ISFET chip driving circuit of pH probe

Abstract

The invention discloses an ISFET chip driving circuit of a pH probe, and relates to an ISFET driving circuit. The device comprises an ISFET chip, a reference electrode, an operational amplifier, a current source, a resistor, a positive and negative power supply and a reference ground, the ISFET chip serves as a core and converts the concentration of H < + > ions in a solution into an electric signal; the reference electrode is an Ag / AgCl solid mixture and generates stable reference voltage to drive the sensitive grid electrode of the ISFET chip; the operational amplifier generates stable following voltage and applies the following voltage to the drain electrode of the chip; the first current source provides fixed drain-source voltage for the chip; the second current source provides floatable voltage for the source electrode of the chip; the first resistor converts the fixed current into fixed voltage, and the fixed voltage is applied to the drain-source electrode of the chip through the operational amplifier; the second resistor is used for converting the fixed current into voltage and providing partial voltage for the whole circuit; the positive and negative power supplies respectively provide positive and negative working voltages for the circuit, and the reference ground is a zero potential reference point to jointly guarantee normal operation of the circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of ISFET chip driving, and in particular to an ISFET chip driving circuit for a pH probe suitable for high-precision pH detection of solutions such as seawater, fresh water and biological body fluids. Background Art

[0002] The ocean is the largest active carbon reservoir on the earth and plays an irreplaceable role in regulating climate change. The study of ocean carbon cycle and ocean acidification requires on-site monitoring of seawater carbonate parameters. pH describes the acidity and alkalinity of seawater and is one of the four core parameters characterizing seawater carbonate. As a direct indicator parameter of ocean acidification, pH is also one of the core parameters of many international observation programs (such as the Global Ocean Observing System GOOS, the Ocean Acidification Observing Network GOA-ON, BGC-Argo, etc.) and domestic marine monitoring specifications and marine survey specifications. Because the annual decrease in the pH of ocean water is between 0.001 and 0.002, only high-precision pH measurement can meet the research needs of important frontier scientific issues such as ocean acidification.

[0003] At present, the methods for measuring seawater pH mainly include the glass electrode method, the spectrophotometry using pH indicators, and the electrochemistry method based on ISFET. The glass electrode potential method is simple, but has low precision and cannot meet the research needs such as ocean acidification; the spectrophotometry has the advantages of simple operation, high precision, and little influence by the surrounding environment, and has been widely used in research such as conventional ocean surveys and ocean acidification, but has high power consumption, high requirements for the preparation of indicators, and is not suitable for in-situ and deep-sea observations.

[0004] In recent years, the development of ion-sensitive field effect transistor (ISFET) technology has provided a new solution for ocean pH monitoring. ISFET sensors have many advantages: First, their miniaturization characteristics make them easy to integrate into various monitoring platforms; second, ISFETs have the characteristics of fast response and high sensitivity; in addition, their excellent pressure resistance makes them particularly suitable for deep-sea environmental monitoring. In the construction of the ocean acidification monitoring network, ISFET technology shows great potential. Research shows that the monitoring system based on ISFET can realize long-term continuous pH value monitoring and has high measurement accuracy. Especially in the coastal environment, the changes in pH value are often more complex and frequent, which requires more stable and reliable monitoring equipment. However, the existing ISFET driving circuits have deficiencies such as only adopting a voltage source control method and high circuit complexity.

[0005] The key technology of ISFET sensors is that the ISFET chip needs to provide stable constant current and constant voltage conditions. Based on this, this patent develops an ISFET chip driving circuit for a pH probe. Summary of the Invention

[0006] The object of the present invention is to provide an ISFET chip driving circuit for a pH probe with a simple structure, high precision and low temperature drift, aiming at the problems of insufficient voltage control stability, excessive circuit complexity and significant temperature drift existing in the prior art. This circuit is suitable for driving an ISFET chip and is applicable to deep sea and long-term in-situ pH monitoring.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] An ISFET chip driving circuit for a pH probe, comprising an ISFET chip, a reference electrode, an operational amplifier, a first current source, a second current source, a first resistor, a second resistor, a positive power supply, a negative power supply and a reference ground;

[0009] The ISFET chip includes a drain, a source and a sensitive gate; one end of the reference electrode is placed in the solution to be measured together with the sensitive gate of the ISFET chip, and the other end is connected to the reference ground of the circuit; the operational amplifier includes a positive input terminal, a negative input terminal and an output terminal, and the operational amplifier is in a follower mode, applying a fixed follower voltage to the drain of the ISFET chip; the first current source generates a fixed current, and the first current source and the first resistor work together to maintain a constant drain potential through the operational amplifier, thereby providing a stable drain-source voltage for the ISFET chip; the second current source generates a fixed current to provide a floating voltage for the source of the ISFET chip; the first resistor converts the fixed current generated by the first current source into a fixed voltage, which is applied to the drain-source of the ISFET chip after passing through the operational amplifier; the second resistor converts the fixed current of the second current source into a voltage to provide voltage division for the entire circuit; the positive power supply and the negative power supply respectively provide positive and negative working voltages for the circuit, and the reference ground is the zero potential reference point of the circuit.

[0010] Further:

[0011] The ISFET chip is an ion-sensitive field effect transistor sensitive to H + ions; the ISFET chip includes a drain, a source and a sensitive gate with a surface opening and coated with a specific sensitive material.

[0012] The reference electrode is composed of a solid mixture of Ag / AgCl. One end is placed in the solution to be measured together with the sensitive gate of the ISFET chip, and the other end is led out by a thin silver wire and connected to the reference ground of the circuit.

[0013] The operational amplifier includes a positive input terminal, a negative input terminal and an output terminal. The negative input of the operational amplifier is connected to the output terminal to form a follower, applying a fixed follower voltage to the drain of the ISFET chip.

[0014] The first current source generates a fixed microampere-level current; the upper end of the first current source is connected to the positive power supply, and the lower end is connected to the upper end of the first resistor.

[0015] The second current source generates a fixed microampere-level current; the upper end of the second current source is connected to the lower end of the first resistor, and the lower end is connected to the upper end of the second resistor.

[0016] The first resistor converts the fixed current generated by the first current source into a fixed voltage; the upper end of the first resistor is connected to the positive input of the operational amplifier, and the lower end is connected to the source of the ISFET chip.

[0017] The second resistor converts the fixed current generated by the second current source into a fixed voltage; the upper end of the second resistor is connected to the lower end of the second current source, and the lower end is connected to the negative power supply.

[0018] The positive power supply and the negative power supply respectively provide positive and negative working voltages for the circuit, and the reference ground is the zero potential reference point of the circuit.

[0019] The specific sensitive material of the sensitive gate of the ISFET chip includes but is not limited to Ta2O5.

[0020] The output terminal of the operational amplifier is directly connected to the drain (D) of the ISFET chip, and the drain potential is maintained constant through feedback control. At the same time, the source (S) voltage floats with the change of the solution pH value.

[0021] The input bias current of the operational amplifier can be selected to be less than 1 picoampere, and the accuracy of the first resistor and the second resistor can be 0.1%.

[0022] Due to the adoption of the above structure in the present invention, compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The present invention adopts a compact design, with a simple, stable structure and low power consumption; compared with the existing ISFET drive circuit that only adopts the voltage source control method and has a high circuit complexity, the present invention realizes the effective drive of the ISFET chip with a simple structure through the coordinated cooperation of the dual current sources and the dual resistors, and the follower circuit composed of the operational amplifier. By reducing unnecessary components and complex connection relationships, not only the circuit design and manufacturing costs are reduced, but also the stability of the circuit is improved, and the probability of faults is reduced.

[0024] 2. The operational amplifier of the present invention selects a model with an input bias current lower than 1 pA, which greatly reduces noise interference. At the same time, the accuracy of the first resistor and the second resistor reaches 0.1%. The combination of the two enables the entire circuit to accurately control voltage and current during operation, effectively improving the accuracy of pH potential output. Moreover, the characteristics of low noise and high precision can also significantly reduce the drift phenomenon of the circuit, ensuring the accuracy and stability of long-term measurement and meeting the requirements of high-precision pH measurement in research such as ocean acidification.

[0025] 3. The present invention adopts the collaborative design of a dual current source and a high-precision resistor to achieve precise control of the drain-source voltage of the ISFET chip. The first current source generates a fixed current, which is converted into a fixed voltage by the first resistor and then applied to the drain-source electrodes to maintain a constant drain potential. The second current source generates a fixed current, which cooperates with the second resistor to provide a floating voltage for the source electrode, enabling the source potential to dynamically float with the change of the solution pH value, thereby achieving high-precision measurement of the solution pH value. Compared with the prior art, it is more precise and flexible in potential control and measurement.

[0026] 4. The drive circuit of the present invention is applicable to pH detection of various solutions such as seawater, fresh water, and biological fluids. The circuit can work stably and reliably, overcoming the limitations of the prior art such as low precision of the glass electrode method and high power consumption and inapplicability to in-situ deep-sea observation of the spectrophotometry method, and has a wider application scenario and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the overall structure of an embodiment of the present invention.

[0028] Each label in the figure is: ISFET chip 1, reference electrode 2, operational amplifier 3, first current source 4, second current source 5, first resistor 6, second resistor 7, positive power supply 8, negative power supply 9, reference ground 10, drain D, source S, and sensitive gate G. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] In order to make the technical problems, technical solutions, and beneficial effects to be solved by the present invention clearer and more understandable, the following further describes the present invention in detail with reference to the drawings and embodiments.

[0030] As Figure 1 shown, an embodiment of the ISFET chip drive circuit of a pH probe of the present invention includes an ISFET chip 1, a reference electrode 2, an operational amplifier 3, a first current source 4, a second current source 5, a first resistor 6, a second resistor 7, a positive power supply 8, a negative power supply 9, and a reference ground 10.

[0031] The ISFET chip 1 is used as a device for detecting H +Ion-sensitive ion-sensitive field-effect transistor, the ISFET chip 1 includes a drain D, a source S, and a sensitive gate G; the drain D is connected to the output terminal of the operational amplifier 3 for receiving the fixed potential applied by the operational amplifier; the source S is connected to the lower end of the first resistor 6, and its potential will float with the change of the solution pH value; the sensitive gate G is immersed in the solution to be measured. A window is opened on the surface of the sensitive gate G and coated with a specific sensitive material for sensing H + ion concentration change. The sensitive gate G is immersed in the solution to be measured to sense the H + ion information in real time. In this embodiment, the sensitive film of the ISFET chip 1 is Ta2O5, and its threshold voltage changes with the solution pH value.

[0032] The reference electrode 2 is composed of a solid mixture of Ag / AgCl. One end of the reference electrode 2 is immersed in the solution to be measured together with the sensitive gate G of the ISFET chip 1 for providing a stable potential reference; the other end of the reference electrode 2 is connected to the reference ground 10 of the circuit to ensure a stable zero-potential reference for the entire circuit.

[0033] The operational amplifier 3 includes a positive input terminal, a negative input terminal, and an output terminal; the output terminal is connected to the negative input terminal to form a follower circuit; this follower applies a fixed follower voltage to the drain D of the ISFET chip, and maintains the constant potential of the drain D through feedback control. The input bias current of the selected operational amplifier should be as small as possible. When selecting, the operational amplifier 3 selects a model with an input bias current lower than 1 picoampere (such as AD8605ARTZ - REEL7) to reduce noise interference and ensure the measurement accuracy of the circuit.

[0034] The first current source 4 is used to generate a fixed microampere-level current. The upper end of the first current source 4 is connected to the positive power supply 8; the lower end of the first current source 4 is connected to the upper end of the first resistor 6 and the positive input terminal of the operational amplifier 3. The fixed current generated by the first current source is converted into a fixed voltage through the first resistor to provide a stable drain-source voltage for the ISFET chip 1. In this embodiment, the output current of the first current source 4 is 50 μA.

[0035] The second current source 5 is used to generate a fixed microampere-level current. The upper end of the second current source 5 is connected to the source S of the first resistor 6 and the ISFET chip 1; the lower end of the second current source 5 is connected to the second resistor 7. The second current source 5 and the second resistor 7 form a voltage division circuit. The fixed current generated by the second current source 5 is converted into a voltage through the second resistor 7, and the circuit formed with the second current source provides a floating voltage for the source S of the ISFET chip 1, so that the potential of the source S floats with the change of the ISFET threshold voltage, and is used to output the pH potential of the solution to be measured. The threshold voltage is related to the pH value of the solution.

[0036] The first resistor 6 is used to convert the fixed current generated by the first current source into a fixed voltage. The upper end of the first resistor 6 is connected to the positive input of the operational amplifier 3, and the lower end of the first resistor 6 is connected to the source S of the ISFET chip. In this embodiment, the resistance of the first resistor is 10 k ohms. According to Ohm's law (U = R*I), the first resistor 6 can generate a fixed voltage drop of 0.5 V, and this voltage drop is applied to the drain-source of the ISFET chip 1 through the follower formed by the operational amplifier 3.

[0037] The second resistor 7 is used to convert the fixed current generated by the second current source 5 into a fixed voltage. The upper end of the second resistor 7 is connected to the lower end of the second current source, and the lower end of the second resistor 7 is connected to the negative power supply 9; the fixed voltage drop generated by the second resistor 7 and the circuit formed by the second current source 5 can generate a floating voltage, and output the pH potential of the solution to be measured for the source S of the ISFET chip 1.

[0038] The accuracy of the first resistor 6 and the second resistor 7 is 0.1%, which is used to improve the stability of voltage conversion. The resistance value of the first resistor 6 is 10 kΩ, and the drain-source voltage is fixed at 0.5 V.

[0039] The positive power supply 8 and the negative power supply 9 respectively provide positive and negative working voltages for the entire circuit to ensure the normal operation of each component in the circuit.

[0040] The reference ground 10 is connected to the zero potential reference point of the entire circuit.

[0041] Through the above detailed circuit design and functional configuration, an ISFET chip driving circuit of a pH probe can realize the function of detecting the pH potential of the solution to be measured.

[0042] The working principle of the circuit of the present invention is as follows:

[0043] When the sensitive gate of the ISFET chip is immersed in the solution to be measured, H in the solution +Ions interact with the sensitive material on the surface of the sensitive gate G, thereby changing the electrical characteristics of the ISFET chip, causing the potential of the source S to float with the change of the solution pH value. The fixed current generated by the first current source is converted into a fixed voltage through the first resistor, and then applied to the drain-source of the ISFET chip through a follower composed of an operational amplifier to maintain the constant potential of the drain D. The fixed current generated by the second current source is converted into a voltage through the second resistor, and the circuit composed of the second current source provides a floating voltage for the source S of the ISFET chip. Finally, the potential change output by the source S reflects the pH value information of the solution to be measured.

[0044] In view of the problems of insufficient voltage control stability, complex circuit and significant temperature drift in the prior art, the present invention proposes a design of dual constant current sources and 0.1% precision resistor voltage division, combines an operational amplifier voltage follower to lock the drain potential of the ISFET, and suppresses noise through a filter capacitor. The first current source and the first resistor generate a fixed drain-source voltage, and the second current source and the second resistor make the source potential float with the pH value. Through the collaborative design of the dual current sources and 0.1% precision resistors, the drain potential is locked by a high-precision operational amplifier, and the source voltage is only affected by the pH change, thereby reducing the temperature drift and noise. The circuit structure is concise, with an accuracy of 0.001pH and a temperature drift less than 0.001 / 24h, suitable for high-precision in-situ monitoring of seawater, fresh water and biological fluids.

[0045] The above embodiments are only preferred embodiments of the present invention and should not be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention application shall still fall within the scope covered by the patent of the present invention.

Claims

1. An ISFET chip driving circuit for a pH probe, characterized in that It includes an ISFET chip, a reference electrode, an operational amplifier, a first current source, a second current source, a first resistor, a second resistor, a positive power supply, a negative power supply, and a reference ground; The ISFET chip includes a drain, a source, and a sensitive gate; One end of the reference electrode is placed in the solution to be measured together with the sensitive gate of the ISFET chip, and the other end is connected to the reference ground of the circuit; The operational amplifier includes a positive input terminal, a negative input terminal, and an output terminal. The operational amplifier is in a follower mode, and a fixed follower voltage is applied to the drain of the ISFET chip; The first current source generates a fixed current. The first current source and the first resistor work together to maintain a constant drain potential through the operational amplifier, thereby providing a stable drain-source voltage for the ISFET chip; The second current source generates a fixed current and provides a floating voltage for the source of the ISFET chip; The first resistor converts the fixed current generated by the first current source into a fixed voltage, which is applied to the drain-source of the ISFET chip after passing through the operational amplifier; The second resistor converts the fixed current of the second current source into a voltage to provide voltage division for the entire circuit; The positive power supply and the negative power supply respectively provide positive and negative working voltages for the circuit, and the reference ground is the zero potential reference point of the circuit.

2. The ISFET chip driving circuit of a pH probe according to claim 1, characterized in that The ISFET chip is an ion-sensitive field-effect transistor sensitive to H + ions; the ISFET chip includes a drain, a source, and a sensitive gate with a surface opening and coated with a specific sensitive material.

3. The ISFET chip driving circuit of a pH probe according to claim 1, characterized in that The reference electrode is composed of a solid mixture of Ag / AgCl.

4. The ISFET chip driving circuit of a pH probe according to claim 1, characterized in that The operational amplifier includes a positive input terminal, a negative input terminal, and an output terminal. The negative input of the operational amplifier is connected to the output terminal to form a follower, and a fixed follower voltage is applied to the drain of the ISFET chip.

5. The ISFET chip driving circuit of a pH probe according to claim 1, characterized in that The first current source generates a fixed microampere-level current; The upper end of the first current source is connected to the positive power supply, and the lower end of the first current source is connected to the upper end of the first resistor.

6. The ISFET chip driving circuit of a pH probe according to claim 1, characterized in that The second current source generates a fixed microampere-level current; The upper end of the second current source is connected to the lower end of the first resistor, and the lower end of the second current source is connected to the upper end of the second resistor.

7. The ISFET chip driving circuit of a pH probe according to claim 1, characterized in that The first resistor converts the fixed current generated by the first current source into a fixed voltage; The upper end of the first resistor is connected to the positive input of the operational amplifier, and the lower end of the first resistor is connected to the source of the ISFET chip.

8. The ISFET chip driving circuit of a pH probe according to claim 1, characterized in that The second resistor converts the fixed current generated by the second current source into a fixed voltage; The upper end of the second resistor is connected to the lower end of the second current source, and the lower end of the second resistor is connected to the negative power supply.

9. The ISFET chip driving circuit of a pH probe as described in claim 1, wherein The positive power supply and the negative power supply respectively provide positive and negative working voltages for the circuit, and the reference ground is the zero potential reference point of the circuit.

10. The ISFET chip driving circuit of a pH probe according to claim 1, characterized in that The output terminal of the operational amplifier is directly connected to the drain of the ISFET chip, and the drain potential is maintained constant through feedback control. At the same time, the source voltage floats with the change of the solution pH value.

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