate electrode. The channel current of the field effect transistor is often several orders of magnitude higher than the change in channel current caused by the supply of the test species at the selected operating point. This places strict requirements on current measurement. The influence of disturbance is, for example, temperature change or sensor deterioration, which changes the channel current and is not due to the presence of the test species. In order to compensate for the influence of disturbance, for example, a reference transistor having no sensitivity compared to the substance to be detected can be used. Advantageously, the semiconductor structure, geometric dimensions and electrical characteristics of the reference element are the same as the semiconductor structure, geometric dimensions and electrical characteristics of the field effect transistor which functions as a measurement sensor. In addition, good thermal coupling is achieved if both field effect transistors are slightly spatially separated. This is realized, for example, by integrating both elements on one chip. In that case, ideally, the difference in channel current between the field effect transistor functioning as the measurement sensor and the field effect transistor functioning as the reference element is caused only by the presence of the substance to be detected. In order to do this, the influence of disturbance on both field effect transistors must be the same. In addition, the field effect transistor also generates intrinsic interference effects such as channel noise and 1 / f noise. Such intrinsic disturbance effects may differ between the reference sensor and the measurement sensor, and thus cannot be compensated as described above. One means for improving the signal to noise ratio (SNR) is to reduce the measurement bandwidth. In order to achieve a particularly small measurement bandwidth, for example, a lock-in amplifier is used. Further, in the case of using an FET, 1 / f noise can be reduced as expected by directly affecting a physical cause by a so-called “switching bias”. In that case, the driving of the transistor is controlled by using a square wave AC voltage or by switching or switching off the driving control voltage. In this way, the transistors operate alternately at two different operating points, i.e. alternately with large integrations and large inversions, thereby reducing the influence of local defects.

FIG. 1 is a circuit diagram of an apparatus 100 for determining a measured value of a chemically sensitive field effect transistor according to an embodiment of the present invention. The apparatus 100 has a timing generator 102 for outputting a timing signal. The timing generator 102 has a first output terminal and a second output terminal. The timing generator 102 outputs a first timing signal at the first output terminal, and the reference potential is used as a reference. A second timing signal inverted with respect to the first timing signal is output at the second output terminal. The first output terminal of the timing generator 102 is connected to the amplifier input terminal of the first variable amplifier 104, and the second output terminal of the timing generator 102 is the amplifier input terminal of the second variable amplifier 106. It is connected to the. The first variable amplifier 104 and the second variable amplifier 106 each receive a signal at each amplifier input terminal, here a timing signal, amplify the signal at a certain amplification factor, and output the signal at each amplifier output terminal. It is configured as follows. To do this, each of the variable amplifiers 104 and 106 has a control input for receiving an amplification factor. The amplifier output terminal of the first variable amplifier 104 is connected to the drain contact D of the chemically sensitive field effect transistor 110 (CF Mess) via a first resistor R _S 108. The amplifier output terminal of the second variable amplifier 106 is connected to the drain contact D of the second chemically sensitive field effect transistor 114 (CF Ref) via the second resistor R _S 112. The chemically sensitive field effect transistor 110 is configured to detect at least one predetermined analyte in the measurement fluid, and the second chemically sensitive field effect transistor 114 is at least one predetermined fluid in the reference fluid. Is configured to detect any analyte. It is also possible to configure the second chemically sensitive field effect transistor not to detect the analyte in the reference fluid. The source contact S of CF Mess 110 is grounded. Similarly, the source contact S of the CF Ref 114 is also grounded. The gate electrode G of the CF Mess 110 affects the potential of the field effect transistor 110 by the adsorption of a predetermined analyte species of the measurement fluid, and thereby the source contact S and drain contact D of the CF Mess 110. It is configured to affect the channel current between. The gate electrode G of the CF Ref 114 affects the potential of the field effect transistor 114 by the adsorption of a predetermined analyte species of the reference fluid, which causes the contact between the source contact S and the drain contact D of the CF Ref 114 It is configured to affect the channel current between. In order to adjust to the operating point, the gate electrodes G of the chemically sensitive field effect transistors 110 and 114 can be biased by a control voltage. This is not shown in FIG. The inverting input terminal of the operational amplifier 120 is connected to the drain contact D of the CF Mess 110 through the resistor 116. The inverting input terminal of the operational amplifier 120 is also connected to the drain contact D of the CF Ref 114 via the resistor 118. The operational amplifier 120 has the inverting input terminal, a positive input terminal (that is, a non-inverting input terminal), and an output terminal. The non-inverting input terminal of the operational amplifier 120 is grounded. A resistor 122 is connected to the inverting input and output of the operational amplifier 120 (in parallel with the operational amplifier 120). The operational amplifier 120 and the resistor 122 are combined to form an inverting adder 124. The output terminal of the inverting adder 124 is connected to the input terminal of the inverting amplifier 126 or the inverter 126. The output terminal of the inverter 126 is connected to the input terminal of the synchronous demodulator 128.

  Further, it is conceivable to use a simpler circuit or configuration for supplying a signal to the inverting adder 124. FIG. 1 shows this circuit or configuration with a broken line. In this configuration, the voltages of resistors 108 and 112 are combined as currents flowing through resistors 116 and 118 and resistor R. The resistor R is connected between a connection point between the resistors 116 and 118 and a ground potential connection end. With such a configuration, the voltage V at the addition point (that is, the connection point) before the capacitance is the sum of the voltage at the resistor 108 and the voltage at the resistor 112. A capacitor (ie, capacitance) C separates the DC component. In this case, unlike FIG. 1, the operational amplifier 120 operates as a positive amplifier (that is, an impedance converter) having an amplification factor of 1, or operates as a positive amplifier exceeding 1. In this case, the inverter 126 is also omitted unlike FIG.

  The synchronous demodulator 128 further has a timing input terminal, a first output terminal, and a second output terminal. The timing input terminal of the synchronous demodulator 128 is connected to the timing output terminal of the timing generator 102. The synchronous demodulator 128 separates the signal input to the input terminal into the first signal component and the second signal component in synchronization with the timing signal input to the timing input terminal, and the first signal component. Is output at the first output end, and the second signal component is output at the second output end. The first output terminal of the synchronous demodulator 128 is connected to the negative input terminal of the integration comparator 132 via a resistor 130, and the second output terminal of the synchronous demodulator 128 is connected via another resistor 130. The integration comparator 132 is connected to the non-inverting input terminal. The inverting input terminal of the integral comparator 132 is connected to the output terminal of the integral comparator 132 via a capacitor 134, and the non-inverting input terminal of the integral comparator 132 is grounded via a capacitor 136. . The integral comparator 132 is configured to output a control value at the output terminal, and the output terminal of the integral comparator 132 is connected to the control input terminal of the first variable amplifier 104. The output terminal of the integration comparator 132 is also connected to the input terminal of the inverter 136. The output terminal of the inverter 136 is connected to the control input terminal of the second variable amplifier 106. The control input terminal of the first variable amplifier 104 is also connected to the first input terminal of the microprocessor μP 138, and the control input terminal of the second variable amplifier 106 is connected to the first input terminal of the microprocessor μP 138. 2 is connected to the input terminal. The microprocessor μP 138 affects the output amount of the first variable amplifier 104 via the first input terminal of the microprocessor, and the second variable value via the second input terminal of the microprocessor. The output amount of the amplifier 106 is affected. Further, the microprocessor μP 138 is configured to output a measurement value obtained from the control value at an output end, for example.

In other words, FIG. 1 shows a measurement circuit 100 including a ChemFET 110 that has an improved signal-to-noise ratio and reduced interference effects, and the measurement circuit 100 performs differential measurement by timing synchronization at the outputs of the two ChemFETs. Circuit. The sensor is composed of two ChemFETs (CF Mess, CF Ref) 110 and 114 and a circuit for performing differential control and measurement of both ChemFETs 110 and 114 that are synchronized in timing. One of the ChemFETs (CF Mess) 110 is in the measurement environment and the other is in the reference environment. Advantageously, the only difference between the measurement environment and the reference environment is that the amount / concentration of the substance to be measured present in the reference environment is determined. FIG. 1 shows a sensor composed of ChemFETs 110 and 114 and a measurement circuit 100. The timing generator 102 generates a square wave signal A (or another periodic signal) having a frequency f. The timing generator 102 also generates a signal B that is 180 ° phase shifted. Via variable amplifiers 104 and 106, which can be controlled separately, signal A is applied to the drain of CF Mess 110 via resistor R _S 108, and signal B is correspondingly CF Ref 114 via resistor R _S 112. Applied to the drain of Each source is connected to ground potential. The voltage applied to the drain of CF Mess 110 and the voltage applied to the drain of CF Ref 114 are summed (eg, by operational amplifier OP 120 configured as inverting adder 124). The signal obtained by this addition is demodulated by the synchronous demodulator 128 via an optional amplifier / impedance converter 126. The signal components corresponding to both half waves are compared with each other by, for example, the integration comparator 132. By this comparison, control values for the variable amplifiers 104 and 106 are derived, and the amplitudes of the signals A and B are eliminated by this control value so that the component synchronized with the timing signal at the input terminal of the synchronous demodulator 128 disappears. Follow-up control. This control value is regarded as the original measured value. It is advantageous to incorporate a microcontroller 138. This is because the measured value can be further processed directly and further intervention means are possible in the control circuit 100.

  FIG. 2 is a circuit diagram of an apparatus 100 for determining a measured value of a chemically sensitive field effect transistor 110 according to another embodiment of the present invention. As a difference from the configuration of the device shown in FIG. 1, the device 100 shown in FIG. 2 includes an amplifier output terminal of the first variable amplifier 104 and a gate electrode G of the chemically sensitive field effect transistor 110. It has a connection part to connect. A Schmitt trigger ST 200 and a resistor R 202 are arranged at this connection portion. A normal comparator can be used instead of the Schmitt trigger. That is, the Schmitt trigger ST having no hysteresis can be used. Here, the input end of the Schmitt trigger ST 200 is connected to the amplifier output end of the first variable amplifier 104. The output end of the Schmitt trigger ST 200 is connected to the gate electrode G of the chemically sensitive field effect transistor 110 via a resistor R 202. The device 100 further includes a connection for connecting the amplifier output terminal of the second variable amplifier 106 and the gate electrode G of the chemically sensitive field effect transistor 114. A Schmitt trigger ST 204 and a resistor R 206 are arranged at this connection portion. Here, the input terminal of the Schmitt trigger ST 204 is connected to the amplifier output terminal of the first variable amplifier 106. The output end of the Schmitt trigger ST 204 is connected to the gate electrode G of the chemically sensitive field effect transistor 114 via the resistor R 206.

  A difference from the circuit shown in FIG. 1 is that the circuit shown in FIG. 2 biases the gates of ChemFETs 110 and 114 in synchronization with the square wave signals A and B, thereby “switching bias”. The scheme can be implemented. The combination with the suppression of the 1 / f noise component by the “switching bias” is particularly advantageous. By first applying a bias to the gate electrodes of the ChemFETs 110 and 114, the ChemFETs 110 and 114 become operating points (“operational state”). Signals A and B consist of two half-waves, and a source-drain voltage different from 0 is applied between the drain and source of ChemFET 110, 114 only during each half-wave period. Therefore, during this period, ChemFET 110, 114 is not in operation anyway. In synchronization with this, the operating points of the FETs 110 and 114 are appropriately shifted, and the FETs 110 and 114 are in a “rest-state”. When switching between the “operational state” and the “stationary state”, the FETs 110 and 114 are switched between large inversion and large integration. This can be understood from FIG. In this figure, it can be seen that the square wave signal A or the signal is taken out after the variable amplifiers 104 and 106 and applied to the gate electrodes of the ChemFETs 110 and 114 via the optional pre-resistors R 202 and 206. In order to maintain a predetermined level, for example, Schmitt triggers (ST) 200 and 204 can be connected in front or an inverter can be connected in front. Alternatively, the square wave signal can alternatively be extracted already upstream of the variable amplifiers 104, 106 (ie directly in the timing generator 102).

FIG. 3 is a circuit diagram of an apparatus 100 for determining the measured values of the chemically sensitive field effect transistor 110 according to an embodiment of the present invention. Unlike FIG. 1, the drain contact D of the chemically sensitive field effect transistor CF Mess 110 is connected to the voltage source V _DS 300 via the resistor R _S in FIG. Furthermore, the drain contact D of the chemically sensitive field effect transistor CF Ref 114 is connected to the voltage source V _DS 302 via the resistor R _S. 1 differs from the configuration of the apparatus shown in FIG. 1 in that the apparatus 100 of the circuit diagram of FIG. 3 is connected to the amplifier output terminal of the first variable amplifier 104 via the resistor R 202 and the chemically sensitive field effect transistor 110. A connecting portion for connecting to the gate electrode G. The device 100 further includes a connection for connecting the amplifier output terminal of the second variable amplifier 106 and the gate electrode G of the chemically sensitive field effect transistor 114 via a resistor R 206.

Thus, in FIG. 3, another drive control configuration in which “switching bias” is implicitly implemented uses a “switching bias” scheme in which a constant voltage V _DS is applied across contacts S and D of one or both transistors. A circuit for realizing this is disclosed. Instead of determining the source-drain voltage by the square wave signals A and B, a constant voltage V _DS is applied between S and D. Similar to the embodiment shown in FIG. 2, a square wave signal is applied to the gate electrode through optional pre-resistors R 202,206. This depends on the amplitude of the square wave signal source - drain current I _DS is changed, therefore, the voltage measured at the shunt resistor 108 and 112 is changed. The source-drain current also depends on the chemical substance to be measured, as in the prior art. By such control, when the chemical substance to be measured exists in the CF Mess 110, the difference in voltage measured at the shunt resistors 108 and 112 disappears depending on the concentration of the chemical substance to be measured. In addition, the amplitude of the square wave signal is adapted.

  FIG. 4 is a flowchart of a method 400 for determining a measured value of a chemically sensitive field effect transistor according to an embodiment of the present invention. This method 400 can be implemented, for example, on a device according to an embodiment of the invention as shown in FIG. The method includes a preparation step 402, a supply step 404, a comparison step 404, and an evaluation step 408. In a preparation step 402, a first signal and a second signal are prepared. At least the first signal is amplified with a certain amplification factor. In the supplying step 404, output information is obtained by supplying the first signal to the chemically sensitive field effect transistor. A measurement fluid is supplied to the chemically sensitive field effect transistor. Further, in order to obtain reference information, the second signal is supplied to the reference transistor. The reference transistor is in a standard environment. In the comparison step 406, the output information is compared with the reference information, and the amplification factor is adapted according to the comparison result. In this case, for example, the amplification factor is changed greatly as the deviation between the output information and the reference information increases. In the evaluation step 408, the amplification factor is evaluated to obtain the measured value. At that time, the measurement value is obtained from the amplification factor, or the measurement value is obtained by comparison with a stored comparison table.

  FIG. 5 is a block circuit diagram of an apparatus 100 for determining a measured value of the chemically sensitive field effect transistor 110 according to an embodiment of the present invention. The apparatus 100 includes a preparation device 502, a supply device 504, a comparison device 506, and an evaluation device 508. The preparation device 502 is configured to prepare a first signal and a second signal. At least the first signal is amplified with a certain amplification factor. The supply device 504 is configured to supply the first signal to the chemically sensitive field effect transistor 110 to obtain output information. A measurement fluid is supplied to the chemically sensitive field effect transistor. The supply device 504 is further configured to supply the second signal to the reference transistor 114 to obtain reference information. The reference transistor is in a standard environment. The comparison device 506 is configured to compare the output information with the reference information in order to adapt the amplification factor depending on the comparison result between the output information and the reference information. In this case, for example, the amplification factor can be changed greatly as the deviation between the output information and the reference information increases. The evaluation device 508 is configured to evaluate the amplification factor to obtain the measurement value. In that case, the measurement value is directly obtained from the amplification factor, or the measurement value is obtained by comparison with a stored comparison table.

  The embodiments shown in the drawings and described above are merely selected as examples, and the various embodiments can be combined with each other completely or individually. One embodiment can also be supplemented with features of another embodiment.

  Also, the method steps of the present invention can be repeated and performed in an order different from that described herein.

102 timing generator 104 first variable amplifier 106 second variable amplifier 108 first resistor R _S
110 Chemically Sensitive Field Effect Transistor (CF Mess)
112 Second resistance R _S
114 Second chemically sensitive field effect transistor (CF Ref)
116, 118, 122, 130 Resistance 120 Operational amplifier 124 Inverting adder 126 Inverting amplifier / inverter 128 Synchronous demodulator 132 Integral comparator

Claims (10)

A method (400) for determining a measured value of a chemically sensitive field effect transistor (110) comprising:
The method (400) includes:
Preparing a first signal and a second signal and amplifying at least the first signal with a certain amplification factor (402);
Output information is obtained by supplying the first signal to the chemically sensitive field effect transistor (110) to which a measurement fluid is applied, and the second signal is supplied to a reference transistor (114) in a reference environment. A supplying step (404) in which reference information is obtained by supplying;
A comparison step (406) that compares the output information with the reference information, and changes the amplification factor according to a result of the comparison;
An evaluation step (408) for evaluating the amplification factor to obtain the measured value. In the comparison step (406), as the deviation between the output information and the reference information increases, the amplification factor is changed greatly.
The method (400) of claim 1. A calibration step of placing the chemically sensitive field effect transistor (110) and the reference transistor (114) in a calibration environment;
The method (400) of claim 2. In the preparation step (402), the amplitude of the first signal is an alternating amplitude, and the second signal is prepared as a signal inverted with respect to the first signal with reference to a reference potential,
In the comparison step (406), the output information and the reference information are compared using the first signal or the second signal.
The method (400) according to any one of claims 1 to 3. In the supplying step (404),
If the first signal has a first amplitude, the output information represents a concentration of at least one substance in the measurement fluid;
When the first signal has a second amplitude, the potential of the gate electrode of the chemically sensitive field effect transistor is changed and / or the channel is inverted.
The method (400) of claim 4. The method (400) includes an integration step for generating overall information including the output information and the reference information between the supply step (404) and the comparison step (406);
In the comparison step (406), the overall information is separated into a first part representing the output information and a second part representing the reference information.
The method (400) according to any one of the preceding claims.   The method (400) according to any one of the preceding claims, wherein in the evaluation step (408), the amplification factor is influenced according to given amplification information. An apparatus (100) for determining a measured value of a chemically sensitive field effect transistor (110) comprising:
The device (100)
A preparation device (502) for preparing the first signal and the second signal;
A reference transistor in a reference environment for supplying the first signal to the chemically sensitive field effect transistor (110) to which a measurement fluid is supplied in order to obtain output information and for obtaining reference information A supply device (504) for supplying the second signal to (114),
At least the first signal is amplified by an amplification factor;
The apparatus (100) further includes
A comparison device (506) for comparing the output information with the reference information and changing the amplification factor according to the comparison result;
An apparatus (100) comprising an evaluation device (508) for evaluating the amplification factor in order to obtain the measured value. The preparation device (502)
A timing generator (102) configured to output the first signal and the second signal;
Having at least one amplifier (104, 106) configured to amplify the first signal at the amplification factor;
The supply device (504)
Applying the first signal or a signal derived from the first signal to at least one gate electrode (G) and / or source electrode (S) of the chemically sensitive field effect transistor (100); and Or
The second signal or a signal derived from the second signal is applied to at least the gate electrode (G) and / or the source electrode (S) of the reference transistor (114). ,
The output information represents a current flowing between a drain contact (D) and a source contact (S) of the chemically sensitive field effect transistor (110),
The reference information represents a current flowing between a drain contact (D) and a source contact (S) of the reference transistor (114),
The comparison device (506) has a controller,
The apparatus (100) of claim 8.   A computer program comprising program code for performing the method according to any one of claims 1 to 7 when the program is executed on a signal processing device.

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