Miniaturized 90-degree coupling line bridge suitable for millimeter wave integrated circuit

Abstract

The invention aims to provide a miniaturized 90-degree coupling line bridge suitable for a millimeter wave integrated circuit, and belongs to the technical field of integrated circuits. According to the 90-degree coupling line bridge, two spiral coupling lines are adopted to construct a main body, and each coupling line is divided into an upper section and a lower section, so that the 90-degree coupling line bridge has interlayer wide-side coupling and same-layer narrow-side coupling at the same time; and meanwhile, uniform and equally-spaced grid-shaped wires are added in the space between the two layers of coupling lines, so that the coupling mode of a defected ground structure and a slow-wave structure is achieved at the same time. A plurality of coupling modes coexist, the size of the bridge is reduced to a great extent, meanwhile, a process metal density design rule is met, interconnection lines, bias lines and ground structures are simultaneously incorporated into a 90-degree bridge structure of bridge design, the size of the bridge is further miniaturized, and meanwhile, the problems of maturity and universality of bridge modular design are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated circuits, and in particular relates to a miniaturized 90-degree coupled line bridge suitable for millimeter wave integrated circuits. Background Art

[0002] With the continuous advancement of integrated processes and communication technologies, millimeter-wave integrated circuits (MMW) play a crucial role in 5G applications, and research on these devices is becoming an increasing focus. Unlike traditional board-level RF circuit design, MMW IC design offers greater freedom. This allows for a wider range of passive component designs, and the 90° bridge is a widely used component in MMW IC design, holding significant research value.

[0003] 90° bridges can be used in various RF microwave systems. For example, they can be used as power combiners or splitters with a 90-degree phase shift. They are particularly useful in many components, such as balanced power amplifiers and balanced mixers. In theory, a 90° bridge is typically a four-port device: the input, the isolation port, the through port, and the coupled port. When used as a power splitter, the input port serves as the signal input port, while the through port and the coupled port serve as output ports. These two output ports have equal power and a 90° phase shift. When used as a power combiner, the through port and the coupled port serve as inputs, receiving signals of equal amplitude but a 90° phase shift, while the signals are output from the input port. The 90° bridge is also highly symmetrical, meaning any port can serve as input. The output port is on the side opposite the input port, while the isolation port is the remaining port on the same side as the input port.

[0004] The 90° bridges used in integrated circuits typically employ branch-line bridges and coupled-line bridges. Branch-line bridges are microstrip-based structures whose dimensions are proportional to the wavelength. In integrated circuit design, they often occupy a large area. Furthermore, this structure places stringent requirements on the reference ground structure, making its design even more complex in integrated processes without a back ground layer, such as CMOS processes. Coupled-line bridges, on the other hand, break free from the constraints of microstrip lines and are smaller than branch-line bridges in the same frequency band, often enabling orders of magnitude reduction in area. However, existing 90° coupled-line bridge designs are often not small enough compared to other circuit structures. On the one hand, they occupy an excessively large layout, affecting the layout of other circuit structures. On the other hand, a larger area translates to higher costs. In addition, the previous 90° bridge design did not consider the metal density of the integrated process. When used in actual circuits, it cannot be used directly as a mature module, which will increase the design cost. For example, the coupled line bridge designed based on 28-nm CMOS process disclosed in the literature [1] (V. Qunaj and P. Reynaert, "A Ka-Band Doherty-Like LMBA for High-Speed Wireless Communication in 28-nm CMOS," in IEEE Journal of Solid-State Circuits, vol. 56, no. 12, pp. 3694-3703, Dec. 2021, doi: 10.1109 / JSSC.2021.3110168.), although its bridge structure is composed of only the top two layers of metal routing, when the final chip layout is drawn, in order to meet the process metal density rules, it has to add a certain amount of metal dummies to the lower metal layer, and the addition of these metal dummies will have a certain impact on the performance of the bridge, so that users of this structural bridge have to face the optimization of the bridge structure and metal dummies again; secondly, the previous 90° bridge design did not consider the impact of the larger-sized bridge in the integrated circuit on the subsequent circuit unit interconnection lines and power supply bias lines, and the chip RF ground routing, making the board routing and chip ground design a difficult point in the final chip layout design.

[0005] Therefore, how to greatly reduce the physical size of the bridge and improve the versatility of the designed 90° coupled line bridge without affecting the performance of the designed passive components is an urgent problem to be solved. Summary of the Invention

[0006] In response to the problems existing in the background technology, the purpose of the present invention is to provide a miniaturized 90° coupled line bridge suitable for millimeter wave integrated circuits. The 90° coupled line bridge uses two spiral coupled lines to construct the main body, and adds a grid-shaped routing in the space between the coupled lines. Therefore, the bridge of the present invention can simultaneously utilize inter-layer coupling and same-layer coupling and improve space utilization. This allows the present invention to greatly reduce the area and economic cost of the on-chip 90° coupled line bridge design in the millimeter wave band, while still maintaining the excellent performance of low insertion loss, high isolation, and wide bandwidth, solving the problems of versatility and maturity of the bridge module.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A miniaturized 90° coupled line bridge suitable for millimeter wave integrated circuits, comprising two coupled lines and a grid-shaped trace; each coupled line is composed of two spiral rectangular coupled lines;

[0009] Each coupling line consists of two segments, the first segment located in the upper layer and the second segment located in the lower layer, and the two coupling line segments are connected by a vertical metal via. The two segments of the same coupling line are symmetrical about a horizontal axis of symmetry, which is a line connecting the midpoints of the narrow sides of the rectangular coupling line, so that the two ports of the coupling line are located on the same side of a vertical axis of symmetry, which is a line connecting the midpoints of the wide sides of the rectangular coupling line. The starting point and end point of the two coupling lines on the same layer in the first and second coupling lines are both located at the diagonal positions of the rectangle.

[0010] The first coupling line is located in the upper layer, the second coupling line is located in the lower layer, and the starting points and end points of the two coupling lines located in the same layer of the first coupling line and the second coupling line are respectively located on opposite sides of the rectangle;

[0011] The first coupling line and the second coupling line are centrally symmetrical, with the center of symmetry being the center point of the miniaturized 90° coupling line bridge, so that the ports of the two coupling lines are located on different sides of the vertical symmetry axis;

[0012] The four ports of the two coupled lines serve as the input, through, coupling and isolation terminals of the 90° coupled line bridge respectively;

[0013] A number of grid-like traces are evenly spaced at the center of the 90° coupled line bridge, and the grid-like traces are parallel to the vertical symmetry axis;

[0014] The first segment of the first coupling line and the first segment of the second coupling line are single-layer metal or multi-layer metal, and the second segment of the first coupling line and the second segment of the second coupling line are multi-layer metal; the gate routing is multi-layer metal, and the metal layer in the middle of the gate routing is connected to the outside, and the other layers are floating and not connected to other structures.

[0015] Furthermore, the external connection, ie the grid-shaped wiring, is connected to a DC bias or a radio frequency ground.

[0016] Furthermore, the choice of metal layers for the coupling line and the grid trace, the number of turns of the coupling line, the width Wc of the coupling line, the spacing Gc of the coupling lines on the same plane, the width Wg of the grid trace, and the spacing Gg between two adjacent grid traces jointly determine the operating frequency band of the 90° coupled line bridge.

[0017] Furthermore, the distance d that each side of the grid trace extends beyond the coupling line is related to the operating frequency band and is selected based on actual operating conditions while ensuring that the bridge module is not affected by external circuits.

[0018] Furthermore, the material and number of metal layers of the coupling lines and the gate traces are determined by the integration process actually used to design and manufacture the bridge.

[0019] Furthermore, the integration process of the coupling lines and the gate wiring is any multi-layer metal integration process, preferably a GaAsHBT process, a 65-nm CMOS process or a 45-nm SOI CMOS process.

[0020] Furthermore, the first metal via and the second metal via are used to realize inter-layer transmission of signals, and their sizes depend on the process and the overcurrent capability required by the actual circuit.

[0021] The mechanism of the present invention is:

[0022] Traditional 90° coupled-line bridges improve the coupling degree of the coupled lines through methods such as wire winding, interlayer wide-edge coupling, defective ground structures, or slow-wave structures, increasing the effective electrical length of the coupled-line bridge and thus reducing its size. However, existing designs fail to simultaneously reduce the bridge size in multiple ways. Furthermore, previous bridge designs fail to consider practical applications and require the addition of additional metal blocks to meet the metal density design requirements of integrated circuit processes without compromising bridge performance. This makes previously designed 90° bridges unsuitable for direct use as complete modules in integrated circuits. The present invention proposes a miniaturized 90° coupled line bridge suitable for millimeter wave integrated circuit design, which is composed of two coupling lines, each of which is divided into two sections of an upper and lower layer, so that the present invention has both inter-layer wide-side coupling and same-layer narrow-side coupling; in addition, the design of uniformly spaced grid routing enables the coupling mode of both defective ground structure and slow-wave structure to be combined; multiple coupling modes coexist, while greatly reducing the size of the bridge, it will also meet the process metal density design rules and the 90° bridge structure that incorporates interconnect lines, bias lines, and ground structures into the bridge design, thereby further miniaturizing the bridge size while solving the maturity and versatility problems of the modular design of the bridge.

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] 1. The 90° coupled-line bridge proposed in this invention utilizes a centrally symmetrically distributed, rectangular, spiral multilayer coupled line structure to provide a RF signal path. Each coupled line consists of two spiral segments, one on top and one on the bottom. This routing significantly improves the coupling degree and equivalent electrical length of the coupled lines, while also increasing the line length per unit area. Through these two aspects, the bridge structure proposed in this invention significantly reduces the size of the 90° bridge.

[0025] 2. The 90° coupled-line bridge proposed in this invention features a grid-like pattern of evenly spaced, symmetrically arranged lines perpendicular to the horizontal axis of symmetry, arranged in the middle of the spiral coupled lines. The centermost layer of the grid serves as a ground or bias line, while the remaining layers are left floating. By rationally designing the length, width, and spacing of the grid lines, each metal layer of the bridge meets the metal density design rules for the integrated circuit process. Furthermore, a pre-defined path is reserved for the bridge lines to pass through, increasing flexibility in overall chip layout design.

[0026] 3. The 90° coupled-line bridge proposed in this invention is orders of magnitude smaller than previous bridge designs. It also offers excellent performance, including low insertion loss, high isolation, and broadband. More importantly, the bridge structure design incorporates process design rules and the requirements of overall chip layout drawing, allowing the bridge based on this structural design to be used directly as a circuit module, addressing the maturity and versatility of modular bridge design. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic structural diagram of the miniaturized 90° coupled line bridge suitable for millimeter wave integrated circuits proposed in the present invention.

[0028] Figure 2 Schematic diagram of the structure of a coupled line in a 90° coupled line bridge of the present invention.

[0029] Figure 3 This is a coupled-line 90° bridge with a center frequency of 30 GHz, designed based on the TSMC 65-nm CMOS1P9M_6X1Z1U process.

[0030] Figure 4 This is the simulation result diagram of the bridge designed by the present invention.

[0031] Among them, (a) is the transmission coefficient between each port of the designed bridge; (b) is the amplitude balance and phase balance of the designed bridge; (c) is the port matching of each port of the designed bridge. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation methods and drawings.

[0033] A miniaturized 90° coupled line bridge suitable for millimeter wave integrated circuits, the structural diagram of which is shown in FIG. Figure 1 As shown, it includes three-dimensional spiral coupling lines and grid-like routing;

[0034] The three-dimensional spiral coupling line is the core structure of the 90° coupling line bridge for radio frequency signal transmission, which includes two coupling lines. The structure of each coupling line is shown in the figure below. Figure 2 As shown, each coupling line consists of two spiral rectangular coupling lines; the first segment of the first coupling line and the first segment of the second coupling line are both located in the upper layer, and the second segment of the first coupling line and the second segment of the second coupling line are both located in the lower layer; the second port of the first segment of the first coupling line and the second port of the second segment of the first coupling line are connected through a first metal via, and the second port of the first segment of the second coupling line and the second port of the second segment of the second coupling line are connected through a second metal via;

[0035] The starting points of the two coupling lines in the first coupling line and the second coupling line, which are located in the same layer, are respectively located at the opposite corners of the rectangle, and the first metal via and the second metal via are also located at the opposite corners of the rectangle;

[0036] The two segments of the same coupling line are symmetrical about a horizontal axis of symmetry, which is a line connecting the midpoints of the narrow sides of the rectangular coupling line, so that the two ports of the coupling line are located on the same side of a vertical axis of symmetry, which is a line connecting the midpoints of the wide sides of the rectangular coupling line. The first coupling line and the second coupling line are rotationally symmetrical about the geometric center of the bridge, so that the ports of the two coupling lines are located on different sides of the vertical axis of symmetry.

[0037] The width of each coupling line is Wc, and the spacing between coupling lines in the same layer is Gc;

[0038] The first and second segments of each coupled line have the same routing direction; the first ports of the four coupled lines serve as the input, through, coupling, and isolation terminals of the 90° coupled line bridge, respectively;

[0039] Several grid-like traces are evenly spaced at the center of the 90° coupling line bridge, i.e., located between the upper and lower spaces of the first coupling line and the second coupling line, and the grid-like traces are parallel to the vertical symmetry axis; the width of the grid-like trace is Wg, the spacing between two adjacent grid-like traces is Gg, and the distance between the grid-like trace and the outermost coupling line is d (i.e., the length of the grid-like trace extending on both sides of the coupling line);

[0040] The first segment of the first coupling line and the first segment of the second coupling line are single-layer metal or multi-layer metal, and the second segment of the first coupling line and the second segment of the second coupling line are multi-layer metal; the gate routing is multi-layer metal, and the middle metal layer of the gate routing is connected to the outside, and the other layers are floating and not connected to other structures.

[0041] Example 1

[0042] Figure 3 This is a 90° coupled-line bridge with a center frequency of 30 GHz, designed based on the TSMC 65-nm CMOS1P9M_6X1Z1U process. The bridge has nine metal layers: the upper coupled lines are in the M9 layer, the lower coupled lines are in the M1-M4 metal layers, and the gate traces are in the middle metal layers, M5-M8.

[0043] With port 1 as the input port, a metal trace on the M9 layer is first run in a spiral to the center, then through a metal via to the M1 layer. Then, a metal trace on the M1-M4 layers is run in a spiral under the M9 layer to port 2, the through port. Another coupled line runs from port 3 to port 4, with ports 3 and 4 forming the coupled port and the isolated port, respectively. The line width (Wc) of both coupled lines is 6μm.

[0044] Between the upper and lower metal layers of the coupling line, M5-M8 serve as metal layers for gate routing. The M7 layer serves as a ground or bias line, connecting to the chip's overall ground or power supply port. The M5, M6, and M8 lines are floating and not connected to other structures. The gate routing's line width (Wg) and spacing (Gg) are both 2μm. The length (d) of the gate routing extending beyond the coupling line's edges is 10μm.

[0045] The grid-like routing adopts a defective ground structure to reduce the coupling capacitance between the coupling line and the ground, and increase the effective electrical length of the coupling line. At the same time, the grid-like routing adopts a slow-wave structure, that is, the ground structure is set as a series of equally spaced ground lines perpendicular to the signal routing, which can also increase the effective electrical length of the signal routing.

[0046] The module size of the coupled line 90° bridge of the present invention is 120μm×72μm, and the area is only 0.00864mm 2The structure proposed by the present invention has a significant size advantage. At the same time, since the bridge itself already meets the metal density rules of the M1-M9 layers, for example, within the bridge range, the density of the M7 metal is 32.2%, which meets the M7.DN.1 requirement of greater than 10% and less than 80%; the density of the M9 metal layer is 54.5%, which also meets the M9.DN.1 requirement of greater than 10% and less than 80%. For any range of 20μm×20μm, the metal density of M1-M9 is less than 90%, meeting the Mx.DN.2 rule. Therefore, in use, the bridge structure of the present invention can be used directly as a fixed module without making any modifications to the bridge structure, reflecting the maturity and versatility of the 90° bridge module design.

[0047] Figure 4 Figure 3 is the S-parameter simulation result of the designed 90° bridge, where (a) is the transmission coefficient of the other ports when port 1 of the bridge is used as the input. It can be seen that at its center frequency, the insertion loss is only 0.76dB, and the isolation is better than -33dB; (b) is the amplitude balance and phase balance of the designed bridge. Within 20-45GHz, the output power difference between the through-port and the coupled-port is less than 3dB, and the phase difference is between 90° and 97°; (c) is the port matching of each port of the designed bridge. At its center frequency, the reflection coefficients of the four ports are all less than -20dB, and less than -16.5dB within the bandwidth.

[0048] The miniaturized 90° coupled line bridge provided in this application can significantly reduce the structural size of the coupled line bridge while ensuring excellent performance. It has a simple structure, good maturity and versatility, and can be widely used in millimeter wave frequency band chip circuits.

[0049] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A miniaturized 90° coupled line bridge suitable for millimeter wave integrated circuits, characterized in that: The miniaturized 90° coupled line bridge includes two coupled lines and a grid-shaped trace; each coupled line is composed of two spiral rectangular coupled lines; Each coupling line consists of two segments, the first segment located in the upper layer and the second segment located in the lower layer, and the two coupling line segments are connected by a vertical metal via. The two segments of the same coupling line are symmetrical about a horizontal axis of symmetry, which is a line connecting the midpoints of the narrow sides of the rectangular coupling line, so that the two ports of the coupling line are located on the same side of a vertical axis of symmetry, which is a line connecting the midpoints of the wide sides of the rectangular coupling line. The starting point and end point of the two coupling lines on the same layer in the first and second coupling lines are both located at the diagonal positions of the rectangle. The first coupling line is located in the upper layer, the second coupling line is located in the lower layer, and the starting points and end points of the two coupling lines located in the same layer of the first coupling line and the second coupling line are respectively located on opposite sides of the rectangle; The first coupling line and the second coupling line are centrally symmetrical, with the center of symmetry being the center point of the miniaturized 90° coupling line bridge, so that the ports of the two coupling lines are located on different sides of the vertical symmetry axis; The four ports of the two coupled lines serve as the input end, through end, coupling end and isolation end of the 90° coupled line bridge respectively; A number of grid-like traces are evenly spaced at the center of the 90° coupled line bridge, and the grid-like traces are parallel to the vertical symmetry axis; The upper segments of the two coupling lines are single-layer metal or multi-layer metal, and the lower segments are multi-layer metal; the gate routing is multi-layer metal, and the metal layer in the middle of the gate routing is connected to the outside, and the other layers are floating and not connected to other structures.

2. The miniaturized 90° coupled line bridge according to claim 1, wherein: The external connection, ie, the grid wiring, is connected to a DC bias or a radio frequency ground.

3. The miniaturized 90° coupled line bridge according to claim 1, wherein: The choice of metal layers for the coupling line and the grid trace, the number of turns of the coupling line, the width Wc of the coupling line, the spacing Gc of the coupling lines on the same plane, the width Wg of the grid trace, and the spacing Gg between two adjacent grid traces jointly determine the operating frequency band of the 90° coupled line bridge.

4. The miniaturized 90° coupled line bridge according to claim 3, wherein: The distance d that each side of the grid trace extends beyond the coupling line is related to the operating frequency band. It should be selected based on actual operating conditions while ensuring that the bridge module is not affected by external circuits.

5. The miniaturized 90° coupled line bridge according to claim 1, wherein: The material and number of metal layers for the coupling lines and the gate traces are determined by the integration process actually used to design and manufacture the bridge.

6. The miniaturized 90° coupled line bridge according to claim 5, wherein: The integration process of the coupling lines and the gate wiring is any multi-layer metal integration process.

7. The miniaturized 90° coupled line bridge according to claim 6, wherein: The multi-layer metal integration process is a GaAsHBT process, a 65-nm CMOS process or a 45-nm SOI CMOS process.

8. The miniaturized 90° coupled line bridge according to claim 1, wherein: The first metal via and the second metal via are used to realize inter-layer transmission of signals, and the sizes of the first metal via and the second metal via depend on the process and the overcurrent capability required by the actual circuit.

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