阅读说明：本技术 基于直流偏置下的石墨烯下变频混频器及设计方法 (Graphene down-conversion mixer based on direct current bias and design method ) 是由 方勇 王阳阳 赵志龙 钟晓玲 郭勇 侯学师 盛浩轩 江钰婷 于 2019-08-19 设计创作，主要内容包括：本发明公开了一种基于直流偏置下的石墨烯下变频混频器及设计方法,采用分支线耦合器、混频单元、低通滤波器的结构,分支线耦合器用于将射频信号和本振信号耦合在一起形成耦合信号,经直通端和耦合端输出,混频单元包括依次设置的第一直流偏置器、多层石墨烯和第二直流偏置器；两个直流偏置器用来隔离交流信号和直流信号,第一直流偏置器还连接直流电源激励多层石墨烯。直流信号激励多层石墨烯后能提升其混频性能,从而使耦合信号激励多层石墨烯后,更好的产生中频信号和高频信号,并利用低通滤波器滤除高频信号,从而得到中频信号,采用本发明设计的下变频混频器,驻波比低、输入功率线性度宽、变频损耗降低,有利于提高系统的灵敏度。(The invention discloses a graphene down-conversion frequency mixer based on direct current bias and a design method thereof, which adopt the structure of a branch line coupler, a frequency mixing unit and a low-pass filter, wherein the branch line coupler is used for coupling a radio frequency signal and a local oscillator signal together to form a coupled signal which is output through a straight-through end and a coupled end, and the frequency mixing unit comprises a first direct current bias, a plurality of layers of graphene and a second direct current bias which are sequentially arranged; the two direct current biasers are used for isolating alternating current signals and direct current signals, and the first direct current biaser is also connected with a direct current power supply to excite the multilayer graphene. The frequency mixing performance of the multi-layer graphene can be improved after the multi-layer graphene is excited by the direct current signal, so that after the multi-layer graphene is excited by the coupling signal, an intermediate frequency signal and a high frequency signal are better generated, and the high frequency signal is filtered by the low-pass filter, so that the intermediate frequency signal is obtained.)

1. The utility model provides a graphite alkene down conversion mixer based on direct current biasing down, includes the branch line coupler, the branch line coupler includes input, keeps apart the end, passes through the end and the coupling end, the radio frequency signal is connected to the input, keeps apart the end and connects the local oscillator signal, and the branch line coupler is used for forming the coupling signal with the coupling together of radio frequency signal and local oscillator signal, exports through passing through the end and coupling end, its characterized in that:

the direct connection end and the coupling end are respectively connected with a frequency mixing unit, and the frequency mixing unit comprises multilayer graphene, a first direct current biaser positioned at the front end of the multilayer graphene and a second direct current biaser positioned at the rear end of the multilayer graphene;

the first direct current biaser and the second direct current biaser have the same structure and comprise a radio frequency end, a direct current biaser end and a radio frequency direct current end;

the radio frequency ends of the two first direct current biasers are respectively connected with the straight-through end and the coupling end through microstrip lines, the two direct current biasers are connected with a direct current power supply, the two radio frequency direct current ends are respectively connected with the front ends of the corresponding multilayer graphene through microstrip lines, and the direct current power supply is used for generating direct current signals for exciting the multilayer graphene;

the radio frequency direct current ends of the two second direct current biasers are respectively connected with the rear ends of the corresponding multilayer graphene through microstrip lines, the direct current bias ends are grounded, and the two radio frequency ends are connected with the input end of the low-pass filter through the microstrip lines;

coupling signals output by the straight-through end and the coupling end respectively enter corresponding frequency mixing units, and are sent into the multilayer graphene together with direct current signals to excite the graphene;

wherein: the direct current signal is recovered by a second direct current biaser after passing through the multilayer graphene;

the coupling signal is sent into a low-pass filter through an intermediate frequency signal and a high frequency signal generated at the rear end of the multilayer graphene, and the low-pass filter filters the high frequency signal and then outputs the intermediate frequency signal.

2. The graphene down-conversion mixer based on direct current bias according to claim 1, wherein: the branch line coupler is a 90-degree branch line coupler.

3. The graphene down-conversion mixer based on direct current bias according to claim 1, wherein: the microstrip line is a copper microstrip line with impedance of 50 omega, and sequentially comprises a copper conductor strip layer, a dielectric substrate layer and a grounding copper clad layer from top to bottom, wherein a gap is arranged on the copper conductor strip layer, the gap distance is 0.3mm, and a plurality of layers of graphene covers the gap.

4. The method according to claim 1, wherein the method comprises: the method comprises the following steps:

(1) presetting the frequency of an input radio frequency signal to be fr, the frequency of a local oscillation signal to be fl, and the frequency of an output intermediate frequency signal to be fi = fr-fl, and designing a branch line coupler according to the frequency of the radio frequency signal;

(2) according to the parameters in the step (1), a graphene down-conversion mixer based on direct current bias is built;

(3) the input end of the low-pass filter is connected with a radio frequency signal, the isolation end of the low-pass filter is connected with a local oscillator signal, the initial value of the direct current power supply is set to zero, the output end of the low-pass filter is connected with a frequency spectrograph, and the graphene down-conversion frequency mixer based on direct current bias is started;

(4) acquiring the optimal direct current voltage of a direct current power supply;

the breakdown voltage of the multilayer graphene is voltage A, the initial voltage value of the direct-current power supply is 0, the voltage increases at equal intervals from 0 to voltage A, the frequency spectrogram of the output end of the low-pass filter under different direct-current voltages is recorded, the frequency spectrogram with the maximum power is found, and the direct-current voltage value corresponding to the frequency spectrogram is the optimal direct-current voltage;

(5) fixing a direct-current power supply to the optimal direct-current voltage, disassembling a frequency spectrograph, completing the design of a graphene down-conversion frequency mixer based on direct-current bias, and starting to work.

5. The method for designing a graphene down-conversion mixer based on DC bias as claimed in claim 5, wherein: in the step (5), the design of the graphene down-conversion mixer based on direct current bias is completed, and the specific work is started as follows:

(51) a radio frequency signal with frequency fr and a local oscillation signal with frequency fl are respectively sent into a branch line coupler through an input end and an isolation end, form two paths of coupling signals with different phases through the branch line coupler, and respectively output through a straight end and a coupling end;

(52) exciting the multilayer graphene by using a direct current signal and a coupling signal to generate a signal;

the direct current power supply generates a direct current signal, the direct current signal passes through the first direct current biaser, is sent into the multilayer graphene and is recovered by the second direct current biaser at the rear end of the multilayer graphene;

the coupling signals respectively enter the corresponding frequency mixing units, are sent into the multilayer graphene through the first direct current biaser, and generate an intermediate frequency signal fi = fr-fl and a high frequency signal at the rear end of the multilayer graphene;

(53) the intermediate frequency signal and the high frequency signal are sent into a low pass filter, and after the low pass filter filters the high frequency signal, only the intermediate frequency signal is output.

Technical Field

The invention relates to a down-conversion mixer, in particular to a graphene down-conversion mixer based on direct current bias and a design method.

Background

The down-conversion mixer is an important component of the radio frequency front end of the microwave receiver, the front end of the down-conversion mixer receives radio frequency signals amplified from the low noise amplifier, and the radio frequency signals are mixed with local oscillator signals to obtain down-conversion intermediate frequency signals which are output to a back end component. The mixer is used as a second-stage circuit of the radio frequency front end of the receiver, and plays an important role in improving the receiving sensitivity of the system. In recent years, graphene, as a two-dimensional material, attracts many researchers due to its unique mechanical, thermal and electrical properties, and is very suitable for application of microwave and millimeter wave circuits, such as mixers.

The two-dimensional electrons and holes of graphene are described by the effective dirac equation where the effective mass disappears. Thus, the electromagnetic response of graphene is strongly nonlinear. Compared with a traditional non-linear dual-port device (such as a Schottky diode), the output harmonic current of the graphene-non-linear device is reduced very slowly along with the reduction of the harmonic order. The graphene circuit has natural uniform harmonic suppression characteristics, and is very suitable for manufacturing nonlinear devices such as harmonic mixers and frequency multipliers.

But the graphene mixer has high conversion loss and a low 1dB compression point. The high conversion loss degrades the receiving sensitivity of the system. The linear range of the output power of the mixer is affected by the 1dB compression point, although the output power can be improved by increasing the local oscillation power, after reaching a certain value, the output power does not change linearly with the local oscillation power. The graphene mixer cannot well meet the actual index requirements. Through a large number of experimental tests, the performance of the mixer can be remarkably improved by adding direct current bias at two ends of graphene. Graphene can be likened to two inverted diodes, with the output having only odd harmonic components. The graphene with the direct-current bias voltage is equivalent to one of the diodes which is conducted, and the harmonic component output by the single diode has both even harmonic and odd harmonic, so that the output power of the mixer can be improved, and the frequency conversion loss is reduced. The linearity of the graphene mixer added with the direct current bias is also improved. The reflection loss of the output end and the isolation end of the branch line coupler is low, radio frequency power and local oscillator power are fully utilized to be coupled to the straight-through end and the coupling end, and the standing-wave ratio of the frequency mixer is reduced.

Disclosure of Invention

The present invention is directed to solve the above problems, and an object of the present invention is to provide a graphene downconversion mixer based on dc bias and a design method thereof, which can reduce the conversion loss of the graphene mixer and increase the linearity.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a graphene down-conversion frequency mixer based on direct current bias comprises a branch line coupler, wherein the branch line coupler comprises an input end, an isolation end, a through end and a coupling end, the input end is connected with a radio frequency signal, the isolation end is connected with a local oscillator signal, the branch line coupler is used for coupling the radio frequency signal and the local oscillator signal together to form a coupled signal, and the coupled signal is output through the through end and the coupling end;

the direct connection end and the coupling end are respectively connected with a frequency mixing unit, and the frequency mixing unit comprises multilayer graphene, a first direct current biaser positioned at the front end of the multilayer graphene and a second direct current biaser positioned at the rear end of the multilayer graphene;

the first direct current biaser and the second direct current biaser have the same structure and comprise a radio frequency end, a direct current biaser end and a radio frequency direct current end;

the radio frequency ends of the two first direct current biasers are respectively connected with the straight-through end and the coupling end through microstrip lines, the two direct current biasers are connected with a direct current power supply, the two radio frequency direct current ends are respectively connected with the front ends of the corresponding multilayer graphene through microstrip lines, and the direct current power supply is used for generating direct current signals for exciting the multilayer graphene;

the radio frequency direct current ends of the two second direct current biasers are respectively connected with the rear ends of the corresponding multilayer graphene through microstrip lines, the direct current bias ends are grounded, and the two radio frequency ends are connected with the input end of the low-pass filter through the microstrip lines;

coupling signals output by the straight-through end and the coupling end respectively enter corresponding frequency mixing units, are sent into the multilayer graphene together with direct current signals to excite the graphene,

wherein: the direct current signal is recovered by a second direct current biaser after passing through the multilayer graphene;

the coupling signal is sent into a low-pass filter through an intermediate frequency signal and a high frequency signal generated at the rear end of the multilayer graphene, and the low-pass filter filters the high frequency signal and then outputs the intermediate frequency signal.

Preferably, the method comprises the following steps: the branch line coupler is a 90 DEG branch line coupler.

Preferably, the method comprises the following steps: the microstrip line is a copper microstrip line with impedance of 50 omega, and sequentially comprises a copper conductor strip layer, a dielectric substrate layer and a grounding copper clad layer from top to bottom, wherein a gap is arranged on the copper conductor strip layer, the gap distance is 0.3mm, and a plurality of layers of graphene covers the gap.

A design method of a graphene down-conversion mixer based on direct current bias comprises the following steps:

(1) presetting the frequency of an input radio frequency signal to be fr, the frequency of a local oscillation signal to be fl, and the frequency of an output intermediate frequency signal to be fi = fr-fl, and designing a branch line coupler according to the frequency of the radio frequency signal;

(2) according to the parameters in the step (1), a graphene down-conversion mixer based on direct current bias is built;

(3) the input end of the low-pass filter is connected with a radio frequency signal, the isolation end of the low-pass filter is connected with a local oscillator signal, the initial value of the direct current power supply is set to zero, the output end of the low-pass filter is connected with a frequency spectrograph, and the graphene down-conversion frequency mixer based on direct current bias is started;

(4) acquiring the optimal direct current voltage of a direct current power supply;

the breakdown voltage of the multilayer graphene is voltage A, the initial voltage value of the direct-current power supply is 0, the voltage increases at equal intervals from 0 to voltage A, the frequency spectrogram of the output end of the low-pass filter under different direct-current voltages is recorded, the frequency spectrogram with the maximum power is found, and the direct-current voltage value corresponding to the frequency spectrogram is the optimal direct-current voltage;

(5) fixing a direct-current power supply to the optimal direct-current voltage, disassembling a frequency spectrograph, completing the design of a graphene down-conversion frequency mixer based on direct-current bias, and starting to work.

Preferably, the method comprises the following steps: in the step (5), the design of the graphene down-conversion mixer based on direct current bias is completed, and the specific work is started as follows:

(51) a radio frequency signal with frequency fr and a local oscillation signal with frequency fl are respectively sent into a branch line coupler through an input end and an isolation end, form two paths of coupling signals with different phases through the branch line coupler, and respectively output through a straight end and a coupling end;

(52) exciting the multilayer graphene by using a direct current signal and a coupling signal to generate a signal;

the direct current power supply generates a direct current signal, the direct current signal passes through the first direct current biaser, is sent into the multilayer graphene and is recovered by the second direct current biaser at the rear end of the multilayer graphene;

the coupling signals respectively enter the corresponding frequency mixing units, are sent into the multilayer graphene through the first direct current biaser, and generate an intermediate frequency signal fi = fr-fl and a high frequency signal at the rear end of the multilayer graphene;

(53) the intermediate frequency signal and the high frequency signal are sent into a low pass filter, and after the low pass filter filters the high frequency signal, only the intermediate frequency signal is output.

The principle of the invention is as follows: the graphene material is suitable for being used as an electronic device due to the characteristics of low resistivity and high electron mobility, and can be used in the field of microwave frequency conversion due to the strong nonlinear characteristic. The branch line coupler is used for coupling radio frequency and local oscillation signals and reducing the standing-wave ratio of the frequency mixer. Graphene can be likened to two inverted diodes, with the output having only odd harmonic components. The graphene with the direct-current bias voltage is equivalent to one of the diodes which is conducted, and the harmonic component output by the single diode has both even harmonic and odd harmonic, so that the output power of the mixer can be improved, and the frequency conversion loss is reduced.

Compared with the prior art, the invention has the advantages that: the invention adopts the branch line coupler to reduce the reflection loss of the input port and the isolation port and reduce the standing-wave ratio of the frequency mixer. The direct current bias voltage is increased at the two ends of the graphene, namely the reverse parallel diode is changed into a single diode, so that the harmonic component of the graphene is increased, the output power of the mixer is improved, and the frequency conversion loss is reduced. And the linearity of the graphene mixer added with the direct current bias is also improved.

Drawings

FIG. 1 is a schematic block diagram of the circuit of the present invention;

FIG. 2 is a schematic diagram of a microstrip gap structure according to the present invention;

FIG. 3 is a circuit diagram according to embodiment 2 of the present invention;

FIG. 4 is a schematic diagram of a branch line coupler structure;

FIG. 5 is a line graph of the output spectrum of the DC unbiased and DC biased mixers of the present invention.

In the figure: 1. a branch line coupler; 2. a first DC biaser; 3. multilayer graphene; 4. a second DC biaser; 5. a low-pass filter; 6. a dielectric substrate layer; 7. an input end; 8. a straight-through end; 9. a coupling end; 10. an isolation end; 11. a first section of microstrip line; 12. a second section of microstrip line; 13. a third microstrip line section; 14. a fourth segment of microstrip line; 15. a fifth section of microstrip line; 16. a sixth section of microstrip line; 17. a seventh segment of microstrip line; 18. an eighth segment of microstrip line; 19. a copper conductor tape layer; 20. a grounded copper clad layer.

Detailed Description

The invention will be further explained with reference to the drawings.