Balun circuit and radio frequency chip

Abstract

The invention is suitable for the technical field of communication, 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; the first end of the primary coil serves as the first input end of the balun unit, the second end of the primary coil serves as the second input end of the balun unit, the first end of the first inductor is connected with the first end of the primary coil, the second end of the first inductor is connected with the first end of the second inductor, and the second end of the second inductor is connected with the second end of the primary coil. The second end of the first inductor and the first end of the second inductor are respectively connected with external power supply voltage. Compared with the prior art, the Balun unit is optimized, and the first inductor and the second inductor are utilized to convert from high resistance to low resistance, so that the impedance conversion ratio of the circuit of the Balun unit can be reduced, the matching bandwidth can be improved, and the matching insertion loss can be reduced.

Description

Technical Field

[0001] The present invention is applicable to the field of communication technologies, and particularly relates to a balun circuit and a radio frequency chip. Background Art

[0002] A balun is mainly used in the inter-stage and output matching circuits of differential power amplifiers. Especially in the output matching circuit, the balun not only functions to convert differential to single-ended, but also can perform impedance matching synchronously. Therefore, the efficiency and matching bandwidth of differential power amplifiers largely depend on the design of the balun structure. This traditional circuit design is simple, and the system has been widely applied in practice.

[0003] The existing output balun structure is as Figure 1 shown. OUTP and OUTN are two differential terminals respectively, and Pout is a load 50-ohm port. The capacitor C is mainly used to cancel the non-ideal factor of impedance being inductive due to the leakage inductance introduced by the balun.

[0004] However, in the existing output balun structure, there are two problems that are difficult to solve: 1. Generally, a balun is required to convert a 50-ohm impedance into a single-ended impedance of about 5 ohms required by the amplification stage of a power amplifier. The impedance conversion ratio is relatively high, so the required coil turns ratio is also relatively high. In an actual balun structure, parasitic capacitance will be introduced, resulting in the self-resonant frequency being close to or within the operating frequency, thus affecting the impedance conversion of the output balun. 2. The relatively high impedance conversion ratio will greatly affect the balance of the balun during the actual implementation of the balun, resulting in inconsistent power at both differential ends and reducing the efficiency of the differential power amplifier.

[0005] Therefore, there is an urgent need for a new balun circuit and radio frequency chip to solve the above technical problems. Summary of the Invention

[0006] The present invention provides a balun circuit and a radio frequency chip, aiming 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.

[0007] In a first aspect, the present invention provides a balun circuit for converting two differential signals into one single-ended signal and then outputting. 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, 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, 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 end of the first inductor and the first end 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 the first inductor or the second inductor.

[0008] 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 after being serially connected with the first capacitor, and the second end of the second inductor is connected to the second end of the primary coil after being serially connected with the second capacitor.

[0009] Preferably, the center tap of the primary coil is connected to an external power supply voltage.

[0010] Preferably, the center tap of the primary coil is grounded.

[0011] Preferably, the output matching circuit includes a third capacitor and a fourth capacitor; the first end of the third capacitor serves as the first input terminal of the output matching circuit, and the second end of the third capacitor serves as the output terminal of the output matching circuit; the first end of the fourth capacitor serves as the second input terminal of the output matching circuit and the first end of the fourth capacitor is grounded, and the second end of the fourth capacitor is connected to the second end of the third capacitor.

[0012] In a second aspect, the present invention further provides a radio frequency chip, which includes the balun circuit as described in any one of the above embodiments.

[0013] Compared with the prior art, by optimizing the balun unit, the present invention adds a first inductor and a second inductor as part of the matching on the basis of the traditional balun unit, and uses the first inductor and the second inductor to perform conversion from high impedance to low impedance, so as to reduce the impedance conversion ratio of the balun unit itself, improve the matching bandwidth and reduce the matching insertion loss; at the same time, the first inductor or the second inductor is coupled with the primary coil, further reducing the inductance of the primary coil and the secondary coil of the balun unit, thereby improving the overall Q value of the balun unit and further reducing the matching insertion loss. Brief Description of the Drawings

[0014] The present invention will be described in detail below with reference to the drawings. Through the detailed description in conjunction with the following drawings, the above or other aspects of the present invention will become clearer and easier to understand. In the drawings: Figure 1 is a schematic structural diagram of a balun circuit of the related art; Figure 2 is a schematic structural diagram of a balun circuit provided by an embodiment of the present invention Figure 1 ; Figure 3 is a schematic structural diagram of a balun circuit provided by an embodiment of the present invention Figure 2 ; Figure 4 is a schematic structural diagram of a balun circuit provided by an embodiment of the present invention Figure 3 ; Figure 5 is a schematic structural diagram of a balun circuit provided by an embodiment of the present invention Figure 4 ; Figure 6 is a schematic diagram of the real part curve of the relative bandwidth of a balun circuit provided by an embodiment of the present invention; Figure 7 is a schematic diagram of the imaginary part curve of the relative bandwidth of a balun circuit provided by an embodiment of the present invention; Figure 8 is a schematic diagram of the insertion loss curve of a balun circuit provided by an embodiment of the present invention. Detailed Embodiments

[0015] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0016] Embodiment 1 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 then outputting, and the balun circuit 100 includes a balun unit 1 and an output matching circuit 2; 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; 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, 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, 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 end of the first inductor L1 and the first end 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 alternative embodiment, the primary coil L3 may be coupled to the second inductor L2. Wherein, the coupling coefficient between the primary coil L3 and the first inductor L1 or the second inductor L2 is k1.

[0017] Specifically, the present invention controls the distance between the first inductor L1 or the second inductor L2 and the primary coil L3, so that the first inductor L1 or the second inductor L2 and the primary coil L3 achieve forward coupling or reverse coupling, and uses the first inductor L1 and the second inductor L2 to perform conversion from high impedance to low impedance, thereby reducing the impedance conversion ratio of the balun unit 1 itself, improving the matching bandwidth and reducing the matching insertion loss, and further reducing the inductance of the primary coil L3 and the secondary coil L4 of the balun unit 1; reference can be made to Figure 2 , the impedance of the balun unit 1 can be deduced according to the following conditions:

[0018] Wherein, Zin is the unilateral impedance at the differential end of the balun circuit 100; Zload is the impedance of the single-ended load terminal of the balun circuit 100; L1 is the unilateral 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 unilateral 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 unilateral 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 unilateral 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; Cin is the isolation capacitance between the first inductor L1 and the second inductor L2 and the primary coil L3.

[0019] In the embodiment of the present 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 after being connected in series with the first capacitor C1, and the second end of the second inductor L2 is connected to the second end of the primary coil L3 after being connected in series with the second capacitor C2. Wherein, the first capacitor C1 and the second capacitor C2 are isolation capacitors.

[0020] In the embodiment of the present invention, the center tap of the primary coil L3 is connected to an external power supply voltage VCC. In another alternative embodiment, the center tap of the primary coil L3 is grounded.

[0021] In the embodiment of the present 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.

[0022] Specifically, the relative bandwidth and insertion loss of the balun circuit 100 proposed in the embodiment of the present invention are tested, and the curve graph is as Figures 6 - 8 shown. It can be seen that the balun circuit 100 proposed in the embodiment of the present invention can achieve a relative bandwidth of 50%, and the insertion loss remains below 1.5 dB. The power amplifier equipped with the balun circuit 100 proposed in the embodiment of the present invention can greatly reduce the matching insertion loss and matching bandwidth of the power amplifier, thereby improving the conversion efficiency of the power amplifier.

[0023] Compared with the prior art, by optimizing the balun unit, the present invention adds a first inductor and a second inductor as part of the matching on the basis of the traditional balun unit, and uses the first inductor and the second inductor to perform conversion from high impedance to low impedance, thereby reducing the impedance conversion ratio of the balun unit itself, improving the matching bandwidth and reducing the matching insertion loss. At the same time, the first inductor or the second inductor is coupled with the primary coil, further reducing the inductance of the primary coil and the secondary coil of the balun unit, thereby improving the overall Q value of the balun unit and further reducing the matching insertion loss.

[0024] Embodiment II The embodiment of the present invention further provides a radio frequency chip, which includes the balun circuit 100 as described in the above embodiment and can achieve the same technical effects. Refer to the description in the above embodiment, and details are not described herein again.

[0025] It should be noted that in this article, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including that element.

[0026] The embodiments of the present invention have been described above with reference to the accompanying drawings. What is disclosed is only the preferred embodiments of the present invention, but the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can make many equivalent changes in form without departing from the spirit and scope of the present invention as protected by the claims, and all of them fall within the protection scope of the present invention.

Claims

1. A balun circuit for converting two differential signals into one single-ended signal and then outputting, 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, 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, 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, and the second end of the first inductor and the first end 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 the first inductor or the second inductor.

2. The balun circuit according to claim 1, characterized in that, 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 after being connected in series with the first capacitor, and the second end of the second inductor is connected to the second end of the primary coil after being connected in series with the second capacitor.

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

4. The balun circuit according to claim 1, characterized in that, The center tap of the primary coil is grounded.

5. The balun circuit according to claim 1, characterized in that The output matching circuit includes a third capacitor and a fourth capacitor; the first end of the third capacitor serves as the first input terminal of the output matching circuit, and the second end of the third capacitor serves as the output terminal of the output matching circuit; the first end of the fourth capacitor serves as the second input terminal of the output matching circuit and the first end of the fourth capacitor is grounded, and the second end of the fourth capacitor is connected to the second end of the third capacitor.

6. A radio frequency chip, characterized in that, The RF chip includes the balun circuit according to any one of claims 1-5 above.

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