Symmetrical split-type planar transformer

Abstract

This disclosure relates to a symmetrical split-plane transformer. This document discloses a symmetrical split-plane transformer in the context of a DC-DC isolated converter. This symmetrical split-plane transformer reduces or eliminates the asymmetry of parasitic capacitance distribution across an isolation barrier extending from one end of the primary coil to the other, thereby reducing undesirable electromagnetic interference (EMI) caused by common-mode dipole emissions across the isolation barrier. In some embodiments, the primary winding is divided into at least first and second coils, each occupying a different region on a substrate side-by-side. The transformer is symmetrical in the same sense as the capacitive coupling from the first coil to the secondary winding, thereby reducing common-mode EMI. Each coil may include stacked helical coil portions in multiple metal planes to increase the inductance density across the isolation barrier. Furthermore, in some embodiments, the first and second coils may have opposite helical directions, thereby reducing far-field radiation effects from the transformer.

Description

Technical Field

[0001] This disclosure generally relates to radio frequency (RF) transformers, and more particularly to isolation transformers used in isolated DC-DC converters. Background Technology

[0002] Transformers are typically used to couple the two sides of an electrical system, sometimes referred to as the primary side and the secondary side. The two sides are usually electromagnetically coupled and separated by a current isolation barrier.

[0003] Transformers can be used to transmit information or energy across current isolation barriers, form isolated communication channels, or power different parts of a circuit for safety and / or data integrity reasons. Both data and power flows can be unidirectional or bidirectional, depending on the application requirements.

[0004] Some isolated DC-DC converters include a driver that drives the primary winding of a transformer to transfer power across an isolation barrier to the secondary winding of the transformer. The rectifier converts the voltage received at the secondary winding of the transformer into an output DC voltage.

[0005] There are many different construction techniques and topologies for transformers. Typically, a transformer contains wires wound to form loops that generate and collect magnetic fields on the respective sides of an isolation barrier. Optionally, magnetic materials may be provided in the transformer to help guide and contain the magnetic field.

[0006] A miniature transformer or planar transformer is a transformer that has conductors integrated in a semiconductor package (e.g., embedded in a substrate).

[0007] When a transformer is excited by an electrical signal, the magnetic field coupling between its two sides can be represented by a coupled inductor in a simplified circuit model, while the electric field across the isolation barrier can be represented by a capacitor across the barrier. When the transformer operates with signals or RF signals in the MHz to GHz range, the capacitive effect between the two sides of the isolation barrier becomes more pronounced compared to low-frequency operation. Circuit system designs using RF transformers can sometimes model the transformer as a single electromagnetic device, which is an inductor with parasitic capacitance effects. Summary of the Invention

[0008] This paper discloses a symmetrical split-plane transformer in the context of a DC-DC isolated converter. This symmetrical split-plane transformer reduces or eliminates the asymmetry of parasitic capacitance distribution across an isolation barrier extending from one end of the primary coil to the other, thereby reducing undesirable electromagnetic interference (EMI) due to common-mode dipole emissions across the isolation barrier.

[0009] In some embodiments, the primary winding is divided into at least a first coil and a second coil, each occupying a different region on the substrate side-by-side. The transformer is symmetrical in the same sense as the capacitive coupling from the first coil to the secondary winding, thereby reducing common-mode EMI. Each coil may include stacked helical coil portions in multiple metal planes to increase the inductance density across the isolation barrier. Furthermore, in some embodiments, the first and second coils may have opposite helical directions, thereby reducing far-field radiation effects from the transformer.

[0010] In some embodiments, a transformer is disclosed. The transformer includes a substrate having a first surface and a second surface opposite to the first surface; a primary winding having a first coil contacting the first surface and defining a first closed region on the first surface, and a second coil contacting the first surface and defining a second closed region on the first surface. The first and second closed regions are arranged side-by-side and separated from each other. The transformer also includes a secondary winding having a third coil and a fourth coil, each contacting the second surface. The capacitive coupling between the first and third coils is equal to the capacitive coupling between the second and fourth coils.

[0011] In some embodiments, an isolated DC-DC converter is disclosed. The isolated DC-DC converter includes a substrate having a first surface and a second surface opposite to the first surface; a first transformer including a first coil contacting the first surface and defining a first closed region on the first surface, and a third coil contacting the second surface. At least a portion of the first coil is aligned with at least a portion of the third coil along a vertical direction perpendicular to the first surface. The isolated DC-DC converter also includes a second transformer including a second coil contacting the second surface and defining a second closed region on the second surface, and a fourth coil contacting the second surface, at least a portion of the second coil being aligned with at least a portion of the fourth coil along a vertical direction. The first closed region and the second closed region are arranged side-by-side and separated from each other. The capacitive coupling between the first coil and the third coil is equal to the capacitive coupling between the second coil and the fourth coil.

[0012] In some embodiments, a split-type planar transformer is disclosed. The split-type planar transformer includes a substrate having a first surface and a second surface opposite to the first surface; a first transformer including a first coil in contact with the first surface and a third coil in contact with the second surface. The first coil is aligned with the third coil in a vertical direction perpendicular to the first surface. The split-type planar transformer also includes a second transformer including a second coil in contact with the second surface and a fourth coil in contact with the second surface. The second coil is aligned with the fourth coil in a vertical direction. The first coil and the second coil are arranged side-by-side in a transverse direction along the first surface and are separated from each other by a certain distance. The capacitive coupling between the first coil and the third coil is equal to the capacitive coupling between the second coil and the fourth coil. Attached Figure Description

[0013] Various aspects and embodiments of this disclosure will be described with reference to the following accompanying drawings. It should be understood that these drawings are not necessarily drawn to scale. Items appearing in multiple drawings are denoted by the same reference numerals in all the drawings in which they appear. For clarity, not every component can be labeled in every drawing.

[0014] Figure 1 This is a schematic diagram illustrating an example of electromagnetic interference in an isolated DC-DC converter;

[0015] Figure 2A This is a simplified circuit diagram of an exemplary symmetrical transformer according to the first aspect of this disclosure;

[0016] Figure 2B It is shown as Figure 2A A simplified circuit diagram of a symmetrical transformer, a variant of the transformer in the diagram;

[0017] Figure 3 This is a simplified circuit diagram illustrating a DC-DC converter with a symmetrical transformer according to some embodiments;

[0018] Figure 4A and Figure 4B These are, respectively, a cross-sectional view and a top view of a planar transformer according to some embodiments, which can be used in... Figures 1 to 3 Implementing a symmetrical transformer in a DC-DC converter;

[0019] Figures 5A to 5C These are top and perspective views of an interleaved planar transformer according to some embodiments;

[0020] Figure 6A and Figure 6B Is as Figures 5A to 5C Top view and perspective view of another exemplary variant of the planar transformer 500, namely an interleaved planar transformer 600;

[0021] Figure 7 Is as Figure 6A and Figure 6B A top view of an exemplary interleaved planar transformer 700, a variant of the planar transformer 600 shown;

[0022] Figure 8 This is a schematic diagram of a symmetrical split transformer implemented in a solenoid structure according to some embodiments;

[0023] Figure 9 This is a simplified circuit diagram illustrating a DC-DC converter with a symmetrical transformer according to a second aspect of this disclosure;

[0024] Figure 10A and Figure 10B These are, respectively, a cross-sectional view and a top view of a split-plane transformer according to some embodiments, which can be used to achieve, for example... Figure 9 The transformer shown;

[0025] Figure 10C It is shown that it contains Figure 10A A perspective view of the coil portions in different metal planes of each coil in the transformer 1000;

[0026] Figure 10D It is shown Figure 10C A series of cross-sectional views of the coil portion in four different metal planes; and

[0027] Figure 11 This is a schematic plan view of a split-type planar transformer according to some embodiments. The split-type planar transformer is... Figure 10B A variant of the transformer with added magnetic material. Detailed Implementation

[0028] Some aspects of this disclosure relate to a symmetrical transformer design in the context of a DC-DC isolated converter. This symmetrical transformer reduces or eliminates the asymmetry in the distribution of parasitic capacitance across an isolation barrier extending from one end of the primary coil to the other, thereby reducing undesirable electromagnetic interference (EMI) due to common-mode dipole emissions across the isolation barrier.

[0029] The first aspect relates to a split-type transformer design in which the primary winding is divided into a separate first coil and a second coil, with a series impedance connected between the first and second coils. The transformer is symmetrical in the same sense as the capacitive coupling from the first coil to the secondary winding, thereby reducing common-mode EMI. The series impedance can be a single capacitor used as capacitance in the resonant LLC network of a DC-DC converter, saving cost and reducing complexity compared to a circuit design with a pair of capacitors arranged outside the primary winding. In some embodiments, the transformer is a planar transformer spanning multiple metal layers, and the series impedance can be connected to a pair of center-tapped terminals in the primary winding.

[0030] The second aspect relates to a split-type transformer design in which the primary winding of the transformer is divided into at least a first coil and a second coil, each coil occupying a different region on a substrate side-by-side. The transformer is symmetrical in the same sense as the capacitive coupling from the first coil to the secondary winding, thereby reducing common-mode EMI. In some embodiments, each coil may include stacked helical coil portions located in more than one metal plane, such that the magnetic fields generated in these coil portions overlap as current flows to increase the inductance density across the isolation barrier, resulting in higher inductance in a given region. Furthermore, in some embodiments, the first and second coils may have opposite helical directions, such that the magnetic fields they generate have opposite polarities. Therefore, far-field radiation effects from the transformer can be reduced.

[0031] Figure 1 This is a schematic diagram illustrating an example of electromagnetic interference in an isolated DC-DC converter. Figure 1 A DC-DC converter 100 is shown, which includes a primary side 1 having a primary winding 30 with a driver 10 and a transformer 40. The DC-DC converter 100 also includes a rectifier 70 and a secondary winding 50 of the transformer 40 on the secondary side 2.

[0032] In the DC-DC converter 100, the driver 10 is powered by a DC voltage V. cc The power supply drives the primary winding 30 of transformer 40 between terminals P1 and P2. The primary winding 30 is electromagnetically coupled to the secondary winding 50 across an isolation barrier 42, which may be formed of a dielectric. The secondary winding 50 is coupled to rectifier 70 via terminals S1 and S2 to convert the signal received in the secondary winding 50 into an output DC voltage V. ISOOUT The driver 10 can take any suitable form and in some embodiments can be a resonant circuit. In a preferred embodiment, the driver 10 can be a full-bridge driver.

[0033] See you again Figure 1It shows the distributed parasitic capacitances C1 and C2 across the isolation barrier 42. It should be understood that although two capacitor symbols C1 and C2 are used, they are simplified representations of distributed capacitive coupling from one end P1 of the primary winding 30 to the other end P2 of the primary winding, where C1 represents the capacitive coupling between the portion of the primary winding adjacent to terminal P1 and the secondary winding, and C2 is the reverse.

[0034] like Figure 1 As shown, when transformer 40 is excited by AC drive signal 12 from driver 10, common-mode AC current 72 is injected across isolation barrier 42. Common-mode current 72 has no physical return path and will form a dipole antenna between the voltage domain in primary side 1 and the voltage domain in secondary side 2, which can radiate and generate electromagnetic interference (EMI) emissions 74.

[0035] The inventors recognize and understand that the net capacitive current across the isolation barrier is related to the asymmetry in the DC-DC converter system. For example, if the drive signal is fully differential and the capacitance across the barrier is balanced (e.g., C1 equals C2), then the capacitive current injected near terminal P1 will cancel out the capacitive current injected near terminal P2, resulting in a net sum of 0.

[0036] It is well known that asymmetries that can lead to poor EMI performance can include, but are not limited to: asymmetries in the active switches of the transformer driver and rectifier; timing asymmetries in the driver and rectifier; transformer asymmetries; and impedance asymmetries connecting the power stage (driver and rectifier) ​​to the transformer. Aspects of this disclosure relate to reducing transformer asymmetries, i.e., asymmetries in capacitance distribution (e.g., with...). Figure 1 The C2 in the formula is different from the C1 in order to improve EMI performance by reducing common-mode dipole emissions.

[0037] Figure 2A This is a simplified circuit diagram of an exemplary symmetrical transformer according to the first aspect of this disclosure. Figure 2A A transformer 200 with a primary winding 230 and a secondary side 250 is shown. The primary winding is divided into two coils 210 and 220 connected in series. The first coil 210 is coupled between terminals P1 and P2. The second coil 220 is coupled between terminals P3 and P4. The secondary winding 230 is coupled between terminals P5 and P6. According to some embodiments, the transformer 200 is symmetrical because the capacitance C1 between the first coil 210 and the secondary winding 250 is equal to the capacitance C2 between the second coil 220 and the secondary winding 250.

[0038] although Figure 2A Only the secondary winding with a single coil is depicted, but it should be understood that the split coil design in the primary winding 230 can also be applied to the secondary winding to provide a symmetrical transformer.

[0039] Figure 2B It is shown as Figure 2A A simplified circuit diagram of a symmetrical transformer, a variant of the transformer in the diagram. Figure 2B In this transformer 260, there is a primary winding 235 and a secondary winding 250. The primary winding 235 is divided into two separate coils 215 and 225, each coil having a capacitance equal to that of the secondary winding 250. Transformer 260 and... Figure 2A The difference in transformer 200 is that the two coils 215 and 225 are not connected in series, but in parallel, such that each of these coils is coupled between terminals P1 and P2. According to one aspect, connecting coils in parallel within the primary winding increases the magnetic field and thus increases the inductive coupling in the transformer.

[0040] Figure 3 This is a simplified circuit diagram illustrating a DC-DC converter with a symmetrical transformer according to some embodiments. Figure 3 A DC-DC converter 30 is shown, which includes a driver 32, a transformer 300, and a rectifier 37. The driver 32 is coupled to terminals P1 and P4 of the primary winding 330 of the transformer 300 to drive RF signals through the primary winding. The rectifier 37 is coupled to terminals P5 and P6 of the secondary winding 350 of the transformer 300 to convert signals received in the secondary winding 350 into an output DC voltage.

[0041] See still Figure 3 Transformer 300 is a symmetrical transformer with a split primary winding 330, which includes a first coil 310, a second coil 320, and an impedance 340 connected in series along a current path 34. Transformer 300 is symmetrical because the capacitance C1 between the first coil 310 and the secondary winding 350 is equal to the capacitance C2 between the second coil 320 and the secondary winding 350.

[0042] exist Figure 3 In this configuration, a first coil 310 is coupled between terminals P1 and P2. A series impedance 340 is coupled between terminals P2 and P3. A second coil 320 is coupled between terminals P3 and P4. The series impedance 340 may include a capacitor. In some embodiments, the DC-DC converter 30 may be a resonant DC-DC converter, and the series capacitor 340, when combined with the inductance L of the transformer 300, forms a symmetrical LLC resonant network driven by the driver 32. Zhao et al. describe an example of a DC-DC converter with a transformer-based LLC resonant network in U.S. Patent 10,003,267, the entire contents of which are incorporated herein by reference. It should be understood that aspects of this disclosure are not limited to providing a series capacitor, and the series impedance 340 may include other reactive components.

[0043] Figure 4A and Figure 4B These are, respectively, a cross-sectional view and a top view of a planar transformer according to some embodiments, which can be used in... Figures 1 to 3 A symmetrical transformer is implemented in the DC-DC converter.

[0044] Figure 4B A transformer 400 with a primary winding 430 and a secondary winding 450 on a substrate 401 is shown. The substrate 401 may be a printed circuit board (PCB), and additional circuit components (although not shown) may be provided on the PCB. In some embodiments, the substrate 401 may be integrated in the same package as a DC-DC converter using semiconductor manufacturing techniques known in the art.

[0045] Figure 4A It is substrate 401 along Figure 4B The diagram shows a cross-sectional view along line A-A', illustrating that the primary winding 430 and the secondary winding 450 each include multiple coil portions 432, 452 arranged on opposite surfaces of the core layer 404 of the substrate 401. The core layer 404 comprises an insulating dielectric material and serves as current isolation between the primary and secondary windings.

[0046] The coil portions 432 in the primary winding 430 include conductors coplanar on the first plane 412. Each of the coil portions 432 may include a conductive material, such as metal, fabricated on the top surface of the core layer 404 by any suitable fabrication method known in the art (such as, but not limited to, mask deposition, etching, or combinations thereof). In such embodiments, the plane 412 may be a metal layer of a process flow. Figure 4B As shown, the coil portion 432 can be a long, thin conductor of substantially the same width, although uniform width is not required and any suitable size can be used.

[0047] See still Figure 4B The conductor in the primary winding 430 is wound within the plane 412 and extends from terminal P1 to terminal P4 (see example). Figure 3 (Circuit diagram in the diagram). The primary winding can be formed as a spiral extending clockwise from terminal P1, with the conductor in coil portion 433 initially contracting within a closed region to avoid short-circuiting itself. As the primary winding reaches the minimum closed region, it continues to extend clockwise while extending outward via coil portion 435, thus increasing the closed region towards terminal P4. To prevent short-circuiting between coil portion 433 and coil portion 435, vias 442 and bridges 444 are provided, allowing coil portion 435 to be in a plane different from plane 412 ( Figure 4A (Not shown in the image) intersects with coil section 433. Refer to the following... Figures 5A to 5C The examples in the text discuss the details of hole 442 and bridge 444.

[0048] See you again Figure 4A This illustrates a secondary winding 450 coupled between terminals P5 and P6 and having a coil portion 452 coplanar with a second plane 414. In some embodiments, the second plane 414 may be another metal layer in the substrate 401. Figure 4A and Figure 4B As shown, coil portion 452 in the secondary winding is perpendicularly aligned with coil portion 432 in the primary winding 432. Since capacitance is proportional to the area and distance between two adjacent conductive objects, distributed capacitive coupling between the conductors in coil portions 432 and 452 can remain uniform along the entire length of the primary winding 430 when the distance between the coil portion pairs is kept uniformly spaced based on the thickness of the core layer 404, and when the lateral dimensions of coil portions 432 and 452 are matched to each other. It should be understood that, although in Figure 4B The details are obscured, but the secondary winding 450 may additionally include vias and bridges extending to a plane different from plane 414 to allow the winding coil portions 452 to cross each other in a manner similar to that of the primary winding 430 without short-circuiting.

[0049] See you again Figure 4B The diagram shows that the primary winding 430 has a break point 445 that divides the primary winding into two coils. The first coil 410 includes a coil portion 433 coupled to terminal P1 and further coupled to terminal P2 via a conductive structure 446a. The second coil 420 includes a coil portion 435 coupled to terminal P4 and further coupled to terminal P3 via a conductive structure 446b. In this embodiment, the break point 445 is chosen such that the capacitance between the first coil 410 and the secondary winding 450 is equal to the capacitance between the second coil 420 and the secondary winding 450, and the transformer 400 is symmetrical in this respect.

[0050] It should be understood that the breakpoint 445 is not necessarily located at the geometric center of the primary winding 430, even if it appears to be located at the bottom center of the primary winding 430 along the x-direction. The exact geometry of the primary winding 430, where it is divided into a first coil and a second coil, can be determined during the design phase of a symmetrical transformer. For example, using simulation methods known in the art, the differences in distributed capacitance between the first coil and the secondary winding, and between the second coil and the secondary winding, can be iteratively calculated while adjusting the coil geometry until the transformer becomes symmetrical. In addition to the location of the breakpoint in the primary winding, size, dimensions, and dielectric barrier thickness are also exemplary parameters of the coils that can be adjusted to achieve symmetry, as is known to those skilled in the art of RF transformers.

[0051] Despite Figure 4B Not shown in the diagram, but in a preferred embodiment, such as Figure 3The impedance 340 in the middle can be coupled to terminals P2 and P3, and is connected in series to the first coil 410 and the second coil 420 in the current path from terminal P1 to terminal P4.

[0052] Figure 4A An insulating layer 402 disposed above core layer 404 and an insulating layer 406 disposed below core layer 404 are also shown. Insulating layers 402 and 406 encapsulate the primary winding 430 and secondary winding 450, respectively, and provide mechanical support and electrical isolation for the conductors disposed on core layer 404. Insulating layers 402 and 406 may comprise any suitable dielectric material known in the PCB manufacturing industry, such as, but not limited to, oxides, nitrides, ceramics, polymers, and mixtures thereof. In a preferred embodiment, insulating layers 402 and 406 comprise a prepreg layer.

[0053] Figure 4A An insulating layer 407 in contact with the surface of insulating layer 402 and an insulating layer 408 in contact with the surface of insulating layer 406 are also shown. Layers 407 and 408 may comprise polymeric materials, such as welding masks.

[0054] It should be understood that, for illustrative purposes only, substrate 401 is shown as comprising a combination of five layers 402, 404, 406, 407, and 408, and additional materials and layers may be present. It is not required that the core layer 404 and the insulating layers 402 and 406 have different compositions. Furthermore, although... Figure 4A Only one metal layer on either surface of the core layer 404 is shown, but additional metal layers may be provided in the substrate 401.

[0055] Figures 5A to 5C These are top and perspective views of an interleaved planar transformer according to some embodiments. Figures 5A to 5C A planar transformer 500 is shown, having a primary winding 530 coupled between terminals P1 and P4 and a secondary winding 550 separated and isolated from the primary winding 530 by a core layer (not shown for simplicity). The secondary winding 550 is coupled between terminals P5 and P6.

[0056] Figure 5A The primary winding 530 is shown to be divided into a first coil 520 and a second coil 530. The first coil 520 is coupled to terminals P1 and P3 via traces 546 and pads 547. The second coil 530 is coupled to terminals P3 and P4 via traces 546 and pads 547. The traces 546 are elongated conductors that fan out in the xy plane to couple the individual coils to the pads 547, which serve as terminals, to accommodate different spacing and dimensions between the pads and conductors in the coils.

[0057] like Figure 5BAs shown, the primary winding 530 includes a coil portion primarily located in the first metal layer 512, while the trace 546 and pad 547 are arranged in a second metal layer 513 that is offset and located above the first metal layer 512. A via 542 is provided to vertically interconnect the trace 546 with a corresponding coil portion in the underlying metal layer.

[0058] Transformer 500 is a symmetrical transformer, in which there is a breakpoint 545 in the primary winding, such that the capacitance between the first coil 510 and the secondary winding 550 is equal to the capacitance between the second coil 520 and the secondary winding 550. Although in Figure 5A Not shown, but in a preferred embodiment, such as Figure 3 The impedance 340 in the middle is connected in series with the impedance and coupled to terminals P2 and P3, and is connected in series with the first coil 510 and the second coil 520 in the current path from terminal P1 to terminal P4.

[0059] like Figure 5A As shown, the second coil 520 includes multiple coil portions, such as coil portions 532a and 532b. The second coil 520 intersects the first coil 510 using a bridge 544, which is connected to adjacent coil portions 532a and 532b using a pair of vertical vias 542. The bridge 544 is arranged in a plane different from the first metal layer 512. In a preferred embodiment, the bridge 544 includes a conductor located in the same second metal layer 513 as the traces 546 and pads 547. In the illustrated embodiment, at least one bridge 544 is closed on at least two sides by a pair of traces 546a and 546b connected to terminals P3 and P2.

[0060] Figure 5A and Figure 5B The secondary winding 550 is shown to have a coil portion 552 that is perpendicularly aligned with the coil portion in the primary winding 530. Figure 5C It shows the relationship with Figure 5B The perspective view is a flipped view of the transformer 500 compared to the perspective view in the figure, showing the coil portions of the secondary winding 550 arranged in a third plane or third metal layer 514. A bridge 545 is arranged in the secondary winding 550 to allow the coil portions 552 to cross each other without short-circuiting. In some embodiments, the bridge 545 includes a conductor arranged in a fourth metal layer 515, which is offset from the metal layer 514 and away from the metal layers 512 and 513 of the primary winding.

[0061] like Figure 5A As shown, the two terminals of the secondary windings P5 and P6 are arranged on the top of the transformer 500, opposite to the terminals P1 and P4 of the primary winding along the y-direction. In a preferred embodiment, terminals P5 and P6 are implemented as pads 547 arranged in the second metal layer 513 (the same layer as the pads 547 and traces 546 of terminals P1 to P4). Figure 5B and Figure 5C A pair of vertical interconnects 543 are shown passing through insulating material and connecting the coil portion of the secondary winding in the third metal layer 514 to corresponding pads 547 serving as terminals P5 and P6. In such embodiments, all six terminals are arranged in the same metal plane on one side of the substrate to make the pads more accessible for electrical connection to other components.

[0062] although Figures 5A to 5C The illustrated embodiments involve conductors in four metal layers 512, 513, 514, and 515; however, it should be understood that aspects of this application are not limited thereto, as one or more components may be arranged in additional metal layers. It should also be understood that although the embodiments show wiring above or below the coil portion to avoid short circuits via bridges or traces / pads, such wiring can be performed using lower-level channels and crossovers relative to the coil portion, and aspects of this disclosure are not limited thereto.

[0063] Figure 6A and Figure 6B Is as Figures 5A to 5C Top and perspective views of another exemplary variant of the planar transformer 500, an interleaved planar transformer 600. Transformer 600 is similar to transformer 500 in many respects, with identical parts labeled with the same reference numerals. The difference between transformer 600 and transformer 500 is that, instead of using traces to couple the series impedance in the primary winding 530, a pair of junction lines 649a, 649b are provided.

[0064] like Figure 6A As shown, one end of the first coil 510 is coupled to a bonding pad 647b, and the bonding pad 647b is connected via a bonding wire 649b to a bonding pad 647d serving as terminal P4. Similarly, one end of the second coil 520 is coupled to a bonding pad 647a, and the bonding pad 647a is connected via a bonding wire 649a to a bonding pad 647c serving as terminal P3. In some embodiments, the two terminals P1 and P4 may be directly connected to the ends of the coil portions in the first and second coils without using traces. This is in Figure 6A As shown in the example, bonding pads 647e and 647f serve as terminals P1 and P4, respectively, and are vertically interconnected to conductors in corresponding first coils 510 and second coils 520 in the first metal layer 512 using vias. In some embodiments, pads 647a, 647b, 647c, 647d, 647e, and 647f are arranged in the second metal layer 513.

[0065] Figure 7 Is as Figure 6A and Figure 6BA top view of an exemplary interleaved planar transformer 700, a variant of the planar transformer 600, is shown. Transformer 700 is similar to transformer 600 in many respects, with identical components labeled using the same reference numerals. The difference between transformer 700 and transformer 600 is that, instead of using bonding wires to couple the series impedance to bonding pads 6147a, 617b, discrete component 734 can be directly mounted to the bonding pads, such as... Figure 7 As shown. Discrete component 734 may be a passive component such as a capacitor, and when mounted on bonding pads 617a, 617b, it is connected in series within the primary winding 530. In a preferred embodiment, component 734 is a surface mount component and can be mounted using soldering.

[0066] Although so far regarding Figure 4 to Figure 7 The embodiments discussed are based on planar transformers integrated into a substrate, but aspects of this disclosure are not limited thereto. For example, symmetrical split transformers with series impedance can be implemented in non-planar coil topologies, such as, but not limited to, toroidal coils or solenoids.

[0067] Figure 8 This is a schematic diagram of a symmetrical split-type transformer implemented in a solenoid structure according to some embodiments. Figure 8 In the solenoid transformer 800, there are a primary winding 830 and a secondary winding 850, both of which are wound around a magnetic core 860. Since the conductors of the primary winding 830 and the secondary winding 850 are intertwined but isolated from each other, there is a distributed capacitance between the primary winding and the secondary winding along the length of the primary winding 830 from terminal P1 to terminal P4.

[0068] The primary winding 830 is divided into a first coil 810 coupled between terminals P1 and P2 and a second coil 820 coupled between terminals P3 and P4, such that the capacitance between the first coil 810 and the secondary winding 850 is equal to the capacitance between the second coil 820 and the secondary winding 850. An impedance 834 is coupled to terminals P2 and P3 such that the first coil 810, the second coil 820, and the impedance 834 are connected in series, and a current path 840 flows through each of the first coil 810, the impedance 834, and the second coil 820.

[0069] A second aspect of this disclosure relates to a planar transformer design having a primary winding divided into a first coil and a second coil, each coil enclosing a different region side-by-side on a substrate. In some embodiments, the secondary winding is also divided into a third coil and a fourth coil, each of the third and fourth coils aligned below the corresponding first and second coils of the primary winding, thereby dividing the planar transformer into two series-connected half-transformers.

[0070] Figure 9 This is a simplified circuit diagram illustrating a DC-DC converter with a symmetrical transformer according to a second aspect of this disclosure. Figure 9 A DC-DC converter 90 is shown, which includes a driver 92, a transformer 900, and a rectifier 97. The driver 92 is coupled to terminals P1 and P6 of the primary winding 901 of the transformer 900 to drive an RF signal through the primary winding. The rectifier 97 is coupled to terminals P3 and P8 of the secondary winding 850 of the transformer 900 to convert a signal received in the secondary winding 902 into an output DC voltage.

[0071] See still Figure 9 The primary winding 901 of transformer 900 is divided into a first coil 910, a second coil 920, and an impedance 94 connected in series along the current path 96. The secondary winding 902 of transformer 900 is divided into a third coil 930 and a fourth coil 940 connected in series. Transformer 900 is symmetrical because the capacitance C1 between the first coil 910 and the third coil 930 is equal to the capacitance C2 between the second coil 920 and the fourth coil 940.

[0072] exist Figure 9 In the circuit, the first coil 910 is coupled between terminals P1 and P2. The series impedance 94 can be similar to... Figure 3 The impedance 94 is shown as 340 and coupled between terminals P2 and P5. The second coil 920 is coupled between terminals P5 and P4. The third coil 930 is coupled between terminals P3 and P4, and the fourth coil 940 is coupled between terminals P7 and P8. The second coil 920 is coupled between terminals P5 and P4. In a preferred embodiment, the series impedance 94 includes a capacitor.

[0073] See still Figure 9 Since the first coil 910 is inductively coupled to the third coil 930, this pair forms a half-transformer or transformer A. Similarly, the second coil 920 and the fourth coil 940 form transformer B.

[0074] Figure 10A and Figure 10B These are, respectively, a cross-sectional view and a top view of a split-plane transformer according to some embodiments, which can be used to achieve, for example... Figure 9 The transformer shown.

[0075] Figure 10A It is the substrate 1090 along Figure 10B The cross-sectional view of B-B' in the diagram. Figure 10AA transformer 1000 is shown having a split primary winding including a first coil 1010 and a second coil 1020. The transformer 1000 also has a secondary winding including a third coil 1030 and a fourth coil 1040. Each of the first coil 1010 and the second coil 1020 includes conductors arranged in two metal planes M1 and M2. Each of the third coil 1030 and the fourth coil 1040 includes conductors arranged in two metal planes M3 and M4.

[0076] See still Figure 10A The coils are arranged in a substrate 1090, which can be similar to... Figure 4A The substrate 401 is shown. In the illustrated example, the substrate 1090 includes an insulating core layer 404. The core layer 404 includes an insulating dielectric material and serves as current isolation between the primary winding and the secondary winding. A first coil 1010 and a second coil 1020 of the primary winding are arranged on a first surface 404a of the core layer 404. A third coil 1030 and a fourth coil 1040 are arranged on a second surface 404b of the core layer 404.

[0077] Figure 10A An insulating layer 407 in contact with the surface of insulating layer 402 and an insulating layer 408 in contact with the surface of insulating layer 406 are also shown. Layers 407 and 408 may comprise polymeric materials, such as welding masks.

[0078] Now go to Figure 10B The top view shows a first coil 1010 enclosing region S1 on the first surface 404a of the core layer, while a second coil 1020 enclosing region S2 on the first surface 404a, which is adjacent to but separate from region S1. Therefore, the transformer 1000 is divided into two half-transformers 1000A and 1000B, each occupying different regions S1 and S2 on the surface of the semiconductor substrate 1090. Within transformer 1000A, at least a portion of the first coil 1010 is perpendicularly aligned and overlaps with at least a portion of the third coil 1030. Similarly, within transformer 1000B, at least a portion of the second coil 1020 is perpendicularly aligned and overlaps with at least a portion of the fourth coil 1040.

[0079] exist Figure 10B In this design, two half-transformers, 1000A and 1000B, are arranged side-by-side, and each half-transformer is shaped like a long, narrow racetrack, with its legs along the y-direction longer than those along the x-direction. While there are no restrictions on the shape and size of the primary winding, secondary winding, and each half-transformer, as... Figure 10B As shown, the two half-transformers 1000A and 1000B (each half-transformer is shaped like a half-width transformer) occupy a small space on the substrate 1090.

[0080] The operation and connection between the terminals within transformer 1000 will refer to Figure 10C and Figure 10D To explain. Figure 10C It is shown that it contains Figure 10A A perspective view of the coil portions in different metal planes of each coil of the transformer 1000. Figure 10D It is shown Figure 10C A series of cross-sectional views of the coil portion in four different metal planes.

[0081] On the primary side of the 1000A semi-transformer, Figure 10C , Figure 10D The first coil 1010 is shown to include at least two coil portions 1011, 1012, each coil portion arranged in corresponding metal layers M1, M2. Since the first coil 1010 spans two different metal layers, vias 1042 are used to vertically interconnect the coil portions 1011, 1012, such that the first coil 1010 includes a helix with two turns. Although Figure 10C The diagram shows coil portions in two metal layers, but the first coil 1010 may include coil portions in more than two layers, because more coil portions mean a higher number of turns and a higher inductance value in the first coil.

[0082] When a clockwise current I flows from terminal P1 through the first coil 1010 to terminal P2, a magnetic field is generated in the downward-facing region S1. The strength of this magnetic field is proportional to the number of turns of the first coil. Therefore, compared to a single-metal layer coil, the transformer 1000 can generate a magnetic field several times higher within the same unit area on the substrate. One advantage of the multi-metal planar coil design in the transformer 1000 is that each of the multiple metal planes can be used to carry the helical coil, without needing to utilize the metal planes to form bridges as lower-level channels and overpasses, such as... Figure 4B Bridge 444 is shown. Therefore, considering the secondary effect of the number of turns on the transformer inductance, high inductance can be achieved within a relatively small footprint on the substrate.

[0083] On the primary side of the semi-transformer 1000B, Figure 10C , Figure 10D The second coil 1020 is shown to include at least two coil portions 1021 and 1022, which are spiraled in the opposite direction to the first coil 1010, such that when current I flows through terminal P5 to terminal P6 via interconnect 1046, a counterclockwise current generates an upward magnetic field in region S2. Therefore, when current flows serially through the primary coils 1010 and 1020 of transformer 1000, the magnetic fields generated in half-transformers 1000A and 1000B point in opposite directions. Since the two magnetic fields cancel each other out, far-field radiation from transformer 1000 is reduced.

[0084] Return to the secondary side of the 1000A half-transformer. Figure 10C , Figure 10D The third coil 1030 is shown to include at least two coil portions 1031 and 1032, each arranged in a corresponding metal layer M3, M4. When the first coil 1010 is isolated from the third coil 1030 by the core layer 404, there is high capacitive coupling between the coil portion 1011 on layer M2 (connected to P2) and the coil portion 1031 on layer M3 (connected to P4) compared to the low capacitive coupling between the coil portion 1012 on M1 and the coil portion 1032 on M4 (these two coil portions are more widely spaced in the vertical direction). In some embodiments, such nodes are driven by equal and opposite voltages, thus eliminating the effect of such capacitors on the common-mode current. In some embodiments, the transformer 1000 may be designed to be symmetrical such that the capacitance between the first coil 1010 and the third coil 1030 is equal to the capacitance between the second coil 1020 and the fourth coil 1040.

[0085] In some embodiments, due to the symmetry of the transformer 1000, terminal pairs P1 / P6, P3 / P8, P2 / P5, and P4 / P7 will be driven by equal and opposite voltages, thus eliminating the influence of such capacitors on the common-mode current across the isolation barrier and reducing EMI emissions.

[0086] Back Figure 10C The terminals P1 to P8 of transformer 1000 can be implemented in any suitable manner, such as, but not limited to, Figure 10B Pads, traces, or other conductive structures within the substrate 1090 shown. The number of accessible terminals allows for flexible design of the transformer 1000. For example, in Figure 10C In the illustrated embodiment, the first coil 1010 and the second coil 1020 can be connected in series via interconnect 1046. Interconnect 1046a can further couple impedance 94 in series between terminals P2 and P5. In the same embodiment, interconnect 1046b can couple the third coil 1030 in series to the fourth coil 1040 by connecting terminal P4 to terminal P7.

[0087] In an alternative embodiment, the primary winding of transformer 1000 can be reconfigured to have a parallel connection between the two half-windings 1010 and 1020, for example, in a configuration similar to... Figure 2B In the configuration of the primary side.

[0088] Figure 11 This is a schematic plan view of a split-type planar transformer according to some embodiments. The split-type planar transformer is... Figure 10B A variant of the transformer with added magnetic material. Figure 11Two halves 1000A and 1000B of a transformer 1000 arranged in a substrate 1190 are shown. The two halves 1000A and 1000B are magnetically coupled via a magnetic material 1180 arranged on the substrate 1190 to increase the total inductance on the primary and secondary sides, thereby increasing the coil quality factor. In some embodiments, the magnetic material 1180 may include one or more magnetic material cores shared between the two transformer halves 1000A and 1000B.

[0089] exist Figure 11 In the illustrated embodiment, a single magnetic core 1180 is arranged through a first hole 1170a and a second hole 1170b in a substrate 1190. The first hole and the second hole each pass through a region enclosed by coils within corresponding half-transformers 1000A and 1000B, such that the magnetic core 1180 magnetically couples the two half-transformers.

[0090] Several aspects of at least one embodiment of the technology have thus been described, and it should be understood that various changes, modifications and improvements will readily occur to those skilled in the art.

[0091] For example, although the aspect of symmetrical transformers is discussed in the context of DC-DC converter applications, the disclosed transformers can be used in any suitable RF transformer application and are not limited to use in DC-DC converters or with soft-switching schemes.

[0092] Various aspects of this technology may be used individually, in combination, or in various arrangements not specifically discussed in the embodiments described above, and are therefore not limited to the details and arrangements of their application to the components set forth in the above description or shown in the accompanying drawings. For example, an aspect described in one embodiment may be combined in any way with aspects described in other embodiments.

[0093] Furthermore, this technology can be embodied as a method, examples of which have been provided. Actions performed as part of this method can be ordered in any suitable manner. Therefore, embodiments can be configured to perform actions in a different order than those shown, which may include performing some actions simultaneously, even those shown sequentially in the exemplary embodiments.

[0094] Unless otherwise expressly stated, the indefinite articles “a” and “an” used in this specification and claims shall be understood as “at least one”.

[0095] The phrase “and / or” as used herein in the specification and claims should be understood to mean “one or both” of the elements that are combined, i.e., elements that are combined in some cases but not in others.

[0096] As used herein in the specification and claims, the phrase "at least one" in relation to a list of one or more elements should be understood to mean at least one element selected from any one or more elements in the list of elements, but not necessarily including at least one of each element specifically listed in the list of elements, and does not exclude any combination of elements in the list of elements. This definition also allows for the optional presence of elements other than those specifically identified in the list of elements referred to by the phrase "at least one," whether related to or unrelated to those specifically identified elements.

[0097] The terms "about" and "approximately" can be used to indicate within ±20% of the target value in some embodiments, within ±10% of the target value in some embodiments, within ±5% of the target value in some embodiments, but within ±2% of the target value in some embodiments. The terms "about" and "approximately" may include the target value.

Claims

1. A transformer, the transformer comprising: A substrate having a first surface and a second surface opposite to the first surface; A primary winding having a first coil that contacts the first surface and defines a first closed region on the first surface and a second coil that contacts the first surface and defines a second closed region on the first surface, wherein the first closed region and the second closed region are arranged side by side and separated from each other; The secondary winding has a third coil and a fourth coil, each in contact with the second surface, wherein... The capacitive coupling between the first coil and the third coil is equal to the capacitive coupling between the second coil and the fourth coil. The first coil includes: The first coil portion is arranged in a first plane; The second coil portion is arranged in a second plane that is parallel to and offset from the first plane; and At least one via, the at least one via connecting the first coil portion and the second coil portion.

2. The transformer according to claim 1, wherein At least a portion of the first coil is aligned with at least a portion of the third coil along a vertical direction perpendicular to the first surface, and At least a portion of the second coil is aligned with at least a portion of the fourth coil along the vertical direction.

3. The transformer according to claim 1, wherein The third coil includes: The third coil portion is arranged in the third plane; The fourth coil portion is arranged in a fourth plane that is parallel to and offset from the third plane; and At least one via, the at least one via connecting the third coil portion and the fourth coil portion.

4. The transformer according to claim 3, wherein the first coil portion, the second coil portion, the third coil portion and the fourth coil portion are aligned along a vertical direction perpendicular to the first plane.

5. The transformer of claim 1, further comprising a current path including a first coil and a second coil connected in series, the current path being configured to generate magnetic fields in opposite directions in the first enclosed region and the second enclosed region, respectively, when current flows along the current path.

6. The transformer of claim 5, wherein the current path further includes an impedance disposed between the first coil and the second coil and connected in series with the first coil and the second coil.

7. The transformer according to claim 1, wherein the first coil and the second coil are connected in parallel.

8. The transformer of claim 1, wherein each of the first closed region and the second closed region includes a hole through the substrate, and wherein the transformer further includes magnetic material disposed in the hole in both the first closed region and the second closed region.

9. An isolated DC-DC converter, the isolated DC-DC converter comprising: A substrate having a first surface and a second surface opposite to the first surface; A first transformer includes a first coil that contacts the first surface and defines a first closed region on the first surface, and a third coil that contacts the second surface, wherein at least a portion of the first coil is aligned with at least a portion of the third coil in a vertical direction perpendicular to the first surface. The second transformer includes a second coil that contacts the second surface and defines a second closed region on the second surface, and a fourth coil that contacts the second surface, wherein at least a portion of the second coil is aligned with at least a portion of the fourth coil along the vertical direction. The first enclosed region and the second enclosed region are arranged side by side and separated from each other, and wherein The capacitive coupling between the first coil and the third coil is equal to the capacitive coupling between the second coil and the fourth coil. The first coil includes: The first coil portion is arranged in a first plane; The second coil portion is arranged in a second plane that is parallel to and offset from the first plane; and At least one via, the at least one via connecting the first coil portion and the second coil portion.

10. The isolated DC-DC converter of claim 9, further comprising a current path including a first coil and a second coil connected in series, the current path being configured to generate magnetic fields in opposite directions in the first enclosed region and the second enclosed region, respectively, when current flows along the current path.

11. The isolated DC-DC converter of claim 10, wherein the current path further includes an impedance disposed between the first coil and the second coil and connected in series with the first coil and the second coil.

12. The isolated DC-DC converter according to claim 9, wherein the first coil and the second coil are connected in parallel.

13. A split-type planar transformer, the split-type planar transformer comprising: A substrate having a first surface and a second surface opposite to the first surface; A first transformer includes a first coil in contact with the first surface and a third coil in contact with the second surface, wherein the first coil is aligned with the third coil in a direction perpendicular to the first surface. The second transformer includes a second coil in contact with the second surface and a fourth coil in contact with the second surface, wherein the second coil is aligned with the fourth coil along the vertical direction; The first coil and the second coil are arranged side by side in the transverse direction along the first surface and are separated from each other by a certain distance, and wherein The capacitive coupling between the first coil and the third coil is equal to the capacitive coupling between the second coil and the fourth coil. The first coil includes: The first coil portion is arranged in a first plane; The second coil portion is arranged in a second plane that is parallel to and offset from the first plane; and At least one via, the at least one via connecting the first coil portion and the second coil portion.

14. The split-plane transformer of claim 13, further comprising a current path including a first coil, an impedance, and a second coil connected in series, wherein the impedance is arranged between the first coil and the second coil.

15. The split-type planar transformer according to claim 13, wherein the first coil and the second coil are connected in parallel.

16. The split-plane transformer according to claim 13, further comprising magnetic material disposed in both the first coil and the second coil.

17. The split-type planar transformer according to claim 13, wherein the third coil comprises: The third coil portion is arranged in the third plane; The fourth coil portion is arranged in a fourth plane that is parallel to and offset from the third plane; and at least one via, the via connecting the third coil portion and the fourth coil portion, and wherein The first coil portion, the second coil portion, the third coil portion, and the fourth coil portion are aligned along a vertical direction perpendicular to the first plane.

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