CN207010630U - A Terahertz Mixer Circuit Based on Monolithic Integration Technology - Google Patents

Abstract

A kind of Terahertz mixting circuit based on single slice integration technique, including radio frequency 3dB branch-waveguides directional coupler, 135 degree of phase shift 3dB branch-waveguides directional couplers of local oscillator, coaxial probe, Medium link ring, intermediate-freuqncy signal and two Terahertz sub-harmonic mixers, the Terahertz sub-harmonic mixer includes radio-frequency plumbing microstrip transition, single-chip integration Schottky diode to, local oscillator Waveguide-microbelt transition, intermediate-frequency filter and local oscillator low pass filter；Wherein, the single-chip integration Schottky diode is to the diode pair for reverse parallel connection.Harmonic mixer in the utility model Terahertz mixting circuit is obtained using semiconductor technology, accurately controls diode location and the size of microstrip circuit, and error is much smaller than manual assembly, greatly reduces influence of the rigging error to mixting circuit performance；Meanwhile the mixting circuit can effectively eliminate local oscillator noise, the noiseproof feature and efficiency of system are improved.

Description

A Terahertz Mixer Circuit Based on Monolithic Integration Technology

technical field

The utility model relates to a terahertz frequency mixing circuit based on monolithic integration technology.

Background technique

Terahertz (THz) waves refer to electromagnetic waves with frequencies in the range of 0.1 THz to 10 THz (wavelengths of 0.03 mm to 3 mm). It is an important member of the electromagnetic spectrum family, between infrared light waves and microwaves, the long wave band coincides with millimeter waves and submillimeter waves, and the short wave band coincides with infrared light. Its basic theory, research methods and technologies are also related to microwave, The two disciplines of light and wave are connected and compatible with each other. It is a comprehensive discipline formed by the rapid development at the end of the last century and the beginning of this century. The unique location of terahertz waves in the electromagnetic spectrum makes it transient, broadband, coherent, and low-energy, and it has important research value in the fields of information science, space science, medicine, and material science.

In the field of information science, the application of terahertz technology mainly includes: (1) radar system; due to the increase of frequency, terahertz radar has higher resolution than traditional microwave radar in terms of imaging and detection. It has great application prospects in weather radar and weather radar. (2) Communication system; with the rapid development of information science, modern communication systems require higher speed and stronger security performance. Compared with microwaves, terahertz waves have narrow beams and low side lobes, allowing extremely high Directional communication has extremely high research value in high-speed wireless communication between local area networks and satellites. (3) Security inspection system; terahertz waves have high penetrability and low energy. Therefore, a security inspection system based on terahertz waves will not cause damage to the human body, and has higher use value than X-ray security inspection equipment.

Terahertz radiometer is one of the important applications of terahertz in the field of information science. Terahertz radiometer is a high-sensitivity system for measuring electromagnetic radiation. It is a passive microwave remote sensing device. It does not emit electromagnetic waves itself, but passes passive The electromagnetic wave energy radiated by the observed scene is accurately received to detect the characteristics of the target. As an important part of the radiometer front-end system, the mixer's performance directly affects the overall indicators of the radiometer. The noise in the front end of the terahertz radiometer mainly comes from the diode in the local oscillator drive source and the mixer, where the amplitude modulation in the local oscillator signal and even the thermal noise of the amplifier in the local oscillator link will be introduced into the receiver system , which deteriorates the noise figure, resulting in a decrease in system sensitivity. Suppressing the noise introduced by the LO link not only improves the noise temperature of the receiver, but also improves the overall system sensitivity and dynamic range. However, there is no solution to eliminate the noise introduced by the local oscillator port in the current front-end of the terahertz radiometer. On the other hand, due to the limitation of processing conditions, the existing receiver circuit usually adopts multi-level circuit arrangement when there are multiple input and output ports. The overall circuit requires multiple substrates and cavities, and requires To connect waveguide or probe, the processing is complicated, the cost is high, and the transmission loss is large. In addition, as the core of the nonlinear effect of the mixer, the performance and assembly of the diode directly affect the performance of the mixer. When processing and assembling in the low frequency band, the circuit size is relatively large, and the "flip-chip" method is often used to use conductive glue to The diode is attached upside down to the microstrip of the circuit. However, when it reaches the terahertz frequency band, the size of the circuit decreases sharply, and the manual assembly method can no longer ensure its accuracy.

Utility model content

The utility model proposes a terahertz frequency mixing circuit based on monolithic integration technology aiming at the defects in the background technology. The harmonic mixer in the terahertz mixing circuit of the utility model is obtained by using semiconductor technology, which can accurately control the position of the diode and the size of the microstrip circuit, and the error is much smaller than manual assembly, which greatly reduces the impact of assembly error on the performance of the mixing circuit At the same time, the mixing circuit can effectively eliminate the noise of the local oscillator, and improve the noise performance and efficiency of the system.

The technical scheme of the utility model is as follows:

A terahertz mixing circuit based on monolithic integration technology, including radio frequency 3dB branch waveguide directional coupler 1, local oscillator 135 degree phase shift 3dB branch waveguide directional coupler 5, coaxial probe 8, intermediate frequency coupling ring 9, intermediate frequency signal 10 and two terahertz subharmonic mixers 2 comprising RF waveguide-microstrip transition 3, monolithically integrated Schottky diode pair 4, local oscillator waveguide-microstrip Band transition 6, intermediate frequency filter 7 and local oscillator low-pass filter 11; Wherein, described monolithic integrated Schottky diode pair 4 is the diode pair of antiparallel connection;

The radio frequency signal is coupled into two signals with a phase difference of 90 degrees by the radio frequency 3dB branch waveguide directional coupler 1, and then enters two terahertz subharmonic mixers 2 respectively; After the waveguide directional coupler 5 couples into two signals with a phase difference of 135 degrees, they respectively enter into two terahertz subharmonic mixers 2; the monolithically integrated Schottky diode pair 4 in the terahertz subharmonic mixer The input RF signal and the local oscillator signal are mixed. After the other components generated by the mixing are filtered by the intermediate frequency filter, only the intermediate frequency component is output through the corresponding intermediate frequency filter and enters the intermediate frequency coupling ring 9. After a 180° phase After conversion, an intermediate frequency signal 10 is output.

Further, the monolithic integrated Schottky diode pair 4 is directly produced on a GaAs substrate with a thickness of 5 μm to 15 μm, and the diode pad and the transmission line are connected by a beam-type thin gold strip, which can greatly reduce the assembly time. errors and improve circuit performance.

Further, the intermediate frequency filter 7 is an intermediate frequency high and low impedance line low-pass filter, and its output end is realized by a 50-ohm microstrip impedance line, which has the characteristics of wide-band suppression of spurious passbands, and can effectively prevent harmonic signals, local oscillators The signal and radio frequency signal are output by the intermediate frequency band and reflected back, which improves the efficiency of frequency multiplication and mixing.

Further, the local oscillator low-pass filter 11 is an intermediate frequency high and low impedance line low-pass filter, its function is to make the local oscillator signal reach the diode pair with a small loss to drive it to work, and suppress the radio frequency signal to prevent the radio frequency signal Leakage from the LO port improves port isolation.

Among them, after the radio frequency signal and the local oscillator driving signal are input through the local oscillator and radio frequency ports of two terahertz subharmonic mixers, they are mixed in the antiparallel monolithic integrated Schottky diode pair 4; where , the two local oscillator drive signals with a phase difference of 135 degrees are fed into the monolithic integrated Schottky diode pair 4 to generate various harmonic components, the phase difference of the second harmonic component is 270 degrees, and the phase difference of the two radio frequency signals is 90 degrees , so that the phase difference of the signal generated by the RF signal and the second harmonic component of the local oscillator driving signal after mixing is 180 degrees. After other components in the signal generated by frequency mixing are filtered out by the corresponding intermediate frequency filter, only the intermediate frequency component is output and enters the intermediate frequency coupling ring 9, and the phase difference of the two output intermediate frequency signals is 180 degrees. The intermediate frequency coupling ring 9 performs 180° phase transformation, and since the noise is randomly distributed, it is meaningless to perform phase transformation on the noise, and after being mixed by the mixer and filtered by the intermediate frequency filter, the noise introduced by the local oscillator is amplified by the power amplifier , at this time, under the new noise floor, the noise introduced by the local oscillator can be considered as a small signal. After the 180-degree phase transformation is output, the local oscillator noise is suppressed in reverse, and the two intermediate frequency signals are superimposed and output in the same direction, and the final output is passed through The noise-suppressed intermediate frequency signal 10 achieves the purpose of suppressing local oscillator noise.

The beneficial effects of the utility model are:

1. In the terahertz frequency mixing circuit of the present invention, two single-chip integrated subharmonic mixers based on planar Schottky diode pairs are used, which are arranged in parallel to form a frequency mixing circuit, and the 135-degree and 90-degree branch line waveguides are used The directional coupler changes the phase of the two local oscillators and RF signals, so that the two intermediate frequencies generated by the mixing of the second harmonic component of the local oscillator and the RF signal have a phase difference of 180 degrees. After entering the intermediate frequency coupling ring, the two intermediate frequency signals After the 180-degree phase transformation, the output is superimposed in the same direction, and the two noise signals introduced by the local oscillator are counteracted in reverse to achieve the purpose of eliminating the noise of the local oscillator, thereby improving the noise performance and efficiency of the system.

2. The pair of Schottky diodes in the terahertz mixing circuit of the present invention is obtained by using semiconductor monolithic integration technology, which effectively solves the problem of low accuracy of manual assembly. The pair of Schottky diodes is directly grown on the GaAs substrate and combined with The microstrip lines on the GaAs substrate are directly connected, and at the same time, beam leads are generated on the substrate to provide grounding for the diode and support the entire circuit monolith. The schottky diode pair in the terahertz frequency mixing circuit of the utility model is obtained through semiconductor technology, which can accurately control the position of the diode and the size of the microstrip circuit, and the error is much smaller than that of manual assembly, which greatly reduces the impact of assembly error on the performance of the frequency mixing circuit Impact.

3. In the terahertz mixing circuit of the utility model, a coaxial probe is used to connect the two intermediate frequency output ports with the intermediate frequency coupling ring arranged on another layer. This structure makes the intermediate frequency coupling ring circuit and the microstrip line of the mixer The structure can be built in the same cavity, which avoids the cumbersome connection of multiple circuit modules, rationally utilizes the space inside the module, reduces the transition structure, and simplifies the circuit structure.

4. The subharmonic mixer is adopted in the terahertz frequency mixing circuit of the utility model. The subharmonic mixer only needs to receive the local oscillator frequency half of the radio frequency frequency to realize mixing reception, which greatly reduces the influence on the terahertz solid-state source. The demand is conducive to the miniaturization of the entire transceiver system, which is of great significance to the wide application of terahertz technology.

Description of drawings

Figure 1 is a schematic diagram of the overall structure of a terahertz frequency mixing circuit based on monolithic integration technology provided by the present invention;

Fig. 2 is the three-dimensional model of the monolithic integrated Schottky diode of the present invention;

Fig. 3 is a structural schematic diagram of the utility model terahertz subharmonic mixer 2;

Fig. 4 is the structural representation of the utility model radio frequency 3dB branch waveguide directional coupler;

Fig. 5 is the simulation result of the utility model radio frequency 3dB branch waveguide directional coupler;

Fig. 6 is a structural schematic diagram of the utility model local oscillator 135 degree phase shift 3dB branch waveguide directional coupler;

Fig. 7 is a schematic structural diagram of the intermediate frequency coupling ring of the present invention.

detailed description

As shown in Figure 1, it is a schematic diagram of the overall structure of a terahertz mixing circuit based on monolithic integration technology provided by the present invention; it includes a radio frequency 3dB branch waveguide directional coupler 1, a local oscillator with a phase shift of 135 degrees and a 3dB branch waveguide directional Coupler 5, coaxial probe 8, intermediate frequency coupling ring 9, intermediate frequency signal 10 and two terahertz subharmonic mixers 2, said terahertz subharmonic mixers 2 including radio frequency waveguide-microstrip transition 3 , monolithic integrated Schottky diode pair 4, local oscillator waveguide-microstrip transition 6, intermediate frequency filter 7 and local oscillator low-pass filter 11; wherein, the monolithic integrated Schottky diode pair 4 is antiparallel pair of diodes;

Among them, the standard waveguide WR-2.8 is used as the RF input terminal to input the RF signal, and the RF signal enters from the RF 3dB branch waveguide directional coupler 1, and the standard waveguide WR-5.1 is used as the local oscillator input terminal to input the local oscillator signal, and the local oscillator signal comes from the local oscillator 135 degree phase shift 3dB branch waveguide directional coupler 5 enters; the radio frequency signal is coupled by the radio frequency 3dB branch waveguide directional coupler 1 into two signals with a phase difference of 90 degrees, and then coupled to the microstrip line through the waveguide height reduction and enters two terahertz Subharmonic mixer 2; the local oscillator driving signal is coupled into two signals with a phase difference of 135 degrees by the 135-degree phase shift 3dB branch waveguide directional coupler 5 of the local oscillator, and then coupled to the microstrip line through the waveguide to reduce the height and enter the two channels respectively. A terahertz subharmonic mixer 2; the monolithic integrated Schottky diode in the terahertz subharmonic mixer performs frequency mixing processing on 4 pairs of input RF signals and local oscillator signals, and other components generated by mixing After being filtered out by the intermediate frequency filter, only the intermediate frequency component is output through the corresponding intermediate frequency filter, enters the intermediate frequency coupling ring 9, and outputs the intermediate frequency signal 10 after 180° phase transformation.

Among them, after the radio frequency signal and the local oscillator driving signal are input through the local oscillator and radio frequency ports of two terahertz subharmonic mixers, they are mixed in the antiparallel monolithic integrated Schottky diode pair 4; where , the two local oscillator drive signals with a phase difference of 135 degrees are fed into the monolithic integrated Schottky diode pair 4 to generate various harmonic components, the phase difference of the second harmonic component is 270 degrees, and the phase difference of the two radio frequency signals is 90 degrees , so that the phase difference of the signal generated by the RF signal and the second harmonic component of the local oscillator driving signal after mixing is 180 degrees. After other components in the signal generated by frequency mixing are filtered out by the corresponding intermediate frequency filter, only the intermediate frequency component is output and enters the intermediate frequency coupling ring 9, and the phase difference of the two output intermediate frequency signals is 180 degrees. The intermediate frequency coupling ring 9 performs 180° phase transformation, and since the noise is randomly distributed, it is meaningless to perform phase transformation on the noise, and after being mixed by the mixer and filtered by the intermediate frequency filter, the noise introduced by the local oscillator is amplified by the power amplifier , at this time, under the new noise floor, the noise introduced by the local oscillator can be considered as a small signal. After the 180-degree phase transformation is output, the local oscillator noise is suppressed in reverse, and the two intermediate frequency signals are superimposed and output in the same direction, and the final output is passed through The noise-suppressed intermediate frequency signal 10 achieves the purpose of suppressing local oscillator noise.

Among them, the radio frequency waveguide-microstrip transition 3 and the local oscillator waveguide-microstrip transition 6 adopt the form of waveguide height reduction, which can make the matching better.

Among them, the standard waveguide WR-2.8 has the effect of suppressing low-frequency signals, so intermediate frequency signals and local oscillator signals will not be output from the radio frequency end.

As shown in Figure 2, it is the three-dimensional model of the monolithic integrated Schottky diode pair of the present invention; the diode is the core device of the mixer, and its performance is directly related to the level of frequency conversion loss and the operating bandwidth of the mixer. In the terahertz frequency band, the wavelength is very small, and the package size of the diode will have a great impact on its performance. Try to choose a diode with a relatively small cascade resistance and junction capacitance, but as the frequency increases, it is necessary to reduce the cascade resistance at the same time. Resistance and junction capacitance, which are difficult to realize in semiconductor technology. The single-chip integrated Schottky diode pair in the subharmonic mixer of the utility model integrates two Schottky junctions in one package through semiconductor technology, and forms an anti-parallel structure, which ensures maximum The symmetry of the two tubes reduces the parasitic parameters of the package; then remove the substrate of the diode pair to directly generate a diode model on the substrate, and connect it to the microstrip line through the gold strip, as shown in Figure 2.

As shown in Figure 3, it is a schematic structural diagram of a terahertz subharmonic mixer 2 of the present invention; the terahertz subharmonic mixer 2 includes a radio frequency waveguide-microstrip transition 3, a monolithic integrated Schottky diode To 4, local oscillator waveguide-microstrip transition 6, intermediate frequency filter 7 and local oscillator low-pass filter 11, wherein, described monolithic integrated Schottky diode pair 4 is the diode pair of antiparallel connection, with monolithic integrated on a gallium arsenide substrate.

Among them, the microstrip at the RF end is in contact with the cavity wall to realize the grounding of the RF and DC signals; the transition from the input waveguide to the probe couples the electric field in the waveguide to the microstrip through a coupling probe, and then uses A quarter wavelength is impedance transformed to achieve impedance matching with a standard microstrip transmission line.

Wherein, the intermediate frequency filter 7 is an intermediate frequency high and low impedance line low-pass filter, and its function is to extract the intermediate frequency signal generated by mixing from the circuit, and to useless frequency signals, mainly local oscillators with strong energy The signal is suppressed to prevent the loss of local oscillator signal energy and the impurity of the intermediate frequency output spectrum caused by its output from the intermediate frequency port. At the same time, the IF filter also needs to reduce the insertion loss in the passband as much as possible, so that the IF signal can be output with less loss, and the suppression of the local oscillator frequency can be improved.

Wherein, the local oscillator low-pass filter 11 is an intermediate frequency high-low impedance line low-pass filter, and its function is to make the local oscillator signal reach the diode pair with less loss to drive its work, and suppress the radio frequency signal to prevent the radio frequency signal from The leakage of the local oscillator port improves the isolation of the port, and at the same time avoids the loss of radio frequency signals due to leakage, and can concentrate energy on the diode pair for mixing.

In the utility model, both the local oscillator low-pass filter and the intermediate frequency low-pass filter adopt high and low impedance line low-pass filters, and the microstrip high and low impedance line low-pass filter has a simple structure and is easy to process, and is often used as a frequency selection device in the system Suppresses interfering signals and harmonic signals.

As shown in Figure 4, it is the structural representation of the utility model radio frequency 3dB branch waveguide directional coupler; This radio frequency branch waveguide directional coupler is formed based on standard waveguide WR-2.8, mainly by input end (port 1), through end (port 2 ), coupled terminal (port 3) and isolated terminal (port 4), where the isolated terminal is connected to a matching load, the straight-through terminal and the coupled terminal are used as output ports, and the two output signals have a 90° phase difference. The radio frequency 3dB branch waveguide directional coupler of the utility model has the characteristics of matching of each port, high isolation degree, small insertion loss, etc., and improves the deficiency of the three-port element. Fig. 5 is the simulation result of the radio frequency 3dB branch waveguide directional coupler of the present invention, can find out that this radio frequency branch waveguide directional coupler return loss (S11) is better than 20dB in the frequency range 150GHz～180GHz by the simulation result, straight-through port and The coupling port isolation (S23) is also better than 20dB, and it can also be seen from S21 and S31 that it has good characteristics of power equalization. The good transmission performance of the radio frequency branch waveguide directional coupler of the utility model enables the radio frequency signal to be loaded onto the two mixers with a relatively small loss in a wide frequency band range, laying a good foundation for realizing a low loss mixing circuit Base.

As shown in Figure 6, it is a structural schematic diagram of the utility model local oscillator 135 degree phase shift 3dB branch waveguide directional coupler; the local oscillator branch waveguide directional coupler is formed based on the standard waveguide WR-5.1, mainly by the input terminal (port 1) , straight-through (port 2), coupled (port 3) and isolated (port 4) four ports, where the isolated end is connected to a matching load, the straight-through and coupled are output ports, and the two output signals exist 90 ° phase difference. Since the mixer in the terahertz mixing circuit of the present invention is a subharmonic mixer, in order to ensure that the phases of the two intermediate frequency signals are opposite after the second harmonic and the radio frequency signal are mixed, it is necessary to add an extra phase of 45 degrees at the through end. Move the branches so that the difference between the straight-through end 2 and the coupling end 3 is 135 degrees.

As shown in FIG. 7 , it is a structural schematic diagram of the intermediate frequency coupling ring of the present invention. The utility model adopts the classic hybrid ring model based on microstrip line, 2 ports are connected with matching load, the intermediate frequency signal enters the coupling ring circuit through port 1 and port 3 respectively, and the output of port 4 is the difference of the two signals, that is, the signal is reversely superimposed.

The RF power splitter in the utility model adopts an orthogonal branched waveguide directional coupler structure, which is connected with the radio frequency port of the subharmonic mixer through the waveguide-microstrip transition; the local oscillator power splitter adopts a 135-degree branched waveguide directional coupler structure , directly connected to the local oscillator port of the subharmonic mixer through a microstrip line. The two intermediate frequency output ports are connected to the intermediate frequency coupling ring on the other layer through coaxial probes. This structure enables the intermediate frequency coupling ring circuit and the microstrip line structure of the mixer to be built in the same cavity, avoiding the The cumbersome connection of multiple circuit modules rationally utilizes the space inside the module, simplifies the circuit, and reduces the loss inside the circuit.

In the terahertz frequency mixing circuit of the utility model, two single-chip integrated subharmonic mixers based on planar Schottky diodes are used, which are arranged in parallel to form a frequency mixing circuit. After the local oscillator and RF ports of the subharmonic mixer are input, the frequency mixing process is performed in the anti-parallel monolithic integrated Schottky diode pair 4; the noise is randomly distributed, and the noise is phase-transformed in the frequency mixing circuit It has no practical significance, but due to the phase shift effect of the RF signal and the local oscillator signal, the phase of the intermediate frequency signal at the time of the mixing output is opposite, and after the action of the intermediate frequency filter, the noise amplified by the local oscillator can be reduced under the new noise floor. It is considered to be a small signal. After entering the intermediate frequency coupling ring 9, the two intermediate frequency signals are superimposed and output in the same direction after a 180-degree phase transformation, and the two noise signals introduced by the local oscillator are counteracted in reverse to achieve the purpose of eliminating the local oscillator noise. This in turn improves the noise performance and efficiency of the system.

Claims (3)

1. A terahertz mixing circuit based on monolithic integration technology, including a radio frequency 3dB branch waveguide directional coupler (1), a local oscillator 135-degree phase shift 3dB branch waveguide directional coupler (5), a coaxial probe (8 ), an intermediate frequency coupling ring (9), an intermediate frequency signal (10) and two terahertz subharmonic mixers (2), and the terahertz subharmonic mixer (2) includes a radio frequency waveguide-microstrip transition ( 3), monolithically integrated Schottky diode pair (4), local oscillator waveguide-microstrip transition (6), intermediate frequency filter (7) and local oscillator low-pass filter (11); wherein, the monolithic integrated The Schottky diode pair (4) is a diode pair connected in antiparallel; The radio frequency signal is coupled into two signals with a phase difference of 90 degrees by the radio frequency 3dB branch waveguide directional coupler, and then enters two terahertz subharmonic mixers respectively; After the coupler is coupled into two signals with a phase difference of 135 degrees, they enter two terahertz subharmonic mixers respectively; the monolithic integrated Schottky diode in the terahertz subharmonic mixer pairs the input RF signal Perform frequency mixing with the local oscillator signal. After the other components generated by the mixing are filtered out by the intermediate frequency filter, only the intermediate frequency component is output through the corresponding intermediate frequency filter and enters the intermediate frequency coupling loop. After 180°phase transformation, the intermediate frequency signal is output . 2. The terahertz frequency mixing circuit based on monolithic integration technology according to claim 1, wherein the intermediate frequency filter is an intermediate frequency high and low impedance line low-pass filter. 3. The terahertz frequency mixing circuit based on monolithic integration technology according to claim 1, wherein the local oscillator low-pass filter is an intermediate frequency high-low impedance line low-pass filter.