阅读说明：本技术 基于dds的谐振式微悬臂梁传感器智能激励电路及拾振信号放大电路 (Resonance type micro-cantilever sensor intelligent exciting circuit based on DDS and vibration pickup signal amplifying circuit ) 是由 郑蓓蓉 周晨 薛伟 鞠益 何玥 王权 于 2021-08-25 设计创作，主要内容包括：本发明提供了一种基于DDS的谐振式微悬臂梁传感器智能激励电路及拾振信号放大电路,该激励电路由DDS发生器、椭圆滤波器、直流偏置电路、加法电路、反向放大电路组成。通过DDS发生器产生离散的正弦信号,经椭圆滤波器平滑后叠加上DAC输出的直流信号,再将该信号进过反向放大电路转换为正向的驱动信号,最终将产生的直流偏置的正弦信号用于驱动谐振式微悬臂梁传感器。该电路可以通过程序实现直流信号幅值、交流信号频率的高精度调节,使用方便且性能可靠。(The invention provides a resonance type micro-cantilever sensor intelligent exciting circuit based on a DDS (direct digital synthesizer) and a vibration pick-up signal amplifying circuit. A discrete sine signal is generated by the DDS generator, the discrete sine signal is smoothed by the elliptical filter and then superposed with a direct current signal output by the DAC, the signal enters the reverse amplification circuit to be converted into a forward driving signal, and finally the generated direct current biased sine signal is used for driving the resonant micro-cantilever sensor. The circuit can realize high-precision adjustment of the amplitude of the direct current signal and the frequency of the alternating current signal through a program, and is convenient to use and reliable in performance.)

1. The utility model provides a resonant mode micro-cantilever sensor intelligence excitation circuit based on DDS which characterized in that includes:

the direct current bias circuit is used for outputting a stable direct current bias excitation signal;

the DDS generator is used for adjusting and outputting a discrete sine excitation signal according to the change of the resonant frequency in the sampling process;

the elliptic filter is used for smoothing the discrete sine excitation signal sent by the DDS generator to obtain a more stable sine signal;

the addition circuit is used for calculating the direct current bias excitation signal output by the direct current bias circuit and the sine excitation signal processed by the elliptic filter to realize the signal superposition function;

and the reverse amplification circuit is used for inverting the signal output by the addition circuit again so that the negative voltage of the signal is converted into positive voltage.

2. The DDS based resonant micro-cantilever sensor smart driver circuit of claim 1, wherein the DDS generator comprises an AD9850 chip, an active crystal oscillator Y₁Adjustable resistance R₁₈Resistance R₁₄、R₁₅、R₁₆Capacitor C₁₁、C₁₂、C₁₃The active crystal oscillator Y₁The No. 3 output pin is connected with a CLKIN pin of the AD9850 chip and is used as an external reference clock; active crystal oscillator Y₁The No. 4 power supply input pin forms a filter network by connecting a capacitor C11, a capacitor C12 and a capacitor C13 in parallel; the adjustable resistor R₁₈The voltage regulator is connected with a VINN pin of the AD9850 chip in series and is grounded; the pins D0 and D1 of the AD9850 chip are connected with a +5V power supply, and the pin D2 is grounded, so that the AD9850 chip enters a serial port input mode; the IOUT is connected with a 200 ohm resistor in series and grounded so as to convert the DAC voltage of the AD9850 chip into a sinusoidal signal to be output, the output current of the DAC voltage is regulated through an external resistor RSET, and the regulation relation is ISET 32 x (1.148V/RSET); the DDS generator then sends the generated sinusoidal signal to the elliptic filter through the IOUT pin.

3. The DDS based resonant micro-cantilever sensor smart driver circuit of claim 2, wherein the active crystal oscillator Y₁Has a frequency of 125MHz and an adjustable resistor R₁₈Resistance R₁₄、R₁₅、R₁₆The resistance of the capacitor is respectively 10K omega, 200 omega, 4.7K omega and 100 omega, and the capacitance C₁₁、C₁₂、C₁₃Electricity (D) fromThe capacity sizes are 10 muF, 100nF, respectively.

4. The DDS based resonant micro-cantilever sensor smart pump circuit of claim 1, wherein the elliptical filter circuit is comprised of an inductor L₁、L₂Capacitor C₆、C₇、C₈、C₉、C₁₀The IOUT pin of the AD9850 chip is simultaneously connected with one end of an inductor L1, a capacitor C6 and a capacitor C8, the inductor L1 is connected with the inductor L2 in series, the capacitor C6 is connected with the capacitor C7 in series, wherein the inductor L1 and the inductor L2 are respectively connected with capacitors C6 and C7 in parallel; the other end of the inductor L1 is connected with one ends of the inductor L2, the capacitor C7 and the capacitor C9, and is connected with the other end of the capacitor C6; the inductor L2 is connected with one end of the capacitor C10, the resistor R17 and the resistor R6 and connected with the other end of the capacitor C7; the capacitors C8, C9 and C10 are connected in parallel, and the other end of the capacitors is grounded; inductor L₁、L₂The size is 390nH, and the capacitance sizes are 10pF, 33pF, 100pF, 150pF and 100pF respectively.

5. The DDS based resonant micro-cantilever sensor intelligent excitation circuit of claim 1, wherein the DC bias circuit comprises an LM358 operational amplifier chip, resistors R18, R19, R20, capacitors C48, C50, C51, resistors R18, R19, R20 having resistance sizes of 2K Ω, 1K Ω, respectively, and capacitors C48, C50, C51 having capacitance sizes of 100nF, 10 μ F, 100nF, respectively; the C48 is used for stabilizing voltage signals output by the MCU, the C50 and the C51 are used for stabilizing voltages output after amplification, a DAC function pin of the MCU outputs direct-current voltages, and the DAC voltages and the output power are amplified through the operational amplifier.

6. The DDS based resonant micro-cantilever sensor smart driver circuit of claim 1, wherein the adder circuit comprises an operational amplifier AD8066 chip and a capacitor C₄Resistance R₅、R₆、R₇、R₁₀、R₁₁Capacitor C₄Has a capacitance of 100nF and a resistance R₅、R₆、R₇、R₁₀、R₁₁Is divided into2K Ω, 1K Ω, 2K Ω, and 1K Ω, respectively; the sine signal after filtering processing enters an adding circuit through R6; meanwhile, a direct current bias signal DAC _ DC series connection R7 generated by the direct current bias circuit enters the addition circuit, and power supply noise is filtered through the parallel connection C4; the sine signal and the DAC _ DC are subjected to superposition operation by an addition circuit; the filtered signal cancels the effect of the bias current by the parallel R17.

7. The DDS based resonant micro-cantilever sensor smart pump circuit of claim 6, further comprising a decoupling capacitor C in the summing circuit₃And C₅For filtering out high frequency noise in the power supply; capacitor C₃、C₅Are all 100 nF.

8. The DDS based resonant micro-cantilever sensor smart pump circuit of claim 1, wherein the reverse amplification circuit is composed of an AD8066 operational amplifier circuit and a resistor R₈、R₉And R₁₃、R₁₄The resistance values of the resistors are all 1K omega.

9. The DDS based resonant micro-cantilever sensor smart pump circuit of claim 1, wherein the frequency is changed by changing the phase by way of digital control.

10. The vibration pickup signal amplifying circuit corresponding to the intelligent exciting circuit of any one of claims 1 to 7, which is characterized by comprising a first-stage amplifying circuit, a low-pass filter circuit and a second-stage amplifying circuit.

Technical Field

The invention belongs to the field of detection application of resonant micro-cantilever sensors, and relates to an intelligent excitation circuit driven by the sensor and based on a direct digital frequency synthesizer.

Background

With the development of science and technology, micro-electromechanical sensors are widely used with the advantages of small size, high precision, fast response and the like. In recent years, due to the continuous development of mems technology, resonant sensors have been the leading research focus with excellent performance such as high resolution and high sensitivity, and among them, micro-cantilever resonators have attracted much attention with advantages such as simple structure and easy preparation. The invention is suitable for the micro-cantilever resonator of electrothermal excitation, the electrothermal excitation is to apply an alternating electric signal on an excitation resistor to generate a bimetal effect, thereby causing the periodic vibration of the micro-cantilever. In the process of manufacturing the resonant micro-cantilever sensor, factors such as different resonant beam sizes, different masses, different resistance values of the excitation resistor and the like can cause the requirement of a required excitation signal to change, so that the design of an excitation circuit compatible with the factors is very important. The excitation signal is usually a direct current biased sinusoidal signal, and the design of a compatible excitation circuit requires that not only the direct current voltage to be excited is adjustable, but also the input alternating current signal is adjustable. The traditional excitation mode is mostly a mode of using adjustable resistance adjustment, the adjustment precision of the mode is poor, and the operation is very complicated, so that a portable intelligent excitation circuit capable of realizing program adjustment is urgently needed to be designed so as to meet the requirements of compatibility and excitation function realization.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the resonance type micro-cantilever sensor intelligent exciting circuit based on the DDS, which is used for exciting resonance type micro-cantilever sensors with different sizes so as to meet the requirements of compatibility and excitation function realization.

The present invention achieves the above-described object by the following technical means.

The utility model provides a resonant mode micro-cantilever sensor intelligence excitation circuit based on DDS which characterized in that includes:

the direct current bias circuit is used for outputting a stable direct current bias excitation signal;

the DDS generator is used for adjusting and outputting a discrete sine excitation signal according to the change of the resonant frequency in the sampling process;

the elliptic filter is used for smoothing the discrete sine excitation signal sent by the DDS generator to obtain a more stable sine signal;

the addition circuit is used for calculating the direct current bias excitation signal output by the direct current bias circuit and the sine excitation signal processed by the elliptic filter to realize the signal superposition function;

and the reverse amplification circuit is used for inverting the signal output by the addition circuit again so that the negative voltage of the signal is converted into positive voltage.

Further, the DDS generator comprises an AD9850 chip and an active crystal oscillator Y₁Adjustable resistance R₁₈Resistance R₁₄、R₁₅、R₁₆Capacitor C₁₁、C₁₂、C₁₃The active crystal oscillator Y₁The No. 3 output pin is connected with a CLKIN pin of the AD9850 chip and is used as an external reference clock; active crystal oscillator Y₁The No. 4 power supply input pin forms a filter network by connecting a capacitor C11, a capacitor C12 and a capacitor C13 in parallel; the adjustable resistor R₁₈The voltage regulator is connected with a VINN pin of the AD9850 chip in series and is grounded; the pins D0 and D1 of the AD9850 chip are connected with a +5V power supply, and the pin D2 is grounded, so that the AD9850 chip enters a serial port input mode; the IOUT is connected with a 200 ohm resistor in series and grounded so as to convert the DAC voltage of the AD9850 chip into a sinusoidal signal to be output, the output current of the DAC voltage is regulated through an external resistor RSET, and the regulation relation is ISET 32 x (1.148V/RSET); the DDS generator then sends the generated sinusoidal signal to the elliptic filter through the IOUT pin.

Further, an active crystal oscillator Y₁Has a frequency of 125MHz and an adjustable resistor R₁₈Resistance R₁₄、R₁₅、R₁₆The resistance of the capacitor is respectively 10K omega, 200 omega, 4.7K omega and 100 omega, and the capacitance C₁₁、C₁₂、C₁₃Respectively, of 10 muf, 100 nF.

Further, the elliptic filter circuit is composed of an inductor L₁、L₂Capacitor C₆、C₇、C₈、C₉、C₁₀Composition, IOU of AD9850 chipThe T pin is simultaneously connected with one ends of an inductor L1, a capacitor C6 and a capacitor C8, the inductor L1 is connected with the inductor L2 in series, and the capacitor C6 is connected with the capacitor C7 in series, wherein the inductor L1 and the inductor L2 are respectively connected with capacitors C6 and C7 in parallel; the other end of the inductor L1 is connected with one ends of the inductor L2, the capacitor C7 and the capacitor C9, and is connected with the other end of the capacitor C6; the inductor L2 is connected with one end of the capacitor C10, the resistor R17 and the resistor R6 and connected with the other end of the capacitor C7; the capacitors C8, C9 and C10 are connected in parallel, and the other end of the capacitors is grounded; inductor L₁、L₂The size of the capacitor is 390nH, and the sizes of the capacitors are 10pF, 33pF, 100pF, 150pF and 100pF respectively; the filtered signal cancels the effect of the bias current by the parallel R17.

Further, the direct current bias circuit comprises an LM358 operational amplifier chip, resistors R18, R19 and R20, capacitors C48, C50 and C51, wherein the resistors R18, R19 and R20 are respectively 2K omega, 1K omega and 1K omega, and the capacitors C48, C50 and C51 are respectively 100nF, 10 muF and 100 nF; the C48 is used for stabilizing voltage signals output by the MCU, the C50 and the C51 are used for stabilizing voltages output after amplification, a DAC function pin of the MCU outputs direct-current voltages, and the DAC voltages and the output power are amplified through the operational amplifier.

Further, the addition circuit comprises an operational amplifier AD8066 chip and a capacitor C₄Resistance R₅、R₆、R ₇、R₁₀、R₁₁Capacitor C₄Has a capacitance of 100nF and a resistance R₅、R₆、R ₇、R₁₀、R₁₁The resistance values of the resistor are respectively 2K omega, 1K omega, 2K omega and 1K omega; the sine signal after filtering processing enters an adding circuit through R6; meanwhile, a direct current bias signal DAC _ DC series connection R7 generated by the direct current bias circuit enters the addition circuit, and power supply noise is filtered through the parallel connection C4; the sinusoidal signal and DAC _ DC are added by an addition circuit.

Furthermore, the addition circuit also comprises a decoupling capacitor C₃And C₅For filtering out high frequency noise in the power supply; capacitor C₃、C₅Are all 100 nF.

Further, the reverse amplifying circuit is composed of an AD8066 operational amplifier circuit and a resistor R₈、R₉And R₁₃、R₁₄The resistance values of the resistors are all 1K omega.

Further, the phase is changed by means of digital control, so that the frequency is changed.

The vibration pickup signal amplifying circuit corresponding to the intelligent exciting circuit is characterized by comprising a primary amplifying circuit, a low-pass filter circuit and a secondary amplifying circuit.

The invention has the beneficial effects that: the direct current bias sinusoidal signal is synthesized by combining the functions of the DDS generator and the DAC and superposing the sinusoidal signal and the direct current signal, the DDS generator and the DAC output signal have high precision, a program-controlled excitation signal source can be formed by the mode, a more precise signal can be conveniently output when the resonant micro-cantilever resonator is tested, and the excitation mode also makes preliminary exploration on a resonant micro-cantilever excitation circuit for future researchers.

Drawings

FIG. 1 is a schematic diagram of a cantilever structure for electrothermal excitation and piezoresistive detection.

FIG. 2 is a schematic diagram of an intelligent excitation circuit of the resonant micro-cantilever sensor.

FIG. 3 is a schematic diagram of a resonant micro-cantilever sensor detection circuit.

Detailed Description

The present invention is further illustrated by the following figures and specific examples, which are to be understood as illustrative only and not as limiting the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereof which may occur to those skilled in the art upon reading the present specification.

The DDS-based resonant micro-cantilever sensor intelligent excitation circuit is mainly used for driving a resonant micro-cantilever sensor, so that excitation and oscillation of the sensor are realized. The excitation circuit adopts electrothermal excitation, and the vibration pickup circuit adopts piezoresistive vibration pickup. The electrothermal excitation is to apply an alternating electric signal to the exciting resistor to generate a bimetal effect, so as to cause the periodic vibration of the micro-cantilever. The alternating electric signal used for excitation can be divided into an alternating current signal and a direct current biased alternating current signal, and the structure of the resonant micro-cantilever sensor is shown in figure 1. The electrothermal excitation is to apply an alternating electric signal to the exciting resistor to generate a bimetal effect, so as to cause the periodic vibration of the micro-cantilever. The alternating electrical signal used for excitation can be divided into an alternating signal and a direct current biased alternating signal. The direct current component can generate fixed temperature on the micro-cantilever beam, and the alternating current component can enable the micro-cantilever beam to vibrate. The ac signal excitation is such that the beam vibrates at twice the excitation frequency, and superimposing the dc biased ac signal excitation is such that the cantilever beam produces a signal having a frequency of vibration that is the sum of the excitation frequency and twice the excitation frequency. Piezoresistive detection mainly utilizes the piezoresistive effect of semiconductor materials. The principle of piezoresistive vibration pickup is that resistance value variation is converted into voltage variation by a Wheatstone bridge through the effect of resistance value variation of piezoresistive materials under external pressure. The used micro-cantilever sensor vibration pickup circuit is composed of four piezoresistors, and the output voltage Vout formula is as follows:

where Vin is the power supply voltage, R is the varistor resistance, and Δ R is the varistor variation.

As shown in fig. 2, the resonant micro-cantilever sensor intelligent excitation circuit based on DDS is composed of a DDS generator, an elliptic filter, a dc bias circuit, an adder circuit, and a reverse amplifier circuit.

The working principle of DDS is to sample, encode and quantize the sine signal to form a sine function table, which is stored in EPROM, and when synthesizing, the phase increment, that is, the step length, is changed by changing the frequency word of the phase accumulator. The difference in phase increment causes a difference in sampling point within one cycle, and the frequency is changed by a change in phase with a constant clock frequency, i.e., sampling frequency. The core of the DDS chip is a phase accumulator which consists of an adder and an N-bit phase register. The working voltage of an AD9850 chip selected by the DDS generator is 5V, and the output frequency range is 0.1 Hz-40 MHz.

The DDS generator mainly comprises an AD9850 chip and an active crystal oscillator Y₁Adjustable resistance R₁₈、R₁₄、R₁₅、R₁₆Capacitor C₁₁、C₁₂、C₁₃Composition in which there is an active crystal oscillator Y₁Has a frequency of 125MHz and an adjustable resistor R₁₈、R₁₄、R₁₅、R₁₆The resistance of the capacitor is respectively 10K omega, 200 omega, 4.7K omega and 100 omega, and the capacitance C₁₁、C₁₂、C₁₃Respectively, of 10 muf, 100 nF. The CLKIN pin of the AD9850 chip is connected with an active crystal oscillator Y₁The No. 3 output pin is used as an external reference clock; active crystal oscillator Y₁The No. 4 power supply input pin forms a filter network by connecting a capacitor C11, a capacitor C12 and a capacitor C13 in parallel. The pins D0 and D1 of the AD9850 chip are connected to a +5V power supply, the pin D2 is grounded, so that the AD9850 chip enters a serial port input mode, and the pins D3, D4, D5 and D6 which cannot be used are grounded in order to avoid signal interference. The IOUT is connected with a 200 ohm resistor in series to be grounded so as to convert the DAC voltage of the AD9850 chip into a sinusoidal signal to be output, the output current of the DAC voltage is regulated through an external resistor RSET, and the regulation relation is ISET 32 x (1.148V/RSET). The DDS generator then sends the generated sinusoidal signal to the elliptic filter through the IOUT pin.

The elliptic filter is composed of an inductor L₁、L₂Capacitor C₆、C₇、C₈、C₉、C₁₀The signal output by the DDS generator is a discrete signal, and the discrete signal can be smoothed easily by the elliptical filter, so that a smoother sinusoidal signal is obtained. When the circuit is designed, the inductance and the capacitance can be adjusted to proper values through simulation, so that the distortion of each frequency signal is greatly reduced. The size of the inductor is 390nH, and the sizes of the capacitors are 10pF, 33pF, 100pF, 150pF and 100pF respectively. The IOUT pin is connected with one end of an inductor L1, a capacitor C6 and a capacitor C8 at the same time, the inductor L1 is connected with the inductor L2 in series, the capacitor C6 is connected with the capacitor C7 in series, wherein the inductor L1 and the inductor L2 are respectively connected in parallel to be electrically connectedC6, C7; the other end of the inductor L1 is connected with one ends of the inductor L2, the capacitor C7 and the capacitor C9, and is connected with the other end of the capacitor C6; the inductor L2 is connected with one end of the capacitor C10, the resistor R17 and the resistor R6 and connected with the other end of the capacitor C7; the capacitors C8, C9 and C10 are connected in parallel, and the other end of the capacitors is grounded. These devices together form a low pass filter network.

The direct current bias circuit comprises an LM358 operational amplifier chip, resistors R18, R19 and R20, capacitors C48, C50 and C51, wherein the resistors R18, R19 and R20 are respectively 2K omega, 1K omega and 1K omega, and the capacitors C48, C50 and C51 are respectively 100nF, 10 muF and 100 nF. The C48 is used for stabilizing the voltage signal output by the MCU, and the C50 and the C51 are used for stabilizing the voltage output after amplification. And a DAC function pin of the MCU outputs direct-current voltage, and the amplification of the DAC voltage and the output power is realized through the operational amplifier.

The sine signal after filtering enters the adding circuit through R6, and meanwhile, a direct current offset signal DAC _ DC output by a DAC pin of the MCU is connected in series with R7 to enter the adding circuit, and power supply noise is filtered through parallel C4.

The adder circuit comprises an operational amplifier AD8066 chip and a capacitor C₃、C₄、C₅Resistance R₅、R₆、R₇、R₁₀、R₁₁Capacitor C₃、C₄、C₅The capacitance of (1) is 100nF, and the resistance R is₅、R₆、R₇、R₁₀、R₁₁The resistance values of (a) are 2K omega, 1K omega, 2K omega and 1K omega respectively. The filtered signal cancels the effect of the bias current by the parallel R17.

Adding the DAC _ DC output by the DAC function in the MCU and the signal output by the DDS through an operational amplifier AD8066 chip, thereby realizing the signal superposition function; the formed addition circuit has the main function of superposing a direct current signal and a sinusoidal signal to form a direct current biased sinusoidal signal, the direct current signal can preheat the resonant micro-cantilever sensor, and the sinusoidal signal can make the resonant micro-cantilever sensor vibrate. Wherein, the capacitor C₃And C₅For the decoupling capacitor, high frequency noise in the power supply can be effectively filtered.

The reverse amplifying circuit is composed of an AD8066 operational amplifier circuit and a resistor R₈、R₉And R₁₃、R₁₄The resistance values of the resistors are all 1K omega. The main function is to invert the signal output from the preceding-stage addition circuit again, so that the negative voltage of the signal is positive voltage, and the signal is used for driving the resonant micro-cantilever sensor. The DAC _ DC is direct-current bias voltage output through a DAC peripheral function in the MCU, the voltage value of an output DAC signal is between 0 and 3.3V, and the adjustable range is limited. And an addition circuit is used for designing the amplification factor of the DAC output signal to be 2 times, so that different preheating and oscillation starting requirements of the micro-cantilever sensor are met.

The resonant micro-cantilever intelligent exciting circuit can respectively control the DDS function and the DAC function through programs, so that the output of exciting signals aiming at different requirements can be realized.

Fig. 3 shows a vibration pickup signal amplifying circuit of the resonance detecting system, which mainly comprises a first-stage amplifying circuit, a low-pass filter circuit and a second-stage amplifying circuit. The primary amplifying circuit aims to amplify signals and enable the signals to be detected to obtain high input impedance, and signal characteristics are kept as much as possible. The low-pass filtering can reduce the interference of high-frequency signals in the circuit by connecting a small capacitor C47 in parallel, and reduce the noise of the signals. The secondary amplification is used for further amplifying the signal, and is helpful for distinguishing the change of the amplitude of the output signal under different frequencies.

The present invention is not limited to the above-described embodiments, and any obvious improvements, substitutions or modifications can be made by those skilled in the art without departing from the spirit of the present invention.