Low leakage current voltage limiting protection circuit

Abstract

The invention discloses a low leakage current voltage limiting protection circuit, and relates to the technical field of weak current detection. The circuit comprises a sampling circuit, a protection branch and a voltage driver. The protection branch is connected in parallel with two ends of the sampling circuit and is composed of a bidirectional voltage limiter and a leakage current protection device which are connected in series. The voltage driver follows the voltage of the low potential side of the sampling circuit in real time and drives the midpoint of the protection branch to be equipotential with the sampling circuit, so that the voltage difference between the two ends of the leakage current protection device is eliminated, and a leakage current path is blocked during normal work; when overvoltage occurs, the protection branch is conducted to discharge overcurrent. By introducing an isolation resistor, phase compensation in a loop and a dual feedback technology, the oscillation problem during capacitive load driving is solved, and the following precision is ensured; and a bootstrap power supply and a transient clamping technology are further combined, so that the high-voltage common-mode range and the anti-surge capability of the circuit are expanded, and high-precision weak current protection under a low-cost device is realized.

Description

Technical Field

[0001] This application relates to the field of weak current detection, and in particular to a low leakage current limiting voltage protection circuit. Background Technology

[0002] Weak current detection technology is widely used in scientific fields such as analytical chemistry, biomedical monitoring, materials physics research, and precision testing and measurement. In these applications, the signal to be measured is often very low in amplitude, typically in the picoampere or even femtoampere range. This means that the front-end acquisition circuit needs to have a very high input impedance and signal-to-noise ratio. To prevent damage to expensive precision sampling resistors and subsequent processing chips from unexpected large currents or transient high voltages, an overvoltage protection circuit is usually connected in parallel at the signal input in engineering designs.

[0003] Traditional overvoltage protection schemes typically involve directly connecting nonlinear components such as Zener diodes, varistors, or transient voltage suppressors in parallel across the sampling resistor. These protective components operate by utilizing their breakdown characteristics at specific voltages to limit the voltage amplitude. However, these semiconductor devices are not ideal insulators under normal operating conditions, below their breakdown voltage. Due to the physical characteristics of semiconductors, a certain amount of reverse leakage current always exists within the device. In conventional current measurements, this leakage current may be negligible, but in weak current detection, the leakage current amplitude of the protective component may be on the same order of magnitude as, or even exceed, the measured signal.

[0004] The presence of this leakage current creates a bypass current, directly causing the current flowing through the sampling resistor to be less than the actual input current, thus introducing measurement errors. More complexly, the leakage current generated by protection devices typically has a non-linear relationship with the voltage difference across the device and is highly sensitive to changes in ambient temperature. This means that the error caused by leakage current is difficult to calculate using simple linear formulas, and subsequent software algorithms struggle to accurately model and compensate for it.

[0005] To mitigate the impact of leakage current, current technologies typically employ expensive, ultra-low leakage current specialized devices or use complex screening processes to select qualified components, significantly increasing hardware design costs and manufacturing complexity. Furthermore, even with high-performance devices, leakage current cannot be completely eliminated physically when a voltage difference exists between the two ends. Summary of the Invention

[0006] To provide a circuit scheme for achieving high-precision measurement using conventional components, this application provides a low leakage current voltage limiting protection circuit.

[0007] Firstly, this application provides a low leakage current voltage limiting protection circuit, which adopts the following technical solution: A low leakage current voltage limiting protection circuit includes: The sampling circuit receives the signal to be measured at the input terminal and forms a low potential side at the output terminal; A protection branch is connected in parallel across the two ends of the sampling circuit; the protection branch includes a bidirectional voltage limiter and a leakage current protection device connected in series, and the connection node of the two is defined as a common connection point; wherein, the bidirectional voltage limiter is connected between the input terminal of the measured signal and the common connection point, and the leakage current protection device is connected between the common connection point and the low potential side of the sampling circuit. A voltage driver is provided, with its input coupled to the low-potential side of the sampling circuit and its output coupled to the common connection point. The voltage driver is configured to follow the voltage of the low-potential side of the sampling circuit in real time and drive the common connection point to a potential substantially equal to that of the low-potential side of the sampling circuit, thereby eliminating the voltage difference across the leakage current protection device. When the voltage drop across the sampling circuit exceeds a preset voltage threshold, the leakage current protection device and the bidirectional voltage limiter are turned on together to discharge the overcurrent.

[0008] By adopting the above technical solution, the voltage driver tracks the voltage on the low-potential side of the sampling circuit in real time and drives the common connection point to equipotential, eliminating the voltage difference across the leakage current protection device. This physically blocks the path of leakage current to the sampling circuit, solving the problem of weak signal measurement error caused by nonlinear leakage current in traditional protection devices. The series-connected bidirectional voltage limiter and leakage current protection device maintain high-impedance isolation during normal operation using the equipotential state of the common connection point. When the voltage drop across the sampling circuit exceeds a preset voltage threshold, they conduct together to form a bypass discharge channel, thus achieving overvoltage protection for the sampling circuit without affecting measurement accuracy.

[0009] Optionally, the leakage current protection device includes at least two low leakage current diodes connected in reverse parallel, or a bridge rectifier structure composed of diodes, which is in a zero-bias high-impedance state due to the equal potential at both ends under normal operating conditions; the bidirectional voltage limiter includes a bidirectional transient voltage suppression diode, a varistor, or a Zener diode connected in series back to back.

[0010] By adopting the above technical solution, and utilizing a reverse-parallel low-leakage diode or a diode bridge rectifier structure, the leakage current protection device possesses bidirectional conduction capability, enabling it to adapt to measured signals with varying polarities. Furthermore, by leveraging the extremely high impedance characteristics of the diodes near zero bias, it achieves physical isolation of the sampling circuit under normal operating conditions in conjunction with equipotential drive. This structure blocks the inherent leakage current path of the bidirectional voltage limiter, allowing the selection of low-cost but high-leakage-current bidirectional transient voltage suppression diodes, varistors, or back-to-back Zener diodes as core clamping components. This reduces the cost and difficulty of device selection while ensuring high insulation of the protection circuit for weak signal detection when not activated, and providing bidirectional clamping protection to the sampling circuit during overvoltage through the rapid response characteristics of the bidirectional voltage limiter.

[0011] Optionally, the voltage driver includes: An operational amplifier, wherein the non-inverting input of the operational amplifier is connected to the low-potential side of the sampling circuit; A feedback network is coupled between the output of the operational amplifier and the inverting input of the operational amplifier. A current-limiting resistor is connected in series between the output terminal of the operational amplifier and the common connection point to limit the current flowing out of the operational amplifier in a protected state; wherein the operational amplifier adjusts the output voltage through the feedback network to drive the common connection point.

[0012] By employing the above technical solution, a voltage-following closed loop is constructed using an operational amplifier combined with a feedback network. This replicates the voltage on the low-potential side of the sampling circuit to the common connection point with low impedance characteristics. While ensuring driving capability, the high input impedance of the operational amplifier prevents current shunting of the measured signal. The current-limiting resistor connected in series in the output path acts as a buffer barrier between the active device and the protection network. Under the protection state where the bidirectional voltage limiter and leakage current protection device are conducting to discharge overcurrent, this resistor withstands the voltage difference between the operational amplifier output and the forcibly clamped common connection point. This limits the current amplitude flowing through the operational amplifier output stage, preventing overheating and burnout of the internal transistors due to overcurrent or reverse current sinking, thus ensuring the survivability of the core driving components when a circuit fault occurs and protection actions are executed.

[0013] Optionally, the feedback network includes: A high-frequency feedback capacitor is connected between the inverting input terminal and the output terminal of the operational amplifier. The connection point between the high-frequency feedback capacitor and the output terminal of the operational amplifier is located between the current-limiting resistor and the output terminal of the operational amplifier; the high-frequency feedback capacitor is used to establish a local high-frequency feedback loop to provide leading phase compensation when the protection circuit is in a high-impedance state.

[0014] By employing the above technical solution, a local high-frequency feedback loop without a current-limiting resistor is constructed using a high-frequency feedback capacitor connected between the operational amplifier's output and inverting input. This loop provides a low-impedance direct feedback path for the operational amplifier in the high-frequency range, effectively bypassing the phase lag introduced by the poles formed by the current-limiting resistor and the junction capacitance of the leakage current protection device. This design introduces leading phase compensation into the feedback loop, increasing the system's phase margin and thus eliminating the risk of high-frequency oscillations or overshoot when the operational amplifier drives a protection branch with nonlinear capacitive load characteristics, ensuring the closed-loop stability of the voltage driver over a wide bandwidth.

[0015] Optionally, the feedback network further includes a DC precise feedback path, one end of which is connected to the common connection point and the other end of which is connected to the inverting input terminal of the operational amplifier. The DC precise feedback path and the high-frequency feedback capacitor together form a composite feedback network: the high-frequency feedback capacitor dominates in the high-frequency band to maintain loop stability, while the DC precise feedback path dominates in the DC and low-frequency bands, extending the sampling point of the operational amplifier to the common connection point, thereby forcing the operational amplifier to output a higher voltage to compensate for the voltage drop across the current-limiting resistor.

[0016] By employing the above technical solution, a dual feedback topology consisting of a DC precision feedback path and a high-frequency feedback capacitor is used to resolve the contradiction between voltage following error introduced by the current-limiting resistor and system stability. In the DC and low-frequency operating range, the DC precision feedback path physically extends the voltage sampling point to the common connection point at the rear end of the current-limiting resistor. Closed-loop control forces the operational amplifier to increase the output voltage to offset the voltage drop across the current-limiting resistor caused by input bias current or minor leakage current, achieving Kelvin-like precise following of the sampling circuit potential. Simultaneously, in the high-frequency range, the high-frequency feedback capacitor dominates the loop response, bypassing external hysteresis poles. This ensures microvolt-level zero-dropout accuracy while maintaining the closed-loop stability of the drive circuit for capacitive loads.

[0017] Optionally, the voltage driver further includes a bootstrap power supply network, the operational amplifier having a positive power supply terminal and a negative power supply terminal connected to the bootstrap power supply network; the bootstrap power supply network is configured to float following the low-potential side of the sampling circuit, such that the supply voltage of the operational amplifier is always maintained within a fixed differential voltage range relative to the measured signal.

[0018] By employing the above technical solution, the power rail of the operational amplifier is driven by a bootstrap power network to float synchronously with the low-potential side of the measured signal, ensuring that the supply voltage of the operational amplifier remains constant relative to the input signal. This design eliminates the voltage withstand limitation imposed by high common-mode voltage on the operational amplifier's input stage and power supply pins, ensuring that the device always operates in a safe, relatively low-voltage environment. Thus, a conventional low-voltage operational amplifier is used to detect and protect weak current signals under high common-mode voltage conditions, significantly expanding the system's common-mode input range.

[0019] Optionally, it also includes a transient input clamping circuit, the transient input clamping circuit comprising: A first clamping diode is connected between the non-inverting input terminal and the positive power supply terminal of the operational amplifier; The second clamping diode is connected between the non-inverting input terminal and the negative power supply terminal; When the rise rate of the measured signal exceeds the tracking rate of the bootstrap power network, the first clamping diode and the second clamping diode clamp the input stage voltage difference of the operational amplifier within a safe range.

[0020] By employing the above technical solution, the problem of operational amplifier input overvoltage caused by response lag in bootstrap power networks when facing high-speed transient signals is solved. When the rate of change of the input signal exceeds the settling speed of the power network, the clamping diode connected between the input terminal and the power rail quickly conducts, providing a discharge path for transient current and limiting the voltage difference between the input terminal and the power supply terminal within the diode's forward voltage drop range. This mechanism prevents the operational amplifier input stage from breaking down or latching up due to stress exceeding the instantaneous power supply voltage, ensuring the safety and reliability of the drive circuit throughout the full dynamic range.

[0021] In summary, this application includes at least one of the following beneficial technical effects: 1. This application utilizes a voltage driver to track the voltage on the low-potential side of the sampling circuit in real time and drive the common connection point of the protection branch. This physically eliminates the potential difference across the leakage current protection device, effectively blocking the path of leakage current to the sampling circuit during normal operation. This solution solves the problem of reduced measurement accuracy of weak signals caused by the nonlinear leakage current of protection devices in traditional overvoltage protection circuits, enabling designers to achieve picoampere-level or even lower current detection protection using conventional low-cost components. 2. This application resolves the contradiction between stability and voltage tracking accuracy when an operational amplifier drives a large capacitive load by introducing a composite feedback control topology consisting of a current-limiting resistor, a high-frequency feedback capacitor, and a DC precision feedback path. The high-frequency feedback loop provides necessary lead phase compensation to suppress self-oscillation, while the DC precision feedback loop forces the operational amplifier to output a compensation voltage to offset the voltage drop across the current-limiting resistor, thereby ensuring the stability of the circuit closed loop while achieving accurate replication of the sampled potential. 3. This application combines a bootstrap power network with a transient input clamping circuit to construct a power supply environment that dynamically floats with the input signal, significantly expanding the common-mode operating range of the protection circuit. The bootstrap structure enables the operational amplifier to operate normally at high common-mode voltages far exceeding its own withstand voltage limit, while the transient clamping mechanism effectively prevents input stage overvoltage damage caused by power-up lag for nanosecond-level fast-edge signals, thereby ensuring the versatility of the core driving device in complex electromagnetic environments and high-voltage application scenarios. Attached Figure Description

[0022] Figure 1 A block diagram illustrating the overall structure of a low leakage current voltage limiting protection circuit in one embodiment of the present invention is shown.

[0023] Figure 2 A schematic diagram of a voltage drive unit circuit is shown in one embodiment of the present invention.

[0024] Figure 3 A schematic diagram of a voltage driver circuit is shown in one embodiment of the present invention. Detailed Implementation

[0025] The present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the application and are not intended to limit the scope of the application.

[0026] In the following description, numerous specific details are set forth for purposes of explanation in order to provide a thorough understanding of the inventive concept. As part of this specification, some of the accompanying drawings of this disclosure are block diagrams illustrating structures and devices to avoid complicating the disclosed principles. For clarity, not all features of the actual embodiment need to be described. Furthermore, the language used in this disclosure has been primarily chosen for readability and instructional purposes and may not have been chosen to define or limit the subject matter of the invention, thus requiring the necessary claims to determine such inventive subject matter. References to “an embodiment” or “an embodiment” in this disclosure mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment, and multiple references to “an embodiment” or “an embodiment” should not be construed as necessarily referring to the same embodiment.

[0027] Unless explicitly defined, the terms “a,” “an,” and “the” are not intended to refer to a singular entity, but rather to include a general category whose specific examples can be used for illustration. Therefore, the use of the terms “a” or “an” can mean any number of at least one, including “a,” “one or more,” “at least one,” and “one or more.” The term “or” means any of the options and any combination of the options, including all options unless explicitly indicated that the options are mutually exclusive. The phrase “at least one of” when combined with a list of items refers to a single item in the list or any combination of items in the list. The phrase does not require all items listed unless explicitly defined as such. Example 1

[0028] This embodiment provides a low leakage current voltage limiting protection circuit for use in a weak current detection system. The circuit mainly consists of three parts: a sampling circuit, a protection branch, and a voltage driver.

[0029] Sampling circuits typically include high-precision sampling resistors connected in series in the transmission path of the measured signal. The sampling circuit receives a weak measured current signal (e.g., picoampere or femtoampere level current) at its input. After the signal flows through the sampling resistor, a low-potential side is formed at the output. This low-potential side is typically connected to the input of a subsequent transimpedance amplifier or analog-to-digital converter.

[0030] A protection branch is connected in parallel across the sampling circuit to prevent excessive input voltage from damaging the sampling circuit or subsequent devices. The protection branch includes a bidirectional voltage limiter and a leakage current protection device connected in series. Their connection point is defined as the common connection point (node ​​A). One end of the bidirectional voltage limiter is connected to the input terminal (high potential side) of the measured signal, and the other end is connected to the common connection point; one end of the leakage current protection device is connected to the common connection point, and the other end is connected to the low potential side of the sampling circuit.

[0031] In specific selection, the leakage current protection device preferably includes at least two low-leakage diodes connected in reverse parallel (e.g., the gate-drain junction of a low-leakage current JFET or a dedicated low-leakage diode), or a bridge rectifier structure consisting of four diodes. This structure utilizes the physical characteristic of diodes having extremely high impedance at zero bias voltage to achieve isolation. The bidirectional voltage limiter can be a bidirectional transient voltage suppressor diode, a varistor (MOV), or two Zener diodes connected back-to-back in series, with its breakdown voltage set according to the maximum withstand voltage allowed by the sampling circuit.

[0032] The input of the voltage driver is coupled to the low-potential side of the sampling circuit, and the output is coupled to the common connection point. The voltage driver is configured as a unity-gain voltage follower system, which monitors the voltage fluctuations on the low-potential side of the sampling circuit in real time and drives the common connection point (node ​​A) to a potential substantially equal to that of the low-potential side.

[0033] Working principle analysis: Under normal measurement conditions, the amplitude of the measured signal is within a safe range. The voltage driver ensures that the potential at the common connection point strictly follows the potential on the low-potential side of the sampling circuit, so that the voltage difference across the leakage current protection device is within acceptable limits. Approaching zero. According to Ohm's law and the characteristics of semiconductor PN junctions, under zero bias, the leakage current flowing through the leakage current protection device is extremely small (theoretically approaching zero), thus blocking the leakage current path shunted through the protection branch and realizing high-precision measurement of weak current.

[0034] When a circuit fault occurs, if the voltage drop across the sampling circuit exceeds the preset voltage threshold (i.e., exceeds the sum of the breakdown voltage of the bidirectional voltage limiter and the forward conduction voltage drop of the leakage current protection device), the bidirectional voltage limiter breaks down and conducts, and the leakage current protection device conducts in the forward direction. At this time, the protection branch forms a low-impedance discharge path, bypassing the overcurrent to ground or discharging it to a low potential, clamping the voltage across the sampling circuit within a safe range. Example 2

[0035] like Figure 2 As shown, the voltage driver mainly includes an operational amplifier, a feedback network, and a current-limiting resistor. The non-inverting input of the operational amplifier is connected to the low-potential side of the sampling circuit as a reference input. The current-limiting resistor... This resistor is connected in series between the output of the operational amplifier and the common connection point. Its function is crucial: when the protection branch conducts to discharge overcurrent, the potential at the common connection point is forcibly clamped. At this time, the operational amplifier still attempts to output a following voltage. The current-limiting resistor absorbs the voltage difference between the two, limiting the current flowing out of the operational amplifier and preventing overload and burnout.

[0036] However, the leakage current protection device has a nonlinear junction capacitance, which, together with the current-limiting resistor, forms a low-pass filter. This introduces additional phase hysteresis into the feedback loop, easily causing the operational amplifier to oscillate. To solve this problem, this embodiment employs a dual feedback architecture: The first layer of feedback is a high-frequency feedback capacitor. It is connected between the inverting input and output of the operational amplifier (i.e., before the current-limiting resistor). This capacitor establishes a local loop (high-frequency feedback loop). At higher signal frequencies, due to the reduced capacitor impedance, the feedback signal is mainly transmitted through this path, providing lead phase compensation, effectively offsetting the phase lag caused by the load capacitor, and ensuring loop stability.

[0037] The second feedback loop is a DC precision feedback path, with one end connected to the point of common coupling (after the current-limiting resistor) and the other end connected to the inverting input of the operational amplifier. This path dominates feedback control in the DC and low-frequency range. It physically extends the sampling point beyond the current-limiting resistor, forming a Kelvin connection. This means the operational amplifier must output a voltage slightly higher than the low-potential side to accurately compensate for the voltage drop across the current-limiting resistor caused by input bias current or minor leakage current. The potential of the common connection point is forced to be exactly equal to the low potential side of the sampling circuit.

[0038] Through the aforementioned composite feedback network, this embodiment utilizes capacitor dominance to maintain stability in the high-frequency band and DC path dominance to eliminate errors caused by current-limiting resistors in the low-frequency band, while achieving excellent dynamic stability and extremely high static tracking accuracy. Example 3

[0039] like Figure 3 As shown, this embodiment features enhanced design for high common-mode voltage input and transient surge conditions.

[0040] In actual industrial settings, weak current signals are often superimposed on common-mode voltages of tens or even hundreds of volts. The supply voltage of ordinary operational amplifiers is typically limited by... The left and right sides cannot directly process high common-mode signals. Therefore, this embodiment introduces a bootstrap power supply network. The positive power supply terminal of the operational amplifier... and negative power supply terminal Instead of grounding, it is connected to a bootstrap power network. This network floats with the low-potential side of the sampling circuit as a reference ground. For example, a Zener diode or a floating power module can be used to enable... Always 15V higher than the low potential side. It is always 15V lower than the low potential side. Regardless of the fluctuation of the common-mode voltage, the supply voltage difference across the operational amplifier remains constant, thus enabling it to operate safely in high-voltage environments far exceeding its absolute withstand voltage limit.

[0041] In addition, to handle nanosecond-level rapid transient pulses (such as ESD electrostatic discharge), the circuit includes a first clamping diode D1 (connected to the non-inverting input and...). (between) and the second clamping diode D2 (connected to the non-inverting input terminal and) between).

[0042] When the measured signal undergoes a very rapid transition, the voltage build-up speed of the bootstrap power supply network may lag behind the input signal because the network typically includes energy storage capacitors. This time difference can cause the input voltage of the operational amplifier to momentarily exceed the power rail voltage, potentially damaging the device. At this point, a clamping diode quickly conducts, forcibly clamping the input stage voltage difference within a safe range of the diode's forward voltage drop (approximately 0.7V) until the bootstrap power supply network completes voltage tracking. This mechanism significantly improves the circuit's robustness in harsh electromagnetic environments.

[0043] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A low leakage current voltage limiting protection circuit, characterized in that, include: The sampling circuit receives the signal to be measured at the input terminal and forms a low potential side at the output terminal; A protection branch is connected in parallel across the two ends of the sampling circuit; the protection branch includes a bidirectional voltage limiter and a leakage current protection device connected in series, and the connection node of the two is defined as a common connection point; wherein, the bidirectional voltage limiter is connected between the input terminal of the measured signal and the common connection point, and the leakage current protection device is connected between the common connection point and the low potential side of the sampling circuit. A voltage driver is provided, with its input coupled to the low-potential side of the sampling circuit and its output coupled to the common connection point. The voltage driver is configured to follow the voltage of the low-potential side of the sampling circuit in real time and drive the common connection point to a potential substantially equal to that of the low-potential side of the sampling circuit, thereby eliminating the voltage difference across the leakage current protection device. When the voltage drop across the sampling circuit exceeds a preset voltage threshold, the leakage current protection device and the bidirectional voltage limiter are turned on together to discharge the overcurrent.

2. The low leakage current voltage limiting protection circuit according to claim 1, characterized in that: The leakage current protection device includes at least two low leakage current diodes connected in reverse parallel, or a bridge rectifier structure composed of diodes, which is in a zero-bias high impedance state due to the equal potential at both ends under normal operating conditions; the bidirectional voltage limiter includes a bidirectional transient voltage suppression diode, a varistor, or a Zener diode connected in series back to back.

3. The low leakage current voltage limiting protection circuit according to claim 1, characterized in that, The voltage driver includes: An operational amplifier, wherein the non-inverting input of the operational amplifier is connected to the low-potential side of the sampling circuit; A feedback network is coupled between the output of the operational amplifier and the inverting input of the operational amplifier. A current-limiting resistor is connected in series between the output terminal of the operational amplifier and the common connection point to limit the current flowing out of the operational amplifier in a protected state; wherein the operational amplifier adjusts the output voltage through the feedback network to drive the common connection point.

4. The low leakage current voltage limiting protection circuit according to claim 3, characterized in that, The feedback network includes: A high-frequency feedback capacitor is connected between the inverting input terminal and the output terminal of the operational amplifier. The connection point between the high-frequency feedback capacitor and the output terminal of the operational amplifier is located between the current-limiting resistor and the output terminal of the operational amplifier; the high-frequency feedback capacitor is used to establish a local high-frequency feedback loop to provide leading phase compensation when the protection circuit is in a high-impedance state.

5. The low leakage current voltage limiting protection circuit according to claim 4, characterized in that, The feedback network also includes a DC precise feedback path, one end of which is connected to the common connection point and the other end of which is connected to the inverting input terminal of the operational amplifier. The DC precise feedback path and the high-frequency feedback capacitor together form a composite feedback network: the high-frequency feedback capacitor dominates in the high-frequency band to maintain loop stability, while the DC precise feedback path dominates in the DC and low-frequency bands, extending the sampling point of the operational amplifier to the common connection point, thereby forcing the operational amplifier to output a higher voltage to compensate for the voltage drop across the current-limiting resistor.

6. The low leakage current voltage limiting protection circuit according to claim 5, characterized in that, The voltage driver further includes a bootstrap power supply network, and the operational amplifier has a positive power supply terminal and a negative power supply terminal connected to the bootstrap power supply network; the bootstrap power supply network is configured to float following the low-potential side of the sampling circuit, such that the supply voltage of the operational amplifier is always maintained within a fixed differential voltage range relative to the measured signal.

7. The low leakage current voltage limiting protection circuit according to claim 6, characterized in that, It also includes a transient input clamping circuit, which includes: A first clamping diode is connected between the non-inverting input terminal and the positive power supply terminal of the operational amplifier; The second clamping diode is connected between the non-inverting input terminal and the negative power supply terminal; When the rise rate of the measured signal exceeds the tracking rate of the bootstrap power network, the first clamping diode and the second clamping diode clamp the input stage voltage difference of the operational amplifier within a safe range.

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