CN114244280A - Terahertz monolithic integration subharmonic mixer based on single-ended structure - Google Patents
Terahertz monolithic integration subharmonic mixer based on single-ended structure Download PDFInfo
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Abstract
The invention provides a terahertz monolithic integration subharmonic mixer based on a single-ended structure, and relates to the technical field of terahertz mixers. The mixer comprises a substrate, a mixing circuit is formed on the substrate, a local oscillator input port is respectively connected with one end of a local oscillator matching filter structure and one end of a bias circuit through the output end of a blocking capacitor, the other end of the local oscillator matching filter structure is connected with a grid electrode of a mixing element, and the other end of the bias circuit is connected with a Vg power-on end; the radio frequency port is respectively connected with the radio frequency matching structure and the intermediate frequency filtering structure through the radio frequency filtering structure, the other end of the radio frequency matching structure is connected with a drain electrode of the mixing element, and the other end of the intermediate frequency filtering structure is connected with the intermediate frequency port. The frequency mixing element is a common source structure FET/HEMT tube core, the scheme utilizes the square law characteristic of the frequency mixing element to realize the terahertz monolithic integration subharmonic mixer based on a single-ended structure, and the terahertz monolithic integration subharmonic mixer has performance indexes such as low frequency conversion loss, small size, high port isolation degree and the like in a broadband range.
Description
Technical Field
The invention belongs to the technical field of terahertz frequency mixers, and particularly relates to a terahertz monolithic integration subharmonic frequency mixer based on a single-ended structure.
Background
The terahertz frequency has many advantages of high carrier frequency, high penetrability, large bandwidth and the like, so that the terahertz frequency has a good application prospect in the aspects of high-speed wireless communication, terahertz radar, detection and the like. The terahertz mixer serves as a key component, and the quality of technical indexes such as working bandwidth, frequency conversion loss and noise coefficient of the terahertz mixer affects the overall performance of the terahertz system to a great extent.
Terahertz frequency band monolithic integration subharmonic mixers mainly fall into two categories: the mixer is a balanced subharmonic mixer based on an FET/HEMT, and the mixer is a subharmonic mixer based on an Anti-Parallel Diode Pair (APDP) structure. The balanced subharmonic mixer based on the FET/HEMT usually needs to adopt two frequency mixing units, local oscillator signals provided for the two frequency mixing units mostly adopt a branch line form to realize 90-degree or 180-degree phase shift, the broadband characteristic is difficult to realize, the chip size is large, and the requirement on local oscillator driving power is doubled. The subharmonic mixer based on the APDP structure needs a tape-out process compatible with a Schottky barrier diode process, has more limitations on the process, and can correspondingly increase the manufacturing cost.
Cut-off frequency fTGenerally considered as an index for measuring the upper limit of the working frequency of the FET/HEMT, the shortening of the grid length is generally adopted to reduce the channel carrier transit time and increase the cut-off frequency fT. Limited by the state of the art, and short channel effects, the gate length cannot be infinitely shortened, thereby limiting the cutoff frequency f of compound semiconductor process FET/HEMTsT. Terahertz mixer is used as an indispensable frequency conversion function realization component in a transmitting-receiving front end, and how to realize the FET/HEMT cut-off frequency f higher than that of the existing compound semiconductor processTThe frequency band has considerable technical indexes such as working bandwidth, frequency conversion loss, noise coefficient and the like, and is a very worthy direction to be explored at present. For example, Sten E.Gunnarsson of Chalmers University of Technology in Sweden designs a 220GHz (G-band) monolithic integrated single-ended resistive fundamental wave mixer by adopting a 0.1um GaAs mHEMT process, and the cutoff frequency f of the 2x20um mHEMT based on the processTOnly 170GHz, below the operating frequency of the mixer. The minimum value of the conversion loss of the mixer is 8.7dB, and the flatness of the mixer is good in the frequency band of 200-220 GHz. But the conversion loss of the mixer is difficult to be further improved due to the shortage of the output power of the oscillator.
Therefore, the cutoff frequency f of the terahertz frequency band compound semiconductor process FET/HEMT is consideredTThe improvement difficulty, the lack of a high-performance intrinsic vibration source in a terahertz high frequency band and the like are caused, and the improvement of the prior art is needed.
Disclosure of Invention
The invention aims to solve the technical problem of the prior art and provides a terahertz monolithic integration subharmonic mixer based on a single-ended structure.
The technical scheme of the invention is as follows: the utility model provides a terahertz is monolithic integration subharmonic mixer now based on single-ended structure which characterized in that: includes a substrate having a mixer circuit formed thereon. The frequency mixing circuit comprises a local oscillator input port, a blocking capacitor, a bias circuit, a local oscillator matching filter structure, a frequency mixing circuit, a radio frequency matching structure, a radio frequency filter structure, a radio frequency port, an intermediate frequency filter structure and an intermediate frequency port; the local oscillator input port is respectively connected with one end of a local oscillator matching filter structure and one end of a bias circuit through the output end of the blocking capacitor, the other end of the local oscillator matching filter structure is connected with a grid electrode of the frequency mixing element, and the other end of the bias circuit is connected with a Vg power-on end; the radio frequency port is respectively connected with the radio frequency matching structure and the intermediate frequency filtering structure through the radio frequency filtering structure, the other end of the radio frequency matching structure is connected with a drain electrode of the mixing element, and the other end of the intermediate frequency filtering structure is connected with the intermediate frequency port.
The mixing element is a common source structure FET/HEMT tube core. When the radio frequency signal is an input signal, mixing the radio frequency signal with second harmonic of a local oscillation signal, filtering an intermediate frequency signal generated by mixing the radio frequency signal by an intermediate frequency filtering structure, and outputting the intermediate frequency signal; when the intermediate frequency signal is an input signal, the intermediate frequency signal is mixed with the second harmonic of the local oscillation signal, and the radio frequency signal generated by mixing is output after being matched and filtered by the radio frequency matching structure and the radio frequency filtering structure.
The mixing circuit of the mixer is designed as a microstrip line. The local oscillator port is connected with one end of the local oscillator matching filter structure and one end of the bias circuit through the output end of a blocking flat capacitor, and the bias circuit is in a structure that a high-impedance resistor is connected in parallel with a capacitor to the ground in series. The blocking capacitor and the parallel capacitor adopt an upper metal layer and a lower metal layer of a compound semiconductor process to form an upper electrode plate and a lower electrode plate of the capacitor, and the high impedance resistance adopts a thin film resistance process in the compound semiconductor process.
The radio frequency filtering structure of the frequency mixer is a high-pass filter and adopts a parallel coupling line filter design.
The intermediate frequency filtering structure of the mixer is a two-stage low-pass filter. The first-stage filter adopts a structure that the series microstrip lines are connected with the open-circuit stub in parallel, wherein the equivalent electrical length of the series microstrip lines and the open-circuit stub in parallel is one fourth of the radio frequency wavelength, and the second-stage filter adopts a structure that the series microstrip lines are connected with the capacitor in parallel to the ground.
The frequency of the radio frequency signal of the frequency mixer is the sum of two times of the frequency of the local oscillation signal and the frequency of the intermediate frequency signal.
With the above scheme, common source structure FET/HEMT die is used as the mixing element. When the radio frequency signal is an input signal, the radio frequency signal is input through a drain electrode of the FET/HEMT tube, and is mixed with second harmonic of a local oscillation signal pumped through a grid under the condition of grid bias voltage, and an intermediate frequency signal generated by mixing is filtered through an intermediate frequency filtering structure and then is output. When the intermediate frequency signal is an input signal, the intermediate frequency signal is input through a drain electrode of the FET/HEMT tube, is mixed with second harmonic of a local oscillation signal pumped by a grid under the condition of grid bias voltage, and a radio frequency signal generated by mixing is output after being matched and filtered through a radio frequency matching structure and a radio frequency filtering structure. The frequency interval between the radio frequency signal and the local oscillator signal is large enough, and the isolation from the local oscillator to the radio frequency port can be effectively improved through the radio frequency high-pass filter. The structure realizes second harmonic mixing of local oscillation signals by using square law characteristics of a mixing element, not only can solve the problem that a terahertz high-frequency band is lack of a high-performance local oscillation source, but also can effectively utilize the cut-off frequency f of a FET/HEMTTThe low-cost compound semiconductor process is lower than the radio frequency working frequency and higher than the local oscillation working frequency. When the drain electrode of the common source structure FET/HEMT tube is not biased, the drain electrode port of the FET/HEMT tube has the characteristic of nearly pure resistance in a wide bandwidth, so that radio frequency and intermediate frequency signals connected with the drain electrode of the FET/HEMT tube have flat response in the wide bandwidth. Compared with the conventional balanced sub-harmonic based on FET/HEMTThe wave mixer has a simple circuit structure, and the transmission paths of radio frequency and local oscillation signals are short, so that low-loss transmission is realized.
Therefore, the circuit structure not only effectively solves the cut-off frequency f of the terahertz frequency band compound semiconductor process FET/HEMTTThe terahertz frequency mixer has the advantages that the terahertz frequency mixer is low, and the terahertz high-frequency band lacks a high-performance local oscillation source, so that the working bandwidth of the terahertz monolithic integration subharmonic frequency mixer is effectively increased, the conversion loss of the frequency mixer is reduced, the isolation from a local oscillation to a radio frequency port is improved, and the size of a chip is reduced. The terahertz monolithic integration subharmonic mixer has the performance indexes of low frequency conversion loss, low manufacturing cost, high port isolation degree and the like in a broadband range.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a schematic diagram of a subharmonic mixer according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a 220GHz subharmonic mixer according to an embodiment of the invention;
FIG. 3 is a graph of the conversion loss simulation results for the subharmonic mixer of FIG. 2;
FIG. 4 is a diagram of a simulation result of local oscillator to RF port isolation for the subharmonic mixer of FIG. 2;
FIG. 5 is a graph of a simulation result of local oscillator to intermediate frequency port isolation for the subharmonic mixer of FIG. 2;
fig. 6 is a graph of simulation results of the rf-to-if port isolation of the subharmonic mixer of fig. 2.
Detailed Description
The technical solution in the embodiments of the present invention is described in detail below with reference to the accompanying drawings.
First, the frequency range in which the present invention is applied will be described, and the most suitable frequency range in which the present invention is applied is the low end of the frequency of terahertz waves. At the low end of the terahertz frequency, the cut-off frequency f is limited by the FET/HEMT of the compound semiconductor processTAnd a high-performance local oscillation source required by a fundamental wave mixer, and the development of the terahertz monolithic integrated mixer is subjected to bottleneck. The invention designs a sheet-basedThe terahertz monolithic integration subharmonic mixer with the end structure just solves the problems.
As shown in fig. 1, the embodiment of the invention discloses a terahertz monolithic integrated subharmonic mixer based on a single-ended structure, which includes a substrate 12, a mixer circuit formed on the substrate 12, the mixer circuit being designed as a microstrip line, the local oscillator input port 1 being connected to one end of a local oscillator matching filter structure 5 and one end of a bias circuit 3 respectively through an output end of a blocking capacitor 2, the bias circuit 3 being a structure in which a high impedance resistor is connected in series and a capacitor is connected in parallel to the ground, the other end of the local oscillator matching filter structure 5 being connected to a gate of a mixer element 6, the other end of the bias circuit 3 being connected to a Vg supply terminal 4, and the local oscillator signal power requirement being reduced by adjusting a gate bias voltage. The radio frequency port 11 is respectively connected with the radio frequency matching structure 7 and the intermediate frequency filtering structure 9 through the radio frequency filtering structure 10. The radio frequency filtering structure (10) is a high-pass filter, a parallel coupling line filter design is adopted, and the filter has a direct current isolation function at the same time without additionally increasing a direct current blocking plate capacitor. The other end of the radio frequency matching structure 7 is connected with the drain electrode of the mixing element 6, and the other end of the intermediate frequency filtering structure 9 is connected with the intermediate frequency port 8. The intermediate frequency filter structure 9 is designed as a two-stage low-pass filter, the first-stage filter adopts a structure that a series microstrip line is connected with an open-circuit stub in parallel, wherein the equivalent electrical length of the series microstrip line and the open-circuit stub in parallel is one fourth of the radio frequency wavelength and is mainly used for inhibiting the leakage of radio frequency signals, and the second-stage filter adopts a structure that a series microstrip line is connected with a capacitor in parallel to the ground, so that the isolation from a local oscillator to the intermediate frequency port 8 is improved. The mixing circuit is a common source structure FET/HEMT tube core. When the radio frequency signal is an input signal, the radio frequency signal is mixed with the second harmonic of the local oscillation signal, and an intermediate frequency signal generated by the mixing is filtered by the intermediate frequency filtering structure 9 and then output. When the intermediate frequency signal is an input signal, the intermediate frequency signal is mixed with the second harmonic of the local oscillation signal, and the radio frequency signal generated by mixing is output after being matched and filtered by the radio frequency matching structure 7 and the radio frequency filtering structure 10. Compared with the coplanar waveguide, the microstrip line has lower transmission loss at high frequency, not only can simplify the design layout, but also can effectively reduce the size of a complex multifunctional chip. Therefore, the microstrip line is used as the transmission line of the mixing circuit, which is beneficial to further reducing the size of the chip and reducing the manufacturing cost.
Fig. 2 is a schematic structural diagram of a terahertz monolithically integrated subharmonic mixer based on a single-ended structure. Fig. 3 shows the simulation result of the frequency conversion loss of the above-mentioned mixer, and the working conditions are as follows: the radio frequency range is 210GHz to 230GHz, the local oscillator is 105GHz, and the intermediate frequency range is DC to 20 GHz. Fig. 4 is a simulation result of the isolation from the local oscillator port to the radio frequency port, where the working conditions are as follows: the radio frequency range is 210GHz to 230GHz, the local oscillator is 105GHz, and the intermediate frequency range is DC to 20 GHz. Fig. 5 is a simulation result of the isolation from the local oscillation port to the intermediate frequency port, where the working conditions are as follows: the radio frequency range is 210GHz to 230GHz, the local oscillator is 105GHz, and the intermediate frequency range is DC to 20 GHz. Fig. 6 shows the result of the isolation simulation from the rf port to the if port, under the following operating conditions: the radio frequency range is 210GHz to 230GHz, the local oscillator is 105GHz, and the intermediate frequency range is DC to 20 GHz.
The terahertz monolithic integration subharmonic mixer based on the single-ended structure has the following characteristics and innovations:
(1) the cost is low: the frequency mixer not only effectively reduces the cutoff frequency f of the prior frequency mixer to the compound semiconductor process FET/HEMTTThe requirement of (3) reduces the manufacturing cost, and also solves the requirement of expensive high-performance intrinsic vibration source;
(2) the working frequency bandwidth is wide: the mixer adopts the FET/HEMT tube with a common source structure, and when the drain electrode of the FET/HEMT tube is not biased, the drain electrode port has the characteristic of almost pure resistance in a wide bandwidth, so that radio frequency and intermediate frequency signals connected with the drain electrode of the FET/HEMT tube have flat response in a wide operating frequency band. Compared with the traditional balanced subharmonic mixer based on the FET/HEMT, the phase shift of 90 degrees or 180 degrees is realized without adopting a branch line form, and the broadband characteristic is also well realized;
(3) the conversion loss is low: compared with the traditional balanced subharmonic mixer based on the FET/HEMT, the circuit has a simple structure, a radio frequency and local oscillator signal transmission path is short, and low-loss transmission is realized;
(4) the size is small: the mixer adopts a microstrip line design, so that the layout is simplified; the second harmonic mixing of the local oscillation signal is realized by utilizing the square law characteristic of the mixing element, so that the size of a chip is reduced;
(5) the isolation is high: the frequency interval between the radio frequency signal and the local oscillator signal is large enough, and the isolation from the local oscillator to the radio frequency port is effectively improved through the radio frequency high-pass filter; the intermediate frequency filtering structure adopts a two-stage low-pass filter design, and well inhibits leakage of radio frequency signals and local oscillation signals to an intermediate frequency port.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.
Claims (6)
1. The utility model provides a terahertz is monolithic integration subharmonic mixer now based on single-ended structure which characterized in that: the circuit comprises a substrate, wherein a mixing circuit is formed on the substrate, and the mixing circuit comprises a local oscillator input port, a blocking capacitor, a bias circuit, a local oscillator matching filter structure, a mixing element, a radio frequency matching structure, a radio frequency filter structure, a radio frequency port, an intermediate frequency filter structure and an intermediate frequency port; the local oscillator input port is respectively connected with one end of a local oscillator matching filter structure and one end of a bias circuit through the output end of a blocking capacitor, the other end of the local oscillator matching filter structure is connected with a grid electrode of the frequency mixing element, and the other end of the bias circuit is connected with a Vg power-on end; the radio frequency port is respectively connected with the radio frequency matching structure and the intermediate frequency filtering structure through the radio frequency filtering structure, the other end of the radio frequency matching structure is connected with a drain electrode of the mixing element, and the other end of the intermediate frequency filtering structure is connected with the intermediate frequency port;
the frequency mixing element is a common source structure FET/HEMT tube core, when the radio frequency signal is an input signal, the frequency mixing element is mixed with the second harmonic of a local oscillation signal, and an intermediate frequency signal generated by frequency mixing is filtered by an intermediate frequency filtering structure and then is output; when the intermediate frequency signal is an input signal, the intermediate frequency signal is mixed with the second harmonic of the local oscillation signal, and the radio frequency signal generated by mixing is output after being matched and filtered by the radio frequency matching structure and the radio frequency filtering structure.
2. The terahertz monolithically integrated subharmonic mixer based on the single-ended structure of claim 1, wherein: the frequency mixing circuit is designed as a microstrip line, the local oscillator port is respectively connected with one end of a local oscillator matched filter structure and one end of a bias circuit through the output end of a blocking flat capacitor, and the bias circuit is in a structure that a high-impedance resistor is connected in series and a capacitor is connected in parallel to the ground.
3. The terahertz monolithically integrated subharmonic mixer based on the single-ended structure of claim 1, wherein: the blocking plate capacitor and the parallel capacitor adopt plate capacitors with metal-insulator-metal structures in a compound semiconductor process, and the high impedance resistor adopts a film resistor in the compound semiconductor process.
4. The terahertz monolithically integrated subharmonic mixer based on the single-ended structure of claim 1, wherein: the radio frequency filtering structure is a high-pass filter and is designed by adopting a parallel coupling line filter.
5. The terahertz monolithically integrated subharmonic mixer based on the single-ended structure of claim 1, wherein: the intermediate frequency filter structure is a two-stage low-pass filter, the first-stage filter adopts a structure that a series microstrip line is connected with an open-circuit stub in parallel, the equivalent electrical length of the series microstrip line and the open-circuit stub in parallel is one fourth of the radio frequency wavelength, and the second-stage filter adopts a structure that the series microstrip line is connected with a capacitor in parallel to the ground.
6. The single-ended structure based terahertz monolithic integration subharmonic mixer of claim 1, wherein: the frequency of the radio frequency signal is the sum of two times of the frequency of the local oscillation signal and the frequency of the intermediate frequency signal.
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