A terahertz mixer integrated with a local oscillator source

Abstract

The present invention discloses a terahertz mixer integrated with a local oscillator, belonging to the field of terahertz radio frequency technology. It includes: an indium phosphide (InP) substrate circuit, a metal cavity, a radio frequency waveguide, and a height-reducing waveguide. The InP substrate circuit is successively provided with a radio frequency grounding structure, a radio frequency probe transition structure, a radio frequency matching structure, a reverse parallel resonant tunneling diode pair, a local oscillator matching structure, a local oscillator low-pass filtering structure, a local oscillator duplexing structure, a local oscillator source structure based on resonant tunneling diodes, and an intermediate frequency low-pass filter structure; the non-linear device is realized by a monolithic integrated reverse parallel resonant tunneling diode and is located between the radio frequency matching structure and the local oscillator matching structure; the local oscillator source is realized based on resonant tunneling diodes and is fed into the reverse parallel diodes through the local oscillator duplexing structure. The present invention is realized in a fully monolithic integrated manner. The resonant tunneling diode provides the local oscillator signal for the mixer, reducing the volume, lowering the complexity, improving the conversion loss, and enhancing the stability of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz radio frequency, and specifically to a terahertz mixer integrated with a local oscillator source. Background Art

[0002] Terahertz waves usually refer to electromagnetic waves with frequencies in the range of 0.1 - 10 THz and wavelengths between 0.03 - 3 mm. The terahertz frequency band is in the "gap" position between electronics and optics. Its low-frequency band coincides with millimeter waves (sub-millimeter waves), and its high-frequency band coincides with infrared. Due to its special position in the electromagnetic spectrum, terahertz waves have great development potential and application value in fields such as high-speed communication, atmospheric detection, target imaging, military, and security. A terahertz mixer is a very important device in the field of terahertz applications. Usually, it down-converts terahertz high-frequency signals to low frequencies to achieve spectral down-conversion, or up-converts low-frequency signals to high frequencies to achieve spectral up-conversion. The performance of the mixer largely affects the overall performance of the terahertz system. Therefore, the development of high-performance mixers has important engineering practical value.

[0003] The frequency conversion of a mixer mainly utilizes the non-linear effect of non-linear devices for frequency conversion. Schottky diodes are currently common non-linear devices used in terahertz mixers. In addition, there are also transistor-based mixers, hot electron bolometer (HEB) mixers, and superconducting-insulating-superconducting (SIS) mixers, etc. Transistor mixers have frequency conversion gain, but the processing technology is complex. SIS and HEB mixers have good performance, but can only operate in an ultra-low temperature environment. Schottky diode mixers can operate at room temperature, have mature technology, low loss, and are easy to integrate, and are currently the mainstream in the design of terahertz mixers.

[0004] Currently, the mixer circuits based on Schottky diodes are divided into hybrid integrated circuits and monolithic integrated circuits. Hybrid integrated circuits use discrete diodes and circuits to achieve terahertz mixing functions, and are generally more applied below 500 GHz; monolithic integrated circuits use GaAs substrates to co-design and process circuits and diodes. Hybrid integrated circuits have poor consistency and repeatability due to the need for manual assembly of diodes, and also have a greater impact on performance; for GaAs monolithic integrated circuits, because the dielectric constant of GaAs is large and the loss is relatively serious in the terahertz frequency band, the performance of the mixing monolith is affected. At the same time, both of them require high-performance local oscillator signals. The local oscillator signals generally use frequency multipliers and amplifiers to multiply the frequency to the local oscillator signals required by the mixer. During the signal conversion process, coaxial-microstrip, microstrip-waveguide, and waveguide interconnection transmissions are required, resulting in large losses and a large volume in the entire local oscillator signal transmission process, high costs, great implementation difficulties, and at the same time reducing the phase noise of the local oscillator source. Summary of the Invention

[0005] The object of the present invention is to address the above deficiencies and propose a terahertz mixer integrated with a local oscillator source. On the one hand, it reduces the requirement for local oscillator power. On the other hand, it is easy to implement in a fully integrated manner, reducing the volume and complexity. At the same time, it has low conversion loss and broad application prospects in terahertz mixers.

[0006] To achieve the above invention, the present invention provides the following technical solutions:

[0007] A terahertz mixer integrated with a local oscillator source, characterized in that it includes an indium phosphide (InP) substrate circuit, a radio frequency waveguide, and a reduced-height waveguide, and the InP substrate circuit is fixed in a suitable metal cavity.

[0008] The InP substrate circuit is successively provided with a radio frequency grounding structure, a radio frequency probe transition structure, a radio frequency matching structure, a pair of back-to-back resonant tunneling diodes (RTDs), a local oscillator matching structure, a local oscillator low-pass filter structure, a local oscillator duplexer structure, a local oscillator source structure based on resonant tunneling diodes, and an intermediate frequency low-pass filter structure;

[0009] A pair of back-to-back resonant tunneling diodes is provided between the radio frequency matching structure and the local oscillator matching structure and is implemented by a monolithic integration process;

[0010] The local oscillator source is implemented based on resonant tunneling diodes and is fed into the back-to-back diodes through the local oscillator duplexer structure.

[0011] Preferably, the mixer circuit substrate is implemented using indium phosphide material.

[0012] Preferably, the mixer circuit is implemented in a monolithic integration manner.

[0013] Preferably, the non-linear device used in the mixer is a pair of back-to-back resonant tunneling diodes.

[0014] Preferably, the local oscillator source is implemented using a resonant tunneling diode oscillator source and is fed into the back-to-back diode pair through the local oscillator duplexer structure.

[0015] Preferably, the local oscillator source is implemented using a resonant tunneling diode oscillator source and is fed into the back-to-back diode pair through the local oscillator duplexer structure.

[0016] Preferably, the InP substrate circuit is a planar integrated circuit and can be implemented using transmission structures such as microstrip lines and suspended microstrip lines.

[0017] Preferably, the local oscillator low-pass filter and the intermediate frequency low-pass filter can be implemented using high-low impedance microstrip lines or compact microstrip resonator units, etc.

[0018] Preferably, the local oscillator can be implemented by means such as a single tube, a pair of tubes, and power combining.

[0019] Preferably, the resistors used are thin-film resistors, and the capacitors are metal-insulator-metal (MIM) capacitors.

[0020] Preferably, when the oscillation frequency generated by the local oscillator is (f RF ±f IF ), an N - harmonic oscillator can be realized. When the oscillation frequency generated by the local oscillator is (f RF ±f IF ), fundamental - frequency mixing can be realized.

[0021] The present invention has the following advantages and beneficial effects:

[0022] 1. The terahertz mixer integrated with a local oscillator provided by the present invention is realized by means of full monolithic integration using InP material, and has the advantages of simple process and high reliability. Compared with the current GaAs material system, InP can achieve higher frequencies and better circuit performance.

[0023] 2. The terahertz mixer integrated with a local oscillator provided by the present invention uses resonant tunneling diode pairs as the nonlinear devices of the mixer. Resonant tunneling diodes have characteristics such as high frequency, low voltage, and the nonlinear characteristics are not affected by the thermal index. Compared with Schottky diodes, they require lower local oscillator power and have low conversion loss.

[0024] 3. The terahertz mixer integrated with a local oscillator provided by the present invention uses resonant tunneling diodes to provide the local oscillator signal, and integrates the local oscillator circuit and the mixing circuit, reducing the module volume and improving the phase noise of the local oscillator. At the same time, with the increase in the number of products, the cost is significantly reduced. Description of the Drawings

[0025] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0026] Figure 1 is a schematic structural diagram of the present invention;

[0027] Figure 2 is a schematic diagram of the DC characteristic curve of the resonant tunneling diode.

[0028] The labels in the drawings and the corresponding component names:

[0029] 1. RF DC ground wire, 2. RF waveguide, 3. Height-reducing waveguide, 4. RF transition structure, 5. RF matching structure, 6. Antiparallel resonant tunneling diode pair, 7. Local oscillator matching structure, 8. Local oscillator low-pass filter, 9. Local oscillator source, 91. Thin film resistor, 92. MIM capacitor, 93. Resonant tunneling diode, 10. Local oscillator duplexer structure, 11. Coplanar waveguide - microstrip line transition structure, 12. Intermediate frequency low-pass filter, 13. Intermediate frequency output, 14. Metal cavity, 15. InP substrate. Detailed implementation manners

[0030] The technical solutions of the exemplary embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The described embodiments are only for illustrative purposes and are not a limitation on the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] Figure 1 It is a schematic diagram of a terahertz mixer structure with an integrated local oscillator source provided by an embodiment of the present invention. As Figure 1 shown, the terahertz mixer structure with an integrated local oscillator source provided by the embodiment includes an InP substrate circuit 15, a metal cavity 14, an RF waveguide 2, and a height-reducing waveguide 3.

[0032] The InP substrate circuit is sequentially provided with an RF grounding structure 1, an RF probe transition structure 4, an RF matching structure 5, an antiparallel resonant tunneling diode (RTD) pair 6, a local oscillator matching structure 7, a local oscillator low-pass filtering structure 8, a local oscillator duplexer structure 10, a local oscillator source structure 9 based on a resonant tunneling diode, an intermediate frequency low-pass filter structure 12, and an intermediate frequency output 13.

[0033] The local oscillator source based on a resonant tunneling diode includes a thin film resistor 91, a MIM capacitor 92, and a resonant tunneling diode 93.

[0034] The RF signal is fed in through the standard waveguide 2, coupled to the microstrip line through the RF height-reducing waveguide 3 and the RF probe transition structure 4, and after passing through the RF matching structure 5, the RF signal is loaded onto the antiparallel resonant tunneling diode pair 6. Due to the presence of the local oscillator low-pass filter 8, the RF signal cannot leak to the local oscillator port and the intermediate frequency port, improving the port isolation.

[0035] After the local oscillator source is powered on, a local oscillator signal required for the local oscillator is generated. Among them, the thin film resistor 91 is a stabilizing resistor, mainly used to suppress the low-frequency oscillation of the bias circuit. The MIM capacitor is a bypass capacitor, which shorts the local oscillator signal generated by the oscillation to the ground, avoiding signal loss through the thin film resistor. The local oscillator signal generated by the local oscillator source 9 is loaded onto the antiparallel resonant tunneling diode pair 6 after passing through the local oscillator duplex structure 10, the local oscillator low-pass filtering structure 8, and the local oscillator matching structure 7, and is mixed with the radio frequency signal to generate an intermediate frequency signal.

[0036] The intermediate frequency signal passes through the local oscillator matching structure 7, the local oscillator low-pass filter 8, the local oscillator duplex structure 10, the intermediate frequency low-pass filter 12, and the intermediate frequency output structure 13, and then the intermediate frequency signal is output through the SMA connector.

[0037] Due to the existence of the intermediate frequency low-pass filter 12, the local oscillator signal cannot leak to the intermediate frequency port. At the same time, considering the cut-off characteristic of the waveguide itself, the local oscillator signal cannot leak to the radio frequency port either.

[0038] In summary, there are good isolation characteristics among the local oscillator, radio frequency, and intermediate frequency ports.

[0039] Figure 2 It is a schematic diagram of the DC characteristic curve of the resonant tunneling diode adopted in the embodiment of the present invention. Due to its special DC characteristics, the resonant tunneling diode can be used for the design of an oscillator source or as a nonlinear device for the design of a mixer.

[0040] There are two nonlinear regions (a) and (b) on the DC characteristic curve. The (a) region is similar to the nonlinearity of the Schottky diode, mainly depending on the device material structure. The nonlinearity at (b) is stronger than that at (a) because this nonlinearity is mainly related to the broadening of the quantum well tunneling subband rather than the thermal index. Therefore, when used in a mixer, the resonant tunneling diode operates in these two regions.

[0041] The NDR region on the DC characteristic curve is the negative resistance characteristic region, which can be used for the design of an oscillator source. Therefore, the resonant tunneling diode adopted in the local oscillator source in this design operates in this region.

[0042] The terahertz mixer scheme with an integrated local oscillator source proposed by the present invention has the characteristics of small volume, compact structure, good stability, and excellent performance. At the same time, it is designed in a monolithic full-integration manner, improving the assembly accuracy and to a certain extent improving the overall performance of the mixer module.

[0043] The above-described specific embodiments have elaborated on the technical solutions and beneficial effects of the present invention. It should be understood that the above is only the optimal embodiment of the present invention and does not limit the present invention. Any modifications, supplements, equivalent replacements, etc. made within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A terahertz mixer integrating a local oscillator source, characterized in that, It includes an indium phosphide (InP) substrate circuit, a metal cavity, a radio frequency (RF) waveguide, and a height-reducing waveguide. The InP substrate circuit is fixed in a suitable metal cavity; On the InP substrate circuit, there are successively arranged an RF grounding structure, an RF probe transition structure, an RF matching structure, a reverse parallel resonant tunneling diode pair, a local oscillator (LO) matching structure, an LO low-pass filtering structure, an LO duplexing structure, an LO source structure based on a resonant tunneling diode, and an intermediate frequency (IF) low-pass filter structure; A reverse parallel resonant tunneling diode pair is arranged between the RF matching structure and the LO matching structure and is realized by a monolithic integration process; The LO source is realized based on a resonant tunneling diode and is fed into the reverse parallel diode through the LO duplexing structure.

2. The terahertz mixer integrating a local oscillator according to claim 1, characterized in that The mixer circuit substrate is realized by using indium phosphide material.

3. The terahertz mixer integrating a local oscillator according to claim 1, characterized in that, The mixer circuit is realized in a monolithic integration manner.

4. The terahertz mixer integrating a local oscillator according to claim 1, characterized in that, The non-linear device used in the mixer is a reverse parallel resonant tunneling diode pair.

5. The terahertz mixer integrating a local oscillator according to claim 1, characterized in that, The LO source is realized by a resonant tunneling diode oscillator and is fed into the reverse parallel diode pair through the LO duplexing structure.

6. The terahertz mixer integrating a local oscillator according to claim 1, characterized in that The InP substrate circuit is a planar integrated circuit and is realized by using microstrip lines or suspended microstrip lines.

7. The integrated local oscillator terahertz mixer according to claim 1, characterized in that, The LO low-pass filtering structure and the IF low-pass filter structure are realized by using high-low impedance microstrip lines or compact microstrip resonant units.

8. The terahertz mixer integrating a local oscillator according to claim 5, characterized in that, The LO source can be realized by a single transistor, a transistor pair, or a power combining method.

9. The terahertz mixer integrating a local oscillator source according to claim 5, characterized in that, The resistors used in the LO source are thin-film resistors, and the capacitors are metal-insulator-metal capacitors.

10. The terahertz mixer integrating a local oscillator according to claim 5, characterized in that, When the oscillation frequency generated by the local oscillator source is (f RF ±f IF ) / N, an N - harmonic oscillator can be realized. When the oscillation frequency generated by the local oscillator source is (f RF ±f IF ), fundamental - wave mixing can be realized.

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