阅读说明：本技术 一种基于差分振荡器的介电常数测量装置 (Dielectric constant measuring device based on differential oscillator ) 是由 史哲 张莽 石昊云 郭嘉帅 于 2021-09-24 设计创作，主要内容包括：本发明实施例公开了一种基于差分振荡器的介电常数测量装置,包括用于输出两路差分振荡信号的差分振荡器、分别与所述差分振荡器的两个输出端连接的检测支路和参考支路、混频器以及电压测量机构；一路所述差分振荡信号依次经过所述检测支路中的第一隔直电容、第一移相单元和第一敏感元件后传输至所述混频器的一个输入端,另一路所述差分振荡信号依次经过所述参考支路中的第二隔直电容、第二移相单元和第二敏感元件后传输至所述混频器的另一个输入端；所述第一敏感元件和所述第二敏感元件结构相同,所述电压测量机构与所述混频器的输出端连接,通过上述方式,本发明能够抑制有效环境因素造成的共模干扰,且有利于实现便携性和小型化。(The embodiment of the invention discloses a dielectric constant measuring device based on a differential oscillator, which comprises a differential oscillator for outputting two paths of differential oscillation signals, a detection branch and a reference branch which are respectively connected with two output ends of the differential oscillator, a frequency mixer and a voltage measuring mechanism, wherein the detection branch and the reference branch are connected with two output ends of the differential oscillator; one path of the differential oscillation signal sequentially passes through a first blocking capacitor, a first phase shifting unit and a first sensitive element in the detection branch and then is transmitted to one input end of the frequency mixer, and the other path of the differential oscillation signal sequentially passes through a second blocking capacitor, a second phase shifting unit and a second sensitive element in the reference branch and then is transmitted to the other input end of the frequency mixer; the first sensitive element and the second sensitive element have the same structure, and the voltage measuring mechanism is connected with the output end of the mixer.)

1. A dielectric constant measuring device based on a differential oscillator is characterized by comprising a differential oscillator for outputting two paths of differential oscillation signals, a detection branch and a reference branch which are respectively connected with two output ends of the differential oscillator, a frequency mixer and a voltage measuring mechanism;

the detection branch comprises a first blocking capacitor, a first phase shifting unit and a first sensitive element for placing a sample to be detected, which are sequentially connected in series, and one path of the differential oscillation signal is transmitted to one input end of the frequency mixer after sequentially passing through the first blocking capacitor, the first phase shifting unit and the first sensitive element;

the reference branch circuit comprises a second blocking capacitor, a second phase shifting unit and a second unloaded sensitive element which are sequentially connected in series, and the other path of differential oscillation signal is transmitted to the other input end of the frequency mixer after sequentially passing through the second blocking capacitor, the second phase shifting unit and the second sensitive element;

the first sensitive element and the second sensitive element have the same structure, and the voltage measuring mechanism is connected with the output end of the frequency mixer and used for detecting the output voltage value of the frequency mixer so as to realize the dielectric constant measurement of the sample to be measured.

2. The differential oscillator-based permittivity measurement device of claim 1, wherein the differential oscillator includes a differential filter, a first transistor, and a second transistor;

two input ends of the differential filter are respectively connected with the input ends of the first transistor and the second transistor, two output ends of the differential filter are used as two output ends of the differential oscillator and are respectively connected with the output ends of the first transistor and the second transistor, and the two output ends of the differential filter are also respectively connected with the first blocking capacitor and the second blocking capacitor.

3. The differential oscillator-based dielectric constant measurement device as claimed in claim 1, wherein the two differential oscillation signals output by the differential oscillator have the same amplitude and phase differenceA first phase shift unit for shifting the phase of the differential oscillation signal passing therethroughThe second phase shift unit is used for the pairDifferential oscillating signal phase shift passing through itSo that the phase difference of the two paths of differential oscillation signals output by the differential oscillator becomes after passing through the first phase shifting unit and the second phase shifting unit respectively。

4. The differential oscillator-based permittivity measurement device of claim 3, wherein the first phase-shifting unit includes a first capacitance, a second capacitance, and a first inductance;

one end of the first capacitor is connected with the first blocking capacitor, the other end of the first capacitor is connected with one end of the second capacitor and one end of the first inductor, the other end of the second capacitor is connected with the input end of the first sensitive element, and the other end of the first inductor is grounded.

5. The differential oscillator-based permittivity measurement device of claim 3, wherein the second phase-shifting unit includes a second inductance, a third inductance, and a third capacitance;

one end of the second inductor is connected with the second blocking capacitor, the other end of the second inductor is connected with one end of the third inductor and one end of the third capacitor, the other end of the third inductor is connected with the input end of the second sensitive element, and the other end of the third capacitor is grounded.

6. The differential oscillator-based permittivity measurement device of claim 1, wherein the voltage measurement mechanism is a multimeter.

7. The differential oscillator-based permittivity measurement device of claim 1, wherein the first sensitive element and the second sensitive element are implemented using microstrip lines.

Technical Field

The invention relates to the technical field of dielectric constant measurement, in particular to a dielectric constant measuring device based on a differential oscillator.

Background

The high-precision dielectric constant measuring system is widely applied to the fields of agriculture, industry, medical treatment and the like. For example, in the agricultural field, the maturity degree of crops can be analyzed by analyzing the difference of the dielectric constants of seeds by utilizing the characteristic that the dielectric constant of water is large; in the medical field, the detection of cancer cells can be realized by analyzing the dielectric constant of cells; in the industrial production field, the chemical components of the process substances can be analyzed by analyzing the dielectric constant of the process substances, so that the production efficiency is improved.

Common measurement methods include a transmission line method, a resonant cavity method, a free space method and the like, but these measurement methods need to use a large-scale instrument such as a Vector Network Analyzer (VNA), so that a proper signal reading circuit needs to be designed to replace the VNA. As shown in fig. one, some researchers propose to utilize a negative resistance oscillator to reversely derive a real part of a dielectric constant by analyzing an oscillation frequency offset, specifically, to place a sample to be measured in a sensing element 001, and to connect a capacitor 002, which is a gate blocking capacitor, to an MOS transistor 004 through a gate matching network 003. When the following start-up conditions are satisfied:

；

an oscillation signal is generated, passes through the drain matching 005, is input to the dc blocking capacitor 006, and is finally input to the spectrum analyzer 008 via the coaxial line 007 for analysis.

However, the above measuring device is easily interfered by environmental factors, the MOS transistor in the oscillator belongs to an active device, and the bias circuit of the oscillator is sensitive to environmental interference, such as indoor temperature, humidity and other factors, thereby easily causing common mode interference; furthermore, although VNA is avoided, a spectrum analyzer is required, and it is difficult to achieve portability and miniaturization.

Disclosure of Invention

The embodiment of the invention provides a dielectric constant measuring device based on a differential oscillator, which can effectively inhibit common-mode interference caused by environmental factors and is beneficial to realizing portability and miniaturization.

In order to solve the above technical problem, in one aspect, the present invention provides a dielectric constant measuring device based on a differential oscillator, including a differential oscillator for outputting two paths of differential oscillation signals, a detection branch and a reference branch respectively connected to two output ends of the differential oscillator, a mixer, and a voltage measuring mechanism;

the detection branch comprises a first blocking capacitor, a first phase shifting unit and a first sensitive element for placing a sample to be detected, which are sequentially connected in series, and one path of the differential oscillation signal is transmitted to one input end of the frequency mixer after sequentially passing through the first blocking capacitor, the first phase shifting unit and the first sensitive element;

the reference branch circuit comprises a second blocking capacitor, a second phase shifting unit and a second unloaded sensitive element which are sequentially connected in series, and the other path of differential oscillation signal is transmitted to the other input end of the frequency mixer after sequentially passing through the second blocking capacitor, the second phase shifting unit and the second sensitive element;

the first sensitive element and the second sensitive element have the same structure, and the voltage measuring mechanism is connected with the output end of the frequency mixer and used for detecting the output voltage value of the frequency mixer so as to realize the dielectric constant measurement of the sample to be measured.

Further, the differential oscillator includes a differential filter, a first transistor, and a second transistor;

two input ends of the differential filter are respectively connected with the input ends of the first transistor and the second transistor, two output ends of the differential filter are used as two output ends of the differential oscillator and are respectively connected with the output ends of the first transistor and the second transistor, and the two output ends of the differential filter are also respectively connected with the first blocking capacitor and the second blocking capacitor.

Furthermore, the two paths of differential oscillation signals output by the differential oscillator have the same amplitude and phase differenceA first phase shift unit for shifting the phase of the differential oscillation signal passing therethroughA second phase shift unit for shifting the phase of the differential oscillation signal passing therethroughSo that the phase difference of the two paths of differential oscillation signals output by the differential oscillator becomes after passing through the first phase shifting unit and the second phase shifting unit respectively。

Further, the first phase shift unit includes a first capacitor, a second capacitor and a first inductor;

one end of the first capacitor is connected with the first blocking capacitor, the other end of the first capacitor is connected with one end of the second capacitor and one end of the first inductor, the other end of the second capacitor is connected with the input end of the first sensitive element, and the other end of the first inductor is grounded.

Further, the second phase shift unit includes a second inductor, a third inductor, and a third capacitor;

one end of the second inductor is connected with the second blocking capacitor, the other end of the second inductor is connected with one end of the third inductor and one end of the third capacitor, the other end of the third inductor is connected with the input end of the second sensitive element, and the other end of the third capacitor is grounded.

Further, the voltage measuring mechanism is a multimeter.

Further, the first sensitive element and the second sensitive element are both implemented by microstrip lines.

Has the advantages that: the dielectric constant measuring device based on the differential oscillator comprises the differential oscillator for outputting two paths of differential oscillation signals, a detection branch and a reference branch which are respectively connected with two output ends of the differential oscillator, a frequency mixer and a voltage measuring mechanism; the detection branch comprises a first blocking capacitor, a first phase shifting unit and a first sensitive element for placing a sample to be detected, which are sequentially connected in series, and one path of the differential oscillation signal is transmitted to one input end of the frequency mixer after sequentially passing through the first blocking capacitor, the first phase shifting unit and the first sensitive element; the reference branch circuit comprises a second blocking capacitor, a second phase shifting unit and a second unloaded sensitive element which are sequentially connected in series, and the other path of differential oscillation signal is transmitted to the other input end of the frequency mixer after sequentially passing through the second blocking capacitor, the second phase shifting unit and the second sensitive element; the first sensitive element and the second sensitive element have the same structure, the voltage measuring mechanism is connected with the output end of the frequency mixer and is used for detecting the output voltage value of the frequency mixer so as to realize the dielectric constant measurement of the sample to be measured, and by the mode, the scheme can be finally realized only by one voltage detecting mechanism capable of measuring the voltage value, such as a voltmeter or a multimeter and other small-sized voltage detecting equipment, so that the miniaturization and the portability are convenient to realize; in addition, the scheme realizes the output of the differential oscillation signal through the differential oscillator, and is more favorable for inhibiting the common-mode interference caused by factors such as environment and the like compared with a single-ended output mode, and the detection branch and the reference branch are two branches with symmetrical structures, thereby playing a certain role in inhibiting the common-mode interference.

Drawings

The technical solution and the advantages of the present invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a dielectric constant measuring apparatus according to the prior art;

FIG. 2 is a schematic structural diagram of a differential oscillator-based dielectric constant measurement apparatus according to an embodiment of the present invention;

FIG. 3 is a circuit diagram of a first phase shifting unit according to an embodiment of the present invention;

FIG. 4 is a circuit diagram of a second phase shifting unit provided in an embodiment of the present invention;

fig. 5 is a phase difference simulation curve of two paths of differential oscillation signals respectively passing through a first phase shifting unit and a second phase shifting unit according to the embodiment of the present invention;

fig. 6 is a simulation curve of the dc voltage value of the output of the mixer according to the embodiment of the present invention.

Detailed Description

Referring to the drawings, wherein like reference numbers refer to like elements, the principles of the present invention are illustrated as being implemented in a suitable computing environment. The following description is based on illustrated embodiments of the invention and should not be taken as limiting the invention with regard to other embodiments that are not detailed herein.

Referring to fig. 1, in a dielectric constant measuring apparatus 100 based on a differential oscillator according to an embodiment of the present invention, the dielectric constant measuring apparatus 100 includes a differential oscillator 11 for outputting two differential oscillation signals, a detection branch 12 and a reference branch 13 respectively connected to two output ends of the differential oscillator 11, a mixer 14, and a voltage measuring mechanism 15.

The detection branch 12 includes a first blocking capacitor 121, a first phase shift unit 122, and a first sensing element 123 for placing a sample to be detected, which are sequentially connected in series, and one path of the differential oscillation signal is transmitted to one input end of the mixer 14 after passing through the first blocking capacitor 121, the first phase shift unit 122, and the first sensing element 123 in sequence. The reference branch 13 includes a second blocking capacitor 131, a second phase shift unit 132, and a second no-load sensing element 133, which are sequentially connected in series, and the other path of the differential oscillation signal is transmitted to the other input end of the mixer 14 after passing through the second blocking capacitor 131, the second phase shift unit 132, and the second no-load sensing element 133 sequentially. The first sensor 123 and the second sensor 133 have the same structure, that is, the first sensor 123 and the second sensor 133 are completely symmetrical sensors. The voltage measuring mechanism 15 is connected to the output end of the mixer 14, and is configured to detect the output voltage value of the mixer 14, so as to measure the dielectric constant of the sample to be measured.

Therefore, with the measuring apparatus 100 of the present embodiment, the dielectric constant can be measured only by one voltage detection mechanism 15 capable of measuring a voltage value, and therefore, the function of the voltage detection mechanism 15 can be realized only by a small-sized device such as a multimeter or a voltmeter, and the measuring apparatus 100 of the present invention is more easily miniaturized and portable than a conventional method using a VNA or a spectrum analyzer; in addition, according to the scheme, the differential oscillator 11 is used for outputting the differential oscillation signal, compared with a single-ended output mode, the method is more favorable for inhibiting common-mode interference caused by factors such as environment and the like, and the detection branch 12 and the reference branch 13 are two branches with symmetrical structures, so that a certain effect of inhibiting the common-mode interference is achieved.

Further, the differential oscillator 11 includes a differential filter 111, a first transistor 112, and a second transistor 113. Two input ends of the differential filter 111 are respectively connected to the input ends of the first transistor 112 and the second transistor 113, two output ends of the differential filter 111 are respectively connected to the output ends of the first transistor 112 and the second transistor 113 as two output ends of the differential oscillator 11, and two output ends of the differential filter 111 are further respectively connected to the first dc blocking capacitor 121 and the second dc blocking capacitor 131. Therefore, the differential oscillator 11 is formed by the differential filter 111 and the two transistors 112 and 113, so that differential output is realized by using the characteristics of the differential filter 111 that differential mode signals and common mode signals are filtered, and common mode interference caused by environmental factors can be well inhibited.

The oscillation starting condition can be optimized through simulation, and when the oscillation starting condition is met, the differential filter 111 outputs two paths of differential oscillation signals. Specifically, two input ends of the differential filter 11 are respectively 1 port and 2 ports, and two output ends are respectively 3 ports and 4 ports, and the mixed mode S parameter of the differential filter 111 can be expressed as:

wherein S11 denotes a reflection coefficient of 1 port, S13 denotes a transmission coefficient of 3 ports to 1 port, S13 denotes a transmission coefficient of 1 port to 3 ports, S21 denotes a transmission coefficient of 1 port to 2 ports, S23 denotes a transmission coefficient of 3 ports to 2 ports, S41 denotes a transmission coefficient of 1 port to 4 ports, S43 denotes a transmission coefficient of 3 ports to 4 ports, S12 denotes a transmission coefficient of 2 ports to 1 port, S22 denotes a reflection coefficient of 2 ports, Sdd11 denotes a differential mode reflection coefficient, Sdd21 denotes a differential mode transmission coefficient, Scc11 denotes a common mode reflection coefficient, and Scc11 denotes a common mode transmission coefficient. Of mixed mode S parametersThe file is brought into ADS software for simulation design, and the length of the microstrip line is designed to meet the oscillation starting condition of the differential oscillator 11, so that the differential oscillator oscillates, and two paths of differential oscillation signals are generated.

In the embodiment of the present invention, the two paths of differential oscillation signals output by the differential oscillator 11 have the same amplitude and the same phase differenceThe first phase shift unit 122 is used for shifting the phase of the differential oscillation signal passing through (referring to the first phase shift unit 122)The second phase shift unit 132 is used for shifting the phase of the differential oscillation signal passing through (referring to the second phase shift unit 132)So that the phase difference of the two differential oscillation signals outputted from the differential oscillator 11 becomes after passing through the first phase shift unit 122 and the second phase shift unit 123 respectively。

The first phase shift unit 122 may be implemented by a low-pass phase shift network, and the second phase shift unit 132 may be implemented by a high-pass phase shift network. Specifically, as shown in fig. 3, the first phase shift unit 122 includes a first capacitor C1, a second capacitor C2, and a first inductor L1. One end of the first capacitor C1 is connected to the first dc blocking capacitor 121, the other end of the first capacitor C1 is connected to one end of the second capacitor C2 and one end of the first inductor L1, the other end of the second capacitor C2 is connected to the input end of the first sensor 123, and the other end of the first inductor L1 is grounded. As shown in fig. 4, the second phase shift unit 132 includes a second inductor L2, a third inductor L3, and a third capacitor C3. One end of the second inductor L2 is connected to the second dc blocking capacitor 131, the other end of the second inductor L2 is connected to one end of the third inductor L3 and one end of the third capacitor C3, the other end of the third inductor L3 is connected to the input end of the second sensor 133, and the other end of the third capacitor C3 is grounded.

Through the mode, the phase shifting unit formed by the LC network is adopted, and compared with a microstrip line mode, the phase shifting unit formed by the LC network is beneficial to reducing the area of a measuring device. The values of the capacitance and the inductance in the first phase shift unit 122 can be calculated according to the phase shift value Φ 1, and the values of the capacitance and the inductance in the second phase shift unit 132 can be calculated according to the phase shift value Φ 2. Taking the first phase shift unit 122 as an example, the ABCD matrix thereof can be expressed as:

wherein the content of the first and second substances,representing the impedance of the capacitor C1 and the capacitor C2, the capacitor C1 and the capacitor C2 are of the same size,representing the impedance of the inductor L1. Converting the ABCD matrix to S parameters can yield:

the S21 phase can be expressed as:

thus, by the above formula, the phase shift value can be determined according toThe sizes of the capacitors C1, C2 and the inductor L1 were calculated. As shown in fig. 5, at the operating frequencyThen, after the two differential oscillating signals pass through the first phase shifting unit 122 and the second phase shifting unit 132, respectively, the phase difference becomesI.e. the phase difference at the location point of m2 in the figure.

In the embodiment of the present invention, the first sensing element 123 and the second sensing element 133 are implemented by microstrip lines, but may also be implemented by other sensing devices. The voltage detection mechanism 15 may be a multimeter, and the measurement principle of the measurement device according to the embodiment of the present invention will be described below by taking a multimeter as an example.

The first sensor 123 and the second sensor 133 are completely symmetrical sensors, during measurement, the second sensor 133 is idle, after a sample to be measured is placed on the first sensor 123, a certain delay is generated in the phase of the first sensor 123, the delay is determined by the real part of the dielectric constant, and then the phase difference between the signals output by the first sensor 123 and the second sensor 133 is extracted through the mixer 14.

The first sensor 123, the second sensor 133, and the multimeter 15 form a zero-if receiver structure, and when the first sensor 123 and the second sensor 133 are both idle, the output dc voltage can be expressed as:

whereinIn order to be the conversion gain of the mixer,、corresponding to the signal amplitudes of the first pick-off 123 and the second pick-off 133, respectively. After the sample to be tested is loaded on the first sensor 123, the signal output by the first sensor 123 generatesThe dc voltage output by the mixer 14 can be expressed as:

when in useAt the same time, the DC voltage value and the phase shift value outputted by the mixer 14One-to-one correspondenceAs shown in fig. 6, fig. 6 is a simulation curve of the dc voltage value output by the mixer changing with the phase difference of the two differential oscillation signals, which can also be regarded as the output voltage value changing with the phase shift valueThe abscissa is the phase difference of the two paths of differential oscillation signals, and the ordinate is the direct-current voltage value output by the mixer. The output DC voltage value of the mixer 14 is detected by using the multimeter 15 and substituted into the above DC voltage formula, so that the corresponding phase shift value can be calculatedAccording to the phase shift valueAnd (4) reversely deducing to obtain the real part of the dielectric constant, thereby realizing the function of measuring the dielectric constant.

The dielectric constant measuring device based on the differential oscillator provided by the embodiment of the invention is described in detail above, and the principle and the implementation of the invention are explained in the present document by applying specific examples, and the description of the above embodiments is only used to help understanding the method of the invention and the core idea thereof; meanwhile, for those skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.