Method and apparatus for automatic gain control

Abstract

A gain control apparatus and method for a circuit for measuring a parameter is provided.SOLUTION: The apparatus includes a sine wave generation module and a gain control signal generation module. The sine wave generation module is configured to receive a first signal and a second signal. The first signal is proportional to a sine wave of the parameter to be measured and the second signal corresponds to the first signal shifted by one fourth of a period of the sine wave. The sine wave generation module is further configured to generate an approximate sine wave function over time by determining values of a shifted sine function having a first frequency at a plurality of sampling points. The phase shift and the amplitude of the shifted sine function are based on the first signal and the second signal.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates to automatic gain control, and more particularly to a method and apparatus for automatic gain control of a sensor circuit. [Background technology]

[0002] Automatic gain control (AGC) is a critical component in the field of sensor circuits, designed to maintain a consistent output signal level despite changes in input signal strength. The development and implementation of AGC systems addresses the challenges posed by the fluctuating signal conditions inherent in many sensor-based applications. This technique improves the reliability and accuracy of sensor performance by keeping the output signal within a desired amplitude range.

[0003] The primary purpose of AGC is to increase the reliability and accuracy of sensor measurements by compensating for changes that can lead to signal distortion and data loss. By automatically adjusting the gain, AGC helps optimize the signal-to-noise ratio (SNR), thereby improving the clarity and quality of the sensor's output.

[0004] An example of a sensor that can be AGCed is a differential transformer, where the output signal has an amplitude that is indicative of the measurand.

[0005] Differential transformers, such as linear variable differential transformers (LVDTs) and rotary variable differential transformers (RVDTs), are widely used in precision measurement applications due to their high accuracy and reliability in sensing linear and angular displacement, respectively. Both LVDTs and RVDTs operate on the principle of electromagnetic induction, accurately converting mechanical movement into a measurable electrical signal. However, the output signal from these devices can vary significantly due to changes in excitation voltage, temperature fluctuations, and mechanical variations. To address these challenges and improve the performance of LVDTs and RVDTs, automatic gain control (AGC) is employed.

[0006] In an LVDT, an AC excitation voltage is applied to the primary coil, creating a magnetic field that induces voltages in the two secondary coils. The position of the moving core within the transformer affects the differential voltage between the secondary coils. This differential voltage is used to determine displacement. Similarly, in an RVDT, the angular position of the rotating core changes the magnetic coupling between the primary and secondary windings, generating a differential voltage proportional to the angular displacement.

[0007] The purpose of AGC in a differential transformer is to maintain a constant amplitude of the differential output signal, ensuring accurate position or angle measurements regardless of changes in excitation voltage or other environmental conditions. This is typically achieved by dynamically adjusting the gain of the signal conditioning circuitry that processes the LVDT or RVDT output.

[0008] LVDTs and RVDTs can improve performance and accuracy by employing receiving coils wound in sine and cosine wave patterns. These special configurations are particularly effective in applications requiring high precision and sensitivity, such as angular displacement measurement. By taking advantage of the inherent properties of these sine and cosine wave windings, these transformers can achieve improved signal quality and resolution.

[0009] 1A and 1B show non-limiting examples of LVDT and RVDT configurations with sine and cosine windings. The LVDT includes sine and cosine receive coils 2 and 3, each with one positive and one negative cycle. The sine and cosine receive coils 2 and 3 are surrounded by a transmit coil 4.

[0010] In an LVDT, coils 2, 3, and 4 are arranged along a linear path to detect linear motion of target 8. In an RVDT, coils 2, 3, and 4 are arranged in a circle to detect rotational motion of target 8. Target 8 can be any type of metal, such as aluminum, steel, or a printed circuit board (PCB) with a copper layer printed on it.

[0011] For example, Figure 2A shows the output signal of a sinusoidal receive coil 2 in an RVDT configuration. A high frequency AC voltage (excitation signal) is applied to the transmit coil 4, for example, A*sin(wt), where A represents the amplitude of the AC voltage and w represents the angular frequency.

[0012] Energizing the transmit coil 4 with a high frequency AC voltage generates a magnetic field that interacts with the target 8. As the target 8 passes through the magnetic field, voltages are induced in the sine wave receive coil 2 and the cosine wave receive coil 3. Specifically, the output signal in the receive coil corresponds to an amplitude modulation of the signal in the transmit coil, and the amplitude is directly proportional to the measurand. In the example of FIG. 2A, the amplitude of the output signal in the sine wave receive coil 2 of the RVDT is directly proportional to sin(φ), where φ represents the angular displacement of the target 8.

[0013] The output signal is demodulated to measure the measurand. An example of the demodulated signal in an RVDT is shown in Figure 2B. The demodulated signal may be an analog signal. The demodulated signals in the sine wave receiving coil 3 and the cosine wave receiving coil 4 are proportional to the measurand, e.g., angle. Because the demodulated signal depends not only on the amplitude of the excitation signal in the transmitting coil 4 but also on the characteristics of the target, the demodulated signal may vary over a wide range of values. Therefore, an AGC is used to adjust the gain of the output signal in the receiving coil to a desired range of values, e.g., a range optimal for the circuit elements used for demodulation or for analog-to-digital conversion.

[0014] An example of such a circuit is shown in Figure 3. The sensor 10 may be an LVDT or RVDT, as described above. An LC oscillator generates an excitation signal for the transmit coil 4. The modulated output signals at the two receive coils are gain-controlled via programmable gain amplifiers (PGAs) controlled based on signals from the AGC 100. The gain-adjusted output signals are demodulated by a synchronous demodulator, which outputs signals such as those shown in Figure 2B. These signals are also inputs to the AGC 100.

[0015] To adjust the range, the AGC 100 determines the amplitude of the input signal and provides a corresponding control signal to the PGA. In particular, the AGC 100 determines the signal amplitude by determining the sum of the squares of the demodulated signals at the two receive coils. However, performing these nonlinear mathematical operations in the analog domain is complex and prone to inaccuracies due to process variations and temperature drift. Therefore, it is an object of the present invention to improve the efficiency and accuracy of AGC amplitude determination.

[0016] The amplitude determined by the AGC 100 circuit is then compared with a threshold value. Depending on the comparison result, a digital signal is increased or decreased. This digital signal is then fed to a PGA to apply an appropriate gain to the output signals of the two receive coils. Because digital signals are inherently discrete, changes in gain cause jumps in the output signals at the receive coils. Furthermore, adjusting the gain in the PGA requires multiple gain steps. This can complicate the PGA configuration and increase the circuit area required for the PGA. Therefore, an object of the present invention is to improve the efficiency of applying gain to the output signals at the receive coils. Summary of the Invention

[0017] In view of the above, the present disclosure provides an apparatus and method for automatic gain control having the features of the independent claims set out in the accompanying claims.

[0018] According to a first aspect of the present disclosure, an apparatus for automatic gain control is provided. The apparatus may include a sine wave generation module and a gain control signal generation module. The sine wave generation module may be configured to receive a first signal and a second signal. The first and second signals may be analog signals and may correspond to voltages. The first signal may be proportional to a sine wave of a parameter to be measured (e.g., a measured angle or a measured linear displacement parameter), and the second signal may correspond to the first signal shifted by a quarter of a period of the sine wave. The sine wave generation module may be further configured to generate an approximated sine wave function over time by determining values ​​of a shifted sine function having a first frequency at multiple sampling points. A phase shift and an amplitude of the shifted sine function may be based on the first signal and the second signal. The approximated sine wave function over time may be a step function. The sine wave generation module may be configured to perform a linear operation in the analog domain. The gain control signal generating module may further be configured to generate a third signal proportional to an amplitude spectrum of the approximated sine wave function at a first frequency. The first frequency may correspond to a first harmonic of the approximated sine wave function. The third signal may be an analog signal and may correspond to a voltage. The third signal may be proportional to the amplitude / scaling factor of the first signal and the second signal. The gain control signal generating module may further be configured to output the third signal to a circuit for measuring the parameter of interest. An automatic gain control device may be connected to the circuit, and the third signal may be used for gain control of the circuit.

[0019] By determining a third signal that is proportional to the amplitude / scaling factor of the first and second signals based on linear operations in the analog domain, automatic gain control can be achieved with reduced complexity and increased accuracy.

[0020] In some embodiments, the first signal may be proportional to sin(χ) and the second signal may be proportional to cos(χ), where χ may represent the parameter of interest. In particular, the first signal may be equal to A*sin(χ) and the second signal may be equal to A*cos(χ). The amplitude / scaling factor A may depend on the excitation signal in the circuit for measuring the parameter of interest and the sensor configuration for measuring the parameter of interest.

[0021] In some embodiments, determining values ​​of a shifted sine function having a first frequency at a plurality of sampling points may include configuring the sine wave generation module to determine, for each value and corresponding sampling point, a weighted sum of the first signal and the second signal. The weights of the weighted versions of the first signal and the second signal may correspond to the sine and cosine functions evaluated at a first angle, where the first angle may be based on the sampling point and the first frequency. The weights may be in the range of 1,

[0022]

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[0024] In some embodiments, the sine wave generating module may include a multiplexing module and an adder module. The multiplexing module may be configured to determine a plurality of fourth signals by multiplexing the positive and negative signals and the zero signal of the first and second signals. The adder module may be configured to multiply each of the plurality of fourth signals by a different weight to generate weighted versions of the plurality of fourth signals. The adder module may further be configured to perform a weighted sum of the plurality of fourth signals to generate values ​​of a shifted sine function at the sampling points. The plurality of fourth signals and the weight for each of the plurality of fourth signals may be selected for each sampling point such that a sine function having a first frequency and an amplitude shifted by A is approximated. The adder module may be an analog adder. The multiplexing module may include a plurality of digitally controlled multiplexers configured to multiplex the positive and negative signals and the zero signal of the first and second signals. Furthermore, the sampling points may be determined based on a clock signal having a second frequency. The second frequency may be at least twice the first frequency.

[0025] In some embodiments, the number of the plurality of fourth signals is 1 or 2. In other words, the multiplexing module may include three multiplexers, and for each sampling point, only one or two of the three multiplexers may output a non-zero signal.

[0026] In some embodiments, the sine wave generating module may further include a smoothing module. The smoothing module may be configured to generate a sine wave function over time by smoothing the approximated sine wave function. Furthermore, the gain control signal generating module may include an AC-DC conversion module. The AC-DC conversion module may be configured to generate a third signal from the sine wave function. The AC-DC conversion module may include a rectifier and a first low-pass filter. The rectifier may be a full-wave rectifier or a half-wave rectifier. In the case of a full-wave rectifier, the third signal is

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[0029] In some embodiments, the smoothing module may include a second low-pass filter configured to generate a sinusoidal function over time by filtering the approximated sinusoidal function. The cutoff frequency of the second low-pass filter may correspond to or be close to the first frequency. In other words, the second low-pass filter may be suitable for filtering frequencies of the approximated sinusoidal function over time other than the first harmonic.

[0030] In some embodiments, the smoothing module may further include a high-pass filter configured to operate in conjunction with the second low-pass filter to generate a sinusoidal function over time by smoothing the approximated sinusoidal function, and the cutoff frequency of the high-pass filter may correspond to or be close to the first frequency.

[0031] By using a high-pass filter in addition to the second low-pass filter, temperature-induced drift of the cutoff frequencies of these filters can be reduced in impact on the accuracy of the determined third signal.

[0032] In some embodiments, the apparatus may further include a drift adaptation module configured to adapt the first frequency to temperature-induced drift of the cutoff frequency of the second low-pass filter and / or the high-pass filter.

[0033] By adapting the first frequency in the direction of the drift of the cut-off frequency, the accuracy of the determined third signal may be further improved over a certain temperature range.

[0034] In some embodiments, the gain control signal generation module may include an error signal generation module. The error signal generation module may be configured to generate the error signal by comparing the third signal with a first reference value. The first reference value may be a reference voltage. The reference voltage may be based on desired signal ranges of the first signal and the second signal. The error signal generation module may be further configured to output an error signal to a circuit for measuring a parameter of interest, where the error signal is used for gain control of the circuit.

[0035] In some embodiments, using the error signal for gain control of the circuit for measuring the parameter of the object to be measured may include controlling an LC oscillator with the error signal, the LC oscillator being part of the circuit for measuring the parameter of the object to be measured and configured to provide the excitation signal.

[0036] In some embodiments, using the error signal in a gain control of the circuit for measuring the parameter of interest may include using the error signal to control an analog gain element in the circuit for measuring the parameter of interest. The analog gain element may be located in a signal chain of the parameter of interest. The signal chain may be a high-frequency signal chain or a low-frequency signal chain. The frequency of the high-frequency signal chain may correspond to the frequency of the excitation signal for measuring the parameter of interest. The analog gain element may be an attenuator.

[0037] By providing an analog gain control to the signal chain of the parameter being measured via an LC oscillator or an analog gain element, jumps in the first and second signals can be avoided, making the output signal of the circuit for measuring the parameter being measured more stable.

[0038] In some embodiments, the apparatus may further include an LC calibration module. The LC calibration module may be configured to calibrate the LC oscillator based on the third signal. The LC oscillator may provide an excitation signal to the circuit for measuring the parameter of interest. Calibration of the LC oscillator may be performed upon start-up of the circuit to adapt the circuit to a sensor used to measure the parameter of interest, particularly when the LC calibration module, the sine wave generating module, and the gain control signal generating module share the same resources.

[0039] In some embodiments, the LC calibration module may include a comparison module and a digital output module. The comparison module may be configured to compare the third signal with a second reference value. The second reference value may be a reference voltage. Based on a comparison result, the digital output module may be configured to increase or decrease the digital signal. The digital output module may be further configured to output a digital signal for controlling the LC oscillator.

[0040] According to a second aspect of the present disclosure, there is provided a measurement circuit with automatic gain control. The measurement circuit with automatic gain control may include an apparatus for automatic gain control according to any embodiment of the first aspect. The measurement circuit with automatic gain control may further include a circuit for measuring a parameter of an object to be measured. This circuit may be connected to the apparatus for automatic gain control. In other words, the circuit for measuring the parameter of the object to be measured may output a signal indicative of the parameter of the object to be measured. This signal may include an input of the apparatus for automatic gain control. The apparatus for automatic gain control may provide a gain control signal to the measurement circuit that measures the parameter of the object to be measured.

[0041] In some embodiments, the circuit may be a variable differential transformer circuit. The variable differential transformer may be a linear variable differential transformer or a rotary variable differential transformer. The differential transformer may include a transmit coil and two receive coils. The windings of the two receive coils may be sinusoidally shaped such that a first output signal in the first receive coil is related to a sine wave of the parameter being measured, and a second output signal in the second receive coil is related to a cosine wave of the parameter being measured. The first output signal and the second output signal may be generated based on a high-frequency excitation signal input to the transmit coil.

[0042] In some embodiments, the first signal may correspond to a demodulated first output signal and the second signal may correspond to a demodulated second output signal. Demodulation of the first output signal and the second output signal may be performed by a synchronous demodulator.

[0043] According to a third aspect of the present disclosure, there is provided a method for automatic gain control, the method performing the gain control using an apparatus according to any embodiment of the first aspect.

[0044] It should be noted that the apparatus features and method steps can be interchanged in many ways. In particular, details of the disclosed methods can be implemented by a corresponding apparatus (or system), and vice versa, as will be understood by those skilled in the art. Furthermore, it should be noted that any of the above statements made with respect to a method also apply to a corresponding apparatus (or system), and vice versa. [Brief explanation of the drawings]

[0045] Exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. [Figure 1A] FIG. 1 illustrates a differential transformer based on sine and cosine receiving coils for measuring linear displacement and angle. [Figure 1B] FIG. 1 illustrates a differential transformer based on sine and cosine receiving coils for measuring linear displacement and angle. [Figure 2A] FIG. 10 illustrates the modulated output signal at the sinusoidal receiving coil of the differential transformer. [Figure 2B] FIG. 10 illustrates the demodulated output signals at the sine and cosine receiving coils of the differential transformer. [Figure 3] 1 is a schematic diagram of an automatic gain control circuit and a gain control sensor circuit according to the prior art; [Figure 4] FIG. 2 is a schematic diagram illustrating an automatic gain control circuit according to an embodiment of the present disclosure. [Figure 5] FIG. 2 is a schematic diagram illustrating a first implementation of an automatic gain control circuit and a gain control sensor circuit according to an embodiment of the present disclosure. [Figure 6] FIG. 10 is a diagram illustrating the generation of an approximated sinusoidal function over time according to an embodiment of the present disclosure. [Figure 7] FIG. 10 is a diagram illustrating an exemplary implementation for generating an approximated sinusoidal function over time according to an embodiment of the present disclosure. [Figure 8] FIG. 2 is a schematic diagram illustrating a second implementation of an automatic gain control circuit and a gain control sensor circuit according to an embodiment of the present disclosure. [Figure 9] 1A-1C are schematic diagrams illustrating temperature-induced shifts in cutoff frequencies for low-pass and high-pass filters, as well as shifts in the approximate sinusoidal function of the first harmonic over time. [Figure 10] 1 is a flowchart illustrating an example of a method for automatic gain control according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0046] The accompanying figures and the following description relate to preferred embodiments for purposes of illustration only. It should be noted below that alternative embodiments of the structures and methods disclosed herein are readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed.

[0047] Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying figures. It should be noted that like or similar reference numerals may be used in the figures to indicate like or similar functionality. The figures are for illustrative purposes only and depict embodiments of the disclosed apparatus (or method). Those skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein.

[0048] The general concept of the present invention is illustrated diagrammatically in FIG. 4. In FIG. 4, the AGC 200 may receive demodulated signals (RX_sin, RX_cos) of two receive coils. The demodulated signals may be analog signals. The demodulated signals may also correspond to voltages. More generally, the AGC 200 may receive a first signal proportional to the sine wave of a parameter to be measured, e.g., an angle or linear displacement parameter. Furthermore, the AGC 200 may further receive a second signal corresponding to the first signal shifted by a quarter of the period of the first signal (e.g., phase shifted by 90°), i.e., a signal proportional to the cosine of the parameter to be measured.

[0049] Although the input signal is described above with reference to a differential transformer, that description should not be construed to limit the invention to this particular sensor type, or to sensors in general. The AGC200 can be used to control the gain of a circuit, device, or system, so long as the output of the circuit, device, or system exhibits the sine / cosine of the parameter.

[0050] For example, another application for using the AGC 200 could be phase monitoring in a power grid, since the monitored signal could also correspond to the sine / cosine of the phase.

[0051] The AGC 200 may include a sine wave generation module 202. Instead of using complex calculations in the analog domain to determine the amplitudes of RX_sin and RX_cos, a time-varying sine wave function is generated based on RX_sin and RX_cos to efficiently extract the amplitudes of RX_sin and RX_cos. That is, the value of A is determined when RX_sin = A*sin(φ) and RX_cos = A*cos(φ), where φ represents the measured angle. Similar equations for RX_sin and RX_cos may be determined for other types of parameters to be measured. The sine wave generation module 202 may receive RX_sin and RX_cos and generate an approximated sine wave signal over time. In particular, the approximated sine wave signal over time may be generated by determining values ​​of a shifted sine function at multiple sampling points. The approximated sine wave signal over time may be a step function. The shifted sine function may have a first frequency, which may be a design parameter. In particular, the phase shift and amplitude of the shifted sine function may depend on RX_sin and RX_cos. In other words, the sine wave generation module 202 may aim to generate a shifted sine function with arguments of RX_sin and RX_cos, e.g., a shift corresponding to the angle φ, and an amplitude corresponding to the amplitude scaling factor A of RX_sin and RX_cos. A particularly efficient implementation of this sine wave generation over time is described further below.

[0052] The angle φ may be constantly changing, such as when the target 8 in the sensor is constantly rotating, accelerating, or decelerating. φ can be assumed to be constant or quasi-constant during the generation of the approximated sinusoidal signal over time, for example, over one period of the approximated sinusoidal signal over time. For this assumption to hold, the frequency of the approximated sinusoidal signal over time may be much higher than the rotation frequency of the target 8, for example, 100 times higher than the rotation frequency. Also, the target 8 may not be constantly rotating but may remain in a specific position, i.e., φ may not change over a specific period of time.

[0053] By generating an approximated sine wave signal over time having an amplitude corresponding to the amplitude scaling factor A of RX_sin and RX_cos, A can be determined efficiently and accurately. The determination of A may be performed by the gain control signal generation module 204. The gain control signal generation module 204 may generate a signal based on the approximated sine wave signal over time output by the sine wave generation module 202. In particular, the signal output by the gain control signal generation module 204 may be proportional to the amplitude (e.g., magnitude) of the amplitude spectrum over time of the approximated sine wave signal at the first frequency, i.e., the frequency that was the target frequency for generating the approximated sine wave signal. Therefore, the signal output by the gain control signal generation module 204 may be proportional to the scaling factor A of RX_sin and RX_cos and may therefore be suitable as a gain control signal for a circuit for measuring a parameter of interest. The signal output by the gain control signal generation module 204 may be used for gain control of a measurement circuit. How this signal is used for gain control may depend on the specific implementation. The output signal of the AGC 200 may be an analog signal. Without intended limitation, the output signal may further correspond to a voltage. The signal output by the gain control signal generation module 204 may be further processed to generate a control signal that can be directly used to control the gain of a measurement circuit. Thus, the AGC 200 may be connected to a circuit that processes the sensor's signal by receiving the circuit's demodulated output signal and providing a signal to control the circuit's gain.

[0054] 5 shows an example of an AGC 200 along with a measurement circuit according to an embodiment of the present disclosure. The sine wave generation module 202 may include a sine wave generator 222 that receives an input signal via an RC oscillator 224. The input signal from the RC oscillator 224 may be used to determine the phase of the sine wave at the sampling points. As mentioned above, the purpose of the sine wave generation module 202 may be to generate a sine wave function over time with a phase shift corresponding to the arguments RX_sin and RX_cos and an amplitude corresponding to the scaling factors RX_sin and RX_cos.

[0055] To illustrate the construction of an approximated sine wave over time, FIG. 6 shows an example of an approximated sine wave function according to an embodiment of the present disclosure. In this example, sampling points are selected such that the distance between two sampling points corresponds to a 30° shift (i.e., π / 6). In summary, the purpose of the sine wave generation module 202 may be to generate a function A*sin(φ+ψ), where ψ=ωt, where ω represents the angular frequency and t is the sampling point over time. As mentioned above, in FIG. 6, ωt is selected such that the distance between the two angles corresponding to the two sampling points is equal to 30° (i.e., π / 6).

[0056] Using the well-known trigonometric identity sin(a+b)=sin a cos b+cos a sin b, the value of A*sin(φ+ψ) can be determined by a simple sum of the scaled sin(φ) and cos(φ) terms. When evaluating in multiples of 30°, the scaling of sin(φ) and cos(φ) only needs to be determined in advance: 1,

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[0059] FIG. 7 illustrates an example implementation for generating an approximate sine wave over time according to an embodiment of the present disclosure. In this example, the sine wave generator 222 includes a multiplexing module and an adder module. The adder module may include, for example, an analog adder with a feedback resistor. For example, if the distance between sampled angles is 30°, the multiplexing module only requires three multiplexers, and the adder module only requires three multipliers. The multiplexers are digitally controlled and receive the positive and negative (e.g., inverse) values ​​of RX_sin and RX_cos as inputs. This allows each multiplexer to output the required signal for a particular sampling point to the multiplier. For example, at a sampling point corresponding to a 30° angle, the first multiplexer outputs a zero signal (not shown in FIG. 7), the second multiplexer outputs sin(φ), and the third multiplexer outputs cos(φ). The three scaled signals, RX_sin and RX_cos, are then summed. Since one signal is zero (the zero signal), we simply sum the two signals. In a specific implementation where the distance between sampled angles is 30°, one or two signals will be zero, depending on the angle used to determine the sinusoidal function. Therefore, for each sampling point, we simply sum one or two signals. In this way, the generation of an approximate sine wave over time, with amplitudes corresponding to the arguments RX_sin and RX_cos and the scaling factors for RX_sin and RX_cos, can be efficiently implemented by an analog adder.

[0060] However, the specific example with a distance between sampling angles (30°) should not be construed as a limitation of the present disclosure. The generation of the sine wave may be performed with any distance between sampling points as long as the Nyquist criterion is met. In other words, the frequency of the sampling points may need to be twice the target frequency of the generated sine wave. However, a more efficient implementation can be achieved by selecting a specific sampling point, for example, a corresponding angle of 30°.

[0061] 5, to enable the gain control signal generation module 204 to extract the amplitude of the sine wave, it may be necessary to smooth the approximated sine function over time. This functionality may be implemented by a smoothing module of the sine wave generation module 202. In the example of FIG. 5, the smoothing module may include a low pass filter 226 having a cutoff frequency corresponding to or close to (e.g., slightly above) the first harmonic of the approximated sine wave function over time, i.e., a frequency corresponding to the angular frequency ω used to generate the approximated sine wave function over time.

[0062] Thus, the output of the sine wave generation module 202 may be a smoothed sinusoidal function over time with amplitude corresponding to the scaling factors of the input signals RX_sin and RX_cos.

[0063] The gain control signal generation module 204 may include an AC-DC conversion module for determining the amplitude of the sinusoidal function. In the example of Figure 5, the AC-DC conversion module may include a rectifier 242 and a second low-pass filter 244. The rectifier 242 may be a full-wave rectifier, and the second low-pass filter 244 may have a cutoff frequency that passes only the DC value of the rectified time sinusoidal function.

[0064] By performing an AC-DC conversion of the generated sinusoidal function over time, the output signal will have an amplitude proportional to the scaling factors RX_sin and RX_cos, i.e., proportional to A. In the above example of an AC-DC converter, the output signal is

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[0067] The output signal indicating the amplitude may be used in various ways to control amplification or attenuation in the circuit for measuring the parameter of interest. In the non-limiting example of FIG. 5 , the generated DC signal, i.e., a voltage signal proportional to the scaling factors RX_sin and RX_cos, is used to directly control the amplitude of the LC oscillator used to generate the excitation signal for the differential transformer. To achieve this, the DC output signal of the low-pass filter 244 is compared to a reference voltage to generate an error signal. The reference voltage may depend on the desired range of the output voltage of the circuit for measuring the parameter of interest. The error signal is used to control the LC oscillator. In the example of FIG. 5 , the LC oscillator is current-driven, so the error signal is converted to a current signal by the VI converter 246. Therefore, a control signal corresponding to the DC current is output by the gain control signal generation module 204. The DC current output, together with a reference current signal, is input to the LC oscillator. The reference current signal may correspond to a reference value for controlling the amplitude of the LC oscillator. Therefore, the amplitude of the excitation signal in the differential transformer can be increased or decreased based on the DC output current signal of the AGC 200.

[0068] In an alternative embodiment, the LC oscillator may be voltage driven, in which case no voltage-to-current conversion element is required.

[0069] In the example of Figure 5, the amplitudes of the signals output by the two receiving coils of the differential transformer, corresponding to the scaling factors, can be determined in the analog domain without complex mathematical operations. Furthermore, the gain is controlled by a continuous signal input to the LC oscillator, rather than a discrete signal input to the PGA. In particular, the PGA can have a fixed gain or be replaced by another fixed-gain element. This avoids jumps or discontinuities in the output signal.

[0070] A drawback of the implementation of AGC 200 in FIG. 5 is that only the input / excitation signal is controlled, which may limit the amount of gain control. For applications and use cases requiring a wider range of gain control, FIG. 8 illustrates a different implementation of AGC 200 according to an embodiment of the present disclosure. In particular, AGC 200 may use the same blocks as in FIG. 5 to generate a DC output voltage signal, i.e., the output of low-pass filter 244, and use the output signal for different control elements in the circuit for measuring the parameter of interest. In particular, the DC output voltage signal may be the input to error amplifier ErrAmp 248. ErrAmp 248 compares the DC output voltage signal with a reference voltage and determines the difference, i.e., the error signal. The reference voltage may correspond to a desired range of values ​​for the output signals, i.e., RX_sin and RX_cos, of the circuit for measuring the parameter of interest. Conversely to the embodiment in FIG. 5, the error signal may then be used as the input to an analog gain element in the circuit for measuring the parameter of interest. In other words, the analog gain element may attenuate or amplify the output signals of the two receiving coils of the differential amplifier based on the error signal.

[0071] The location of the analog gain element in the circuit for measuring the parameter of interest in FIG. 8 is merely exemplary and is not intended to limit the present disclosure. For example, the analog gain element could be placed before the synchronous demodulator in FIG. 8 or could apply gain directly to the demodulated output signal. In other words, the analog gain element could be placed in the high-frequency portion, the low-frequency portion, or anywhere between these portions in the signal chain of the parameter of interest. The analog gain element could also be implemented as an attenuator if a certain amount of amplification is additionally applied to the output signals of the two receiving coils (e.g., the high-frequency amplifier and the low-frequency amplifier).

[0072] Optionally, the DC output voltage signal of the low-pass filter may be used to calibrate the LC oscillator via the LC calibration module 300. The LC calibration module 300 may include a comparison module 302 and a digital output module 304. The comparison module 302 may compare the DC output voltage signal to a reference voltage. The reference voltage may be based on a desired value or range of values ​​for the output signals of the two receiving coils of the differential transformer. Based on the comparison, the comparison module 302 outputs a signal to decrease or increase a digital signal in the digital output module 304. The digital output module 304 may output a generated discrete signal to control the amplitude output by the LC oscillator. Notably, in some implementations, when circuit resources are shared between the AGC 200 and the LC calibration module 300, calibration of the LC oscillator via the LC calibration module 300 may be used only during startup of the circuit to measure the parameter of interest. By using the LC calibration module 300, it can be ensured that the range of values ​​at the outputs of the two receiving coils is already close to the desired range, taking into account value drift induced by, for example, aging.

[0073] A further requirement for the AGC 200 may be stability over a certain temperature range, as temperature-induced component value drift can affect the accuracy of the amplitude determined to control the gain.

[0074] Here, temperature-induced component value drift may refer to the phenomenon in which the electrical resistance of a material changes with temperature. This drift affects the accuracy and reliability of the sensor and is an important consideration in the design and operation of circuits that process sensor signals. Elements with temperature-induced value drift may be resistors, capacitors, or inductors, depending on the circuit configuration implemented. In particular, value drift of elements within the AGC200 can result in changes of up to 25% in determined amplitudes in some cases. Therefore, it may be advantageous to implement countermeasures against temperature-induced drift so that the AGC200 can be used reliably over a wide temperature range.

[0075] To achieve this, in addition to the low-pass filter 226, a high-pass filter 228 may be used to smooth the approximated sinusoidal function over time. The high-pass filter 228 is shown as part of a band-pass filter in FIG. 8 . Alternatively, the low-pass filter 226 and the high-pass filter 228 may be implemented separately. The high-pass filter 226 may also have a cutoff frequency corresponding to or close to the angular frequency ω. Using a combination of low-pass and high-pass filters can effectively attenuate unwanted frequencies other than the first harmonic, even if the cutoff frequency shifts due to temperature-induced value drift. FIG. 9 shows an example of a combination of low-pass and high-pass filters and the approximated sinusoidal function amplitude spectrum over time. Using a band-pass filter to smooth the approximated sinusoidal function over time can reduce the variation in the estimated amplitude to approximately 2.5% over the temperature range.

[0076] The accuracy of the AGC 200 can be further improved by taking into account the temperature-induced drift of the cutoff frequency when generating the approximated sinusoidal function over time. In particular, the angular frequency ω can be shifted by a drift adaptation module in a direction corresponding to the drift of the cutoff frequencies of the low-pass and high-pass filters. The shift of the angular frequency ω may be achieved by adapting a clock signal for the AGC 200, for example, by adapting a clock signal for the RC oscillator 224. Thus, the drift adaptation module may be implemented as a clock signal adaptation. By shifting the first harmonic of the approximated sinusoidal function over time (along with the angular frequency ω) in the same direction as the temperature-induced drift of the cutoff frequencies of the low-pass and high-pass filters, the change in estimated amplitude can be reduced to less than 1.5% over the temperature range. The shift of the first harmonic and the cutoff frequency is also shown in FIG. 9.

[0077] By combining the concepts described above in AGC 200, efficient determination of the receive coil output signal amplitude / scaling factor, stability over a specified temperature range, and continuous gain adaptation can be achieved.

[0078] Accordingly, there is provided a method 400 for automatic gain control, as shown in the flowchart of Figure 10. Method 400 may optionally include all of the variations described above with respect to AGC 200 described above with reference to Figures 4-9, in addition to the following method steps:

[0079] In step S201, a first signal and a second signal are received. The first signal is proportional to a sine wave of a parameter to be measured (e.g., angular displacement or linear transient displacement of a target), and the second signal corresponds to the first signal shifted by a quarter of the period of the sine wave (e.g., by 90°). For example, the first signal may be proportional to the sine of the parameter to be measured, and the second signal may be proportional to the cosine of the parameter to be measured.

[0080] In step S202, an approximated sinusoidal function over time is generated. The approximated sinusoidal function over time is generated by determining values ​​of a shifted sinusoidal function having a first frequency at multiple sampling points. A phase shift and an amplitude of the shifted sinusoidal function are based on the first signal and the second signal. For example, the phase shift may be based on a parameter of interest in the first signal and the second signal.

[0081] In step S203, a third signal proportional to the amplitude spectrum of the approximated sinusoidal function at the first frequency is generated. In other words, the third signal may correspond to or be proportional to the amplitude of the first harmonic of the approximated sinusoidal function over time.

[0082] In step S204, the third signal is used for gain control of a circuit for measuring the parameter of the object to be measured. Using the third signal for gain control may be achieved by comparing the third signal with a reference value and using the result to control an element capable of adjusting the gain of the circuit for measuring the parameter of the object to be measured.

[0083] While many specific implementation details are described herein, these should not be construed as limitations on the scope of any invention or what is claimed, but rather as descriptions of features specific to particular embodiments of a particular invention. Certain features described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while these features are described above as working in particular combinations, one or more features may be excluded from the combinations described in the claims, such that the combinations may be limited as subcombinations or variations thereof.

[0084] Similarly, even if operations are shown in a particular order in the figures, this should not be construed as necessarily requiring the operations to be performed in the order or sequence shown, nor is it necessary for all illustrated operations to be performed to achieve desirable results. In certain situations, multitasking or parallel processing may be advantageous. Furthermore, the separation of system components in the above embodiments does not imply that similar separation is required in all embodiments, and it should be noted that the described program components and systems may typically be integrated into a single software product or packaged across multiple software products.

[0085] Unless otherwise specified, and as will become apparent from the following description, it should be noted that, in the present invention, terms such as "processing," "calculating," "calculating," "determining," and "analyzing" refer to operations and / or processes by which a computer or computing system, or similar electronic computing device, manipulates and / or transforms data represented as physical quantities, such as electronic quantities, into other data also represented as physical quantities.

[0086] In the present invention, expressions such as "one embodiment," "some embodiments," or "one example embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of expressions such as "one embodiment," "some embodiments," and "one example embodiment" in various places in this specification do not necessarily all refer to the same embodiment. Furthermore, particular features, structures, or characteristics can be combined as appropriate in one or more embodiments, as would be easily understood by one skilled in the art from the present invention.

[0087] Unless otherwise specified herein, the use of ordinal adjectives such as "first," "second," and "third" to describe a common object merely indicates that the objects are different instances of the same kind of object, and does not imply that the objects must follow any order, whether temporal, spatial, or hierarchical, or any other order.

[0088] It should also be noted that the phraseology and terminology used herein are for descriptive purposes and should not be construed as limiting. The words "including," "comprising," "having," and variations thereof are intended to encompass the items following, equivalents, and additional items. Unless otherwise expressly stated, the words "mounted," "connected," "supported," "coupled," and variations thereof are intended to be interpreted broadly and include both direct and indirect mounting, connecting, supporting, and coupling.

[0089] In the appended claims and this specification, the terms "comprise," "comprises," and the like are open terms meaning the inclusion of at least the following element or feature, but do not exclude other elements. Therefore, "comprises" used in the claims should not be interpreted as being limited to only the means, elements, or steps listed thereafter. For example, the scope of the expression "an apparatus comprising A and B" is not limited to an apparatus consisting of only A and B.

[0090] As described above with respect to example embodiments of the present invention, various features of the present invention may be grouped together in a single embodiment, figure, or description for the purpose of simplifying the description and facilitating understanding of the multiple inventive aspects of the present invention. However, this description should not be interpreted as reflecting an intention to require more features than are expressly recited in each claim. Rather, as reflected in the following claims, inventive aspects may depend on fewer features than all features of a single foregoing disclosed embodiment. Accordingly, the following claims are expressly incorporated into this specification, with each claim intended to stand on its own as an example of a single embodiment of the present invention.

[0091] Furthermore, although some embodiments described herein may include only some of the features included in other embodiments and not include other features, it is understood that combinations of features from different embodiments are also included within the scope of the present invention, and different embodiments can be formed as understood by those skilled in the art. For example, in the appended claims, any of the embodiments described in the claims can be used in any combination.

[0092] Although numerous specific details are described herein, it should be understood that embodiments of the present invention may be practiced without these specific details, and well-known methods, structures, and techniques may not be shown in detail in order to avoid obscuring understanding.

[0093] While what is believed to be the best mode of the present invention has been described above, those skilled in the art will recognize that further modifications can be made thereto without departing from the spirit of the present invention. It is intended to claim such changes and modifications to the extent that they fall within the scope of the present invention. For example, any formulas shown above are merely examples of procedures that may be used. Functions shown in block diagrams may be added or deleted, and operations may be interchanged between functional blocks. Steps may also be added or deleted to methods described within the scope of this disclosure.

Claims

1. 1. An apparatus for automatic gain control, comprising: a sine wave generating module; a gain control signal generation module; Equipped with the sine wave generation module is configured to receive a first signal and a second signal, the first signal being proportional to a sine wave of a parameter to be measured, and the second signal corresponding to the first signal shifted by a quarter of a period of the sine wave; the sine wave generation module is further configured to generate an approximate sine wave function over time by determining values ​​of a shifted sine function having a first frequency at a plurality of sampling points, the phase shift and amplitude of the shifted sine function being based on the first signal and the second signal; the gain control signal generation module is configured to generate a third signal proportional to an amplitude spectrum of the approximated sinusoidal function at the first frequency; the gain control signal generating module is further configured to output the third signal to a circuit for measuring a parameter of a measurement object, the device for automatic gain control is connected to the circuit, and the third signal is used for gain control of the circuit. Device.

2. The apparatus of claim 1 , wherein the first signal, the second signal, and the third signal are analog signals.

3. The apparatus of claim 1 , wherein the sine wave generation module is configured to perform linear operations in the analog domain.

4. 2. The apparatus of claim 1, wherein the first signal is proportional to sin(x) and the second signal is proportional to cos(x), where x represents the parameter being measured.

5. 5. The apparatus of claim 4, wherein the first signal is equal to A*sin(χ) and the second signal is equal to A*cos(χ), where A depends on an excitation signal in a circuit for measuring the parameter of interest and a sensor configuration for measuring the parameter of interest.

6. Determining values ​​of the shifted sine function having the first frequency at the plurality of sampling points includes configuring the sine wave generation module to determine, for each value and corresponding sampling point, a weighted sum of the first signal and the second signal, wherein weights of the weighted versions of the first signal and the second signal correspond to sine and cosine functions evaluated at a first angle, the first angle being based on the sampling point and the first frequency.

10. The apparatus of claim 1.

7. The sine wave generating module includes: a multiplexing module; an addition module; Including, the multiplexing module is configured to determine a plurality of fourth signals by multiplexing positive and negative signals and a zero signal of the first signal and the second signal; The summation module is configured to multiply a weight of each of the plurality of fourth signals by a different weight to generate a weighted version of the plurality of fourth signals. the summing module is further configured to perform a weighted sum of the plurality of fourth signals to generate values ​​of the shifted sine function at the sampling points.

7. The apparatus of claim 6.

8. 8. The apparatus of claim 7, wherein the plurality of fourth signals and a weight for each of the plurality of fourth signals are selected for each sampling point such that the sine function having the first frequency and shifted in amplitude by A is approximated.

9. The apparatus of claim 7 , wherein the number of the plurality of fourth signals is one or two.

10. The weight is 1, [Equation 1] and [Equation 2] 2. The device of claim 1, wherein:

11. the sine wave generating module further includes a smoothing module; the smoothing module is configured to smooth the approximated sinusoidal function to generate a sinusoidal function over time; the gain control signal generation module includes an AC-DC conversion module; the AC-DC conversion module is configured to generate a third signal from the sinusoidal function; 8. The apparatus of claim 7.

12. the smoothing module includes a second low-pass filter configured to filter the approximated sinusoidal function to generate the sinusoidal function over time; the smoothing module further comprises a high-pass filter; the high-pass filter is configured to operate in conjunction with the second low-pass filter to generate the sinusoidal function over time by smoothing the approximated sinusoidal function; 12. The apparatus of claim 11.

13. The apparatus further includes a drift adaptation module; the drift adaptation module is configured to adapt the first frequency to temperature-induced drift of the cutoff frequency of the second low-pass filter and / or the high-pass filter.

13. The apparatus of claim 12.

14. the gain control signal generation module includes an error signal generation module; the error signal generation module is configured to generate an error signal by comparing the third signal with a first reference value; the error signal generation module is further configured to output the error signal to a circuit for measuring the parameter of the object to be measured.

10. The apparatus of claim 1.

15. 15. The apparatus of claim 14, wherein using the error signal for gain control of a circuit for measuring the parameter of the object to be measured comprises controlling an LC oscillator with the error signal, the LC oscillator being part of the circuit for measuring the parameter of the object to be measured and configured to provide an excitation signal.

16. 15. The apparatus of claim 14, wherein using the error signal for gain control of a circuit for measuring the parameter of the object to be measured comprises using the error signal to control an analog gain element in the circuit for measuring the parameter of the object to be measured.

17. further comprising an LC calibration module; 17. The apparatus of claim 16, wherein the LC calibration module is configured to calibrate an LC oscillator based on the third signal, the LC oscillator providing an excitation signal to a circuit for measuring the parameter of interest.

18. The LC calibration module includes: a comparison module; a digital output module; Including, the comparison module is configured to compare the third signal with a second reference value; Based on the comparison result, the digital output module is configured to increase or decrease the digital signal; the digital output module is further configured to output the digital signal for controlling the LC oscillator.

18. The apparatus of claim 17.

19. 1. A measurement circuit having automatic gain control, comprising: An apparatus for automatic gain control according to claim 1; a circuit for measuring a parameter of a target object; Including, connected to the device for automatic gain control; circuit.

20. 10. A method for automatic gain control, comprising using the apparatus of claim 1 to perform the gain control.

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