A Compact Ultra-Wideband Gallium Nitride Phase Shifter

Abstract

The present invention discloses a low-cost compact ultra-wideband gallium nitride phase shifter, which is applied to the field of monolithic microwave integrated circuits. Aiming at the problem of the large size of the existing Lange bridge in phase shifters, the present invention adopts a planar spiral broadband coupling network and a broadband phase compensation network to achieve a compact layout of the phase shift circuit; the planar spiral broadband coupling network adopts a two-stage coil coupling network composed of a primary coil and a secondary coil, simplifies the circuit, and forms a planar spiral layout by bending the two-stage coupling coils multiple times, significantly reducing the area of the coupling network; the broadband phase compensation network uses a lossless bandpass response network composed of inductors and capacitors to compensate the phase of the planar spiral coupling network, improves the high-frequency response, and expands the high-frequency bandwidth; compared with the traditional reflection-type phase shifter of the Lange bridge coupler, the area is significantly reduced, the miniaturization of the GaN phase shifter is achieved, the cost is greatly reduced, which is beneficial to the popularization and application of GaN phase shifters and the multi-functional integration of GaN MMICs.

Description

Technical Field

[0001] The present invention belongs to the field of monolithic microwave integrated circuit design, and particularly relates to a gallium nitride numerically controlled phase shifter technology. Background Art

[0002] Gallium nitride (GaN) is a third-generation semiconductor material belonging to wide-bandgap semiconductors, featuring a large bandgap width and a high breakdown field strength. By utilizing its unique piezoelectric polarization effect and spontaneous polarization effect, a heterojunction can be formed, thereby forming a two-dimensional electron gas with a high electron mobility. Therefore, a gallium nitride high electron mobility transistor (HEMT) manufactured based on this principle can achieve high-power output in the microwave frequency band. Researchers have carried out a large amount of work on the huge advantages of GaN HEMT in terms of power characteristics, and GaN microwave power amplifiers have been greatly developed. With the progress of the process and the continuous increase in the demand for integration in microwave systems, the research on microwave gallium nitride has started to develop towards the direction of multi-functional integration, including low-noise amplification, switching, numerically controlled attenuation, numerically controlled phase shifting, etc. Such highly integrated chips belong to monolithic microwave integrated circuits (MMICs). Although gallium nitride technology has developed rapidly in the past decade, the prices of silicon carbide substrates and heterojunction epitaxy are still high, and currently, the mainstream mature process still uses 4-inch wafers, resulting in the chip cost per unit area being more than ten times that of gallium arsenide. In a phased array system with multiple elements, this cost disadvantage will be further highlighted. It can be said that the high cost is one of the main reasons restricting the popularization and application of GaN MMICs. Therefore, conducting research on low-cost gallium nitride MMICs has practical engineering significance.

[0003] The material cost and process cost of gallium nitride cannot be reduced in a short time. Therefore, the method to reduce the chip cost from the design level is to improve the circuit design and layout design to reduce the chip area. Among the above-mentioned several gallium nitride MMICs, the phase shifter is limited by the wavelength of the electromagnetic wave signal and often occupies a large area. The lower the frequency, the larger the area. A small phase shift amount (not exceeding 45°) circuit can usually achieve broadband phase shift by adopting a high-low pass type structure and has a relatively small area. However, for a large phase shift amount (phase shift amount not less than 45°) circuit to achieve broadband function, a reflection type structure is generally adopted, and its topological structure is as Figure 1As shown. The radio frequency input signal RFIN and the output signal RFOUT are respectively connected to the a port and the isolation end b port of the Lange bridge. The coupling end c port is successively connected to the switching transistor SW1, the capacitor C1 and the ground to form a reflection branch 1; the through end d is successively connected to 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 off through the same control signal VC. When the switching transistors SW1 and SW2 are in the on state, the switching transistors can be equivalent to a resistor Ron1 and Ron2, as Figure 2 shown; when the switching transistors SW1 and SW2 are in the off state, the switching transistors can be equivalent to a capacitor Coff1 and Coff2, as Figure 3 shown. Switching the state of the switching transistors can change the signal path of the reflection branch, and the capacitors Coff1 and Coff2 can significantly change the phase of the microwave signal. Ron1 and Coff1, Ron2 and Coff2 are determined by the switching transistor specifications and their biases. By designing appropriate switching transistors and capacitors, the phase change can be achieved. In the reflective phase shift network, the role of the Lange bridge is to isolate the incident wave and the reflected wave through coil coupling, and its length is equivalent to one-quarter wavelength λ / 4 of the electromagnetic wave in the medium. The Lange bridge itself has a relatively wide bandwidth and good microwave matching characteristics, which simplifies the design of the reflection branch and is the mainstream structure of the current broadband phase shifter. In this structure, the Lange bridge occupies most of the area

[0004] The disadvantage of this structure is that the Lange bridge is large in size. The length of the Lange bridge is almost equivalent to one-quarter wavelength λ / 4 of the electromagnetic wave in the medium. Taking the GaN process with a 100-μm-thick silicon carbide substrate as an example, Figure 4 gives the logarithmic curve of the λ / 4 length versus the frequency Freq. From Figure 4 it can be seen that as the frequency decreases, the λ / 4 increases exponentially. Below 30 GHz, the length of the Lange bridge is already greater than 1 mm; in the lower C band, its length is even greater than 5 mm. The Lange bridge occupies a very large area, which is not conducive to the development of low-cost ultra-wideband GaN phase shifters. Summary of the Invention

[0005] To solve the above technical problems, the present invention proposes a compact ultra-wideband gallium nitride phase shifter, which is based on the reflective phase shift principle, adopts a two-stage coil broadband coupling circuit with a planar spiral layout, and compensates for the phase shift caused by spiral bending and mutual inductance with a broadband phase compensation circuit. The circuit layout is compact, and compared with the traditional phase shifter based on the Lange bridge, the area is significantly reduced, the chip cost is significantly reduced, and it is easy to be further monolithically integrated with circuits such as GaN low-noise amplifiers, GaN power amplifiers, and GaN switches.

[0006] The technical solution adopted by the present invention is as follows: a compact ultra-wideband gallium nitride phase shifter, comprising: a planar spiral broadband coupling network, two broadband phase compensation networks, and two reflection branches; the two broadband phase compensation networks are respectively denoted as the first broadband phase compensation network and the second broadband phase compensation network; the two reflection branches are respectively denoted as the first reflection branch and the second reflection branch;

[0007] The planar spiral broadband coupling network includes four sections of coupling lines, each section of coupling line having a length of one-eighth wavelength, and the four sections of coupling lines are all in a planar spiral shape. The four sections of coupling lines are respectively denoted 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 the ends close to their respective planar spiral centers. The first end of M1 is connected to the first end of M2, and the first end of M3 is connected to the first end of M4;

[0008] The second end of M1 serves as the input port, and the second end of M4 serves as the output port;

[0009] The second end of M3 is connected to the first end of the first broadband phase compensation network. The midpoint of the connection between the first end of M3 and the first end of M4 is connected to the second end of the first broadband phase compensation network. The third end of the first broadband phase compensation network is connected to the first reflection branch;

[0010] The second end of M2 is connected to the first end of the second broadband phase compensation network. The midpoint of the connection between the first end of M1 and the first end of M2 is connected to the second end of the second broadband phase compensation network. The third end of the second broadband phase compensation network is connected to the second reflection branch.

[0011] The present invention is developed based on the gallium nitride monolithic microwave integrated circuit process. The metal layer with a thickness of 5 μm in this process is used as the coupling line, which can improve the coupling strength while reducing the insertion loss of the coupling line. And the metal overlapping and bridging are realized in the form of an air bridge through the surface metal, reducing the parasitic coupling without the need to introduce additional bonding wires.

[0012] The beneficial effects of the present invention: The novel planar spiral broadband coupling network adopted by the present invention greatly reduces the area compared with the Lange bridge coupler by bending the parallel coupling lines, and the non-ideal parasitic effects introduced by the bent spiral structure are phase-compensated by the lossless broadband phase compensation network composed of inductors and capacitors, realizing a compact layout of the phase-shifting circuit. Furthermore, it can miniaturize the GaN phase shifter, greatly reduce the cost, and is conducive to the popularization and application of the GaN phase shifter and the further multi-functional integration of GaN MMIC.

[0013] The structure of the present invention has the following advantages:

[0014] (1) The present invention is based on the gallium nitride monolithic microwave integrated circuit process. The thickness of the coupled line metal is thicker than that of the conventional process, which can achieve lower loss and higher coupling strength. The air bridge process is adopted at the metal overlapping and bridging part to reduce the parasitic coupling, without the need to introduce additional bonding wires, and the consistency is good;

[0015] (2) The present invention adopts a two-stage coil coupling network composed of a primary coil and a secondary coil, which reduces the number of coupled lines by half compared with the traditional Lange bridge composed of five-stage coils, simplifying the circuit;

[0016] (3) In the layout of the present invention, the two-stage coupled coils form a planar spiral layout through multiple bends, compressing the length of the quarter-wavelength line in the transmission direction, and greatly reducing the area of the coupling network;

[0017] (4) The present invention uses a lossless band-pass response network composed of inductors and capacitors to perform phase compensation on the planar spiral coupling network, improving the high-frequency response, expanding the phase high-frequency bandwidth, and avoiding sacrificing bandwidth for area compression;

[0018] (5) The planar spiral coupling network of the present invention combined with the phase compensation network exhibits broadband characteristics, with a compact structure, greatly reducing the area of the phase shifter circuit, which is beneficial to reducing the cost of the GaN phase shifter MMIC and further multi-functional integration of the GaN MMIC. Description of the Drawings

[0019] Figure 1 is the topology circuit of the traditional reflection-type phase shifter network;

[0020] Figure 2 is the equivalent circuit of the reflection branch when the switching transistor is turned on;

[0021] Figure 3 is the equivalent circuit of the reflection branch when the switching transistor is turned off;

[0022] Figure 4 is the λ / 4 length in the GaN process with a 100μm thick silicon carbide substrate;

[0023] Figure 5 is the circuit schematic diagram of the compact ultra-wideband GaN phase shifter of the present invention;

[0024] Figure 6 is the layout schematic diagram of the planar spiral broadband coupling network of the present invention;

[0025] Figure 7 is the layout of an example of a compact ultra-wideband GaN 90° phase shifter applying the present invention;

[0026] Figure 8 is the layout of an example of a GaN 90° phase shifter adopting a traditional structure;

[0027] Figure 9 This is the effect curve of the phase compensation of the broadband phase compensation network for the planar spiral broadband coupling network in the present invention;

[0028] Figure 10 This is the phase shift curve of a compact ultra-wideband GaN 90° phase shifter applying the present invention;

[0029] Figure 11 This is the amplitude modulation curve of a compact ultra-wideband GaN 90° phase shifter applying the present invention;

[0030] Figure 12 This is the insertion loss and return loss curve of a compact ultra-wideband GaN 90° phase shifter applying the present invention. Detailed implementation manners

[0031] To facilitate those skilled in the art to understand the technical content of the present invention, the content of the present invention will be further explained below with reference to the accompanying drawings.

[0032] The present invention adopts the circuit schematic diagram of the compact ultra-wideband GaN phase shifter as shown in Figure 5 and the layout of the planar spiral broadband coupling network as shown in Figure 6 to realize the miniaturization and low cost of the ultra-wideband GaN phase shifter MMIC, and is beneficial to the further multi-functional integration of the GaN MMIC.

[0033] The planar spiral broadband coupling network is composed of four sections of coupling lines M1, M2, M3, and M4. M1 and M2 are the primary coils, and M3 and M4 are the secondary coils. The length of each section of the coupling line is one-eighth wavelength λ / 8. Starting from Figure 6It can be seen that the area occupied by the planar spiral broadband coupled coil is mainly determined by the width and spacing of the coupled lines. To reduce the area, as narrow a coupled line width and spacing as possible should be adopted. Under different processing and manufacturing process conditions, the allowable minimum coupled line width and minimum spacing are different. Coupled lines with a larger width have lower insertion loss, but will deteriorate the port return loss, so a suitable coupled line width should be selected as a compromise. The smaller the coupled line spacing, the higher the coupling strength and the better the amplitude balance. Therefore, the narrowest coupled line spacing should be adopted under the conditions allowed by the manufacturing process. Based on the above requirements, after determining the coupled line width and spacing, the primary coil and the secondary coil are spirally wound synchronously from the inner side to the outer side of the coil, and the spiral ends when the length reaches one-eighth of the wavelength λ / 8. At this time, the number of spiral turns is the optimal. M1 and M3 are coupled to each other, M2 and M4 are coupled to each other. The input signal is input from port a, and the output signal is output from the isolation port b. M1 and M2 are directly interconnected, and the midpoint is f; M3 and M4 are directly interconnected, and the midpoint is e. The coupled network uses two-stage coil coupled lines, reducing the number of coupled lines by half compared with the traditional Lange bridge structure composed of five-stage coils, simplifying the circuit. The two-stage coupled lines form a spiral layout through multiple bends, compressing the length of the quarter-wavelength line in the transmission direction.

[0034] The right angle of the bend will form additional parasitic capacitance, and additional mutual inductance will be introduced between the coupled lines distributed in multiple layers. These will all lead to the deterioration of the coupling phase in the high-frequency band. The present invention corrects the phase through a broadband phase compensation network. The broadband phase compensation network of the present invention is composed of lossless components, capacitors and inductors, and belongs to a band-pass response network. Selecting appropriate devices can compensate for the phase distortion of the planar spiral broadband coupled network in the high-frequency band and expand the high-frequency bandwidth.

[0035] The broadband phase compensation network 1 is composed of a transmission line TL1, capacitors C1b, C1c, and Cx. The broadband phase compensation network 2 is composed of a transmission line TL2, capacitors C2b, C2c, and Cy. One end of the capacitor Cy is connected to f, and the other end is connected to the ground; one end of the capacitor Cx is connected to e, and the other end is connected to the ground. The coupled port c is connected to one end of the capacitor C1c. The other end of C1c is simultaneously connected to one end of the capacitor C1b and one end of the transmission line TL1. The other end of C1b is connected to the ground. The other end of TL1 is connected to the drain D1 of the switching transistor SW1. The source S1 of the switching transistor SW1 is connected to one end of the capacitor C1a. The other end of C1a is connected to the ground. The through port d is connected to one end of the capacitor C2c. The other end of C2c is simultaneously connected to one end of the capacitor C2b and one end of the transmission line TL2. The other end of C2b is connected to the ground. The other end of TL2 is connected to the drain D2 of the switching transistor SW2. The source S2 of the switching transistor SW2 is connected to one end of the capacitor C2a. The other end of C2a is connected to the ground. The gates G1 of the switching transistors SW1 and G2 of the switching transistor SW2 are simultaneously connected to the control signal VC.

[0036] The reflection branch 1 consists of a switching transistor SW1 and a capacitor C1a, and the reflection branch 2 consists of a switching transistor SW2 and a capacitor C2a. The structure of the reflection branch is similar to that of a traditional Lange bridge phase shifter.

[0037] The structures and device parameters of the two broadband phase compensation networks are the same, and the structures and device parameters of the two reflection branches are the same. It is particularly worth noting that one end of the capacitors Cx and Cy in the broadband phase compensation network of the present invention is connected to the ground. The capacitances of these two capacitors are usually relatively small, so the same function can also be achieved by using open stub lines.

[0038] Compared with the traditional reflection-type phase shifter based on the Lange bridge, the present invention significantly compresses the chip area, significantly reduces the chip cost, and at the same time maintains the same ultra-wideband response characteristics as the Lange bridge.

[0039] For low-cost, ultra-wideband GaN phase shifter MMIC applications, the present invention adopts the compact ultra-wideband GaN phase shifter circuit schematic diagram as shown in Figure 5 and the planar spiral broadband coupling network layout as shown in Figure 6 Based on the 0.25μm GaN HEMT process, an ultra-wideband 90° phase shifter chip with a working frequency band covering the C-K band is designed. The specific working frequency band is 5.5GHz - 22GHz, and the relative bandwidth reaches 120%. The chip layout is as shown in Figure 7 The chip size is only 0.85mm × 0.90mm. Figure 8 The layout of an example of a GaN 90° phase shifter with a traditional structure is shown. The chip size reaches 0.95mm × 3.25mm. The present invention can reduce the area and cost to one-fourth of the traditional structure.

[0040] Figure 9 The phase compensation effect of the broadband phase compensation network on the planar spiral broadband coupling network in the present invention is given. The horizontal axis is the frequency freq, and the vertical axis is the phase difference DeltaPhase of the coupling network. Before compensation, the phase difference of the coupling network starts to deviate from 90° continuously as the frequency increases from 5GHz; after phase compensation, it can be maintained near 90° in the frequency range of 3GHz - 22GHz.

[0041] Figure 10 The phase shift curve of a low-cost compact ultra-wideband GaN 90° phase shifter applying the present invention is shown. The horizontal axis is the frequency freq, and the vertical axis is the phase shift Phaseshift;

[0042] Figure 11 The amplitude modulation curve of a low-cost compact ultra-wideband GaN 90° phase shifter applying the present invention is shown. The horizontal axis is the frequency freq, and the vertical axis is the amplitude modulation DeltaMag;

[0043] Figure 12 Insertion loss and return loss curves of a low-cost compact ultra-wideband GaN 90° phase shifter applying the present invention, where the horizontal axis is the frequency freq and the vertical axis is the insertion loss IL and the return loss RL.

[0044] From Figures 10 - 12 It can be seen that within the frequency (Freq) range of 5.5 GHz - 22 GHz, the phase shifter chip of the present invention achieves a phase shift of 90° ± 3°, with an insertion loss less than 3 dB, an amplitude modulation less than 1.1 dB, and a return loss less than -10 dB, meeting the requirements of ultra-wideband applications.

[0045] The present invention discloses a compact ultra-wideband gallium nitride phase shifter, which adopts a reflective phase shift circuit architecture and innovatively uses a novel planar spiral broadband coupling network and a broadband phase compensation network to achieve a compact layout of the phase shift circuit. The planar spiral broadband coupling network adopts a two-stage coil coupling network composed of a primary coil and a secondary coil, simplifies the circuit, and forms a planar spiral layout by bending the two-stage coupling coils multiple times, significantly reducing the area of the coupling network. The broadband phase compensation network uses a lossless bandpass response network composed of inductors and capacitors to perform phase compensation on the planar spiral coupling network, improves the high-frequency response, and expands the high-frequency bandwidth. Compared with the traditional reflective phase shifter based on the Lange bridge coupler, the area of the phase shifter of the present invention is significantly reduced, thereby realizing the miniaturization of the GaN phase shifter, greatly reducing the cost, and being conducive to the popularization and application of the GaN phase shifter and further GaN MMIC multi-functional integration.

[0046] Those of ordinary skill in the art will realize that the embodiments described herein are for helping the reader understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A compact ultra-wideband gallium nitride phase shifter, characterized in that, Comprising: A planar spiral broadband coupling network, two broadband phase compensation networks, and two reflection branches; The two broadband phase compensation networks are respectively denoted as the first broadband phase compensation network and the second broadband phase compensation network; the two reflection branches are respectively denoted as the first reflection branch and the second reflection branch; The planar spiral broadband coupling network includes four coupled lines, each coupled line having a length of one-eighth wavelength, and the four coupled lines are all in a planar spiral shape. The four coupled lines are respectively denoted as: M1, M2, M3, 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 the ends close to their respective planar spiral centers. The first end of M1 is connected to the first end of M2, and the first end of M3 is connected to the first end of M4; The second end of M1 is used as the input port, and the second end of M4 is used as the output port; The second end of M3 is connected to the first end of the first broadband phase compensation network. The midpoint of the connection between the first end of M3 and the first end of M4 is connected to the second end of the first broadband phase compensation network. The third end of the first broadband phase compensation network is connected to the first reflection branch; The second end of M2 is connected to the first end of the second broadband phase compensation network. The midpoint of the connection between the first end of M1 and the first end of M2 is connected to the second end of the second broadband phase compensation network. The third end of the second broadband phase compensation network is connected to the second reflection branch.

2. The compact ultra-wideband gallium nitride phase shifter according to claim 1, characterized in that The structures and device parameters of the two broadband phase compensation networks are the same.

3. The compact ultra-wideband gallium nitride phase shifter according to claim 2, wherein The first broadband phase compensation network includes: a transmission line TL1, a capacitor C1b, a capacitor C1c, and 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 to 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 to 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 broadband phase compensation network includes: a transmission line TL2, a capacitor C2b, a capacitor C2c, and a 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 to 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 to 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 compact ultra-wideband gallium nitride phase shifter according to claim 3, characterized in that The capacitor Cx and the capacitor Cy are respectively replaced with open stub lines.

5. A compact ultra-wideband gallium nitride phase shifter according to any one of claims 2-4, characterized in that, The structures and device parameters of the two reflection branches are the same.

6. The compact ultra-wideband gallium nitride phase shifter according to claim 5, characterized in that The first reflection branch includes: a switching transistor SW1 and a capacitor C1a. The drain of the switching transistor SW1 is connected to the third end of the first broadband phase compensation network. The source of the switching transistor SW1 is connected to the first end of the capacitor C1a, and the second end of C1a is grounded; The second reflection branch includes: a switching transistor SW2 and a capacitor C2a. The drain of the switching transistor SW2 is connected to the third terminal of the second broadband phase compensation network. The source of the switching transistor SW2 is connected to the first terminal of the capacitor C2a, and the second terminal of the C2a is grounded; The gates of the switching transistor SW1 and the switching transistor SW2 are simultaneously connected to the control signal VC.

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