High-precision capacitor capacitance value detection circuit

Abstract

A high-precision capacitor capacitance value detection circuit comprises a reference source circuit formed by a direct current reference source (1) and a common ground (11), a polarity control circuit formed by a first resistor (3), a second resistor (4), a capacitor (10), the common ground (11) and an amplifier (2-1), and a constant current source circuit formed by a third resistor (5), a fourth resistor (6), a fifth resistor (7), a sixth resistor (8), an amplifier (2-2), an amplifier (2-3) and a seventh resistor (9). When the capacitor to be measured is connected between the output end (13) of the circuit and the common ground (11), the output end (12) of the circuit outputs a frequency signal corresponding to the capacitance value of the capacitor to be measured, and the capacitance value of the capacitor to be measured can be accurately measured through frequency signal measurement.

Description

Technical Field

[0001] This utility model relates to a capacitance value detection circuit, and more specifically, to a high-precision capacitor capacitance value detection circuit. Background Technology

[0002] Using a constant current source to measure capacitor capacitance is a relatively mature technology. A precision bipolar constant current source circuit is one of the key circuits for accurately measuring capacitor capacitance. At present, high-precision bipolar current sources integrated into chips rely on high-precision laser correction technology in the manufacturing process. Since the current source is integrated inside the chip, the adjustment range of the chip's output constant current value is limited, which restricts the detection range of the capacitance value of the measured capacitor. Moreover, the generated oscillation signal requires an additional frequency-to-voltage conversion circuit to convert it into a voltage or current signal corresponding to the capacitor capacitance value. This signal needs to be converted from analog to digital before it can be recognized by the microprocessor. The signal conversion process involves many steps and complex conversion control. The accuracy depends on the overall linearity of the circuit and the number of bits in the analog-to-digital conversion circuit, which is costly. Bipolar current source circuits built from discrete components can switch between positive and negative polarities and meet different output range requirements, making them well-suited for measuring capacitors with varying capacitance values. However, these circuits often face challenges such as a large number of discrete electronic components, difficulties in ensuring component consistency, significant impacts on current source accuracy due to switching characteristics, overly complex output current adjustment and control, poor consistency and reliability of output current values, and the fact that the accuracy of capacitor capacitance measurement depends on the stability of the bipolar current source circuit, making the circuit calibration process complex. Therefore, a high-precision capacitor capacitance detection circuit is needed to meet the requirements for accurate capacitor capacitance measurement. Summary of the Invention

[0003] The purpose of this invention is to provide a solution that can achieve high-precision capacitor capacitance measurement over a wide range.

[0004] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0005] A high-precision capacitor capacitance detection circuit is characterized in that the capacitor capacitance detection circuit includes a reference source circuit consisting of a DC reference source (1) and a common ground (11), a polarity control circuit consisting of a first resistor (3), a second resistor (4), a capacitor (10), a common ground (11), and an amplifier (2-1), and a constant current source circuit consisting of a third resistor (5), a fourth resistor (6), a fifth resistor (7), a sixth resistor (8), an amplifier (2-2), an amplifier (2-3), and a seventh resistor (9).

[0006] Beneficial effects of this utility model

[0007] This invention employs a technical solution consisting of a reference source circuit, a polarity control circuit, and a constant current source circuit. Each circuit contains only three components: a resistor, a capacitor, and a rail-to-rail high-precision operational amplifier. It excludes switching components, thus avoiding the adverse effects of switching characteristics on accuracy. The positive and negative polarities are naturally generated by the high and low levels of the high-precision operational amplifier and the relative changes in the reference source. The resistors and capacitors are all low-temperature coefficient, high-precision resistors and capacitors, and the operational amplifier is a rail-to-rail high-precision amplifier. The limited number of components facilitates consistency screening, and the circuit's functional partitioning is clear and simple. The high-precision capacitor capacitance detection circuit uses the polarity control circuit to control the polarity of the constant current source circuit's output current value, and also uses this signal as the frequency signal output corresponding to the capacitance value of the capacitor under test. Since the circuit outputs a frequency signal directly, it is easily recognized by digital circuits. The time base of a common microcontroller can easily reach the nanosecond level, enabling high-precision measurement of frequency signals. Therefore, the high-precision capacitor capacitance detection circuit does not require additional analog-to-digital conversion circuitry to achieve high-precision measurement of capacitor capacitance values, improving measurement accuracy while simplifying the design. Attached Figure Description

[0008] like Figure 1 The diagram shown is a schematic diagram of this utility model.

[0009] like Figure 2 The figure shown is a specific embodiment of this utility model. Detailed Implementation

[0010] like Figure 1 As shown, the high-precision capacitor capacitance detection circuit of this utility model includes a DC reference source (1), a reference source circuit consisting of a common ground (11), a polarity control circuit consisting of a first resistor (3), a second resistor (4), a capacitor (10), a common ground (11), and an amplifier (2-1), and a constant current source circuit consisting of a third resistor (5), a fourth resistor (6), a fifth resistor (7), a sixth resistor (8), an amplifier (2-2), an amplifier (2-3), and a seventh resistor (9).

[0011] The DC reference source (1) is composed of a high-precision DC power supply. The negative terminal of the DC reference source (1) is connected to the common ground (11), and the positive terminal of the DC reference source (1) is the output terminal of the reference source circuit. The positive terminal of the DC reference source (1) is connected to the polarity control circuit through the first resistor (3), and the positive terminal of the DC reference source (1) is connected to the constant current source circuit through the third resistor (5).

[0012] The first resistor (3) and the second resistor (4) are low temperature coefficient, high precision resistors. The capacitor (10) is a low temperature coefficient, high precision capacitor. The amplifier (2-1) is composed of a rail-to-rail high precision amplifier chip. The DC reference source (1) is connected to the non-inverting terminal of the amplifier (2-1) through the first resistor (3). The output terminal of the amplifier (2-1) is connected to the non-inverting terminal of the amplifier (2-1) through the second resistor (4). One end of the capacitor (10) is connected to the common ground (11), and the other end of the capacitor (10) is connected to the inverting terminal of the amplifier (2-1) and the circuit output terminal (13), respectively. The capacitor (10) is the internal load of the circuit, ensuring that when there is no capacitor being measured, the capacitor (10) provides the working load for the constant current source circuit to complete the charging and discharging functions. The output terminal of amplifier (2-1) is led out as the circuit output terminal (12) and connected to the constant current source circuit through the fifth resistor (7). When the voltage at the non-inverting terminal of amplifier (2-1) is higher than the voltage at the inverting terminal, the output terminal of amplifier (2-1) outputs a high level. When the voltage at the non-inverting terminal of amplifier (2-1) is lower than the voltage at the inverting terminal, the output terminal of amplifier (2-1) outputs a low level. The above circuit constitutes a polarity control circuit. The high level output of amplifier (2-1) is used to control the constant current value output by the constant current source, and the low level output of amplifier (2-1) is used to control the constant current value absorbed by the constant current source, thereby completing the polarity control of the constant current source. At the same time, the high and low levels output by amplifier (2-1) constitute an electrical signal of a certain frequency and are output from the output terminal (12).

[0013] The third resistor (5), fourth resistor (6), fifth resistor (7), sixth resistor (8), and seventh resistor (9) are low temperature coefficient, high precision resistors. Amplifiers (2-2) and (2-3) are composed of rail-to-rail high precision amplifier chips. The positive terminal of the DC reference source (1) is connected to the inverting terminal of amplifier (2-2) through the third resistor (5). The output terminal of amplifier (2-2) is connected to the inverting terminal of amplifier (2-2) through the fourth resistor (6). The output terminal of amplifier (2-1) is connected to the non-inverting terminal of amplifier (2-2) through the fifth resistor (7). The output terminal of amplifier (2-2) is connected to the non-inverting terminal of amplifier (2-3) through the seventh resistor (9), which also serves as the circuit output terminal (13). The inverting terminal of amplifier (2-3) is directly connected to the output terminal of amplifier (2-3), forming a voltage follower circuit. The output terminal of amplifier (2-3) is connected to the non-inverting terminal of amplifier (2-2) through the sixth resistor (8). The above devices constitute a constant current source circuit, wherein the value of the seventh resistor (9) controls the current value of the constant current source circuit.

[0014] like Figure 2The following is a specific example of this utility model. The basic principle is as described above. In this embodiment, the circuit output terminal (13) is connected to the measured capacitor (14), the other end of the measured capacitor is connected to the common ground (11), and the circuit output terminal (12) is connected to the microprocessor. When the circuit starts working, the initial voltage of the measured capacitor (14) is 0V. Since one end of the measured capacitor (14) is connected to the inverting terminal of the amplifier (2-1), when the voltage on the measured capacitor (14) is less than the voltage at the non-inverting terminal of the amplifier (2-1), the amplifier (2-1) outputs a high level, and the constant current source circuit outputs a constant current value. The constant current source circuit charges the measured capacitor (14) with a constant current through the circuit output terminal (13). When the voltage on the measured capacitor (14) is greater than the voltage at the non-inverting terminal of the amplifier (2-1), the amplifier (12) outputs a high level. 2-1) The output terminal outputs a low level, controlling the constant current source circuit to absorb the constant current value externally. The constant current source changes the output direction. At this time, the measured capacitor (14) is in a constant current discharge state. When the voltage on the measured capacitor (14) is less than the voltage of the non-inverting terminal of the amplifier (2-1), the output terminal of the amplifier (2-1) outputs a high level, and the constant current source circuit outputs a constant current value externally. The constant current source circuit charges the measured capacitor (14) with constant current through the circuit output terminal (13). The voltage on the measured capacitor (14) rises, and the cycle repeats. At the same time, the output terminal of the amplifier (2-1) is connected to the general input / output pin of the microprocessor (15) through the circuit output terminal (12). The microprocessor (15) can accurately measure the capacitance value of the measured capacitor (14) by measuring the frequency of the high and low level changes of the detection circuit output terminal (12).

Claims

1. A high-precision capacitor capacitance detection circuit, characterized in that the capacitor capacitance detection circuit includes a reference source circuit consisting of a DC reference source (1) and a common ground (11), a polarity control circuit consisting of a first resistor (3), a second resistor (4), a capacitor (10), a common ground (11), and an amplifier (2-1), and a constant current source circuit consisting of a third resistor (5), a fourth resistor (6), a fifth resistor (7), a sixth resistor (8), an amplifier (2-2), an amplifier (2-3), and a seventh resistor (9).

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