Analog signal overvoltage protection circuit for ADC

Abstract

The application discloses an ADC analog signal overvoltage protection circuit, a clamping circuit is connected to a protected ADC port, under normal circumstances, the overall protection branch remains in a high-resistance suspended state, meanwhile, the protection circuit adopts a high-precision voltage reference as an overvoltage reference voltage, uses an open-loop comparator of an operational amplifier to directly sample, detect and compare the voltage of an ADC analog input pin, automatically controls an independent ground discharge channel formed by an NPN transistor, effectively discharges transient overvoltage impact current, avoids impact current from flowing into a system auxiliary power supply, effectively solves the defects of a traditional passive clamping circuit, such as large signal disturbance, existence of a protection blind area and poor signal fidelity, and is suitable for a precise capacitor sensor and a high-precision ADC collection scene, and has excellent protection stability and applicability.

Description

Technical Field

[0001] This application relates to the field of analog signal overvoltage protection circuit technology, specifically to an active clamping protection circuit suitable for precision capacitive sensors and high-precision ADC acquisition systems. Background Technology

[0002] High-precision capacitive displacement detection systems mainly consist of a metal probe, a target conductor, and a back-end signal processing circuit, requiring extremely high sensitivity and stability in signal acquisition. In precision displacement detection circuits, a high-precision, high-resolution ADC is typically used as the core analog-to-digital conversion unit to achieve accurate digital conversion of weak displacement voltage signals. Because the capacitive sensor outputs a high-impedance, weak analog signal, minute power supply disturbances, high-frequency ripple noise, and device leakage interference in the front-end analog path are directly superimposed on the effective detection signal, causing voltage sampling amplitude shifts. This ultimately leads to problems such as decreased displacement measurement accuracy, data drift, and poor detection repeatability.

[0003] In industrial environments, electrostatic discharge (ESD), surges, and electromagnetic coupling interference can easily introduce forward transient overvoltages and short-duration large inrush currents into the analog input ports of ADCs. Existing technologies generally employ passive diode rail-to-rail clamping protection structures, directly connecting the clamping diodes to the system's analog power rails, relying on the system power supply voltage to achieve overvoltage clamping protection for the analog signal. While this type of passive protection circuit has a simple structure, it has several inherent drawbacks in high-precision, weak signal acquisition scenarios. First, during an overvoltage surge, the transient large current directly flows into the system's analog power rail, increasing power ripple and causing drift in on-chip or external precision references, contaminating the analog power supply, and further degrading the acquisition quality of high-precision channels. Second, traditional passive clamping relies solely on the unidirectional conductivity of the diode for protection, lacking active discharge control logic. Third, some protection circuits use indirect sampling detection methods, unable to directly respond to overvoltage signals directly entering the ADC input pins, resulting in protection blind spots and insufficient reliability of the protection response.

[0004] In summary, existing passive clamping protection schemes are insufficient to meet multiple requirements such as power supply anti-interference, low signal disturbance, and fast response protection. It is necessary to propose an improved clamping protection circuit to minimize the pollution of analog power supply by inrush current, reduce the disturbance of high impedance analog signals by the protection branch, improve the response capability to direct overvoltage of ADC port, and improve the reliability of circuit protection. Summary of the Invention

[0005] The purpose of this application is to provide an ADC analog signal overvoltage protection circuit to solve the technical problems of existing passive clamping circuits, such as large power supply pollution, strong signal disturbance, and protection blind zone.

[0006] To achieve the above technical objectives, this application adopts the following technical solution: An ADC analog signal overvoltage protection circuit includes: a diode clamping unit, a high-speed transient voltage discharge unit, and a high-speed transient overvoltage signal identification unit; The input terminal of the diode clamping unit is connected to the ADC analog signal port, and clamps the overvoltage signal of the ADC analog signal port to the protection voltage reference of the ADC analog signal port. The input terminal of the high-speed transient voltage discharge unit is connected to the output terminal of the diode clamping unit; The output terminal of the high-speed transient voltage discharge unit is connected to the ground plane, and the overvoltage signal captured by the diode clamping unit is transiently released to the ground plane; The input terminal of the high-speed transient overvoltage signal identification unit is connected to the output terminal of the diode clamping unit to quickly identify the overvoltage signal; The output terminal of the high-speed transient overvoltage signal identification unit is connected to the control terminal of the high-speed transient voltage discharge unit. After identifying the overvoltage signal, the high-speed transient voltage discharge unit is controlled to open the discharge circuit.

[0007] Specifically, when an overvoltage signal higher than the protection voltage reference is input to the ADC analog signal port, the diode clamping unit is turned on to clamp the signal.

[0008] Preferably, the high-speed transient overvoltage signal identification unit includes a precision comparison unit, a voltage feedback unit, and a precision reference voltage source. The output terminals of the voltage feedback unit and the precision reference voltage source are connected to the input terminal of the precision comparison unit. The precision comparison unit outputs a comparison result by comparing the input signal.

[0009] Preferably, the output terminal of the precision comparator is connected to the control terminal of the high-speed transient voltage discharge unit.

[0010] Preferably, the diode clamping unit includes a clamping diode, an auxiliary power supply, and a resistor network. The auxiliary power supply is connected to the input terminal of the resistor network, the output terminal of the resistor network is connected to the ground plane, the anode of the diode is connected to the analog signal port of the ADC, and the cathode of the clamping diode is connected to the clamping voltage divider node of the resistor network.

[0011] Preferably, the precision comparison unit employs a precision operational amplifier.

[0012] Preferably, the precision reference voltage source includes a precision voltage reference chip, and the reference voltage output terminal is connected to the non-inverting input terminal of the precision operational amplifier.

[0013] Preferably, the reference voltage output terminal is connected to the non-inverting input terminal of the precision operational amplifier through an RC filter network to ensure the stability of the reference voltage.

[0014] Preferably, the voltage feedback unit includes the auxiliary power supply and a three-stage series resistor network. The auxiliary power supply is connected to the input terminal of the first-stage resistor network, the output terminal of the first-stage resistor network is connected to the input terminal of the second-stage resistor network, the output terminal of the second-stage resistor network is connected to the input terminal of the third-stage resistor network, and the output terminal of the third-stage resistor network is connected to the ground plane.

[0015] Preferably, the output of the first-stage resistor network is connected to the cathode of the clamping diode.

[0016] Preferably, the output of the second-stage resistor network is connected to the inverting input of the precision operational amplifier.

[0017] Preferably, the high-speed transient voltage discharge unit includes a power transistor and a Zener diode. The power transistor is an NPN transistor, with its base connected to the output terminal of the precision operational amplifier via a current-limiting resistor, its emitter connected to the cathode of the Zener diode, and its collector connected to ground. The anode of the Zener diode is connected to the cathode of the clamping diode to provide voltage regulation and protection for the emitter voltage of the power transistor, preventing damage to the transistor.

[0018] This circuit achieves the following technical effects through the above structural design: 1. Eliminate power pollution problem: Abandon the traditional power rail clamping method and build an independent discharge path to ground. All transient overvoltage and large current are directed to GND and do not enter the system auxiliary power supply, which greatly improves the measurement accuracy of high-precision ADC and sensors.

[0019] 2. High protection reliability: Directly samples the actual voltage of the ADC pin. Compared with the solution of indirectly sampling the front-end signal, it can accurately respond to overvoltage interference that enters the ADC pin through any path, and provides full coverage protection without blind spots.

[0020] 3. High signal fidelity: Under normal conditions, the protection branch is completely cut off and floats with high impedance, with no leakage current and no junction capacitance nonlinear interference. It is suitable for high impedance weak signal acquisition scenarios of precision capacitive sensors, and the signal quality is significantly better than that of traditional passive clamping circuits. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the application will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Among them: Figure 1 This is a functional block diagram of the overvoltage protection circuit module.

[0022] Figure 2 This is a schematic diagram of an overvoltage protection circuit.

[0023] Explanation of reference numerals in the attached figures: 1-Precision reference voltage source, 2-Precision comparator unit, 3-High-speed transient voltage discharge unit, 4-Diode clamping unit, 5-Voltage feedback unit, 6-Auxiliary voltage unit, 7-ADC input port. Detailed Implementation

[0024] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0025] The orientation or positional relationship indicated in the terminology is based on the orientation or positional relationship shown in the accompanying drawings and is only for the convenience of describing this application and simplifying the description, and is not intended to indicate or imply that the equipment or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0026] The term "connection method" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0027] The embodiments of this application will now be described in further detail with reference to the accompanying drawings. Example

[0028] like Figure 1 As shown, the overvoltage protection circuit is divided into six functional modules, including a precision reference voltage source 1, a precision comparison unit 2, a high-speed transient voltage discharge unit 3, a diode clamping unit 4, a voltage feedback unit 5, and an auxiliary voltage unit 6.

[0029] The precision reference voltage source 1 and the voltage feedback unit 5 are connected to the precision comparison unit 2. The precision comparison unit 2 compares the signal magnitudes of the precision reference voltage source 1 and the voltage feedback unit 5, and outputs two control signals to the input terminal of the high-speed transient voltage discharge unit 3 to control the high-speed transient voltage discharge unit 3 to open or close the discharge circuit.

[0030] The voltage feedback unit 5 acquires the voltage status of the clamping node, generates a monitoring voltage as an output, and connects the output to the input terminal of the precision comparison unit 2.

[0031] The input terminal of diode clamping unit 4 is connected to the input port 7 of the ADC to be protected, and the output terminal is connected to the high-speed transient voltage discharge unit 3. The transient overvoltage signal captured by diode clamping unit 4 at the ADC input port 7 is quickly discharged to the ground plane through the high-speed transient voltage discharge unit 3, maintaining the analog signal at the ADC input port 7 to quickly fall back to the clamping voltage, preventing damage to the ADC input port 7, and avoiding inrush current contamination of the system power supply. Under normal conditions, all protection devices are cut off and the branches are floating with high impedance. Protection is only activated momentarily during overvoltage faults, ensuring the purity of the precision analog signal to the greatest extent.

[0032] like Figure 2 As shown, the specific components include: a precision voltage reference chip U1, a precision operational amplifier U2, a PNP transistor Q1, a Zener diode D1, a clamping diode D2, filter circuits R2 and C1, sampling resistors R3 and R4, a bias resistor R5, a pull-up resistor R6, an output protection resistor R7, and a 5V auxiliary power supply. The connection relationships of each component are as follows: The output of the precision voltage reference chip U1 is connected to the R2 and C1 filter network, and then to the non-inverting input of the precision operational amplifier U2, providing a stable and accurate fixed threshold voltage for the entire comparison protection circuit.

[0033] The ADC input port AVIN1 is connected to the anode of the clamping diode D2 as the protected terminal. D2 is in the off state due to reverse voltage, and the entire protection branch is in a high-impedance state, which does not interfere with the analog signal path and reduces the disturbance to the high-precision acquisition signal.

[0034] The 5V auxiliary power supply is connected in sequence to pull-up resistor R6, parallel sampling resistors R3 and R4, and bias resistor R5, and then connected to GND. The upper end of pull-up resistor R6 is connected to the 5V auxiliary power supply to provide the initial static operating voltage for the clamping branch. The bias resistor R5, together with the sampling resistor network, stabilizes the static potential of the op-amp input.

[0035] A protection resistor R7 is connected in series with the output terminal of the precision operational amplifier U2, and then connected to the base of the PNP transistor Q1. R7 effectively limits the output current of the operational amplifier, realizing overload protection of the output stage.

[0036] Q1 uses a low-level conduction type high-speed PNP transistor with fast protection. Its emitter is connected to the lower end of the pull-up resistor R6 and the cathode of the clamping diode D2 through the Zener diode D1. The collector is directly grounded. The anode of the clamping diode D2 is connected to the protected ADC input port AVIN1, forming a complete ground discharge path.

[0037] D1 is a Zener diode, with its anode connected to the clamping node and its cathode connected to the emitter of the bleeder transistor Q1. When an overvoltage signal triggers protection, the overshoot current of the common clamping node flows into the emitter of Q1 through D1 and is then discharged to ground through the collector of Q1, forming a large current discharge path. During this process, D1 weakens the voltage overshoot generated during the discharge process and suppresses negative transient spikes, preventing negative voltage from being directly applied to the emitter junction of Q1 and preventing the emitter junction of the bleeder transistor from being reverse-biased and broken down.

[0038] When static electricity, electromagnetic interference, or surges enter the ADC input port in an industrial environment, causing a positive overvoltage and a 1A / 100μs transient current surge in AVIN1, the AVIN1 voltage rises rapidly and drives D2 to conduct forward. The overvoltage transient energy is quickly transferred to the common clamp node. The common clamp node voltage is fed to the inverting input of U2 via the sampling network, making the voltage at the inverting input higher than the precision reference voltage at the non-inverting input. The open-loop output of U2 quickly jumps to a saturation low level, and the NPN transistor Q1 instantaneously conducts. The surge current is quickly discharged to ground through the low-impedance discharge path of "AVIN1→D2→common clamp node→D1→Q1→GND", reliably discharging the 1A / 100μs transient surge energy. The entire discharge process is completed independently to ground, and the transient surge current will not flow into the 5V auxiliary power supply, avoiding problems such as analog power supply ripple degradation and reference voltage drift caused by the surge current, and preventing the analog power supply from being contaminated.

[0039] Once the 1A / 100μs transient overvoltage surge energy has been completely dissipated, the AVIN1 pin voltage quickly returns to the normal operating range, the common clamp node voltage decreases synchronously, the sampling voltage at the inverting input of U2 falls below the reference voltage again, the U2 output returns to saturation high level, and the NPN transistor Q1 is immediately turned off. The common clamp node potential returns to the normal threshold, D2 is cut off, the entire protection branch returns to a high-impedance floating state, automatically resets, and quickly returns to high-precision signal acquisition, ready to handle the next transient fault surge.

[0040] This circuit can be widely used in precision capacitive sensors, high-precision SAR and Σ-ΔADC acquisition circuits. Compared with traditional passive rail-to-rail clamping circuits, it has multiple advantages such as high signal fidelity, no power pollution, and blind-zone protection under all working conditions. It has strong resistance to transient impacts and is suitable for high-precision analog acquisition scenarios in industry.

[0041] Although this application has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An ADC analog signal overvoltage protection circuit, characterized in that, include: Diode clamping unit, high-speed transient voltage discharge unit, high-speed transient overvoltage signal identification unit; The input terminal of the diode clamping unit is connected to the ADC analog signal port, and clamps the overvoltage signal of the ADC analog signal port to the protection voltage reference of the ADC analog signal port. The input terminal of the high-speed transient voltage discharge unit is connected to the output terminal of the diode clamping unit; The output terminal of the high-speed transient voltage discharge unit is connected to the ground plane, so as to transiently release the overvoltage signal captured by the diode clamping unit to the ground plane; The input terminal of the high-speed transient overvoltage signal identification unit is connected to the output terminal of the diode clamping unit to quickly identify the overvoltage signal; The output terminal of the high-speed transient overvoltage signal identification unit is connected to the control terminal of the high-speed transient voltage discharge unit.

2. The ADC analog signal overvoltage protection circuit according to claim 1, characterized in that, The high-speed transient voltage discharge unit includes a power transistor and a Zener diode. The anode of the Zener diode is connected to the output terminal of the diode clamping unit, and the cathode of the Zener diode is connected to the emitter of the power transistor.

3. The ADC analog signal overvoltage protection circuit according to claim 2, characterized in that, The high-speed transient overvoltage signal identification unit is configured to: upon identifying the overvoltage signal, control the high-speed transient voltage discharge unit to open the discharge circuit.

4. The ADC analog signal overvoltage protection circuit according to claim 3, characterized in that, The high-speed transient overvoltage signal identification unit includes a precision comparator, a voltage feedback unit, and a precision reference voltage source. The output terminals of the voltage feedback unit and the precision reference voltage source are connected to the input terminal of the precision comparator. The precision comparator employs a precision operational amplifier.

5. The ADC analog signal overvoltage protection circuit according to claim 4, characterized in that, The voltage feedback unit includes an auxiliary power supply and a three-stage series resistor network. The auxiliary power supply is connected to the input terminal of the first-stage resistor network, the output terminal of the first-stage resistor network is connected to the input terminal of the second-stage resistor network, the output terminal of the second-stage resistor network is connected to the input terminal of the third-stage resistor network, and the output terminal of the third-stage resistor network is connected to the ground plane.

6. The ADC analog signal overvoltage protection circuit according to claim 5, characterized in that, The diode clamping unit includes a clamping diode, an auxiliary power supply, and a first-stage resistor network. The auxiliary power supply is connected to the input terminal of the resistor network, the output terminal of the resistor network is connected to the ground plane, the anode of the diode is connected to the ADC input port, and the cathode of the clamping diode is connected to the clamping voltage divider node of the first-stage resistor network.

7. The ADC analog signal overvoltage protection circuit according to claim 4, characterized in that, The power transistor is an NPN transistor with a high-speed response to the base signal. The base is connected to the output of the precision operational amplifier via a current-limiting resistor, the emitter is connected to the cathode of the Zener diode, and the collector is connected to the ground plane.

8. The ADC analog signal overvoltage protection circuit according to claim 4, characterized in that, The precision reference voltage source includes a precision voltage reference chip. The reference voltage output terminal is connected to an RC filter network and then connected to the non-inverting input terminal of the precision operational amplifier to ensure the stability of the reference voltage.

9. The ADC analog signal overvoltage protection circuit according to claim 4, characterized in that, The output terminal of the precision operational amplifier is connected to the base of the power transistor, controlling the power transistor to open or close the discharge circuit.

10. The ADC analog signal overvoltage protection circuit according to claim 5, characterized in that, The output of the second-stage resistor network is connected to the inverting input of the precision operational amplifier.

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