RF transformer that converts input RF signal into output RF signal

Abstract

The present invention relates to a radio frequency transformer (100) for converting an input radio frequency signal into an output radio frequency signal. The radio frequency transformer (100) comprises: a primary winding (101) having a first input terminal and a second input terminal, wherein the primary winding (101) comprises a first part (L1Pa), a second part (L1Pb), a third part (L1Na) and a fourth part (L1Nb), wherein the first part (L1Pa) is electromagnetically coupled to the fourth part (L1Nb), and the second part (L1Pb) is electromagnetically coupled to the third part (L1Nb); and a secondary winding (103) having a first output terminal and a second output terminal, wherein the secondary winding (103) is electromagnetically coupled to the first part (L1Pa), the second part (L1Pb), the third part (L1Na) and the fourth part (L1Nb) of the primary winding (101).

Description

Technical Field

[0001] The present invention relates to the field of radio frequency transformers, and in particular to a radio frequency transformer for converting between balanced and unbalanced terminals. Background Art

[0002] RF transformers are key components in RF systems such as mobile communication systems or radar systems and are used in a wide variety of applications. Typically, RF transformers are used for impedance transformation between primary and secondary windings and for transformation between balanced and unbalanced terminals.

[0003] Specifically, RF transformers are commonly used in RF transmitters and can have a significant impact on their performance. For example, a digital RF transmitter using a direct digital RF modulator (DDRM) or an analog RF transmitter using a 25% duty cycle mixer wants low common mode impedance to terminate the strong common mode current at twice the frequency of the input RF signal. However, common RF transformers have a common mode shunt resonance at nearly twice the differential mode resonant frequency, which degrades the performance of the RF transmitter. Summary of the invention

[0004] The object of the present invention is to provide a radio frequency conversion.

[0005] This object is achieved by the features of the independent claims. Further embodiments are apparent from the dependent claims, the description and the drawings.

[0006] The present invention is based on the discovery that sections within a primary winding of a radio frequency transformer can be electromagnetically coupled to adjust the common mode impedance independently of the differential mode impedance. By tightly coupling the two halves of the primary winding, such as the positive half and the negative half of the primary winding, the common mode inductance can be reduced and the common mode resonant frequency of the radio frequency transformer can be shifted from twice the frequency of the input radio frequency signal to a higher frequency.

[0007] The RF transformer can be used with a modulator, such as a direct digital RF modulator (DDRM), within the RF transformer, wherein the RF transmitter utilizes the specific features of the RF transformer. The RF transmitter can improve performance, such as reducing the second harmonic voltage swing of the modulator drain, increasing the 1dB compression point (P1dB), improving the counter third order intermodulation (C-IM3) performance, and reducing the second harmonic emission.

[0008] The RF transformer and / or the RF transmitter may be used in any kind of RF system, such as a mobile communication system or a radar system.

[0009] According to a first aspect, the present invention relates to a radio frequency transformer for transforming an input radio frequency signal into an output radio frequency signal, the radio frequency transformer comprising: a primary winding having a first input terminal and a second input terminal, wherein the first input terminal and the second input terminal are used to process the input radio frequency signal, the primary winding comprising a first part, a second part, a third part and a fourth part, the first part is electromagnetically coupled to the fourth part, and the second part is electromagnetically coupled to the third part; and a secondary winding having a first output terminal and a second output terminal, wherein: the first output terminal and the second output terminal are used to provide the output radio frequency signal, the secondary winding is electromagnetically coupled to the first part, the second part, the third part and the fourth part of the primary winding. In this way, an effective concept of transforming an input radio frequency signal into an output radio frequency signal is realized.

[0010] The primary winding and / or the secondary winding may have further terminals, for example for providing a supply voltage. Thus, the primary winding and / or the secondary winding may have at least two terminals. The number of turns of the primary winding and the number of turns of the secondary winding may be chosen arbitrarily, i.e. the turns ratio between the primary winding and the secondary winding may be chosen arbitrarily.

[0011] The electromagnetic coupling may include inductive coupling and / or capacitive coupling. The presence of electromagnetic coupling refers to the presence of a high coupling coefficient, for example 0.5 to 1.

[0012] According to the first aspect as described above, in the first implementation form of the RF transformer, the first part is electromagnetically decoupled from the second part, and the third part is electromagnetically decoupled from the fourth part. Therefore, the common mode resonant frequency of the RF transformer can be more efficiently shifted to a higher frequency.

[0013] The electromagnetic decoupling may include inductive decoupling and / or capacitive decoupling. The presence of electromagnetic decoupling refers to the presence of a low coupling coefficient, for example 0 to 0.5.

[0014] According to the first aspect or the first implementation form of the first aspect as described above, in the second implementation form of the RF transformer, the input RF signal is a differential RF signal, and the output RF signal is a single-ended RF signal. In this way, balanced to unbalanced (bal-un) conversion is efficiently achieved. The RF transformer can therefore be used as a RF balanced to unbalanced transformer.

[0015] According to the first aspect or the first implementation form of the first aspect as described above, in a third implementation form of the RF transformer, the input RF signal is a differential RF signal, and the output RF signal is a differential RF signal. In this way, balanced to balanced (bal-bal) conversion is efficiently achieved.

[0016] According to the first aspect or the first implementation form of the first aspect as described above, in a fourth implementation form of the RF transformer, the input RF signal is a single-ended RF signal, and the output RF signal is a differential RF signal. In this way, unbalanced to balanced (un-bal) conversion is efficiently achieved.

[0017] According to the first aspect or the first implementation form of the first aspect as described above, in a fifth implementation form of the RF transformer, the input RF signal is a single-ended RF signal, and the output RF signal is a single-ended RF signal. In this way, unbalanced to unbalanced (un-un) conversion is efficiently achieved.

[0018] According to the first aspect or any of the aforementioned implementation forms of the first aspect, in a sixth implementation form of the RF transformer, the input RF signal includes a signal component at a certain input frequency, wherein the common mode resonant frequency of the RF transformer is greater than twice the input frequency. In this way, the common mode impedance of the RF transformer can be efficiently reduced at twice the input frequency.

[0019] According to the first aspect or any of the aforementioned implementation forms of the first aspect, in a seventh implementation form of the radio frequency transformer, the first part and the second part of the primary winding are connected in parallel, and / or the third part and the fourth part of the primary winding are connected in parallel. In this way, electromagnetic coupling and / or electromagnetic decoupling are efficiently achieved.

[0020] According to the first aspect or any of the aforementioned implementation forms of the first aspect, in an eighth implementation form of the radio frequency transformer, the first part and the second part of the primary winding are connected in series, and / or the third part and the fourth part of the primary winding are connected in series. In this way, electromagnetic coupling and / or electromagnetic decoupling are efficiently achieved.

[0021] According to the first aspect or any of the aforementioned implementation forms of the first aspect, in a ninth implementation form of the radio frequency transformer, the radio frequency transformer is disposed on a semiconductor substrate, wherein: the first portion includes a first wire, the second portion includes a second wire, the third portion includes a third wire, and the fourth portion includes a fourth wire. In this way, the radio frequency transformer is efficiently provided as a radio frequency integrated circuit (RFIC). The radio frequency transformer can be regarded as an on-chip radio frequency transformer.

[0022] According to the ninth implementation form of the first aspect, in a tenth implementation form of the radio frequency transformer, a portion of the first wire is adjacent to a portion of the fourth wire, and / or a portion of the second wire is adjacent to a portion of the third wire. In this way, electromagnetic coupling between adjacent wires is efficiently achieved.

[0023] When no other conductor is placed in between, the portions of the conductor can be regarded as adjacent, thereby providing a high coupling coefficient.

[0024] According to the ninth implementation form or the tenth implementation form of the first aspect, in an eleventh implementation form of the radio frequency transformer, a portion of the first wire and a portion of the fourth wire are placed in different layers on the semiconductor substrate, and / or a portion of the second wire and a portion of the third wire are placed in different layers on the semiconductor substrate. In this way, electromagnetic coupling between wires in different layers is efficiently achieved.

[0025] The layers may be conductive metal layers. The layers may be stacked on the semiconductor substrate to realize a multi-layer integrated circuit. Therefore, a high coupling coefficient may be provided.

[0026] According to the first aspect as described above or any of the aforementioned implementation forms of the first aspect, in a twelfth implementation form of the radio frequency transformer, the primary winding is connected to a supply voltage source, so that the supply voltage can be provided efficiently.

[0027] The supply voltage source may be a supply component for generating the input radio frequency signal, such as a modulator, etc. The supply voltage source may be connected to the primary winding using another terminal.

[0028] According to the twelfth implementation form of the first aspect, in a thirteenth implementation form of the radio frequency transformer, the supply voltage source is connected to the primary winding between the first part and the third part, and / or the supply voltage source is connected to the primary winding between the second part and the fourth part. In this way, an effective symmetrical center tap of the primary winding is achieved.

[0029] According to the first aspect as described above or any of the aforementioned implementation forms of the first aspect, in a fourteenth implementation form of the RF transformer, the number of turns of the primary winding is equal to the number of turns of the secondary winding, so that effective impedance transformation between the primary winding and the secondary winding is achieved.

[0030] The turns ratio between the primary winding and the secondary winding may be 2:2, 4:4 or 8:8, etc. Due to imperfection, an effective turns ratio including a fractional number of turns may be obtained, such as an effective turns ratio of 2:1.9.

[0031] According to a second aspect, the present invention relates to a radio frequency transmitter, the radio frequency transmitter comprising a modulator for generating an input radio frequency signal and a radio frequency transformer according to the first aspect as described above or according to any implementation form of the first aspect, wherein the radio frequency transformer is used to transform the input radio frequency signal into an output radio frequency signal. Thus, an effective radio frequency transmitter is provided.

[0032] The radio frequency transmitter can reduce the second harmonic voltage swing of the modulator drain, increase the 1dB compression point (P1dB), improve the counter third order intermodulation (C-IM3) performance, and reduce the second harmonic emission.

[0033] The output RF signal may be provided directly to another component, such as a power amplifier, RF switch, duplex filter, antenna tuner, or antenna.

[0034] According to the second aspect as described above, in the first implementation form of the radio frequency transmitter, the modulator is used to generate the input radio frequency signal by drawing radio frequency current from the radio frequency transformer, so that the input radio frequency signal can be generated efficiently.

[0035] The source impedance of the modulator may be greater than the load impedance of the RF transformer. The input RF signal may be formed by the RF current.

[0036] According to the second aspect as described above or according to the first implementation form of the second aspect, in a second implementation form of the radio frequency transmitter, the modulator is a direct digital radio frequency modulator (DDRM), so that the input radio frequency signal is directly generated by using switching transistors without an intermediate mixing stage.

[0037] According to the second aspect, the first implementation form of the second aspect, or the second implementation form of the second aspect, in a third implementation form of the RF transmitter, the RF transmitter further comprises a power amplifier for amplifying the output RF signal. Thus, an effective RF transmitter is provided.

[0038] According to a third aspect, the present invention relates to a method for transforming an input radio frequency signal into an output radio frequency signal using a radio frequency transformer, wherein: the radio frequency transformer comprises a primary winding and a secondary winding, the primary winding having a first input terminal and a second input terminal, the secondary winding having a first output terminal and a second output terminal; the method comprises: processing the input radio frequency signal through the first input terminal and the second input terminal of the primary winding, electromagnetically coupling the first part of the primary winding to the fourth part of the primary winding, electromagnetically coupling the second part of the primary winding to the third part of the primary winding, electromagnetically coupling the secondary winding to the first part, the second part, the third part and the fourth part of the primary winding, and providing the output radio frequency signal through the first output terminal and the second output terminal of the secondary winding. In this way, an effective concept of transforming an input radio frequency signal into an output radio frequency signal is realized.

[0039] The method may be performed by the RF transformer and / or the RF transmitter.Other features of the method may be derived directly from the functionality of the RF transformer and / or the RF transmitter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The embodiments of the present invention will be described in conjunction with the following drawings, in which:

[0041] Figure 1 A diagram showing a radio frequency transformer for converting an input radio frequency signal into an output radio frequency signal according to an embodiment is shown;

[0042] Figure 2 A diagram showing a radio frequency transmitter including a modulator and a radio frequency transformer according to an embodiment is shown;

[0043] Figure 3 A diagram showing a method of transforming an input radio frequency signal into an output radio frequency signal according to an embodiment;

[0044] Figure 4 A diagram showing a radio frequency transformer for converting an input radio frequency signal into an output radio frequency signal according to an embodiment is shown;

[0045] Figure 5 A diagram showing a radio frequency transformer for converting an input radio frequency signal into an output radio frequency signal according to an embodiment is shown;

[0046] Figure 6 A diagram showing a radio frequency transformer for converting an input radio frequency signal into an output radio frequency signal according to an embodiment is shown;

[0047] Figure 7 A diagram showing a radio frequency transformer for converting an input radio frequency signal into an output radio frequency signal according to an embodiment is shown;

[0048] Figure 8 Shown is a diagram of a circuit including a primary winding of a radio frequency transformer according to an embodiment;

[0049] Fig. 9 Shown is a graph of common mode load impedance versus frequency of an RF transformer independent of coupling coefficient according to an embodiment;

[0050] Fig.10 A diagram showing a radio frequency transmitter including a modulator and a radio frequency transformer according to an embodiment is shown;

[0051] Fig.11 FIG. 1 is a graph showing output power of a radio frequency transmitter and third-order intermodulation performance of a counter according to an embodiment;

[0052] Fig.12 A diagram showing a reference RF transformer including a primary winding and a secondary winding is shown; and

[0053] Fig.13 Shown is a diagram of a reference RF transformer including a primary winding and a secondary winding. DETAILED DESCRIPTION

[0054] Figure 1 Shown is a diagram of a radio frequency transformer 100 for transforming an input radio frequency signal into an output radio frequency signal according to an embodiment.

[0055] The RF transformer 100 includes a primary winding 101 having a first input terminal and a second input terminal, wherein: the first input terminal and the second input terminal are used to process an input RF signal, and the primary winding 101 includes a first part L1Pa, a second part L1Pb, a third part L1Na and a fourth part L1Nb, the first part L1Pa is electromagnetically coupled to the fourth part L1Nb, and the second part L1Pb is electromagnetically coupled to the third part L1Na.

[0056] The RF transformer 100 further includes a secondary winding 103 having a first output terminal and a second output terminal, wherein the first output terminal and the second output terminal are used to provide an output RF signal, and the secondary winding 103 is electromagnetically coupled to the first part L1Pa, the second part L1Pb, the third part L1Na and the fourth part L1Nb of the primary winding 101.

[0057] Figure 2 The figure shows a radio frequency transmitter 200 including a modulator 201 and a radio frequency transformer 100 according to an embodiment. The modulator 201 is used to generate an input radio frequency signal. The radio frequency transformer 100 is used to transform the input radio frequency signal into an output radio frequency signal.

[0058] The RF transformer 100 includes a primary winding 101 having a first input terminal and a second input terminal, wherein: the first input terminal and the second input terminal are used to process an input RF signal, and the primary winding 101 includes a first part L1Pa, a second part L1Pb, a third part L1Na and a fourth part L1Nb, the first part L1Pa is electromagnetically coupled to the fourth part L1Nb, and the second part L1Pb is electromagnetically coupled to the third part L1Na.

[0059] The RF transformer 100 further includes a secondary winding 103 having a first output terminal and a second output terminal, wherein the first output terminal and the second output terminal are used to provide an output RF signal, and the secondary winding 103 is electromagnetically coupled to the first part L1Pa, the second part L1Pb, the third part L1Na and the fourth part L1Nb of the primary winding 101.

[0060] Figure 3 A diagram of a method 300 for converting an input RF signal into an output RF signal according to an embodiment is shown. The method 300 may be performed using an RF transformer, wherein: the RF transformer includes a primary winding and a secondary winding, the primary winding having a first input terminal and a second input terminal, and the secondary winding having a first output terminal and a second output terminal. The RF transformer may be a combination of Figure 1 or Figure 2 The radio frequency transformer 100 is described.

[0061] The method 300 includes processing 301 an input radio frequency signal through a first input terminal and a second input terminal of a primary winding, electromagnetically coupling 303 a first portion of the primary winding to a fourth portion of the primary winding, electromagnetically coupling 305 a second portion of the primary winding to a third portion of the primary winding, electromagnetically coupling 307 a secondary winding to the first portion, the second portion, the third portion, and the fourth portion of the primary winding, and providing 309 an output radio frequency signal through a first output terminal and a second output terminal of the secondary winding.

[0062] More embodiments of the RF transformer 100 , the RF transmitter 200 , and the method 300 will be described below.

[0063] Figure 4 FIG. 1 is a diagram of a radio frequency transformer 100 for converting an input radio frequency signal into an output radio frequency signal according to an embodiment. The diagram includes a layout and a schematic circuit diagram of the radio frequency transformer 100, wherein the radio frequency transformer 100 is formed as a combination of Figure 1 Possible implementations of the described radio frequency transformer: The radio frequency transformer 100 has a primary winding 101 and a secondary winding 103, wherein the turns ratio between the primary winding 101 and the secondary winding 103 is 2:2.

[0064] The primary winding 101 has a first input terminal in_p and a second input terminal in_n, wherein the first input terminal in_p and the second input terminal in_n are used to process the input radio frequency signal. The secondary winding 103 has a first output terminal out and a second output terminal gnd, wherein the first output terminal out and the second output terminal gnd are used to provide an output radio frequency signal. The input radio frequency signal is a differential radio frequency signal, and the output radio frequency signal is a single-ended radio frequency signal. The primary winding 101 is also connected to a supply voltage source using another terminal vdd.

[0065] The primary winding 101 includes a first portion L1Pa, a second portion L1Pb, a third portion L1Na, and a fourth portion L1Nb, wherein: the first portion L1Pa is electromagnetically coupled to the fourth portion L1Nb, and the second portion L1Pb is electromagnetically coupled to the third portion L1Na. In addition, the first portion L1Pa is electromagnetically decoupled from the second portion L1Pb, and the third portion L1Na is electromagnetically decoupled from the fourth portion L1Nb. The secondary winding 103 is electromagnetically coupled to the first portion L1Pa, the second portion L1Pb, the third portion L1Na, and the fourth portion L1Nb of the primary winding 101. The electromagnetic coupling is illustrated by arrows in the schematic circuit.

[0066] The radio frequency transformer 100 is placed on a semiconductor substrate, wherein: the first part L1Pa includes a first wire, the second part L1Pb includes a second wire, the third part L1Na includes a third wire, and the fourth part L1Nb includes a fourth wire. A portion of the first wire is adjacent to a portion of the fourth wire, and a portion of the second wire is adjacent to a portion of the third wire. The first part L1Pa and the second part L1Pb of the primary winding 101 are connected in parallel, and the third part L1Na and the fourth part L1Nb of the primary winding 101 are connected in parallel.

[0067] Figure 5FIG. 1 is a diagram of a radio frequency transformer 100 for converting an input radio frequency signal into an output radio frequency signal according to an embodiment. The diagram includes a layout and a schematic circuit diagram of the radio frequency transformer 100, wherein the radio frequency transformer 100 is formed as a combination of Figure 1 Possible implementations of the described radio frequency transformer: The radio frequency transformer 100 has a primary winding 101 and a secondary winding 103, wherein the turns ratio between the primary winding 101 and the secondary winding 103 is 4:4.

[0068] The primary winding 101 has a first input terminal in_p and a second input terminal in_n, wherein the first input terminal in_p and the second input terminal in_n are used to process the input radio frequency signal. The secondary winding 103 has a first output terminal out and a second output terminal gnd, wherein the first output terminal out and the second output terminal gnd are used to provide an output radio frequency signal. The input radio frequency signal is a differential radio frequency signal, and the output radio frequency signal is a single-ended radio frequency signal. The primary winding 101 is also connected to a supply voltage source using another terminal vdd.

[0069] The primary winding 101 includes a first portion L1Pa, a second portion L1Pb, a third portion L1Na, and a fourth portion L1Nb, wherein: the first portion L1Pa is electromagnetically coupled to the fourth portion L1Nb, and the second portion L1Pb is electromagnetically coupled to the third portion L1Na. In addition, the first portion L1Pa is electromagnetically decoupled from the second portion L1Pb, and the third portion L1Na is electromagnetically decoupled from the fourth portion L1Nb. The secondary winding 103 is electromagnetically coupled to the first portion L1Pa, the second portion L1Pb, the third portion L1Na, and the fourth portion L1Nb of the primary winding 101. The electromagnetic coupling is illustrated by arrows in the schematic circuit.

[0070] The radio frequency transformer 100 is placed on a semiconductor substrate, wherein: the first part L1Pa includes a first wire, the second part L1Pb includes a second wire, the third part L1Na includes a third wire, and the fourth part L1Nb includes a fourth wire. A portion of the first wire is adjacent to a portion of the fourth wire, and a portion of the second wire is adjacent to a portion of the third wire. The first part L1Pa and the second part L1Pb of the primary winding 101 are connected in parallel, and the third part L1Na and the fourth part L1Nb of the primary winding 101 are connected in parallel.

[0071] Compared to a reference RF transformer having sections L1P and L1N in the primary winding, such as Figure 4 and Figure 5As described, each part L1Pb and L1Nb can be considered to be divided into two parallel parts within the RF transformer 100. For example, L1Pb can be considered to be divided into L1Pa (dotted line) and L1Pb (dashed line), and L1Nb can be considered to be divided into L1Na (dotted line) and L1Nb (double-dotted line).

[0072] Since the total width of adjacent parts, such as L1Pa+L1Nb or L1Na+L1Pb, can be approximately equal to the corresponding width of the reference RF transformer, the differential inductance cannot be changed. In addition, the coupling coefficient between the primary winding and the secondary winding, the quality coefficient (Q factor) of the primary winding and the secondary winding cannot be changed, and therefore the loss cannot be changed. The electromagnetic coupling between L1P and L1N can now be tighter because L1Pa+L1Nb and L1Na+L1Pa can be adjacent or direct neighbors. For example, the coupling coefficient can be increased from about 0.5 to 0.7 to 0.75. In this way, the common mode inductance seen by the first input terminal in_p and the second input terminal in_n can be reduced.

[0073] Figure 6 FIG. 1 is a diagram of a radio frequency transformer 100 for converting an input radio frequency signal into an output radio frequency signal according to an embodiment. The diagram includes a layout and a schematic circuit diagram of the radio frequency transformer 100, wherein the radio frequency transformer 100 is formed as a combination of Figure 1 Possible implementations of the described radio frequency transformer: The radio frequency transformer 100 has a primary winding 101 and a secondary winding 103, wherein the turns ratio between the primary winding 101 and the secondary winding 103 is 2:2.

[0074] The primary winding 101 has a first input terminal in_p and a second input terminal in_n, wherein the first input terminal in_p and the second input terminal in_n are used to process the input RF signal. The secondary winding 103 has a first output terminal out and a second output terminal gnd, wherein the first output terminal out and the second output terminal gnd are used to provide an output RF signal. The input RF signal is a differential RF signal, and the output RF signal is a single-ended RF signal. Optionally, the output RF signal is a differential RF signal, wherein: the first output terminal can be called out_p, and the second output terminal can be called out_n. The primary winding 101 is also connected to a supply voltage source through another terminal vdd.

[0075] The primary winding 101 includes a first portion L1Pa, a second portion L1Pb, a third portion L1Na, and a fourth portion L1Nb, wherein: the first portion L1Pa is electromagnetically coupled to the fourth portion L1Nb, and the second portion L1Pb is electromagnetically coupled to the third portion L1Na. In addition, the first portion L1Pa is electromagnetically decoupled from the second portion L1Pb, and the third portion L1Na is electromagnetically decoupled from the fourth portion L1Nb. The secondary winding 103 is electromagnetically coupled to the first portion L1Pa, the second portion L1Pb, the third portion L1Na, and the fourth portion L1Nb of the primary winding 101. The electromagnetic coupling is illustrated by arrows in the schematic circuit.

[0076] The radio frequency transformer 100 is placed on a semiconductor substrate, wherein: the first part L1Pa includes a first wire, the second part L1Pb includes a second wire, the third part L1Na includes a third wire, and the fourth part L1Nb includes a fourth wire. A portion of the first wire is adjacent to a portion of the fourth wire, and a portion of the second wire is adjacent to a portion of the third wire. The first part L1Pa and the second part L1Pb of the primary winding 101 are connected in series, and the third part L1Na and the fourth part L1Nb of the primary winding 101 are connected in series.

[0077] Figure 7 FIG. 1 is a diagram of a radio frequency transformer 100 for converting an input radio frequency signal into an output radio frequency signal according to an embodiment. The diagram includes a layout and a schematic circuit diagram of the radio frequency transformer 100, wherein the radio frequency transformer 100 is formed as a combination of Figure 1 Possible implementations of the described radio frequency transformer: The radio frequency transformer 100 has a primary winding 101 and a secondary winding 103, wherein the turns ratio between the primary winding 101 and the secondary winding 103 is 4:4.

[0078] The primary winding 101 has a first input terminal in_p and a second input terminal in_n, wherein the first input terminal in_p and the second input terminal in_n are used to process the input RF signal. The secondary winding 103 has a first output terminal out and a second output terminal gnd, wherein the first output terminal out and the second output terminal gnd are used to provide an output RF signal. The input RF signal is a differential RF signal, and the output RF signal is a single-ended RF signal. Optionally, the output RF signal is a differential RF signal, wherein: the first output terminal can be called out_p, and the second output terminal can be called out_n. The primary winding 101 is also connected to a supply voltage source through another terminal vdd.

[0079] The primary winding 101 includes a first portion L1Pa, a second portion L1Pb, a third portion L1Na, and a fourth portion L1Nb, wherein: the first portion L1Pa is electromagnetically coupled to the fourth portion L1Nb, and the second portion L1Pb is electromagnetically coupled to the third portion L1Na. In addition, the first portion L1Pa is electromagnetically decoupled from the second portion L1Pb, and the third portion L1Na is electromagnetically decoupled from the fourth portion L1Nb. The secondary winding 103 is electromagnetically coupled to the first portion L1Pa, the second portion L1Pb, the third portion L1Na, and the fourth portion L1Nb of the primary winding 101. The electromagnetic coupling is illustrated by arrows in the schematic circuit.

[0080] The radio frequency transformer 100 is placed on a semiconductor substrate, wherein: the first part L1Pa includes a first wire, the second part L1Pb includes a second wire, the third part L1Na includes a third wire, and the fourth part L1Nb includes a fourth wire. A portion of the first wire is adjacent to a portion of the fourth wire, and a portion of the second wire is adjacent to a portion of the third wire. The first part L1Pa and the second part L1Pb of the primary winding 101 are connected in series, and the third part L1Na and the fourth part L1Nb of the primary winding 101 are connected in series.

[0081] like Figure 6 and Figure 7 As shown, no division is used in the primary winding 101. However, the sections in the primary winding 101 can still be adjacent. This concept can be extended to any number of turns by continuously alternating between two adjacent turns in the primary winding 101 and two adjacent turns in the secondary winding 103. Compared to the split winding concept, less electromagnetic coupling between the primary winding 101 and the secondary winding 103 occurs, thereby increasing the insertion loss of the RF transformer 100.

[0082] Figure 8 Shown is a diagram of a circuit including a primary winding 101 of a radio frequency transformer according to an embodiment. The circuit includes capacitors with capacitances C1 and C2. The primary winding 101 is represented by an inductor with inductance L1.

[0083] The inductor is electromagnetically coupled and has a coupling coefficient k. A radio frequency current i1 flows through the primary winding 101. Each part within the primary winding 101 and the primary winding 101 and the secondary winding 103 as described above can be considered as an inductor.

[0084] The following exemplary calculation illustrates the reduction in common mode inductance seen by the first input terminal and the second input terminal of the primary winding 101. The exemplary calculation is based on the following equation:

[0085]

[0086]

[0087]

[0088]

[0089] The following table compares the characteristics of the exemplary RF transformer 100 with a reference RF transformer as a calculation example. Assume that both RF transformers have a differential inductance of 2nH, a differential resonance frequency of 1CHz, and a differential input capacitance of 15%, i.e., kC=C2 / Cdiff=0.15.

[0090]

[0091] It can be seen that if the coupling coefficient k is increased from 0.5 to 0.7, which may not seem like a huge change, the common mode inductance L_cm and its common mode impedance XL_cm(2RF) can be reduced by a factor of 1.89. Even more interesting is the fact that the common mode resonant frequency shifts from 1.88 GHz, which is close to 2×RF=2 GHz, to as high as 2.58 GHz, far away from 2×RF. Therefore, the impedance at 2×RF is reduced by using a factor of 5.67 in this example.

[0092] Fig. 9 1 is a graph showing the common mode load impedance of the RF transformer 100 versus frequency independent of the coupling coefficient according to an embodiment. The coupling coefficient k refers to the primary winding 101 of the RF transformer 100 .

[0093] In this figure, the finite quality factor Q of the capacitor and inductor is considered. In this example, the quality factor Q is assumed to be 10. It can be seen from this figure that by using 6.0Ohm / 2.4Ohm=2.5 as the factor, starting from k=0.5 to k=0.7, a benefit can be obtained. The reduction in the factor by using 2.5 can result in a significant C-IM3 improvement within the RF transmitter 200.

[0094] The RF transformer 100 may function as a RF balanced-to-unbalanced transformer, providing low common mode impedance at the balanced terminals. The RF transformer 100 may have tight electromagnetic coupling between the two halves of the primary winding 101. The primary winding 101 may be divided into two parallel sections or windings.

[0095] The RF transformer 100 may have at least one adjacent turn of wire for the primary winding 101 and at least one adjacent turn of wire for the secondary winding 103. Optionally, the RF transformer 100 may have at least 0.5 adjacent turns of wire for the primary winding 101 and at least 0.5 adjacent turns of wire for the secondary winding 103. The RF transformer 100 may be implemented in a thick top metal layer. Tight electromagnetic coupling may also be achieved by stacking two turns of wire on top of each other, for example by using two different metal layers. The RF transformer 100 may also be used in the opposite direction, i.e., the primary winding 101 and the secondary winding 103 may be swapped.

[0096] Fig.10 FIG. 1 is a diagram of a radio frequency transmitter 200 including a modulator 201 and a radio frequency transformer 100 according to an embodiment. The radio frequency transmitter 200 further includes a power amplifier 1001, a duplex filter 1003, an antenna tuner 1005, an antenna 1007, and a receiver 1009. The radio frequency transmitter 200 is formed as a combination of Figure 2 A possible implementation of a radio frequency transmitter 200 is described.

[0097] The modulator 201 is used to generate an input RF signal. The RF transformer 100 is used to transform the input RF signal into an output RF signal. The input RF signal is a differential RF signal, and the output RF signal is a single-ended RF signal. The RF transformer 100 can therefore be used as a RF balanced to unbalanced transformer.

[0098] The primary winding of the RF transformer 100 is connected to a supply voltage source to power the modulator 201. The modulator 201 is used to generate an input RF signal by pulling an RF current from the RF transformer 100. The modulator 201 is a direct digital radio frequency modulator (DDRM) including a core having a plurality of switching transistors. The modulator 201 operates using baseband data, a local oscillator signal and / or a clock signal.

[0099] The RF transmitter 200 can be used in a mobile communication system. The purpose of the RF transformer 100 is to convert the differential RF signal provided by the modulator 201 into a single-ended RF signal as an input to the power amplifier 1001. The power amplifier 1001 can be one of a plurality of (pre) power amplifiers. Another purpose is to provide the output node of the modulator 201 with a drain bias. This is achieved by connecting the supply voltage source to the center tap of the primary winding of the RF transformer 100. The RF transmitter 200 can form a digital RF transceiver.

[0100] Fig.11A graph of output power and counter third order intermodulation (C-IM3) performance of a radio frequency transmitter 200 according to an embodiment is shown. The graph also shows input power and counter third order intermodulation (C-IM3) performance of a reference radio frequency transmitter. The output power and counter third order intermodulation (C-IM3) performance are depicted regardless of the adjustable capacitor setting.

[0101] The output power of the RF transmitter 200 and the reference RF transmitter both behave similarly. The RF transformer 100 in the RF transmitter 200 provides slightly higher output power and therefore has lower losses.

[0102] At the capacitor setting for maximum output power, i.e., when properly tuned to the input frequency, the counter third order intermodulation (C-IM3) level of the RF transmitter 200 is -64.0 dBc compared to -46.1 dBc using the reference RF transmission. Thus, a 17.9 dB improvement can be achieved in this example. This 17.9 dB improvement can be achieved because the 2RF common mode voltage swing can be reduced by 20*log(2.5)=8 dB by reducing the common mode impedance using a factor of 2.5, and counter third order intermodulation (C-IM3) is a third order intermodulation effect.

[0103] Fig.12 A diagram of a reference RF transformer including a primary winding and a secondary winding is shown. The diagram includes a layout and a schematic circuit of the reference RF transformer. The primary winding and the secondary winding have a turns ratio of 2:2.

[0104] The primary winding has a first input terminal in_p, a second input terminal in_n and a further terminal vdd. The secondary winding has a first output terminal out and a second output terminal gnd. The parts of the primary winding are referred to as L1P and L1N. The secondary winding is referred to as L2.

[0105] Fig.13 A diagram of a reference RF transformer including a primary winding and a secondary winding is shown. The diagram includes a layout and a schematic circuit of the reference RF transformer. The primary winding and the secondary winding have a turns ratio of 4:4.

[0106] The primary winding has a first input terminal in_p, a second input terminal in_n and a further terminal vdd. The secondary winding has a first output terminal out and a second output terminal gnd. The parts of the primary winding are referred to as L1P and L1N. The secondary winding is referred to as L2.

[0107] Fig.12 and Fig.13 The reference RF transformer described in can be an on-chip RF transformer. The positive and negative sides of the primary winding can be referred to as L1P and L1N. The secondary winding can be referred to as L2. Due to the turns ratio of 2:2 and 4:4, the input impedance in both cases can be approximately equal to the load impedance. L1P and L1N are loosely coupled because there is always one secondary turn between the primary turns. The coupling coefficient k between the two halves of the primary winding, L1P and L1N, can be approximately 0.5.

[0108] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A radio frequency transformer (100) for converting an input radio frequency signal into an output radio frequency signal, characterized in that: The radio frequency transformer (100) comprises: A primary winding (101) having a first input terminal and a second input terminal, wherein: the first input terminal and the second input terminal are used to process the input radio frequency signal, the primary winding (101) comprises a first part (L1Pa), a second part (L1Pb), a third part (L1Na) and a fourth part (L1Nb), the first part (L1Pa) is electromagnetically coupled to the fourth part (L1Nb), the second part (L1Pb) is electromagnetically coupled to the third part (L1Na); and A secondary winding (103) having a first output terminal and a second output terminal, wherein: the first output terminal and the second output terminal are used to provide the output radio frequency signal, and the secondary winding (103) is electromagnetically coupled to the first part (L1Pa), the second part (L1Pb), the third part (L1Na) and the fourth part (L1Nb) of the primary winding (101); Wherein, the number of turns of the primary winding is equal to the number of turns of the secondary winding; Wherein, two adjacent turns in the primary winding (101) and two adjacent turns in the secondary winding (103) are arranged alternately.

2. The radio frequency transformer (100) according to claim 1, characterized in that: The first portion (L1Pa) is electromagnetically decoupled from the second portion (L1Pb), and the third portion (L1Na) is electromagnetically decoupled from the fourth portion (L1Nb).

3. The radio frequency transformer (100) according to claim 1 or 2, characterized in that: The input radio frequency signal is a differential radio frequency signal, and the output radio frequency signal is a single-ended radio frequency signal.

4. The radio frequency transformer (100) according to claim 1 or 2, characterized in that: The input radio frequency signal includes a signal component at an input frequency, and the common mode resonance frequency of the radio frequency transformer (100) is greater than twice the input frequency.

5. The radio frequency transformer (100) according to claim 1 or 2, characterized in that: The first portion (L1Pa) and the second portion (L1Pb) of the primary winding (101) are connected in parallel, or the third portion (L1Na) and the fourth portion (L1Nb) of the primary winding (101) are connected in parallel.

6. The radio frequency transformer (100) according to claim 1 or 2, characterized in that: The radio frequency transformer (100) is placed on a semiconductor substrate, the first part (L1Pa) includes a first wire, the second part (L1Pb) includes a second wire, the third part (L1Na) includes a third wire, and the fourth part (L1Nb) includes a fourth wire.

7. The radio frequency transformer (100) according to claim 6, characterized in that: A portion of the first conductive line is adjacent to a portion of the fourth conductive line, or a portion of the second conductive line is adjacent to a portion of the third conductive line.

8. The radio frequency transformer (100) according to claim 6, characterized in that: A portion of the first conductive line and a portion of the fourth conductive line are placed in different layers on the semiconductor substrate, or a portion of the second conductive line and a portion of the third conductive line are placed in different layers on the semiconductor substrate.

9. The radio frequency transformer (100) according to claim 1 or 2, characterized in that: The primary winding (101) is connected to a supply voltage source.

10. The radio frequency transformer (100) according to claim 9, characterized in that: The supply voltage source is connected to the primary winding (101) between the first portion (L1Pa) and the third portion (L1Na), or the supply voltage source is connected to the primary winding (101) between the second portion (L1Pb) and the fourth portion (L1Nb).

11. A radio frequency transmitter (200), characterized in that: include: A modulator (201) for generating an input radio frequency signal; as well as The radio frequency transformer (100) according to any one of claims 1 to 8, wherein the radio frequency transformer (100) is used to transform the input radio frequency signal into an output radio frequency signal.

12. The radio frequency transmitter (200) according to claim 11, characterized in that: The modulator (201) is used to generate the input radio frequency signal by drawing a radio frequency current from the radio frequency transformer (100).

13. The radio frequency transmitter (200) according to claim 11 or 12, characterized in that: The modulator (201) is a direct digital radio frequency modulator.

14. The radio frequency transmitter (200) according to claim 11, characterized in that: Also includes: A power amplifier (1001) is used to amplify the output radio frequency signal.

15. A method (300) for converting an input radio frequency signal into an output radio frequency signal using a radio frequency transformer (100), characterized in that: The radio frequency transformer (100) comprises a primary winding (101) and a secondary winding (103), wherein: the primary winding (101) has a first input terminal and a second input terminal, and the secondary winding (103) has a first output terminal and a second output terminal, and the method (300) comprises: processing (301) the input radio frequency signal through the first input terminal and the second input terminal of the primary winding (101); electromagnetically coupling (303) a first portion (L1Pa) of the primary winding (101) to a fourth portion (L1Nb) of the primary winding (101); electromagnetically coupling (305) the second portion (L1Pb) of the primary winding (101) to the third portion (L1Na) of the primary winding (101); electromagnetically coupling (307) the secondary winding (103) to the first portion (L1Pa), the second portion (L1Pb), the third portion (L1Na) and the fourth portion (L1Nb) of the primary winding (101); and providing (309) the output radio frequency signal via the first output terminal and the second output terminal of the secondary winding (103); Wherein, the number of turns of the primary winding is equal to the number of turns of the secondary winding; Wherein, two adjacent turns in the primary winding (101) and two adjacent turns in the secondary winding (103) are arranged alternately.

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