Method and circuit for improving signal-to-noise ratio of eddy current angle sensor

Abstract

The invention discloses a method and circuit for improving the signal-to-noise ratio of an eddy current angle sensor, and the method comprises the steps: inducing an alternating magnetic field generated by a rotor, and generating a high-frequency carrier signal with rotor angle information; respectively demodulating the positive end and the negative end of the high-frequency carrier signal to realize the separation of the sine and cosine signal with the rotor angle information from the high-frequency carrier signal; amplifying the separated sine and cosine signals with the rotor angle information and the high-frequency carrier signals to enable the signal amplitude to be close to the AD measuring range; filtering the high-frequency carrier signal and the harmonic signal thereof to form a group of differential angle signals; and subtraction and sampling are carried out on the differential angle signals. According to the invention, the angle information of the rotor is received by adopting the resonance principle, the amplitude of a high-frequency carrier signal can be greatly improved, and the magnitude of other interference signals can be suppressed. Meanwhile, signal demodulation, amplification, filtering and AD sampling all adopt a differential mode, interference of common-mode signals can be effectively reduced, and the signal-to-noise ratio and the anti-interference capability of the eddy current angle sensor are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of eddy current angle sensors, and in particular to a method and a circuit for improving the signal-to-noise ratio of eddy current angle sensors. Background Art

[0002] Eddy current angle sensors are inductive angle sensors with advantages such as good environmental adaptability and high reliability. Compared with rotary transformers, eddy current angle sensors have advantages such as strong manufacturability, smaller size, lighter weight, and lower cost, and have received widespread attention in the market.

[0003] The eddy current angle sensor consists of two PCBs, with the excitation coil and the receiving coil both engraved on the PCB. Limited by the size of the PCB, the number of turns of the excitation coil is generally small, and there is no magnetic conductor to increase the magnetic flux density. Therefore, the excitation frequency of this type of sensor is relatively high, generally between 2MHz and 4MHz. Also limited by the size of the PCB, the receiving coil of the eddy current angle sensor has only one turn, and the number of pole pairs is limited. Therefore, the amplitude of the angle signal induced on the receiving coil is small.

[0004] The traditional eddy current angle sensor directly demodulates, amplifies and filters the angle signal induced on the receiving coil, and the processing circuit does not use a differential method, resulting in a small original amplitude of the angle signal, and the high-frequency noise coupled by the processing circuit cannot be removed, and the signal-to-noise ratio is relatively low, resulting in poor resolution and accuracy of the eddy current angle sensor. Therefore, it is of great significance to improve the angle signal-to-noise ratio by improving the circuit, thereby improving the resolution and accuracy of the eddy current angle sensor. Summary of the invention

[0005] The object of the present invention is to provide a method and a circuit for improving the signal-to-noise ratio of an eddy current angle sensor, so as to solve the problem in the prior art that the resolution and accuracy of the eddy current angle sensor are low due to the poor signal-to-noise ratio of the angle signal.

[0006] The technical solution to achieve the purpose of the present invention is: a method for improving the signal-to-noise ratio of an eddy current angle sensor, the method comprising the following steps:

[0007] The alternating magnetic field generated by the induction rotor generates a high-frequency carrier signal with rotor angle information;

[0008] The positive end and the negative end of the high-frequency carrier signal are demodulated respectively to separate the sine and cosine signals with rotor angle information from the high-frequency carrier signal;

[0009] Amplify the separated sine and cosine signals with rotor angle information and high-frequency carrier signal to make the signal amplitude close to the AD range;

[0010] Filtering out the high frequency carrier signal and its harmonic signals to form a set of differential angle signals;

[0011] The differential angle signal is subtracted and sampled.

[0012] On the other hand, a circuit for improving the signal-to-noise ratio of an eddy current angle sensor is provided, the circuit comprising an LC resonant coupling circuit module, a differential switch demodulation circuit module, an amplifier circuit module, a low-pass filter circuit module, and a fully differential AD sampling circuit module;

[0013] The LC resonant coupling circuit module is used to sense the alternating magnetic field generated by the rotor and generate a high-frequency carrier signal with rotor angle information;

[0014] The differential switch demodulation circuit module is used to demodulate the positive end and the negative end of the high-frequency carrier signal respectively, so as to separate the sine and cosine signals with rotor angle information from the high-frequency carrier signal;

[0015] The amplifying circuit module is used to amplify the separated sine and cosine signals with rotor angle information and the high-frequency carrier signal, so that the signal amplitude is close to the AD range;

[0016] The low-pass filter circuit module is used to filter out the high-frequency carrier signal and its harmonic signal to form a set of differential angle signals;

[0017] The fully differential AD sampling circuit module is used to implement subtraction and sampling of differential angle signals.

[0018] Furthermore, the LC resonant coupling circuit module includes an equivalent inductance of a receiving coil, a first capacitor and a first capacitor connected in parallel; by adjusting the size of the first capacitor and the first capacitor, the resonant frequency of the LC resonant coupling circuit module is equal to the frequency of the excitation signal, thereby maximizing the amplitude of the received signal and generating a high-frequency carrier signal with rotor angle information.

[0019] Furthermore, the magnitudes of the first capacitor and the second capacitor are calculated by the following formula:

[0020]

[0021] In the formula, ω e is the frequency of the excitation signal, L s , C1, and C2 are respectively the inductance value of the equivalent inductance, the first capacitor, and the capacitance value of the first capacitor.

[0022] Furthermore, the differential switch demodulation circuit module includes a first single-pole double-throw analog switch and a second single-pole double-throw analog switch, and the enable ends of the first single-pole double-throw analog switch and the second single-pole double-throw analog switch are both connected to the PWM output signal; one input end of the first single-pole double-throw analog switch is connected to one end of the receiving coil, and is pulled up to the bias voltage Ref1V25 through a first resistor; the other input end of the first single-pole double-throw analog switch is connected to the bias voltage Ref1V25; one input end of the second single-pole double-throw analog switch is connected to the other end of the receiving coil, and is pulled up to the bias voltage Ref1V25 through a second resistor, and the other input end of the second single-pole double-throw analog switch is connected to the bias voltage Ref1V25; the first single-pole double-throw analog switch and the second single-pole double-throw analog switch respectively process the high-frequency carrier signals at one end and the other end of the receiving coil to generate a pair of differential angle signals.

[0023] Furthermore, the PWM output signal is generated by the MCU, has a frequency that is the same as the frequency of the high-frequency carrier signal, and has a phase difference of 0 with the high-frequency carrier signal.

[0024] Furthermore, the amplifying circuit module amplifies the output signals V2_1 and V2_2 of the first single-pole double-throw analog switch and the second single-pole double-throw analog switch respectively to condition the angle signal so that the DC bias of the angle signal is Ref1V25 and the peak-to-peak value is 0.8 to 0.9 times the AD reference voltage Ref2V5.

[0025] Furthermore, the amplifier circuit module amplifies the output signals V2_1 and V2_2 by a factor of 2 to 10.

[0026] Furthermore, the low-pass filter circuit module adopts a second-order Butterworth low-pass filter, and the cut-off frequency satisfies that it is greater than the angle signal frequency at the highest speed and less than 0.5 times of the AD sampling frequency.

[0027] Furthermore, the fully differential AD sampling circuit module includes a fully differential AD chip, whose positive input terminal and negative input terminal are respectively connected to the differential angle signal to achieve differential angle signal subtraction, while completing the sampling of the angle signal and sending it to the MCU through the SPI interface.

[0028] Compared with the prior art, the present invention has the following significant advantages:

[0029] (1) The present invention connects capacitors C1 and C2 in parallel with the receiving coil to form an LC resonant circuit with the equivalent inductance of the receiving coil. Compared with the traditional capacitor-free solution, the amplitude of the high-frequency carrier signal can be greatly increased, so that the amplitude of the original angle signal is increased by 5 to 10 times. At the same time, the use of two capacitors is conducive to more accurate setting of the resonant frequency and maximization of the amplitude of the original angle signal.

[0030] (2) The present invention sets the PWM output signal of the MCU in the differential switch demodulation circuit module to be of the same frequency and phase as the high-frequency carrier signal. Compared with the traditional switch demodulation circuit, it can ensure that the amplitude of the angle signal does not attenuate during the demodulation process.

[0031] (3) The present invention uses a differential method to process the angle signal throughout the process, and performs subtraction in the fully differential AD, which can effectively suppress the high-frequency interference coupled in the angle signal. At the same time, during the subtraction process, the DC offset in the angle signal is removed, so that the MCU no longer needs to identify the size of the DC offset in the angle signal during calculation, avoiding the problem of accuracy degradation caused by identification errors.

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a circuit principle block diagram for improving the signal-to-noise ratio of an eddy current angle sensor in one embodiment.

[0034] Figure 2 FIG. 4 is a schematic diagram of an LC resonant coupling circuit module in an embodiment.

[0035] Figure 3 FIG. 4 is a schematic diagram of a differential switch demodulation circuit module in an embodiment.

[0036] Figure 4 FIG. 4 is a schematic diagram of an amplifying circuit module in an embodiment.

[0037] Figure 5 FIG. 4 is a schematic diagram of a low-pass filter circuit module in an embodiment.

[0038] Figure 6 FIG. 4 is a schematic diagram of a fully differential AD sampling circuit module in an embodiment. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0040] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0041] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0042] In one embodiment, in combination Figure 1 , provides a method for improving the signal-to-noise ratio of an eddy current angle sensor, the method comprising the following steps:

[0043] The alternating magnetic field generated by the induction rotor generates a high-frequency carrier signal with rotor angle information;

[0044] The positive end and the negative end of the high-frequency carrier signal are demodulated respectively to separate the sine and cosine signals with rotor angle information from the high-frequency carrier signal;

[0045] Amplify the separated sine and cosine signals with rotor angle information and high-frequency carrier signal to make the signal amplitude close to the AD range;

[0046] Filtering out the high frequency carrier signal and its harmonic signals to form a set of differential angle signals;

[0047] The differential angle signal is subtracted and sampled.

[0048] In one embodiment, based on the method, a circuit for improving the signal-to-noise ratio of an eddy current angle sensor is provided, the circuit comprising an LC resonant coupling circuit module, a differential switch demodulation circuit module, an amplification circuit module, a low-pass filter circuit module, and a fully differential AD sampling circuit module;

[0049] The LC resonant coupling circuit module is used to sense the alternating magnetic field generated by the rotor and generate a high-frequency carrier signal with rotor angle information;

[0050] The differential switch demodulation circuit module is used to demodulate the positive end and the negative end of the high-frequency carrier signal respectively, so as to separate the sine and cosine signals with rotor angle information from the high-frequency carrier signal;

[0051] The amplifying circuit module is used to amplify the separated sine and cosine signals with rotor angle information and the high-frequency carrier signal, so that the signal amplitude is close to the AD range;

[0052] The low-pass filter circuit module is used to filter out the high-frequency carrier signal and its harmonic signal to form a set of differential angle signals and realize the anti-aliasing filtering function;

[0053] The fully differential AD sampling circuit module is used to implement the subtraction and sampling of the differential angle signal so that the MCU can solve the digital angle signal.

[0054] Further, in one embodiment, in combination Figure 2 The LC resonant coupling circuit module includes a receiving coil equivalent inductance Ls, a first capacitor C1 and a first capacitor C2 connected in parallel; by adjusting the size of the first capacitor C1 and the first capacitor C2, the resonant frequency of the LC resonant coupling circuit module is equal to the frequency of the excitation signal, thereby maximizing the amplitude of the received signal and generating a high-frequency carrier signal with rotor angle information.

[0055] Here, the receiving coil nn is a positive integer, generally ranging from 1 to 64 cycles of the sinusoidal coil, and the equivalent inductance Ls is measured by an LCR digital bridge tester.

[0056] The sizes of the first capacitor C1 and the first capacitor C2 are calculated by the following formula:

[0057]

[0058] In the formula, ω e The frequency range of the excitation signal is generally between 2MHz and 4MHz. s , C1, and C2 are respectively the inductance value of the equivalent inductance Ls, the capacitance value of the first capacitor C1, and the capacitance value of the first capacitor C2.

[0059] The high-frequency carrier signal generated by the LC resonant coupling circuit module is:

[0060]

[0061] Further, in one embodiment, in combination Figure 3The differential switch demodulation circuit module includes a first single-pole double-throw analog switch N1 and a second single-pole double-throw analog switch N2, and the selection ends of the first single-pole double-throw analog switch N1 and the second single-pole double-throw analog switch N2 are both connected to the PWM output signal; one input end of the first single-pole double-throw analog switch N1 is connected to one end V1_1 of the receiving coil, and is pulled up to the bias voltage Ref1V25 through the first resistor R1; the other input end of the first single-pole double-throw analog switch N1 is connected to the bias voltage Ref1V25; one input end of the second single-pole double-throw analog switch N2 is connected to the other end V1_2 of the receiving coil, and is pulled up to the bias voltage Ref1V25 through the second resistor R2, and the other input end of the second single-pole double-throw analog switch N2 is connected to the bias voltage Ref1V25; the first single-pole double-throw analog switch N1 and the second single-pole double-throw analog switch N2 respectively process the high-frequency carrier signals of one end V1_1 and the other end V1_2 of the receiving coil to generate a pair of differential angle signals.

[0062] Here preferably, the PWM output signal is generated by the MCU, has the same frequency as the high-frequency carrier signal, and has a phase difference of 0 with the high-frequency carrier signal. The amplitude of the angle signal after separation can be further increased by this method.

[0063] refer to Figure 3 The principle of the differential switch demodulation circuit module to achieve demodulation is as follows: the PWM output signal in the differential switch demodulation circuit module is generated by the MCU, and the frequency is ω e , the expression in a complete cycle is:

[0064]

[0065] This signal is multiplied by the high-frequency carrier signal with rotor angle information through the single-pole double-throw analog switch in the differential switch demodulation circuit module to obtain the following signal:

[0066]

[0067] The expression after Fourier expansion is:

[0068]

[0069] This method realizes the angle signal As well as high-frequency carrier and its harmonic signals separation.

[0070] refer to Figure 3The amplitude of the angle signal generated by the differential switch demodulation circuit module is affected by the phase difference ψ between the MCU's PWM output signal and the high-frequency carrier signal. When the phase deviation ψ is 0 or π, the amplitude reaches the maximum. The method for realizing the phase deviation ψ of 0 in the present invention is as follows: the phase difference ψ between the MCU's PWM output signal and the high-frequency carrier signal can be accurately measured by an oscilloscope, and the phase shift between the high-frequency carrier signal and the excitation signal is fixed. The phase shift between the excitation signal and the MCU's PWM output signal can be adjusted to achieve ψ of 0, thereby achieving the maximization of the amplitude.

[0071] Furthermore, in one embodiment, the amplifying circuit module amplifies the output signals V2_1 and V2_2 of the first single-pole double-throw analog switch N1 and the second single-pole double-throw analog switch N2, respectively, with the amplification factor being 2 to 10 times, so as to condition the angle signal so that the DC bias of the angle signal is Ref1V25, and the peak-to-peak value is 0.8 to 0.9 times the AD reference voltage Ref2V5.

[0072] Here, in some embodiments, combined Figure 4 The amplification circuit module includes an ultra-low offset first operational amplifier N3, a second operational amplifier N4, and a third resistor R3 to an eighth resistor R8; the negative input terminal of the first operational amplifier N3 is connected to the output signal V2_1 through the fourth resistor R4, and is connected to the output terminal of the first operational amplifier N3 through the third resistor R3, and the positive input terminal of the first operational amplifier N3 is grounded through the fifth resistor R5; the negative input terminal of the second operational amplifier N4 is connected to the output signal V2_2 through the seventh resistor R7, and is connected to the output terminal of the second operational amplifier N4 through the sixth resistor R6, and the positive input terminal of the first operational amplifier N3 is grounded through the eighth resistor R8. The output terminals of the first operational amplifier N3 and the second operational amplifier N4 output signals V3_1 and V3_2 respectively.

[0073] Further, in one embodiment, in combination Figure 5 The low-pass filter circuit module adopts a typical second-order Butterworth low-pass filter.

[0074] Here, other low-pass circuits can also be used to build, as long as the following requirements are met: the cut-off frequency is greater than the angle signal frequency at the highest speed and less than 0.5 times the AD sampling frequency. This method filters out the high-frequency carrier and its harmonic signals to form a set of differential angle signals:

[0075]

[0076] Where K is the amplitude of the sine and cosine signals, and θ is the rotor angle.

[0077] Further, in one embodiment, in combination Figure 6 The fully differential AD sampling circuit module includes a fully differential AD chip (N7), whose positive input terminal and negative input terminal are respectively connected to the differential angle signal to achieve differential angle signal subtraction, and at the same time complete the sampling of the angle signal and send it to the MCU through the SPI interface. The method realizes the sampling of the angle signal and the filtering of the common mode interference signal.

[0078] In summary, the present invention adopts the resonance principle to receive the angle information of the rotor, which can greatly increase the amplitude of the high-frequency carrier signal and suppress the size of other interference signals. At the same time, signal demodulation, amplification, filtering and AD sampling all adopt a differential method, which can effectively reduce the interference of common-mode signals and improve the signal-to-noise ratio and anti-interference ability of the eddy current angle sensor.

[0079] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the signal-to-noise ratio of an eddy current angle sensor, characterized in that: The method comprises the following steps: The alternating magnetic field generated by the induction rotor generates a high-frequency carrier signal with rotor angle information; The positive end and the negative end of the high-frequency carrier signal are demodulated respectively to separate the sine and cosine signals with rotor angle information from the high-frequency carrier signal; Amplify the separated sine and cosine signals with rotor angle information and high-frequency carrier signal to make the signal amplitude close to the AD range; Filtering out the high frequency carrier signal and its harmonic signals to form a set of differential angle signals; The differential angle signal is subtracted and sampled.

2. A circuit for improving the signal-to-noise ratio of an eddy current angle sensor based on the method of claim 1, characterized in that: The circuit includes an LC resonant coupling circuit module, a differential switch demodulation circuit module, an amplifier circuit module, a low-pass filter circuit module and a fully differential AD sampling circuit module; The LC resonant coupling circuit module is used to sense the alternating magnetic field generated by the rotor and generate a high-frequency carrier signal with rotor angle information; The differential switch demodulation circuit module is used to demodulate the positive end and the negative end of the high-frequency carrier signal respectively, so as to separate the sine and cosine signals with rotor angle information from the high-frequency carrier signal; The amplifying circuit module is used to amplify the separated sine and cosine signals with rotor angle information and the high-frequency carrier signal, so that the signal amplitude is close to the AD range; The low-pass filter circuit module is used to filter out the high-frequency carrier signal and its harmonic signal to form a set of differential angle signals; The fully differential AD sampling circuit module is used to implement subtraction and sampling of differential angle signals.

3. The circuit for improving the signal-to-noise ratio of an eddy current angle sensor according to claim 2, characterized in that: The LC resonant coupling circuit module comprises a receiving coil equivalent inductance (Ls), a first capacitor (C1) and a first capacitor (C2) connected in parallel; by adjusting the size of the first capacitor (C1) and the first capacitor (C2), the resonant frequency of the LC resonant coupling circuit module is equal to the frequency of the excitation signal, so as to maximize the amplitude of the received signal and generate a high-frequency carrier signal with rotor angle information.

4. The circuit for improving the signal-to-noise ratio of an eddy current angle sensor according to claim 3, characterized in that: The magnitudes of the first capacitor (C1) and the second capacitor (C2) are calculated by the following formula: In the formula, ω e is the frequency of the excitation signal, L s , C1, and C2 are respectively the inductance value of the equivalent inductance (Ls), the first capacitor (C1), and the capacitance value of the first capacitor (C2).

5. The circuit for improving the signal-to-noise ratio of an eddy current angle sensor according to claim 2, characterized in that: The differential switch demodulation circuit module comprises a first single-pole double-throw analog switch (N1) and a second single-pole double-throw analog switch (N2); the first single-pole double-throw analog switch (N1) and the second single-pole double-throw analog switch (N2) have their selection ends connected to a PWM output signal; one input end of the first single-pole double-throw analog switch (N1) is connected to one end (V1_1) of a receiving coil and is pulled up to a bias voltage Ref1V25 through a first resistor (R1); the other input end of the first single-pole double-throw analog switch (N1) is connected to the bias voltage Ref1V 25; one input end of the second single-pole double-throw analog switch (N2) is connected to the other end (V1_2) of the receiving coil and is pulled up to a bias voltage Ref1V25 through a second resistor (R2); the other input end of the second single-pole double-throw analog switch (N2) is connected to the bias voltage Ref1V25; the first single-pole double-throw analog switch (N1) and the second single-pole double-throw analog switch (N2) respectively process high-frequency carrier signals at one end (V1_1) and the other end (V1_2) of the receiving coil to generate a pair of differential angle signals.

6. The circuit and method for improving the signal-to-noise ratio of an eddy current angle sensor according to claim 5, characterized in that: The PWM output signal is generated by the MCU, has the same frequency as the high-frequency carrier signal, and has a phase difference of 0 with the high-frequency carrier signal.

7. The circuit and method for improving the signal-to-noise ratio of an eddy current angle sensor according to claim 5, characterized in that: The amplifying circuit module amplifies the output signals V2_1 and V2_2 of the first single-pole double-throw analog switch (N1) and the second single-pole double-throw analog switch (N2) respectively to condition the angle signal so that the DC bias of the angle signal is Ref1V25 and the peak-to-peak value is 0.8 to 0.9 times the AD reference voltage Ref2V5.

8. The circuit and method for improving the signal-to-noise ratio of an eddy current angle sensor according to claim 7, characterized in that: The amplifier circuit module amplifies the output signals V2_1 and V2_2 by 2 to 10 times.

9. The circuit and method for improving the signal-to-noise ratio of an eddy current angle sensor according to claim 2, characterized in that: The low-pass filter circuit module adopts a second-order Butterworth low-pass filter, or other low-pass circuits, which must meet the following requirements: the cut-off frequency is greater than the angle signal frequency at the highest speed and less than 0.5 times the AD sampling frequency.

10. The circuit for improving the signal-to-noise ratio of an eddy current angle sensor according to claim 2, characterized in that: The fully differential AD sampling circuit module comprises a fully differential AD chip (N7), whose positive input terminal and negative input terminal are respectively connected to differential angle signals to achieve differential angle signal subtraction, complete angle signal sampling at the same time, and send the angle signal to the MCU through the SPI interface.

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