Three-coil transformer and low-noise amplifier

Abstract

The three-coil transformer and low-noise amplifier disclosed herein are described. The first and second inductors of the three-coil transformer are closed-shaped coils that overlap. The third inductor is an "8"-shaped coil formed by the first and second main bodies connected by a cross jumper. The first and second main bodies overlap with the first and second inductors, and the cross jumper does not contact the first and second inductors. The low-noise amplifier includes a transistor, a capacitor, and the three-coil transformer. The three coils are connected to the gate, source, and drain of the transistor, respectively, to achieve transconductance enhancement and noise cancellation, thereby increasing circuit gain and reducing noise. It also serves as the first-stage input matching and the first- and second-stage inter-stage matching. The three-coil transformer disclosed herein allows for independent coupling coefficients among the three coils, facilitating circuit design. By simultaneously performing noise cancellation, input matching, and inter-stage matching through the three-coil transformer, the chip area can be significantly reduced.

Description

Technical Field

[0001] This disclosure relates to the field of electronic circuit technology, and in particular to a three-turn transformer and a low-noise amplifier having the three-turn transformer. Background Technology

[0002] Over the past decade, millimeter-wave technology has undoubtedly experienced one of the fastest-growing technologies. As an electromagnetic wave, millimeter waves are primarily used in communications and radar. One of the most critical components in millimeter-wave systems is the low-noise amplifier (LNA), which receives and amplifies small signals from the antenna while maintaining a good signal-to-noise ratio (SNR). Since the LNA is located in the first stage of the receiver, and the first stage determines the noise figure (NF) of the link, it needs to provide sufficient gain to suppress noise in subsequent stages. Therefore, optimizing the noise performance of the LNA and improving its power gain have been crucial issues of concern.

[0003] For reducing noise figure, noise cancellation, proposed by F. Bruccoleri, is an excellent choice. It can reduce the noise figure of low-noise amplifiers over a wide bandwidth. Traditional noise cancellation techniques consist of two amplifiers: one is the main signal path amplifier, called the main amplifier, and the other is called the auxiliary amplifier. The signal flow of the main amplifier is in the same direction as the signal flow of the auxiliary amplifier, and they are superimposed and enhanced; the noise signal flow is in the opposite direction, and their superposition can cancel the noise signal flow of the main amplifier. This cancellation can be proven to be broadband. In addition, transconductance enhancement is another important technique for improving the gain of low-noise amplifiers and reducing their noise. Transconductance enhancement involves directly connecting an inverting amplifier between the gate and source of the transconductance stage transistor in the low-noise amplifier. This inverting amplifier increases the voltage difference between the gate and source of the transconductance stage transistor, effectively increasing the equivalent transconductance of the transconductance transistor.

[0004] In the millimeter-wave band, parasitic effects are more pronounced in circuits, so traditional noise cancellation structures often fail to effectively cancel noise. Furthermore, the parasitic effects introduced by additional auxiliary amplifier paths result in significant gain losses. This means that low-noise amplifiers using traditional noise cancellation techniques in the millimeter-wave band do not offer good noise and gain performance. One method for achieving noise cancellation in the millimeter-wave band is to use a three-coil transformer, without introducing an additional auxiliary amplifier, to simultaneously achieve noise cancellation and transconductance boost. However, regarding the coupling coefficients in a three-coil transformer, the three inductors have a mutual inductance relationship. Therefore, once two coupling coefficients in the three-coil transformer are designed, the third coupling coefficient is fixed. It may not be possible to obtain all three required coupling coefficients simultaneously, necessitating trade-offs between specifications. Summary of the Invention

[0005] This disclosure aims to at least partially address one of the technical problems in the related art.

[0006] Therefore, the three-coil transformer for easy adjustment of coupling coefficient provided in the first aspect embodiment of this disclosure includes:

[0007] The first inductor and the second inductor are both coils with closed shapes, and they overlap.

[0008] The third inductor is an "8" shaped coil formed by the first body and the second body through a cross jumper wire. The first body and the second body overlap with the first inductor and the second inductor, and the cross jumper wire does not contact the first inductor and the second inductor.

[0009] In some embodiments, the third inductor coil is a symmetrical or asymmetrical figure-eight coil.

[0010] In some embodiments, the coupling coefficient between the third inductor and the first inductor is positively correlated with the ratio of the overlapping areas of the first body and the second body to the first inductor.

[0011] In some embodiments, the coupling coefficient between the third inductor and the second inductor is positively correlated with the ratio of the overlapping areas of the first body and the second body to the second inductor.

[0012] In some embodiments, the first inductor and the second inductor are of the same shape.

[0013] In some embodiments, the first inductor and the second inductor are located on the same side or on both sides of the third inductor.

[0014] In some embodiments, the bodies of the first inductor, the second inductor, and the third inductor are made of different metals, and the selected metals should ensure that the resistance loss of each inductor is as small as possible.

[0015] The low-noise amplifier provided in the second aspect of this disclosure includes a three-coil transformer provided in any embodiment of the first aspect of this disclosure.

[0016] In some embodiments, the low-noise amplifier includes a transistor, a capacitor, and a three-coil transformer according to any embodiment of the first aspect of this disclosure.

[0017] The source of the transistor is connected to the ground-signal-ground interface GSG;

[0018] One end of the first inductor is connected to the source of the transistor and the other end is grounded; one end of the second inductor is connected to the gate of the transistor and the other end is connected to the DC bias voltage VB; one end of the third inductor is connected to the drain of the transistor and the other end is connected to the power supply VDD.

[0019] The capacitor and the third inductor form an interstage matching network. One end of the capacitor is connected to the drain of the transistor, and the other end is connected to the load.

[0020] In some embodiments, the transistor is an NMOS transistor.

[0021] The technical features and beneficial effects of this disclosure are as follows:

[0022] 1. Increase the design freedom of three-coil transformers. The figure-eight three-coil transformer allows the coupling coefficients between the three coils in the transformer to be independent, introducing more freedom and facilitating circuit design.

[0023] 2. Improve the noise performance of low-noise amplifiers in the millimeter-wave band. The figure-eight three-coil transformer can achieve noise cancellation. The two inductors connected to the drain and source of the common-gate amplifier form a transformer, which can induce noise voltages that are opposite in phase to their respective noise voltages. The superposition of the noise voltage and the induced noise voltage can achieve the effect of noise cancellation, thereby improving the noise performance of the transistor.

[0024] 3. Improve the gain performance of low-noise amplifiers in the millimeter-wave band. The figure-eight three-coil transformer can enhance transconductance. The two inductors connected to the gate and source of the common-gate amplifier form a transformer, which can increase the gate-source voltage difference of the transistor and improve the equivalent transconductance of the transistor.

[0025] 4. Improve chip compactness and reduce chip area. The figure-eight three-coil transformer in the common-gate stage simultaneously performs the functions of input and interstage impedance matching, eliminating the need for an additional matching network and reducing passive losses and chip area. This disclosure fully utilizes the structural characteristics of the three-coil transformer and adopts a compact layout design, further reducing the chip area. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of a three-coil transformer provided in the first aspect of this disclosure.

[0027] Figure 2 A schematic diagram of the circuit structure of a low-noise amplifier provided in the second aspect of this disclosure;

[0028] Figure 3The simulation results of the signal and noise of the low-noise amplifier provided in the second aspect of the present disclosure are shown. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the application will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining this application and are not intended to limit this application.

[0030] Conversely, this application covers any alternatives, modifications, equivalent methods, and schemes made within the spirit and scope of this application as defined by the claims. Furthermore, to provide the public with a better understanding of this application, certain specific details are described in detail below. However, this application can be fully understood by those skilled in the art even without these detailed descriptions.

[0031] The structures, proportions, and sizes illustrated in the accompanying drawings are solely for illustrative purposes to aid those skilled in the art and to facilitate understanding. They are not intended to limit the scope of this application and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, provided they do not affect the effectiveness or purpose of this application, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of this application. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of this application's implementation.

[0032] See Figure 1 The first aspect of this disclosure provides a three-coil transformer, comprising three inductor coils, wherein:

[0033] The first inductor Ls and the second inductor Lg are located on the same side or on both sides of the third inductor Ld. They are coils with a closed shape and overlap. The first inductor Ls and the second inductor Lg are made of a first metal and a second metal, respectively.

[0034] The third inductor Ld is an "8" shaped coil formed by the first body and the second body through a cross jumper. The first body and the second body are made of a third metal. The first body and the second body overlap with the first inductor Ls and the second inductor Lg, and the cross jumper does not contact the first inductor Ls and the second inductor Lg.

[0035] In some embodiments, the coupling coefficient between the first inductor Ls and the second inductor Lg is K1, the coupling coefficient between the third inductor Ld and the first inductor Ls is K2, and the coupling coefficient between the third inductor Ld and the second inductor Lg is K3. The coupling coefficient K2 is positively correlated with the ratio of the overlapping areas of the first main body and the second main body in the third inductor Ld with the first inductor Ls, respectively, and the coupling coefficient K3 is positively correlated with the ratio of the overlapping areas of the first main body and the second main body in the third inductor Ld with the second inductor Lg, respectively.

[0036] In some embodiments, the first inductor coil Ls is made of any metal layer in the 65nm CMOS process built-in metal layers M1-AP (in order to reduce resistance loss, a higher metal layer is used as much as possible), and can be designed into any closed pattern that meets the requirements of the 65nm CMOS process. In this embodiment, it is designed as an octagon.

[0037] In some embodiments, the second inductor Lg can be located above or below the first inductor Ls. The second inductor Lg is made of any metal layer in the 65nm CMOS process built-in metal layer M1-AP, which is made of a different material than the first inductor Ls (higher metal layers are preferred to reduce resistance loss). It can be designed into any closed pattern that meets the requirements of the 65nm CMOS process, and the second inductor Lg and the first inductor Ls are of the same shape to maximize the coupling coefficient between the second inductor Lg and the first inductor Ls, thereby reducing the insertion loss of the transformer.

[0038] In some embodiments, the third inductor Ld is composed of any two of the 65nm CMOS process-integrated metal layers M1-AP (to reduce losses, higher metal layers are preferred; AP and M9 layers are used as examples below). It is figure-eight shaped. The third inductor Ld can be designed as a symmetrical or asymmetrical figure-eight shape according to the required coupling coefficient. The main body uses metal layer AP, and the intersection is connected by jumpers from metal layer M9. The coupling coefficients between the third inductor Ld and the first inductor Ls and the second inductor Lg can be determined by the overlap area of ​​the first and second main bodies of the third inductor Ld with the first inductor Ls, respectively. The ratio of the first and second main bodies in the third inductor Ld to the second inductor Lg (hereinafter referred to as the area ratio of the first and second main bodies) is determined by the following principle, taking the coupling between the third inductor Ld and the second inductor Lg as an example: Both the first and second main bodies of the third inductor Ld are magnetically coupled to the second inductor Lg, and the larger the overlap area between the coils, the stronger the coupling. Therefore, the coupling coefficient between the first and second main bodies and the second inductor Lg can be controlled by controlling the overlap area of ​​each of the first and second main bodies with the second inductor Lg (e.g., the area ratio of the first and second main bodies to the second inductor Lg). Figure 1 In the diagram, is the overlapping area of ​​the first main body and the second inductor Lg, and is the overlapping area of ​​the second main body and the second inductor Lg. Simultaneously, since the magnetic fields of the first and second main bodies in the third inductor Ld are in opposite directions, their coupling with the magnetic field of the second inductor Lg will cancel each other out. Therefore, by reasonably allocating the overlapping areas of the first and second main bodies and the second inductor Lg in the third inductor Ld, this cancellation effect can be controlled, thereby achieving any desired coupling coefficient (especially a small coupling coefficient). That is, the closer the ratio of the overlapping areas of the first and second main bodies with the second inductor Lg is to 1, the smaller the coupling coefficient K2 between the third inductor Ld and the second inductor Lg will be. For example, simulations show that when the ratio of the areas of the first and second main bodies is 1.3:1, the coupling coefficient between the third inductor Ld and the second inductor Lg is approximately 0.1. In use, the required coupling coefficient can be selected according to design requirements, and the connection method of the three-coil transformer ports can be selected according to the requirements of the same-name and different-name terminals of the transformer in the circuit.

[0039] See Figure 2 The low-noise amplifier with the aforementioned three-coil transformer provided in the second aspect of this disclosure includes a common-gate amplifier, a three-coil transformer, and a capacitor Cd. The common-gate amplifier includes a transistor M1, which may be an NMOS transistor. Transistor M1 constitutes the transconductor in the common-gate amplifier stage. The three-coil transformer is... Figure 1 The three-coil transformer shown serves multiple functions: input matching, transconductance enhancement, and noise cancellation. The third inductor, Ld, and capacitor, Cd, provide output matching. The connections are as follows: the source of transistor M1 is connected to the ground-signal-ground interface (GSG); one end of the first inductor, Ls, is connected to the source of transistor M1, and the other end is grounded; one end of the second inductor, Lg, is connected to the gate of transistor M1, and the other end is connected to the DC bias voltage VB of the common-gate amplifier; one end of the third inductor, Ld, is connected to the drain of transistor M1, and the other end is connected to the power supply VDD. The coupling coefficient between the first inductor, Ls, and the second inductor, Lg, is K1; the coupling coefficient between the third inductor, Ld, and the first inductor, Ls, is K2; and the coupling coefficient between the third inductor, Ld, and the second inductor, Lg, is K3. The interstage matching network consists of the third inductor Ld and capacitor Cd in a three-coil transformer. One end of capacitor Cd is connected to the drain of transistor M1, and the other end is connected to the input of the next stage amplifier (in...). Figure 2In this circuit, the next stage amplifier is represented by the load RL; the source of transistor M1 serves as the input terminal of the common-gate amplifier, and the drain of transistor M1 serves as the output terminal of the main common-source amplifier; a three-coil transformer is used for input matching, noise cancellation, and transconductance enhancement. Specifically, when the input signal enters the source of transistor M1 through the ground-signal-ground interface GSG, the transformer composed of the first inductor Ls and the second inductor Lg in the three-coil transformer induces an inverted voltage at the gate of transistor M1, increasing the equivalent transconductance of transistor M1; the transformer composed of the first inductor Ls and the third inductor Ld in the three-coil transformer can induce a noise voltage opposite in phase to the original noise voltage, which, after superposition, can achieve the effect of noise cancellation. In this circuit, when designing the coupling coefficients (K1, K2, K3) of the three-coil transformer, the gain, noise, and stability of the circuit must be comprehensively considered. The coupling coefficient K1 should be as large as possible to reduce the insertion loss of the transformer. Since the first inductor Ls and the third inductor Ld form a positive feedback, the magnitude of the positive feedback is proportional to the transformer coupling coefficient K2. Excessive positive feedback will affect the stability of the amplifier, and the precise value of K2 needs to be determined through simulation.

[0040] This embodiment employs a single-stage single-ended amplifier structure; wherein input matching and inter-stage matching between the first and second stages are accomplished by an asymmetrical figure-eight three-turn transformer and capacitors. The bias of the common-gate amplifier is provided by the inductor coil of the three-turn transformer, and the bias voltage of the common-source common-gate amplifier and the common-source amplifier are provided by bias resistors.

[0041] In this low-noise amplifier, the bias voltage VB is a known quantity, which is 0.6V in this example.

[0042] The operating principle of the low-noise amplifier disclosed herein is as follows:

[0043] The single-ended input signal is injected into the first-stage single-ended common-gate amplifier through the GSG interface. After amplification, it is output from the drain of the first-stage single-ended common-gate amplifier. The output of the first-stage single-ended amplifier is connected to the input of the subsequent single amplifier through the interstage matching network. The noise signal and the useful signal are respectively processed by the asymmetric figure-eight three-turn transformer, which respectively achieves the effects of noise cancellation and transconductance enhancement.

[0044] Embodiments of the low-noise amplifier based on transconductance enhancement technology and noise cancellation technology disclosed herein are described below:

[0045] This embodiment uses a 65nm CMOS process (a conventional fabrication process in the field) to fabricate a millimeter-wave low-noise amplifier based on a multi-turn transformer that achieves transconductance enhancement and noise cancellation, which can be used as the first stage of a low-noise amplifier.

[0046] Figure 3A comparison graph showing the gain (Gmax) and noise performance (NFmin) of a low-noise amplifier with and without a three-coil transformer is provided. Figure 3 As shown, the gain and noise performance of the low-noise amplifier are improved after using the three-coil transformer proposed in this embodiment. Therefore, this embodiment can improve the noise performance and gain performance of the low-noise amplifier in the millimeter-wave band.

[0047] In summary, the low-noise amplifier provided by this disclosure overcomes the problems of additional noise, large parasitics, and large gain loss introduced by auxiliary amplifiers in traditional noise cancellation techniques. It also solves the problem of the coupling coefficient being uncontrollable in three-coil transformers. This disclosure uses a three-coil transformer with an "8"-shaped inductor coil to achieve noise cancellation and transconductance enhancement for the common-gate amplifier, and utilizes the ratio of the area of ​​the first and second main bodies of the "8"-shaped structure to freely control the coupling coefficient. The three-coil transformer can simultaneously function as an input matching network and an inter-stage matching network. Furthermore, to achieve the different coupling coefficients required by the transformer, an "8"-shaped inductor coil is used in conjunction with a locally enclosed inductor coil.

[0048] The above embodiments verify the correctness and effectiveness of this disclosure. The above description is merely a low-noise amplifier with transconductance enhancement and noise cancellation implemented using a three-turn transformer under specific CMOS processes and frequency bands, and is not intended to limit the scope of protection of this disclosure.

[0049] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0050] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A three-coil transformer, characterized in that, Includes three inductor coils, of which, The first inductor and the second inductor are both coils with closed shapes, and they overlap. The third inductor is an "8"-shaped coil formed by a first body and a second body through a cross jumper. Both the first body and the second body overlap with the first inductor and the second inductor, and the cross jumper does not contact the first inductor and the second inductor. The coupling coefficient between the third inductor and the first inductor is positively correlated with the ratio of the overlap area of ​​the first body and the second body with the first inductor. The coupling coefficient between the third inductor and the second inductor is also positively correlated with the ratio of the overlap area of ​​the first body and the second body with the second inductor.

2. The three-coil transformer according to claim 1, characterized in that, The third inductor coil is a symmetrical or asymmetrical figure-eight coil.

3. The three-coil transformer according to claim 1, characterized in that, The first inductor and the second inductor are of the same shape.

4. The three-coil transformer according to claim 1, characterized in that, The first inductor and the second inductor are located on the same side or on both sides of the third inductor.

5. The three-coil transformer according to claim 1, characterized in that, The bodies of the first inductor, the second inductor, and the third inductor are made of different metals.

6. A low-noise amplifier, characterized in that, Includes the three-coil transformer as described in any one of claims 1 to 5.

7. A low-noise amplifier, characterized in that, Includes transistors, capacitors, and the three-coil transformer as described in any one of claims 1 to 5. The source of the transistor is connected to the ground-signal-ground interface GSG; One end of the first inductor is connected to the source of the transistor and the other end is grounded; one end of the second inductor is connected to the gate of the transistor and the other end is connected to the DC bias voltage VB; one end of the third inductor is connected to the drain of the transistor and the other end is connected to the power supply VDD. The capacitor and the third inductor form an interstage matching network. One end of the capacitor is connected to the drain of the transistor, and the other end is connected to the load.

8. The low-noise amplifier according to claim 7, characterized in that, The transistor is an NMOS transistor.

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