CN116208122A

CN116208122A - Low-cost compact ultra-wideband gallium nitride phase shifter

Info

Publication number: CN116208122A
Application number: CN202310371925.6A
Authority: CN
Inventors: 王向东; 张健; 李沫; 杨帆; 姜昊; 陈飞良; 刘洋
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2023-04-10
Filing date: 2023-04-10
Publication date: 2023-06-02

Abstract

The invention discloses a low-cost compact ultra-wideband gallium nitride phase shifter, which is applied to the field of single-chip microwave integrated circuits, and aims at solving the problem that the Lange bridge of the existing phase shifter is large in size; the planar spiral broadband coupling network adopts a two-stage coil coupling network formed by a primary coil and a secondary coil, so that a circuit is simplified, the planar spiral layout is formed by bending the two-stage coupling coils for many times, and the area of the coupling network is greatly reduced; the broadband phase compensation network adopts a lossless band-pass response network consisting of an inductor and a capacitor to carry out phase compensation on the planar spiral coupling network, thereby improving high-frequency response and expanding high-frequency bandwidth; compared with the traditional reflection type phase shifter of the Lange bridge coupler, the area of the reflection type phase shifter is greatly reduced, the miniaturization of the GaN phase shifter is realized, the cost is greatly reduced, and the popularization and the application of the GaN phase shifter and the multifunctional integration of the GaN MMIC are facilitated.

Description

Low-cost compact ultra-wideband gallium nitride phase shifter

Technical Field

The invention belongs to the field of monolithic microwave integrated circuit design, and particularly relates to a gallium nitride numerical control phase shifter technology.

Background

Gallium Nitride (GaN) is a third-generation semiconductor material, belongs to a wide-bandgap semiconductor, and has the remarkable characteristics of large bandgap and high breakdown field strength. The heterojunction can be formed by utilizing the special piezoelectric polarization effect and the spontaneous polarization effect, so that the two-dimensional electron gas with high electron mobility is formed. Therefore, the gallium nitride high electron mobility transistor (High Electron Mobility Transistor, HEMT) manufactured by adopting the principle can realize high power output in a microwave frequency band, researchers develop a lot of work around the huge advantages of the GaN HEMT in terms of power characteristics, and a GaN microwave power amplifier is greatly developed. Along with the progress of technology and the continuous improvement of the integration level requirement of a microwave system, the research on microwave gallium nitride starts to develop towards the multifunctional integration direction, including low noise amplification, switching, numerical control attenuation, numerical control shift and the like, and the high-integration level chip belongs to a monolithic microwave integrated circuit (Monolithic Microwave Integrated Circuit, MMIC). Despite the rapid development of gallium nitride technology over a decade, silicon carbide substrates and heteroepitaxy are still expensive, and the current mainstream mature process still uses 4 inch wafers, resulting in chip cost per unit area of more than ten times that of gallium arsenide, which cost disadvantage will be further pronounced in multi-array element phased array systems. It can be said that the high cost is one of the main reasons for limiting the popularization and application of GaN MMICs. Therefore, the development of low-cost gallium nitride MMIC research has practical engineering significance.

The gallium nitride material cost and the process cost cannot be reduced in a short time, so that the method for reducing the chip cost from the design level is to improve the circuit design and the layout design and reduce the chip area. In the above gallium nitride MMICs, the phase shifter is limited to the wavelength of the electromagnetic wave signal, and often occupies a very large area, and the lower the frequency is, the larger the area is. The circuit with small phase shift (not more than 45 DEG) can realize broadband phase shift by adopting a high-low pass structure, and the area is smaller. However, in order to realize the broadband function, a circuit with a large phase shift (phase shift is not less than 45 °) generally adopts a reflective structure, and the topology structure of the circuit is shown in fig. 1. The radio frequency input signal RFIN and the output signal RFOUT are respectively connected with an a port and an isolation port b port of the Lange bridge, and a coupling port C port is sequentially connected with a switch transistor SW1, a capacitor C1 and ground to form a reflection branch 1; the direct-current end d is sequentially connected with the switching transistor SW2, the capacitor C2 and the ground to form a reflection branch 2; the switching transistors SW1 and SW2 are simultaneously turned on or simultaneously turned off by the same control signal VC. When the switching transistors SW1 and SW2 are in the on state, the switching transistors may be equivalent to one resistors Ron1 and Ron2, as shown in fig. 2; when the switching transistors SW1 and SW2 are in the off state, the switching transistors can be equivalent to one capacitance Coff1 and Coff2 as shown in fig. 3. Switching the state of the switching transistor can change the signal path of the reflecting branch and the capacitances Coff1 and Coff2 can significantly change the phase of the microwave signal. Ron1 and Coff1, ron2 and Coff2 are determined by the switch transistor specifications and their bias, and phase change can be achieved by designing appropriate switch transistors and capacitors. In a reflective phase shifting network, lange bridges function to isolate incident and reflected waves by coil coupling, the length of which corresponds to a quarter wavelength lambda/4 of an electromagnetic wave in a medium. The Lange bridge has wider bandwidth and good microwave matching property, simplifies the design of a reflection branch, and is a main stream structure of the current broadband phase shifter. In this structure, the Lange bridge occupies most of the area

The disadvantage of this construction is the large size of the Lange bridge. The length of the Lange bridge is almost equivalent to a quarter wavelength lambda/4 of the electromagnetic wave in the medium. Taking a silicon carbide substrate GaN process with a thickness of 100 μm as an example, FIG. 4 shows a logarithmic curve of lambda/4 length versus frequency Freq. As can be seen from fig. 4, lambda/4 increases exponentially as the frequency decreases. Lange bridge lengths are already greater than 1mm below 30 GHz; while in the lower C band its length is even greater than 5mm. The Lange bridge occupies a large area, which is unfavorable for developing the ultra-wideband GaN phase shifter with low cost.

Disclosure of Invention

In order to solve the technical problems, the invention provides a low-cost compact ultra-wideband gallium nitride phase shifter, which is based on a reflection type phase shifting principle, adopts a two-stage coil broadband coupling circuit with planar spiral layout, and uses a broadband phase compensation circuit to compensate phase shift caused by spiral bending and mutual inductance, has compact circuit layout, remarkably reduces the area compared with the traditional phase shifter based on Lange bridges, remarkably reduces the chip cost, and is easy to be further monolithically integrated with circuits such as a GaN low-noise amplifier, a GaN power amplifier, a GaN switch and the like.

The invention adopts the technical scheme that: a low cost compact ultra wideband gallium nitride phase shifter comprising: the device comprises a planar spiral broadband coupling network, two broadband phase compensation networks and two reflection branches; the two broadband phase compensation networks are respectively marked as a first broadband phase compensation network and a second broadband phase compensation network; the two reflection branches are respectively marked as a first reflection branch and a second reflection branch;

the planar spiral broadband coupling network comprises four sections of coupling lines, the length of each section of coupling line is one eighth wavelength, the four sections of coupling lines are all in a planar spiral shape, and the four sections of coupling lines are respectively marked as: m1, M2, M3 and M4, M1 and M2 are primary coils, and M3 and M4 are secondary coils; m1 and M3 are coupled to each other, and M2 and M4 are coupled to each other; the first ends of M1, M2, M3 and M4 are near the respective plane spiral centers, the first end of M1 is connected with the first end of M2, and the first end of M3 is connected with the first end of M4;

the second end of M1 is used as an input port, and the second end of M4 is used as an output port;

the second end of the M3 is connected with the first end of the first broadband phase compensation network, the midpoint of the connection between the first end of the M3 and the first end of the M4 is connected with the second end of the first broadband phase compensation network, and the third end of the first broadband phase compensation network is connected with the first reflection branch;

the second end of the M2 is connected with the first end of the second broadband phase compensation network, the midpoint of the first end of the M1 connected with the first end of the M2 is connected with the second end of the second broadband phase compensation network, and the third end of the second broadband phase compensation network is connected with the second reflection branch.

The invention is developed based on gallium nitride monolithic microwave integrated circuit technology, and utilizes a metal layer with the thickness of 5um in the technology as a coupling line, so that the coupling strength is improved, and meanwhile, the insertion loss of the coupling line can be reduced. And the metal overlapped bridging part is realized in an air bridge mode through surface metal, so that parasitic coupling is reduced, and an additional bonding wire is not required to be introduced.

The invention has the beneficial effects that: the novel planar spiral broadband coupling network adopted by the invention greatly reduces the area compared with a Lange bridge coupler by bending parallel coupling lines, and carries out phase compensation on non-ideal parasitic effects introduced by a bending spiral structure through a lossless broadband phase compensation network consisting of an inductor and a capacitor, so that the compact layout of a phase shifting circuit is realized, the GaN phase shifter can be miniaturized, the cost is greatly reduced, and the popularization and the application of the GaN phase shifter and the further GaN MMIC multifunctional integration are facilitated.

The structure of the invention has the following advantages:

(1) The invention is based on gallium nitride monolithic microwave integrated circuit technology, the metal thickness of the coupling line is thicker than that of the conventional technology, lower loss and higher coupling strength can be realized, the air bridge technology is adopted at the metal overlapping bridging position to reduce parasitic coupling, no extra bonding wire is required to be introduced, and the consistency is good;

(2) The invention adopts a two-stage coil coupling network composed of the primary coil and the secondary coil, reduces the number of half coupling lines compared with the traditional Lange bridge composed of five-stage coils, and simplifies the circuit;

(3) In the layout, the two-stage coupling coils form a planar spiral layout through repeated bending, so that the length of a quarter wavelength line in the transmission direction is compressed, and the coupling network area is greatly reduced;

(4) The invention adopts a lossless band-pass response network composed of an inductor and a capacitor to carry out phase compensation on the planar spiral coupling network, improves high-frequency response, expands phase high-frequency bandwidth and avoids area compression at the cost of bandwidth;

(5) The planar spiral coupling network provided by the invention has broadband characteristics in combination with the phase compensation network, is compact in structure, greatly reduces the area of the phase shifting circuit, and is beneficial to reducing the MMIC cost of the GaN phase shifter and further integrating the GaN MMIC.

Drawings

FIG. 1 is a schematic diagram of a conventional reflection type phase shifting network topology;

FIG. 2 is an equivalent circuit of a reflection branch when the switching transistor is turned on;

FIG. 3 is an equivalent circuit of a reflection branch when the switching transistor is turned off;

FIG. 4 is a graph showing lambda/4 length in a GaN process for a silicon carbide substrate having a thickness of 100 μm;

FIG. 5 is a schematic diagram of a compact ultra wideband GaN phase shifter circuit of the invention;

FIG. 6 is a schematic diagram of a planar spiral broadband coupling network layout of the present invention;

FIG. 7 is an example layout of a low cost compact ultra wideband GaN 90 phase shifter employing the present invention;

FIG. 8 is an example layout of a GaN 90 DEG phase shifter using a conventional structure;

FIG. 9 is a graph showing the effect of a wideband phase compensation network on a planar spiral wideband coupling network according to an embodiment of the present invention;

FIG. 10 is a graph of the amount of phase shift of a low cost compact ultra wideband GaN 90 phase shifter employing the present invention;

FIG. 11 is a graph of amplitude modulation for a low cost compact ultra-wideband GaN 90 phase shifter employing the present invention;

fig. 12 is a graph of insertion loss and return loss for a low cost compact ultra-wideband GaN 90 ° phase shifter embodying the present invention.

Detailed Description

The present invention will be further explained below with reference to the drawings in order to facilitate understanding of technical contents of the present invention to those skilled in the art.

The invention adopts the circuit schematic diagram of the compact ultra-wideband GaN phase shifter shown in fig. 5 and the planar spiral broadband coupling network layout shown in fig. 6 to realize miniaturization and low cost of the MMIC of the ultra-wideband GaN phase shifter, and is beneficial to further multifunctional integration of the GaN MMIC.

The planar spiral broadband coupling network consists of four sections of coupling lines M1, M2, M3 and M4, wherein M1 and M2 are primary coils, and M3 and M4 are secondary coils. Each segment of coupled line has a length of one eighth wavelength lambda/8. As can be seen from fig. 6, the area occupied by the planar spiral broadband coupling coil is primarily determined by the coupling line width and spacing. To reduce the area, the smallest possible coupling line width and pitch should be used. The minimum coupling line width and minimum spacing allowed under different manufacturing process conditions are different. The larger width of the coupled line has lower insertion loss but can deteriorate the return loss of the port, so the proper width of the coupled line should be selected in balance. The smaller the coupling line spacing is, the higher the coupling strength is, and the better the amplitude balance is, so the narrowest coupling line spacing is adopted under the condition allowed by the manufacturing process. Based on the above requirements, after the width and the distance of the coupling lines are determined, the primary coil and the secondary coil synchronously spiral from the inner side to the outer side of the coil, and the spiral is ended when the length reaches the eighth wavelength lambda/8, and the number of spiral turns is optimal. M1 and M3 are coupled to each other, M2 and M4 are coupled to each other, an input signal is input from an a port, and an output signal is output from an isolation terminal b port. M1 and M2 are directly interconnected, and the midpoint is f; m3 and M4 are directly interconnected, and the midpoint is e. The coupling network adopts two-stage coil coupling lines, so that the number of the coupling lines is reduced by half compared with the traditional Lange bridge structure formed by five-stage coils, and the circuit is simplified. The two-stage coupling lines are bent for many times to form a spiral layout, so that the length of the quarter-wavelength line in the transmission direction is compressed.

The bent right angles form extra parasitic capacitance, and extra mutual inductance is introduced between the coupling lines distributed in multiple layers, which can cause deterioration of the coupling phase in a high frequency band. The broadband phase compensation network consists of a lossless element capacitor and an inductor, belongs to a band-pass response network, and can compensate phase distortion of a planar spiral broadband coupling network in a high frequency band by selecting a proper device, and expands the high frequency bandwidth.

The broadband phase compensation network 1 is composed of a transmission line TL1, capacitors C1b, C1C, cx, and the broadband phase compensation network 2 is composed of a transmission line TL2, capacitors C2b, C2C, cy. One end of the capacitor Cy is connected with f, and the other end of the capacitor Cy is connected with ground; one end of the capacitor Cx is connected to e, and the other end is connected to ground. The port of the coupling end C is connected with one end of a capacitor C1C, the other end of the capacitor C1C is simultaneously connected with one end of a capacitor C1b and one end of a transmission line TL1, the other end of the capacitor C1b is connected with the ground, the other end of the TL1 is connected with a drain electrode D1 of a switching transistor SW1, a source electrode S1 of the switching transistor SW1 is connected with one end of a capacitor C1a, and the other end of the capacitor C1a is connected with the ground. The port of the direct end D is connected with one end of a capacitor C2C, the other end of the capacitor C2C is simultaneously connected with one end of a capacitor C2b and one end of a transmission line TL2, the other end of the capacitor C2b is connected with the ground, the other end of the TL2 is connected with a drain electrode D2 of a switching transistor SW2, a source electrode S2 of the switching transistor SW2 is connected with one end of a capacitor C2a, and the other end of the capacitor C2a is connected with the ground. The gate G1 of the switching transistor SW1 is connected to the control signal VC simultaneously with the gate G2 of the switching transistor SW 2.

The reflection branch 1 is composed of a switching transistor SW1 and a capacitor C1a, and the reflection branch 2 is composed of a switching transistor SW2 and a capacitor C2 a. The reflective branch structure is similar to a conventional Lange bridge phase shifter.

The structure and the device parameters of the two broadband phase compensation networks are the same, and the structure and the device parameters of the two reflection branches are the same. It is worth noting in particular that the capacitances Cx, cy in the broadband phase compensation network of the present invention have one end connected to ground. The capacitance of the two capacitors is usually smaller, so that the same function can be realized by adopting an open branch node line.

Compared with the traditional reflection type phase shifter based on the Lange bridge, the invention greatly compresses the chip area, obviously reduces the chip cost, and simultaneously maintains the ultra-wideband response characteristic same as that of the Lange bridge.

Aiming at MMIC application of the ultra wideband GaN phase shifter with low cost, the invention designs an ultra wideband 90 DEG phase shifter chip with a working frequency band covering a C-K wave band based on a 0.25 mu m GaN HEMT technology by adopting a compact ultra wideband GaN phase shifter circuit schematic diagram shown in figure 5 and a planar spiral broadband coupling network layout shown in figure 6, wherein the specific working frequency band is 5.5GHz-22GHz, the relative bandwidth reaches 120%, and the chip layout is shown in figure 7, and the chip size is only 0.85mm multiplied by 0.90mm. Fig. 8 is a layout of an example of a GaN 90 ° phase shifter using a conventional structure, with a chip size of 0.95mm×3.25mm. The invention can reduce the area and the cost to one fourth of the traditional structure.

Fig. 9 shows the phase compensation effect of the wideband phase compensation network of the present invention on a planar spiral wideband coupling network, where the horizontal axis is frequency freq and the vertical axis is the coupling network phase difference DeltaPhase. The phase difference of the coupling network before compensation continuously deviates by 90 degrees along with the increase of the frequency from 5 GHz; and after phase compensation, the frequency range of 3GHz-22GHz can be kept around 90 degrees.

FIG. 10 is a graph of the phase shift of a low cost compact ultra-wideband GaN 90 phase shifter according to the present invention, wherein the horizontal axis is frequency freq and the vertical axis is phase shift Phaseshift;

FIG. 11 is a graph of the amplitude modulation of a low cost compact ultra-wideband GaN 90 phase shifter using the present invention, with the frequency freq on the horizontal axis and the amplitude modulation DeltaMag on the vertical axis;

fig. 12 is a graph of insertion loss and return loss for a low cost compact ultra-wideband GaN 90 ° phase shifter employing the present invention, where the horizontal axis is frequency freq and the vertical axis is insertion loss IL and return loss RL.

As can be seen from fig. 10 to fig. 12, the phase shifter chip of the present invention realizes phase shifting of 90 ° ± 3 ° in the frequency (Freq) range of 5.5GHz-22GHz, insertion loss is less than 3dB, amplitude modulation is less than 1.1dB, return loss is less than-10 dB, and satisfies ultra-wideband application.

The invention discloses a low-cost compact ultra-wideband gallium nitride phase shifter, which adopts a reflective phase shifting circuit architecture, creatively adopts a novel planar spiral broadband coupling network and a broadband phase compensation network, and realizes compact layout of a phase shifting circuit. The planar spiral broadband coupling network adopts a two-stage coil coupling network formed by a primary coil and a secondary coil, so that a circuit is simplified, the planar spiral layout is formed by bending the two-stage coupling coils for many times, and the area of the coupling network is greatly reduced. The broadband phase compensation network adopts a lossless band-pass response network consisting of an inductor and a capacitor to carry out phase compensation on the planar spiral coupling network, thereby improving high-frequency response and expanding high-frequency bandwidth. Compared with the traditional reflection type phase shifter based on the Lange bridge coupler, the phase shifter provided by the invention has the advantages that the area is greatly reduced, the miniaturization of the GaN phase shifter is realized, the cost is greatly reduced, and the popularization and the application of the GaN phase shifter and the further multifunctional integration of the GaN MMIC are facilitated.

Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present invention and should be understood that the scope of the invention is not limited to such specific statements and embodiments. Various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A low cost compact ultra wideband gallium nitride phase shifter, comprising: the device comprises a planar spiral broadband coupling network, two broadband phase compensation networks and two reflection branches; the two broadband phase compensation networks are respectively marked as a first broadband phase compensation network and a second broadband phase compensation network; the two reflection branches are respectively marked as a first reflection branch and a second reflection branch;

2. A low cost compact ultra wideband gallium nitride phase shifter according to claim 1, wherein the two wideband phase compensation networks are identical in structure and device parameters.

3. A low cost compact ultra wideband gallium nitride phase shifter according to claim 2, wherein the first wideband phase compensation network comprises: a transmission line TL1, a capacitor C1b, a capacitor C1C, a capacitor Cx; the first end of the capacitor C1C is used as the first end of the first broadband phase compensation network, the second end of the capacitor C1C is connected with the first end of the capacitor C1b, the second end of the capacitor C1b is grounded, the second end of the capacitor C1C is also connected with the first end of the transmission line TL1, the second end of the transmission line TL1 is used as the third end of the first broadband phase compensation network, the first end of the capacitor Cx is used as the second end of the first broadband phase compensation network, and the second end of the capacitor Cx is grounded;

the second wideband phase compensation network includes: transmission line TL2, capacitor C2b, capacitor C2C, capacitor Cy; the first end of the capacitor C2C is used as the first end of the second broadband phase compensation network, the second end of the capacitor C2C is connected with the first end of the capacitor C2b, the second end of the capacitor C2b is grounded, the second end of the capacitor C2C is also connected with the first end of the transmission line TL2, the second end of the transmission line TL2 is used as the third end of the second broadband phase compensation network, the first end of the capacitor Cy is used as the second end of the second broadband phase compensation network, and the second end of the capacitor Cy is grounded.

4. A low cost compact ultra wideband gallium nitride phase shifter according to claim 3, wherein the capacitances Cx, cy are replaced by open branch lines, respectively.

5. A low cost compact ultra wideband gallium nitride phase shifter according to any of claims 2-4, wherein the two reflective legs have identical structure and device parameters.

6. The low cost compact ultra wideband gallium nitride phase shifter of claim 5, wherein the first reflective branch comprises: the drain electrode of the switching transistor SW1 is connected with the third end of the first broadband phase compensation network, the source electrode of the switching transistor SW1 is connected with the first end of the capacitor C1a, and the second end of the capacitor C1a is grounded;

the second reflection branch includes: the drain electrode of the switching transistor SW2 is connected with the third end of the second broadband phase compensation network, the source electrode of the switching transistor SW2 is connected with the first end of the capacitor C2a, and the second end of the capacitor C2a is grounded;

the gate of the switching transistor SW1 and the gate of the switching transistor SW2 are simultaneously connected to the control signal VC.