Balun circuit and radio frequency chip

Abstract

The application belongs to the field of communication technology, and particularly relates to a balun circuit and a radio frequency chip. The balun circuit comprises a balun unit and an output matching circuit; the balun unit comprises a first inductor, a second inductor, a primary coil and a secondary coil; a first end of the primary coil is used as a first end input end of the balun unit, a second end of the primary coil is used as a second input end of the balun unit, a first end of the first inductor is connected with the first end of the primary coil, a second end of the first inductor is connected with a first end of the second inductor, a second end of the second inductor is connected with the second end of the primary coil, and the second end of the first inductor and the first end of the second inductor are respectively connected with an external power supply voltage. Compared with the prior art, the balun unit is optimized, the first inductor and the second inductor are used to convert from high resistance to low resistance, so that the impedance conversion ratio of the circuit of the balun unit itself can be reduced, the matching bandwidth can be improved, and the matching insertion loss can be reduced.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and in particular to a balun circuit and a radio frequency chip. Background Technology

[0002] Baluns are primarily used in the interstage and output matching circuits of differential power amplifiers. Especially in output matching circuits, baluns not only function as differential-to-single-ended converters but also perform synchronous impedance matching. Therefore, the efficiency and matching bandwidth of the differential power amplifier largely depend on the design of the balun structure. This traditional circuit design is simple, and the system has been widely adopted in practice.

[0003] Existing output Balun structures such as Figure 1 As shown, OUTP and OUTN are two differential terminals, and Pout is the 50-ohm load port. Capacitor C is mainly used to compensate for the non-ideal impedance bias caused by the drain inductance introduced by the balun.

[0004] However, there are two problems in the existing output Balun structure that are difficult to solve:

[0005] 1. Generally, a balun is used to convert a 50-ohm impedance to a single-ended impedance of about 5 ohms required by the amplification stage of a power amplifier. The impedance conversion is relatively high, so the coil turns ratio is also relatively high. In the actual balun structure, parasitic capacitance is introduced, which causes the self-resonant frequency to be close to or inside the operating frequency, thus affecting the impedance conversion of the output balun.

[0006] 2. The high impedance torsional ratio will greatly affect the balance of the balun in actual implementation, resulting in inconsistent power at the differential ends and reducing the efficiency of the differential power amplifier.

[0007] Therefore, a new balun circuit and RF chip are urgently needed to solve the above-mentioned technical problems. Summary of the Invention

[0008] This invention provides a balun circuit and an RF chip, which aims to reduce the matching insertion loss and matching bandwidth of a power amplifier through a simple circuit structure, thereby improving the conversion efficiency of the power amplifier.

[0009] In a first aspect, the present invention provides a balun circuit for converting two differential signals into a single-ended signal and then outputting it. The balun circuit includes a balun unit and an output matching circuit.

[0010] The first input terminal of the balun unit serves as the first differential input terminal of the balun circuit, the second input terminal of the balun unit serves as the second differential input terminal of the balun circuit, the first output terminal of the balun unit is connected to the first input terminal of the output matching circuit, the second output terminal of the balun unit is connected to the second input terminal of the output matching circuit, and the output terminal of the output matching circuit serves as the signal output terminal of the balun circuit.

[0011] The balun unit includes a first inductor, a second inductor, a primary coil, and a secondary coil. The first end of the primary coil serves as the first input terminal of the balun unit, and the second end of the primary coil serves as the second input terminal of the balun unit. The first end of the first inductor is connected to the first end of the primary coil, and the second end of the first inductor is connected to the first end of the second inductor. The second end of the second inductor is connected to the second end of the primary coil. The second ends of the first inductor and the first ends of the second inductor are respectively connected to an external power supply voltage. The primary coil and the secondary coil are coupled to form a transformer structure. The first end of the secondary coil serves as the first output terminal of the balun unit, and the second end of the secondary coil serves as the second output terminal of the balun unit. The primary coil is coupled to either the first inductor or the second inductor.

[0012] Preferably, the balun unit further includes a first capacitor and a second capacitor; the first end of the first inductor is connected to the first end of the primary coil via the first capacitor in series, and the second end of the second inductor is connected to the second end of the primary coil via the second capacitor in series.

[0013] Preferably, the center tap of the primary coil is connected to an external power supply voltage.

[0014] Preferably, the center tap of the primary coil is grounded.

[0015] Preferably, the output matching circuit includes a third capacitor and a fourth capacitor; the first terminal of the third capacitor serves as the first input terminal of the output matching circuit, and the second terminal of the third capacitor serves as the output terminal of the output matching circuit; the first terminal of the fourth capacitor serves as the second input terminal of the output matching circuit and is grounded, and the second terminal of the fourth capacitor is connected to the second terminal of the third capacitor.

[0016] Secondly, the present invention also provides a radio frequency chip, the radio frequency chip comprising a balun circuit as described in any of the above embodiments.

[0017] Compared with existing technologies, this invention optimizes the balun unit by adding a first inductor and a second inductor as part of the matching process. The first and second inductors are used to convert from high impedance to low impedance, thereby reducing the impedance conversion ratio of the balun unit circuit itself, increasing the matching bandwidth, and reducing the matching insertion loss. At the same time, coupling the first or second inductor with the primary coil further reduces the inductance of the primary and secondary coils of the balun unit, thereby increasing the overall Q value of the balun unit and reducing the matching insertion loss. Attached Figure Description

[0018] The present invention will now be described in detail with reference to the accompanying drawings. The above and other aspects of the present invention will become clearer and more readily understood through the detailed description following the accompanying drawings. In the drawings:

[0019] Figure 1 This is a schematic diagram of the structure of a balun circuit in a related technology;

[0020] Figure 2 This is a schematic diagram of the balun circuit provided in an embodiment of the present invention. Figure 1 ;

[0021] Figure 3 This is a schematic diagram of the balun circuit provided in an embodiment of the present invention. Figure 2 ;

[0022] Figure 4 This is a schematic diagram of the balun circuit provided in an embodiment of the present invention. Figure 3 ;

[0023] Figure 5 This is a schematic diagram of the balun circuit provided in an embodiment of the present invention. Figure 4 ;

[0024] Figure 6 This is a schematic diagram of the relative bandwidth real part curve of the balun circuit provided in an embodiment of the present invention;

[0025] Figure 7 This is a schematic diagram of the relative bandwidth imaginary part curve of the balun circuit provided in an embodiment of the present invention;

[0026] Figure 8 This is a schematic diagram of the insertion loss curve of the balun circuit provided in an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] Example 1

[0029] Please refer to Figures 2-5 The present invention provides a balun circuit 100 for converting two differential signals into a single-ended signal and outputting it. The balun circuit 100 includes a balun unit 1 and an output matching circuit 2.

[0030] The first input terminal of the balun unit 1 serves as the first differential input terminal OUTP of the balun circuit 100, the second input terminal of the balun unit 1 serves as the second differential input terminal OUTN of the balun circuit 100, the first output terminal of the balun unit 1 is connected to the first input terminal of the output matching circuit 2, the second output terminal of the balun unit 1 is connected to the second input terminal of the output matching circuit 2, and the output terminal of the output matching circuit 2 serves as the signal output terminal Pout of the balun circuit 100.

[0031] The balun unit 1 includes a first inductor L1, a second inductor L2, a primary coil L3, and a secondary coil L4. The first end of the primary coil L3 serves as the first input terminal of the balun unit 1, and the second end of the primary coil L3 serves as the second input terminal of the balun unit 1. The first end of the first inductor L1 is connected to the first end of the primary coil L3, and the second end of the first inductor L1 is connected to the first end of the second inductor L2. The second end of the second inductor L2 is connected to the second end of the primary coil L3. The second ends of the first inductor L1 and the first ends of the second inductor L2 are respectively connected to an external power supply voltage VCC. The primary coil L3 and the secondary coil L4 are coupled to form a transformer structure (the coupling coefficient between the primary coil L3 and the secondary coil L4 is k). The first end of the secondary coil L4 serves as the first output terminal of the balun unit 1, and the second end of the secondary coil L4 serves as the second output terminal of the balun unit 1. The primary coil L3 is coupled to the first inductor L1. In another optional embodiment, the primary coil L3 may be coupled to the second inductor L2. The coupling coefficient between the primary coil L3 and the first inductor L1 or the second inductor L2 is k1.

[0032] Specifically, this invention controls the distance between the first inductor L1 or the second inductor L2 and the primary coil L3, enabling forward or reverse coupling between them. By utilizing the high-resistance to low-resistance transition of the first inductor L1 and the second inductor L2, the impedance conversion ratio of the balun unit 1 circuit itself can be reduced, the matching bandwidth increased, and the matching insertion loss reduced, further reducing the inductance of the primary coil L3 and the secondary coil L4 of the balun unit 1. (See reference...) Figure 2 The impedance of balun element 1 can be derived based on the following conditions:

[0033]

[0034] Where Zin is the single-sided impedance at the differential terminal of the balun circuit 100; Zload is the resistivity at the single-ended load terminal of the balun circuit 100; L1 is the single-sided inductance of the primary coil L3 in the balun unit 1; R1 is the parasitic resistance of the primary coil L3 in the balun unit 1; L2 is the single-sided inductance of the secondary coil L4 in the balun unit 1; R2 is the parasitic resistance of the secondary coil L4 in the balun unit 1; Lchoke is the single-sided inductance of the power supply terminal (i.e., one end of the first inductor L1 and the second inductor L2) in the balun unit 1; Rchoke is the parasitic resistance of the single-sided inductance of the power supply terminal in the balun unit 1; k is the coupling coefficient between the primary coil L3 and the secondary coil L4; k1 is the coupling coefficient between the first inductor L1 and the primary coil L3; and Cin is the isolation capacitance between the first inductor L1 and the second inductor L2 and the primary coil L3.

[0035] In this embodiment of the invention, the balun unit 1 further includes a first capacitor C1 and a second capacitor C2; the first end of the first inductor L1 is connected to the first end of the primary coil L3 via the first capacitor C1 in series, and the second end of the second inductor L2 is connected to the second end of the primary coil L3 via the second capacitor C2 in series. The first capacitor C1 and the second capacitor C2 are isolation capacitors.

[0036] In one embodiment of the invention, the center tap of the primary coil L3 is connected to an external power supply voltage VCC. In another optional embodiment, the center tap of the primary coil L3 is grounded.

[0037] In this embodiment of the invention, the output matching circuit 2 includes a third capacitor C3 and a fourth capacitor C4; the first end of the third capacitor C3 serves as the first input terminal of the output matching circuit 2, the second end of the third capacitor C3 serves as the output terminal of the output matching circuit 2, the first end of the fourth capacitor C4 serves as the second input terminal of the output matching circuit 2 and the first end of the fourth capacitor C4 is grounded, and the second end of the fourth capacitor C4 is connected to the second end of the third capacitor C3.

[0038] Specifically, the relative bandwidth and insertion loss of the balun circuit 100 proposed in this embodiment of the invention were tested, and the curves are shown below. Figures 6-8 As shown, the balun circuit 100 proposed in this embodiment of the invention can achieve a relative bandwidth of 50% while keeping the insertion loss below 1.5 dB. A power amplifier equipped with the balun circuit 100 proposed in this embodiment of the invention can significantly reduce the matching insertion loss and matching bandwidth of the power amplifier, thereby improving the conversion efficiency of the power amplifier.

[0039] Compared with existing technologies, this invention optimizes the balun unit by adding a first inductor and a second inductor as part of the matching process. The first and second inductors are used to convert from high impedance to low impedance, thereby reducing the impedance conversion ratio of the balun unit circuit itself, increasing the matching bandwidth, and reducing the matching insertion loss. At the same time, coupling the first or second inductor with the primary coil further reduces the inductance of the primary and secondary coils of the balun unit, thereby increasing the overall Q value of the balun unit and reducing the matching insertion loss.

[0040] Example 2

[0041] This invention also provides a radio frequency chip, which includes the balun circuit 100 as described in the above embodiments and can achieve the same technical effect. Please refer to the description in the above embodiments, which will not be repeated here.

[0042] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0043] The embodiments of the present invention have been described above with reference to the accompanying drawings. The disclosed embodiments are merely preferred embodiments of the present invention. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many equivalent changes in form without departing from the spirit and scope of the claims of the present invention, and all such changes are within the protection scope of the present invention.

Claims

1. A balun circuit for converting two differential signals into a single-ended signal and outputting it, characterized in that, The balun circuit includes a balun unit and an output matching circuit; The first input terminal of the balun unit serves as the first differential input terminal of the balun circuit, the second input terminal of the balun unit serves as the second differential input terminal of the balun circuit, the first output terminal of the balun unit is connected to the first input terminal of the output matching circuit, the second output terminal of the balun unit is connected to the second input terminal of the output matching circuit, and the output terminal of the output matching circuit serves as the signal output terminal of the balun circuit. The balun unit includes a first inductor, a second inductor, a primary coil, and a secondary coil. The first end of the primary coil serves as the first input terminal of the balun unit, and the second end of the primary coil serves as the second input terminal of the balun unit. The first end of the first inductor is connected to the first end of the primary coil, and the second end of the first inductor is connected to the first end of the second inductor. The second end of the second inductor is connected to the second end of the primary coil. The second ends of the first inductor and the first ends of the second inductor are respectively connected to an external power supply voltage. The primary coil and the secondary coil are coupled to form a transformer structure. The first end of the secondary coil serves as the first output terminal of the balun unit, and the second end of the secondary coil serves as the second output terminal of the balun unit. The primary coil is coupled to either the first inductor or the second inductor. The balun unit further includes a first capacitor and a second capacitor; the first end of the first inductor is connected to the first end of the primary coil via the first capacitor in series, and the second end of the second inductor is connected to the second end of the primary coil via the second capacitor in series. The output matching circuit includes a third capacitor and a fourth capacitor; the first terminal of the third capacitor serves as the first input terminal of the output matching circuit, and the second terminal of the third capacitor serves as the output terminal of the output matching circuit; the first terminal of the fourth capacitor serves as the second input terminal of the output matching circuit and is grounded, and the second terminal of the fourth capacitor is connected to the second terminal of the third capacitor.

2. The balun circuit as described in claim 1, characterized in that, The center tap of the primary coil is connected to an external power supply voltage.

3. The balun circuit as described in claim 1, characterized in that, The center tap of the primary coil is grounded.

4. A radio frequency chip, characterized in that, The radio frequency chip includes a balun circuit as described in any one of claims 1-3.

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