Wien bridge oscillator and capacitance sensing circuit with multi-parameter programmable characteristics

Abstract

This invention provides a Wien bridge oscillator and a capacitance sensing circuit with multi-parameter programmable characteristics, relating to the field of electronic circuit technology. It includes an amplification unit, a negative feedback loop, and a Wien bridge positive feedback loop. At least two of the first gain resistor, the second gain resistor, the reference positive feedback resistor, and the third resistor are resistive units with programmable resistance values ​​and temperature coefficients. By jointly configuring each resistive unit and the capacitor unit, the oscillation conditions can be adapted to capacitor networks of different specifications. The positive feedback loop also includes a variable feedback resistor controlled by the output state to generate oscillation hysteresis. The beneficial effects are that flexible adaptation of oscillation conditions is achieved through programmable configuration, and a stable hysteresis is generated using the variable feedback resistor, eliminating critical jitter and significantly improving the versatility, stability, and anti-interference capability in capacitance sensing applications.

Description

Technical Field

[0001] This invention relates to the field of electronic and electrical technology, and in particular to a Wien bridge oscillator and a capacitance sensing circuit with multi-parameter programmable characteristics. Background Technology

[0002] In the design of oscillating sensors (such as capacitive proximity sensors), the oscillator is the core detection unit. Traditional Wien Bridge oscillators typically use a resistor-capacitor network with fixed parameters, which results in a lack of versatility and flexibility when faced with external sensing capacitors of different specifications or different application scenarios.

[0003] Specifically, existing technologies suffer from the following problems: First, the start-up and shutdown conditions of traditional oscillators are fixed by hardware parameters, making it difficult to precisely match and adjust for different reference capacitors; second, the drift characteristics of the oscillation system with temperature changes are often difficult to control, making it impossible to perform reverse compensation or fine-tuning for different environments; furthermore, signal jitter easily occurs at the critical state of oscillation start-up and shutdown. Therefore, there is an urgent need for a technical solution that can collaboratively determine oscillation conditions and provide stable hysteresis by programming and configuring multiple feedback parameters. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention provides a Wien bridge oscillator with multi-parameter programmable characteristics, including an amplification unit, a negative feedback loop, and a Wien bridge positive feedback loop; The amplification unit has a non-inverting input terminal, an inverting input terminal, and an output terminal; The negative feedback loop includes a first resistor connected between the inverting input terminal and the reference potential, and a second resistor connected between the output terminal and the inverting input terminal; The Wien bridge positive feedback loop includes a series branch connected between the output terminal and the non-inverting input terminal, and a parallel branch connected between the non-inverting input terminal and the reference potential. At least two of the first resistor, the second resistor, the reference positive feedback resistor in the series branch, and the third resistor in the parallel branch are resistive units with programmable resistance values ​​and temperature coefficients; By jointly configuring the resistive units and the capacitor units in the series and parallel branches, the oscillation conditions of the Wien bridge oscillator are formed in a coordinated manner, so that the oscillation conditions are matched with target capacitor networks of different parameter specifications; wherein, the series branch also includes a variable feedback resistor controlled by the oscillator output state, which is used to form oscillation hysteresis by changing the positive feedback strength.

[0005] Preferably, the programmable resistive unit is composed of at least two resistive elements with different temperature coefficients, and the target resistance value and target temperature coefficient are formed by selecting the combination ratio.

[0006] Preferably, by configuring the ratio of the second resistor to the first resistor and their temperature coefficient combination, the equivalent temperature characteristic of the closed-loop gain of the amplification unit can be adjusted between the positive and negative directions.

[0007] Preferably, the variable feedback resistor includes a first programmable feedback resistor and a second programmable feedback resistor; When the oscillator switches from the oscillation state to the non-oscillation state, the first programmable feedback resistor is connected to reduce the positive feedback strength. When the oscillator switches from a non-oscillating state to an oscillating state, the second programmable feedback resistor is removed or reduced to enhance the positive feedback strength.

[0008] Preferably, the second capacitor in the series branch and / or the first capacitor in the parallel branch are internally programmable capacitors or external sensitive capacitors; When an external sensitive capacitor is connected, the corresponding internal programmable capacitor is disconnected under the action of a control signal.

[0009] Preferably, it also includes a digital configuration circuit consisting of a shift register and an analog switch, used to configure the parameters of the resistive or capacitive unit through configuration codes output from a communication interface or internal non-volatile memory.

[0010] Preferably, the digital configuration circuit receives external instructions through a communication interface, and the shift register configures the parameters of the resistive unit or the capacitor unit according to the external instructions; Alternatively, the non-volatile memory stores pre-configured configuration parameters, and the shift register reads the configuration parameters to configure the parameters of the resistive or capacitive unit.

[0011] The present invention also provides a capacitance sensing circuit, including the Wien bridge oscillator described above, and a buffer amplifier, a peak detection circuit and a comparator connected to the Wien bridge oscillator; The peak detection circuit and comparator are used to detect the amplitude or phase change of the oscillation signal caused by the change of the external sensitive capacitance, and output the sensor signal accordingly.

[0012] Preferably, the output terminal of the amplification unit in the Wien bridge oscillator is connected to the input terminal of the series branch, the input terminal of the buffer amplifier, and the input terminal of the peak detection circuit, respectively. The output terminal of the buffer amplifier serves as the oscillator signal output terminal, used to provide a buffered oscillation signal to the outside world; The output terminal of the peak detection circuit is connected to the input terminal of the comparator, and the output terminal of the comparator serves as the sensor signal output terminal. The control output terminal of the digital configuration circuit is connected to the controlled terminals of the first resistor, the second resistor, the third resistor, the reference positive feedback resistor, the first capacitor, and the second capacitor, respectively.

[0013] Preferably, the signal output by the comparator is connected as a feedback control signal to the Wien bridge positive feedback loop of the Wien bridge oscillator; The feedback control signal is used to control the analog switch to connect or disconnect the variable feedback resistor according to the real-time output state of the Wien bridge oscillator, so as to change the positive feedback strength and form an oscillation hysteresis.

[0014] The above technical solution has the following advantages or beneficial effects: Through programmable configuration of key resistance and capacitance parameters, the oscillator can be flexibly adapted to sensing capacitors of different specifications; and through variable feedback increments controlled by the output state, a stable hysteresis is formed, eliminating signal jitter near the critical point. Therefore, this solution significantly improves the versatility, stability, and anti-interference capability of the oscillator in capacitive sensing applications. Attached Figure Description

[0015] Figure 1 A schematic diagram of a Wien bridge oscillator with multi-parameter programmable characteristics is shown in an embodiment of the present invention. Figure 2 This is a schematic diagram of a capacitive sensing circuit in an embodiment of the present invention. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment; other embodiments that conform to the spirit of the present invention may also fall within the scope of the present invention.

[0017] In a preferred embodiment of the present invention, based on the above-mentioned problems existing in the prior art, several embodiments are provided to illustrate a Wien bridge oscillator with multi-parameter programmable characteristics provided in the present invention.

[0018] Example 1: This embodiment provides a Wien bridge oscillator with multi-parameter programmable characteristics. For example... Figure 1 As shown, the oscillator includes an amplifier unit OC, a negative feedback loop, and a Wien bridge positive feedback loop. The amplifier unit OC has a non-inverting input terminal, an inverting input terminal, and an output terminal.

[0019] The negative feedback loop includes a first resistor R1 and a second resistor R2. R1 is connected between the inverting input and a reference potential (such as ground), and R2 is connected between the output and the inverting input. Both resistors are used to set the closed-loop gain of the amplifier unit. Their relationship is .

[0020] The Wien bridge positive feedback loop consists of a series branch and a parallel branch. The series branch connects the output terminal and the non-inverting input terminal, and includes the reference positive feedback resistor RFO and the second capacitor C2. The parallel branch connects the non-inverting input terminal and the reference potential, and includes the third resistor RC and the first capacitor C1. The frequency characteristics of this network determine its performance at a specific frequency. At this point, its feedback coefficient The maximum phase shift is zero, and f0 is determined by... Joint decision (under ideal conditions, when) .

[0021] The basic principle of oscillation requires loop gain. The total phase shift is 0° (or 360°). In traditional fixed-parameter circuits, this condition is difficult to adapt to different capacitive loads and is easily affected by temperature drift.

[0022] The key features of this invention are: 1. Programmable parameters: At least two of the components are resistive units with programmable resistance values ​​and temperature coefficients. These units are composed of combinations of resistive elements with at least two different temperature coefficients, and their combination ratio is selected by a digital configuration circuit, thereby simultaneously setting the target resistance value and the target temperature coefficient. This allows the circuit to accurately adapt oscillation conditions for target capacitor networks of different specifications (such as sensitive capacitors with different capacitance values ​​and temperature characteristics).

[0023] 2. Hysteresis control: The series branch also includes a variable feedback resistor controlled by the oscillator output state. Its working principle is: when the output state changes, it dynamically adjusts through an analog switch. Connecting or disconnecting changes the total positive feedback resistance. This, in turn, changes the strength of the positive feedback (feedback coefficient). This mechanism, which dynamically adjusts the feedback intensity based on the output state, forms a stable "hysteresis band" at the critical point between oscillation start and stop, effectively preventing critical oscillation jitter caused by minor parameter fluctuations or noise, and significantly improving operational stability.

[0024] By using the above resistive unit ( ) and capacitor unit ( The joint digital configuration of ( ) can coordinately adjust the negative feedback gain. The frequency and amplitude characteristics of the positive feedback network β enable the loop to accurately meet the amplitude and phase conditions of oscillation at the target frequency, and it also has excellent temperature stability and anti-interference ability.

[0025] Specifically, the technical solution in this embodiment directly and effectively solves the three core problems pointed out in the prior art by constructing a multi-parameter programmable Wien bridge oscillator: 1. Solved the problem of insufficient versatility and flexibility: by modifying the key resistor in the oscillator ( The design is intended to allow for programmable resistance values ​​and temperature coefficients of at least two components, and to be used in conjunction with capacitors ( The programmable or switchable configuration of the oscillator means that its core parameters, including closed-loop gain, frequency selection network characteristics, and oscillation conditions, are no longer fixed. Users or systems can dynamically adjust and adapt precise start-up and shutdown conditions for external sensing capacitors of different specifications, capacitance ranges, and parasitic parameters through digital configuration. This fundamentally changes the limitations of the traditional one-circuit-one-application approach, enabling a single hardware platform to be widely adaptable to diverse capacitive sensing scenarios, and greatly improving the versatility and deployment flexibility of the solution.

[0026] 2. Programmable compensation and optimization of temperature characteristics: Because the key resistors are composed of programmable units with different temperature coefficients, the resistance value of each resistor and its temperature-dependent trend (temperature coefficient) can be configured independently. By jointly configuring the temperature coefficients of these resistors, the negative feedback gain can be systematically adjusted. ) and positive feedback networks ( The invention addresses the temperature drift behavior of each sensor, thereby enabling the cancellation or precise control of the equivalent temperature characteristics of the entire oscillation loop. This allows the invention to perform proactive, reverse temperature compensation design for specific application environments (such as high or low temperature conditions) or specific sensor package thermal characteristics, significantly suppressing temperature drift that is difficult to overcome in traditional solutions, and improving measurement consistency and long-term stability.

[0027] 3. Provides stable hysteresis control to eliminate critical jitter: A variable feedback resistor controlled by the oscillator output state is introduced ( This mechanism creatively feeds the output back to the oscillation conditions themselves. Near the thresholds for oscillation start-up and shutdown, by dynamically fine-tuning the positive feedback strength, the distance between the start-up capacitor threshold and the shutdown capacitor threshold is artificially widened, forming a stable, non-sensitive region (hysteresis band). When the measured parameter fluctuates near the theoretical critical point or is subject to noise, the oscillator state will not frequently change, thus completely eliminating the critical signal jitter problem mentioned in the background technology. This results in a clear and stable switching signal output, greatly enhancing anti-interference capability and operational reliability.

[0028] Example 2: This embodiment details the implementation principle of the programmable resistive unit. The unit consists of at least a first group of resistive elements (having a temperature coefficient). ) and the second resistive element group (with temperature coefficient) It can be constructed by parallel, series, or a combination of series and parallel connections. The effective resistance value can be changed by controlling the analog switch to connect different numbers or combinations of components. and its equivalent temperature coefficient Their relationship can be approximated as: ,in This defines the weight of each component group in the total resistance. By programming different combination ratios, the temperature coefficient can be configured to positive, negative, zero, or any target value while achieving the desired nominal resistance. A direct benefit of this principle is that it allows designers to compensate for or program the temperature characteristics of critical resistors in the oscillator (such as gain setting resistors and bridge arm resistors), thereby suppressing temperature drift of the entire system at its source.

[0029] Example 3: This embodiment focuses on illustrating the working principle of adjusting the temperature characteristics of the amplifier's closed-loop gain using a programmable resistor. The closed-loop gain of the amplifier unit... .set up The temperature coefficients are respectively Under the first-order approximation, the closed-loop gain temperature coefficient Mainly depends on The temperature coefficient of the ratio. Their relationship can be approximated as: Therefore, by providing Independently configured programmable resistive units with specific temperature coefficient combinations (as in Example 2) allow for flexible settings. The value of ) thus making The gain temperature characteristics are adjustable within a positive, negative, or near-zero range. This operating principle makes the gain temperature characteristics of the amplification stage a designable degree of freedom, enabling coordinated compensation with the temperature characteristics of the subsequent Wien bridge network to achieve system-level temperature stability optimization.

[0030] Example 4: This embodiment details the variable feedback resistor. The specific working principle and process of implementing hysteresis control. Includes a first programmable feedback resistor ΔRF1 and a second programmable feedback resistor. .

[0031] Oscillation Stopping Process: When the external capacitance increases, causing the positive feedback to weaken, and the oscillation amplitude begins to decrease to a certain threshold, the comparator output state flips. This state signal controls the switch to... Access, and Connecting them in series increases the total positive feedback resistance to According to the formula for calculating the positive feedback coefficient β ( When the bridge arms are balanced (the actual value is affected by the resistance ratio), the increase in positive feedback resistance leads to a decrease in β, thereby accelerating the loop gain. This causes the oscillation to stop rapidly. This process sets a threshold for stopping the oscillation.

[0032] Start-up process: When the external capacitor decreases and the conditions for start-up tend to be met, the comparator outputs another state. This state controls the switch to remove ΔRF2 from the loop (or equivalently reduce its effect). At this time, the total positive feedback resistance decreases (ideally close to...). ), Increase, thus increasing the loop gain It quickly crosses the critical point of ≥1, thus reliably initiating oscillation. This process sets the oscillation threshold.

[0033] because The resistance value can be independently programmed to be different, so that the external capacitance values ​​corresponding to the oscillation stop threshold and the oscillation start threshold are different, thus forming a stable tolerance range (hysteresis band). The beneficial effect is that when the measured capacitance changes slowly near the threshold or when there is noise, the sensor output will not fluctuate frequently, but will produce a clear and stable switching action, which greatly improves anti-interference and reliability.

[0034] Example 5: This embodiment relates to the working principle of capacitor unit configuration mode switching. The positions of C1 and / or C2 can be connected to internal programmable capacitors or external sensitive capacitors. The working mode switching principle is as follows: Calibration / Self-Test Mode: The analog switch is controlled by a digital configuration circuit, connecting the internal programmable capacitor to the circuit while simultaneously disconnecting the external interface. In this mode, the internal capacitor value can be programmed to simulate changes in the external capacitor, used for system calibration, functional self-testing, or fault diagnosis.

[0035] Sensing mode: When an external sensitive capacitor is connected, the control signal completely disconnects the corresponding internal programmable capacitor, ensuring that the external capacitor is the only capacitive element that determines the oscillation conditions, and avoiding the parallel influence of internal capacitors that could lead to measurement errors.

[0036] The advantage of this design is that it enables multiple uses with a single device. The same hardware circuit can be switched between different modes through software configuration, which supports flexible on-site calibration and online self-diagnosis, while ensuring the purity and accuracy of the sensing mode measurement.

[0037] Example 6: To enable flexible configuration of the above parameters, this oscillator also includes a digital configuration circuit. This circuit mainly consists of a shift register SR and a multiplexer analog switch. Its working principle is as follows: the shift register SR acts as a serial-to-parallel data buffer, receiving a configuration bit stream from an external interface or internal memory. Each configuration bit controls the on / off state of one or more analog switches (e.g., ...). Figure 1 , Figure 2 As shown, the control signal output by the shift register SR is also represented by SR. By combining the on and off states of the switches, different resistor network branches or capacitor array units are selected, thereby precisely setting... The parameter values. This digital configuration principle makes complex analog parameter adjustments simple, repeatable, and easy to automate, and is the core hardware foundation for realizing the "multi-parameter programmable" feature.

[0038] Example 7: This embodiment further illustrates two control principles and processes for digital configuration circuits.

[0039] External online configuration principle: The communication interface (such as SPI) receives configuration command packets sent by an external controller. After the command packet is parsed, the specific configuration data bit stream is shifted into the shift register SR. Each bit of data in the register is directly latched and drives the corresponding analog switch, changing the circuit parameters in real time. This method supports dynamic adjustment and remote control.

[0040] Internal autonomous configuration principle: During chip manufacturing or system calibration, optimized configuration parameters (such as configurations for specific temperature compensation curves or specific ranges) are programmed into the on-chip non-volatile memory (OTP / EEPROM). During power-on initialization, the control logic automatically reads the configuration data from the memory and loads it into the shift register, completing the circuit's autonomous configuration. This method ensures that the device is in optimal operating condition upon power-on, without external intervention.

[0041] The advantage of both configuration methods is that they balance flexibility and autonomy, meeting the needs of development, debugging, and field adaptation, and are also suitable for independently operating embedded sensing nodes.

[0042] Example 8: This embodiment provides a complete capacitance sensing circuit and its signal processing working principle. For example... Figure 2 As shown, the circuit includes the aforementioned Wien bridge oscillator, buffer amplifier, peak detection circuit, and comparator.

[0043] Its core working principle chain is as follows: Sensing and Modulation: External Sensing Capacitor (Access) The change in the position of the capacitor directly alters the frequency response characteristics (amplitude and phase) of the Wien bridge positive feedback network. This is equivalent to changing the capacitance. It was modulated onto the oscillation conditions of the oscillator.

[0044] Oscillation state / amplitude change: when When the loop conditions are not met, the oscillator may stop oscillating or its amplitude may decrease drastically; when When varied within a certain range, it may cause continuous changes in the amplitude of the oscillation. The amplitude of the oscillation signal... It contains capacitance information.

[0045] Signal demodulation: Peak detection circuits (such as precision rectifier filter circuits) detect oscillation signals. peak . yes The function.

[0046] Threshold decision: The comparator will With a programmable reference voltage Comparison. When When, it is determined to be a state (e.g., "there is an object"); when When the object is in a certain state, it is determined to be in another state (such as "no object"). The comparator output is the digitized sensor signal.

[0047] This working principle transforms minute capacitance changes, which are difficult to measure directly, into sinusoidal amplitude changes that are easy to detect and process, ultimately converting them into stable digital switching signals.

[0048] Furthermore, the self-test mode in Example 5 verifies whether the capacitance sensing circuit is working properly through the following steps in this example: First, preset the parameters by configuring the resistive units such as R1, R2, RC, and RF0 through the communication interface (such as SPI or I²C) to set an expected reference oscillation state.

[0049] Subsequently, the oscillator generates an oscillation signal based on the internally programmed capacitor and resistor values.

[0050] Results feedback: The peak detection circuit captures the oscillation amplitude. The comparator compares the actual oscillation result with a preset threshold.

[0051] If the output result matches the expected logic in the programming, it proves that the internal analog circuitry of the chip (including amplifiers, feedback networks, and comparators) is completely normal. Online self-diagnosis ensures that the stringent stability requirements of industrial-grade sensors are met.

[0052] Example 9: This embodiment details the specific signal connections and data flow operating principle of the capacitive sensing circuit. The output terminal of the amplification unit in the Wien bridge oscillator is connected to the input terminal of the series branch, the input terminal of the buffer amplifier, and the input terminal of the peak detection circuit, respectively. The output of the buffer amplifier serves as the output of the oscillator signal, used to provide a buffered oscillation signal to the outside world. The output of the peak detection circuit is connected to the input of the comparator, and the output of the comparator serves as the sensor signal output. The control output terminal of the digital configuration circuit is connected to the controlled terminals of the first resistor, the second resistor, the third resistor, the reference positive feedback resistor, the first capacitor, and the second capacitor, respectively.

[0053] Specifically, the signal distribution path is the oscillation signal at the output of the amplification unit. Simultaneously, three paths are fed in: (a) returning to the Wien bridge positive feedback loop (the starting point of the series branch) to form an oscillation closed loop; (b) being sent to the buffer amplifier, which is then isolated and enhanced for external use; and (c) being sent to the peak detection circuit for amplitude extraction.

[0054] Configuration control path: The digital configuration circuit acts as the control center, and its output lines (multi-bit parallel bus) are connected to each programmable resistor. and capacitor The switching control terminal. Based on the received configuration instructions, it coordinates the parameters of all components to ensure that the entire system (oscillation conditions, gain, hysteresis, temperature compensation, etc.) works in harmony.

[0055] This architecture achieves a high degree of integration of sensing, signal conditioning, output, and parameter control, with clear separation of signal flow and control flow, ensuring system stability and configurability.

[0056] Example 10: This embodiment illustrates the closed-loop feedback control principle in the sensing circuit, which is the key to achieving intelligent hysteresis.

[0057] The sensor signal OUT output by the comparator is not only used as the final output, but is also fed back to the Wien bridge oscillator as a status signal to control the variable feedback resistors ΔRF (i.e., ΔRF1 and ΔRF2).

[0058] Its closed-loop control process is as follows: State sensing: The comparator compares peak voltages With threshold It can determine in real time whether the oscillator is in a strong oscillation (OUT=high) or weak oscillation / stopped oscillation (OUT=low) state.

[0059] Feedback adjustment: The OUT signal directly controls the connection. and Analog switch.

[0060] If OUT changes from high to low (approaching cessation of oscillation), then immediately connect. Increase the feedback resistance to accelerate oscillation cessation.

[0061] If OUT changes from low to high (approaching oscillation), disconnect immediately. This reduces the feedback resistance and promotes oscillation.

[0062] Hysteresis is formed: This feedback loop introduces nonlinearity. The capacitance threshold required for oscillation to start ( ) and the capacitance threshold required to stop vibration ( )quilt The settings are separated, and Once it enters an oscillating state, even if the capacitance drops back to slightly below... ,because Disconnected. The oscillation has been restored, but it will continue until the capacitance continues to increase. It will stop then. The reverse is also true.

[0063] This working principle, which feeds back the output state to the oscillation condition itself, creates a bistable characteristic (hysteresis) with memory and anti-interference capabilities. This is the core mechanism of this invention for achieving highly reliable switched capacitive sensing.

[0064] The overall technical solution of this invention constructs a complete and intelligent sensing system, bringing the following global beneficial effects: 1. This invention does not simply change the parameters to be adjustable, but rather achieves an integrated solution by using a collaborative design of multi-parameter joint programmable control and closed-loop state feedback control. This integrates precise matching of oscillation conditions, active suppression of temperature drift, and complete elimination of critical jitter. This enables capacitive sensors based on this solution to maintain high-precision detection and high-reliability operation over a wide temperature range, in complex electromagnetic environments, and under parameter drift conditions, meeting the stringent performance and reliability requirements of industrial-grade sensors.

[0065] 2. The digital and programmable architecture endows this solution with a high degree of intelligence. It not only supports flexible configuration of range, sensitivity, hysteresis, and temperature compensation curves on-site according to actual needs, but also naturally supports advanced functions such as power-on self-test (POST), online calibration, and fault diagnosis through the switching of internal programmable capacitors. The sensor can periodically or controllably switch to self-test mode to verify its own functional integrity and provide early warnings of potential faults, thereby upgrading the traditional silent sensor into an intelligent sensing node with state awareness and management capabilities.

[0066] 3. All programmable functions are implemented through on-chip digital configuration circuitry (shift registers, analog switches) and can be controlled via standard communication interfaces (such as SPI and I²C). This greatly simplifies external circuit design, reduces the complexity of system calibration and debugging, facilitates integration with microprocessors, and enables remote configuration, adaptive adjustment, and networked management. From a manufacturing and application perspective, this solution reduces production and debugging costs and improves the maintainability and user experience of end products.

[0067] In summary, this invention innovatively introduces a multi-parameter programmable mechanism and a closed-loop hysteresis control principle based on output state, achieving comprehensive synergistic optimization of the Wien bridge oscillator from oscillation conditions and temperature characteristics to operational stability. The capacitance sensing circuit built upon this oscillator has a clear working principle, converting capacitance changes into stable digital signals through oscillation modulation, peak detection, and closed-loop feedback. It possesses high precision, high stability, strong anti-interference capabilities, and self-detection functions, and can be widely applied in various intelligent sensing scenarios such as industrial ranging, level detection, and media identification.

[0068] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made using the content of this specification and illustrations should be included within the protection scope of the present invention.

Claims

1. A Wien bridge oscillator with multi-parameter programmable characteristics, characterized in that, This includes an amplification unit, a negative feedback loop, and a Wien bridge positive feedback loop; The amplification unit has a non-inverting input terminal, an inverting input terminal, and an output terminal; The negative feedback loop includes a first resistor connected between the inverting input terminal and the reference potential, and a second resistor connected between the output terminal and the inverting input terminal; The Wien bridge positive feedback loop includes a series branch connected between the output terminal and the non-inverting input terminal, and a parallel branch connected between the non-inverting input terminal and the reference potential. At least two of the first resistor, the second resistor, the reference positive feedback resistor in the series branch, and the third resistor in the parallel branch are resistive units with programmable resistance values ​​and temperature coefficients; By jointly configuring the resistive units and the capacitor units in the series and parallel branches, the oscillation conditions of the Wien bridge oscillator are formed in a coordinated manner, so that the oscillation conditions are matched with target capacitor networks of different parameter specifications; wherein, the series branch also includes a variable feedback resistor controlled by the oscillator output state, which is used to form oscillation hysteresis by changing the positive feedback strength.

2. The Wien bridge oscillator according to claim 1, characterized in that, The programmable resistive unit is composed of at least two resistive elements with different temperature coefficients, and the target resistance value and target temperature coefficient are formed by selecting the combination ratio.

3. The Wien bridge oscillator according to claim 1, characterized in that, By configuring the ratio of the second resistor to the first resistor and their temperature coefficient combination, the equivalent temperature characteristic of the closed-loop gain of the amplifier unit can be adjusted between the positive and negative directions.

4. The Wien bridge oscillator according to claim 1, characterized in that, The variable feedback resistor includes a first programmable feedback resistor and a second programmable feedback resistor; When the oscillator switches from the oscillation state to the non-oscillation state, the first programmable feedback resistor is connected to reduce the positive feedback strength. When the oscillator switches from a non-oscillating state to an oscillating state, the second programmable feedback resistor is removed or reduced to enhance the positive feedback strength.

5. The Wien bridge oscillator according to claim 1, characterized in that, The second capacitor in the series branch and / or the first capacitor in the parallel branch are internally programmable capacitors or external sensitive capacitors. When an external sensitive capacitor is connected, the corresponding internal programmable capacitor is disconnected under the action of a control signal.

6. The Wien bridge oscillator according to claim 1, characterized in that, It also includes a digital configuration circuit consisting of a shift register and an analog switch, used to configure the parameters of the resistive or capacitive unit through configuration codes output from a communication interface or internal non-volatile memory.

7. The Wien bridge oscillator according to claim 6, characterized in that, The digital configuration circuit receives external instructions through a communication interface, and the shift register configures the parameters of the resistive unit or the capacitor unit according to the external instructions. Alternatively, the non-volatile memory stores pre-configured configuration parameters, and the shift register reads the configuration parameters to configure the parameters of the resistive or capacitive unit.

8. A capacitive sensing circuit, characterized in that, It includes the Wien bridge oscillator as described in any one of claims 1 to 7, and a buffer amplifier, a peak detection circuit and a comparator connected to the Wien bridge oscillator; The peak detection circuit and comparator are used to detect the amplitude or phase change of the oscillation signal caused by the change of the external sensitive capacitance, and output the sensor signal accordingly.

9. The capacitive sensing circuit according to claim 8, characterized in that, The output terminal of the amplification unit in the Wien bridge oscillator is connected to the input terminal of the series branch, the input terminal of the buffer amplifier, and the input terminal of the peak detection circuit, respectively. The output terminal of the buffer amplifier serves as the oscillator signal output terminal, used to provide a buffered oscillation signal to the outside world; The output terminal of the peak detection circuit is connected to the input terminal of the comparator, and the output terminal of the comparator serves as the sensor signal output terminal. The control output terminal of the digital configuration circuit is connected to the controlled terminals of the first resistor, the second resistor, the third resistor, the reference positive feedback resistor, the first capacitor, and the second capacitor, respectively.

10. The capacitive sensing circuit according to claim 8, characterized in that, The signal output by the comparator is connected as a feedback control signal to the positive feedback loop of the Wien bridge oscillator. The feedback control signal is used to control the analog switch to connect or disconnect the variable feedback resistor according to the real-time output state of the Wien bridge oscillator, so as to change the positive feedback strength and form an oscillation hysteresis.

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