Small area matching circuit for radio frequency power amplifiers

Abstract

The application discloses a small-area matching circuit for a radio frequency power amplifier, which is connected to the output end of the radio frequency power amplifier and used for matching the impedance between the radio frequency power amplifier and a load; wherein the matching circuit comprises at least one first capacitor and at least one first inductor, the first inductor and the first capacitor are connected in series or in parallel, the first capacitor is used for a capacitor on the radio frequency power amplifier, and the first inductor and the first capacitor form a second-order cascade structure. The matching circuit improves the output power of the power amplifier and greatly reduces the layout area of the whole amplifier.

Description

Technical Field

[0001] This invention relates to the field of radio frequency microwaves, and more specifically to a small-area matching circuit for a radio frequency power amplifier. Background Technology

[0002] For an RF power amplifier chip, one of the key factors affecting its high power and high linearity output is its output matching circuit. To achieve a high-linearity, high-power amplifier design, a reasonable power matching impedance must be found during the RF chip design phase. This is typically achieved using load pull calculations combined with simulation software like Load Pull and Source Pull. However, in practical applications, there is usually a certain degree of component value error, and this error range varies slightly between different components.

[0003] Generally, RF power amplifiers use GaAs HBT or pHEMT technology to simultaneously meet the requirements of high frequency and high power. In the design of RF power amplifiers, multiple transistors are usually connected in parallel to achieve high power output. At this time, the real part of the input impedance is relatively small, and the optimal output power impedance point is usually also relatively small. This means that changes in the values ​​of the components in the output matching circuit have a significant impact on the overall impedance of the entire output matching circuit. Even a 10% error can lead to a large offset in the impedance point.

[0004] Currently, the commonly used matching circuits are two typical LC resonant network topologies: parallel inductor plus parallel capacitor, and series inductor plus series capacitor. Both have the same resonant frequency characteristics. These two topologies can be used independently as filter modules, or cascaded to form a dual-LC composite resonant network, such as... Figure 1 As shown. By selecting component parameters based on matching the termination source impedance, load impedance, and operating frequency, a wide range of impedance matching can be achieved within the target frequency band. However, in addition to configuring parallel inductors, this architecture also requires series inductors in the power-load transmission path, resulting in a high chip layout area occupancy in the signal transmission direction, which is not conducive to the high integration and miniaturization of the entire circuit.

[0005] Therefore, it is necessary to provide an improved small-area matching circuit for RF power amplifiers that reduces amplifier layout area to overcome the above-mentioned shortcomings. Summary of the Invention

[0007] The purpose of this invention is to provide a small-area matching circuit for radio frequency power amplifiers. The matching circuit of this invention improves the output power of the power amplifier and significantly reduces the overall layout area of ​​the amplifier.

[0008] To achieve the above objectives, the present invention provides a small-area matching circuit for an RF power amplifier, connected to the output terminal of the RF power amplifier, for matching the impedance between the RF amplifier and the load; wherein the matching circuit includes at least one first capacitor and at least one first inductor, the first inductor and the first capacitor are connected in series or in parallel, the first first capacitor is reused as a capacitor on the RF power amplifier; and the first inductor and the first capacitor form a two-stage cascaded structure.

[0009] Preferably, the matching unit further includes a second inductor, one end of which is connected to the first first capacitor or the first first inductor, and the other end of which is grounded.

[0010] Preferably, the second inductor is reused as an inductor in the radio frequency power amplifier.

[0011] Preferably, each of the first inductors and the second inductors is replaced with bonding wire.

[0012] Preferably, the length of the bonding gold wire is 300-1200 μm.

[0013] Preferably, when the quality factor of the matching circuit is less than or equal to 3, the matching unit comprises 3 first inductors and 4 first capacitors, and the 3 first inductors and 4 first capacitors form a seven-stage cascaded structure.

[0014] Compared with the prior art, the small-area matching circuit for RF power amplifiers of the present invention can achieve optimal impedance matching between the matching circuit and the RF power amplifier, thereby improving the output power and linearity of the RF power amplifier. At the same time, by reusing the capacitor of the RF power amplifier into the matching circuit and eliminating the need for a resonant network in the matching circuit, the area occupied by the matching circuit is significantly reduced, the overall circuit layout area is reduced, and the circuit integration is improved.

[0015] The invention will become clearer from the following description, taken in conjunction with the accompanying drawings, which are used to explain embodiments of the invention. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an existing matching circuit used in RF power amplifiers.

[0018] Figure 2 This is a schematic diagram of a commonly used radio frequency power amplifier.

[0019] Figure 3 This is a schematic diagram of the small-area matching circuit for an RF power amplifier according to the present invention.

[0020] Figure 4 is a schematic diagram of an embodiment of the small-area matching circuit for an RF power amplifier according to the present invention. Detailed Implementation

[0021] Embodiments of the invention will now be described with reference to the accompanying drawings, in which similar element reference numerals denote similar elements. As described above, the present invention provides a small-area matching circuit for an RF power amplifier, which improves the output power of the RF power amplifier and reduces the overall layout area of ​​the amplifier.

[0022] Please refer to Figure 2 , Figure 2 This is a schematic diagram of a commonly used radio frequency power amplifier. (Example) Figure 2 As shown, the input signal RF_IN of the RF power amplifier is amplified by transistor HBT1, filtered by an LC filter unit, and then output as the RF signal RF_OUT. The LC filter unit is composed of an inductor Lp0 and a capacitor Cp0 connected in parallel. Figure 2 The structure and specific functions of the radio frequency power amplifier shown are well known to those skilled in the art and will not be described in detail here.

[0023] Please refer to the references. Figure 3 , Figure 3 This is a schematic diagram of the small-area matching circuit for an RF power amplifier according to the present invention. The matching circuit of the present invention is connected to the output terminal of the RF power amplifier, that is, the output signal RF_OUT of the RF power amplifier is input to the matching circuit of the present invention. Figure 2 The RF output signal RF_OUT of the RF power amplifier shown is... Figure 3 The matching circuit shown has an RF input signal RF_IN. This matching circuit is used to match the impedance between the RF amplifier and the load, thereby increasing the output power of the RF power amplifier and correspondingly reducing its area. Specifically, the small-area matching circuit for the RF power amplifier of the present invention includes at least one first capacitor C1 and at least one first inductor L1. The first inductor L1 and the first capacitor C1 are connected in series or parallel. The first first capacitor C1 is reused as a capacitor on the RF power amplifier, that is, the capacitor Cp0 on the RF power amplifier can be reused as the matching unit corresponding to the first first capacitor C1. This reduces the use of one capacitor in the matching circuit, thereby reducing the number of components in the matching circuit, and consequently reducing the layout area occupied by the matching circuit, which in turn reduces the overall layout area of ​​the RF power amplifier. Furthermore, one first inductor L1 and one first capacitor C1 form a two-stage cascaded structure; if there are multiple first inductors L1 and first capacitors C1 (e.g., ...), the matching circuit can be further cascaded. Figure 3As shown, capacitors C1, C2, and C3, and inductors L1, L2, and L3 form a six-stage cascaded structure, thus constituting a multi-stage cascaded structure. Furthermore, in this invention, one or more of the first inductors L1 and first capacitors C1 in the matching circuit can be connected in series or parallel, because regardless of the connection method, their resonant frequency characteristics are consistent, and therefore do not affect their impedance matching to the RF power amplifier. Figure 3 shows a series connection, but this connection method is not limited to.

[0024] In radio frequency power amplifier circuits, different electronic components exhibit different impedance characteristics to signals of different frequencies. The matching circuit of this invention combines these components to "convert" the impedance at one end to the impedance value required at the other end (the radio frequency power amplifier end). Figure 3 The circuit uses a first inductor and a first capacitor, which exhibit capacitive or inductive reactance to alternating current, and their impedance varies with frequency. At the set operating frequency, the connection scheme and component values ​​(inductance and capacitance values) will change the overall impedance of the circuit. Therefore, impedance matching with the RF power amplifier can be achieved through a series-parallel structure.

[0025] The matching circuit of the present invention ( Figure 3 ) and existing matching circuits ( Figure 1 By comparison, it was found that the existing circuit architecture requires a separate bias inductor unit in addition to the inductor element of the matching circuit itself; while the matching circuit of the present invention not only does not require a separate bias inductor, but also eliminates the resonant network. As is well known, inductors occupy a much larger area on the chip layout than other devices, especially inductors in the resonant network. Therefore, the matching circuit of the present invention can significantly reduce the area occupancy of the chip layout.

[0026] Please refer to the references. Figure 4 ,like Figure 4 As shown, the matching circuit of the present invention further includes a second inductor L02, one end of which is connected to the first capacitor C1, and the other end of which is grounded. The second inductor L02 and the first capacitor C1 together form a series LC network unit. While the matching circuit performs impedance matching with the RF power amplifier, it can prevent DC or third-order intermodulation signals from the RF power amplifier from flowing into the matching circuit from the circuit input, thereby improving the accuracy of impedance matching.

[0027] In a preferred embodiment of the present invention, each of the first inductors L1 and the second inductors L02 is replaced with bonding wires, and the length of the bonding wires is 300-1200µm. This allows technicians to precisely control the equivalent impedance parameters of the matching circuit by changing the length, curvature, and bonding position of the bonding wires during debugging, ultimately achieving optimal impedance matching with the RF power amplifier. Furthermore, a wire-wound inductor grounding structure is added at the second bonding point of the bonding wires (this structure is typically added to the chip substrate or system board, improving performance while saving chip area). By changing the soldering position of the bonding wires, the adjustment range of the equivalent impedance can be significantly expanded, further enhancing the impedance matching with the RF power amplifier and improving the linearity of the output power.

[0028] As is well known, the bandwidth characteristics of a matching circuit are directly determined by the quality factor Q. The Q value is an indicator that measures the ratio of stored energy to dissipated energy in a circuit, defined as Q = fo / Δf, where fo is the center frequency and Δf is the -3dB bandwidth. A high Q value means narrow bandwidth, high selectivity, and susceptibility to instability; a low Q value corresponds to wide bandwidth and a smooth response.

[0029] The Bode-Fano criterion describes the theoretical limiting relationship between the bandwidth and matching depth of an impedance matching network, constraining the range of values ​​for the emission coefficient Γ(w) across the entire frequency band. The reasoning is as follows: (1) Among them, Γ(w) is determined by the impedance and operating frequency of the circuit and is an important parameter for measuring whether the circuit has reached the optimal matching state.

[0030] Equation (1) shows that for a given load, the matching quality factor Q is a conserved quantity determined by the characteristics of the load itself. Designers need to weigh two options: narrow bandwidth high matching degree and wide bandwidth medium matching degree. Narrow bandwidth high matching degree achieves excellent matching within a limited bandwidth (e.g., |Γ| is close to 0). Wide bandwidth medium matching degree extends the bandwidth but reduces the acceptance matching performance.

[0031] However, ideal reflection-free matching (|Γ|=0) cannot be achieved within a finite bandwidth, otherwise the integral would diverge to infinity (i.e., violate the Bode-Fano limit). The constant value on the right-hand side of the integral is determined by the reactive components of the load (inductors and capacitors). High-Q loads (such as small antennas) have strong reactive characteristics that allow for effective matching only within a very narrow bandwidth; low-Q loads allow for a wider matching bandwidth.

[0032] To ensure sufficient matching bandwidth, the quality factor must be strictly controlled within the range of Q < 3. To strictly control the quality factor Q < 3, the matching circuit of this invention adopts a seven-stage cascaded low-Q matching network topology. In matching circuits, theoretically, the higher the order of the cascaded devices, the better the matching performance. However, increasing the number of components in the circuit not only increases the layout area, but also increases the circuit transmission loss. Therefore, in this invention, to balance the Q value, loss, and layout area of ​​the matching circuit, a seven-stage cascaded structure is preferred. For details, please refer to the reference. Figure 3 ,like Figure 3 As shown, the matching circuit includes three first inductors (L1, L2, L3) and three first capacitors (C1, C2, C3), and the three first inductors and three first capacitors form a six-stage cascaded structure. As described above, in this invention, the first first capacitor reuses the capacitor Cp0 on the RF power amplifier. Figure 3 (Not shown in the image), that is, the three first inductors (L1, L2, L3) and the four first capacitors (Cp0, C1, C2, C3) form a seven-stage cascaded structure; thus, by reusing the capacitor Cp0 on the RF power amplifier, a seven-stage cascaded structure is formed together. The seven-stage cascaded circuit has more adjustable components, which disperses the energy originally concentrated at a single resonant point to multiple poles, thereby weakening the local Q value of each pole and significantly reducing the equivalent Q value of the overall system.

[0033] The connection method of this seven-stage cascaded structure is exactly the same as that of the two-stage cascaded structure. Each first capacitor (C1, C2, C3) and each first inductor (L1, L2, L3) can be connected in series or parallel, which will not be described in detail here. By distributing the impedance transformation ratio of each stage through multi-stage impedance transformation, the equivalent quality factor of the entire matching circuit is effectively reduced, thereby further improving the matching degree with the RF power amplifier.

[0034] To achieve optimal output impedance matching in the matching circuit of this invention, reduce the risk of actual tape-out, and increase post-tasking adjustability, multiple sets of output matching circuits with different impedance values ​​are implemented simultaneously during the layout design stage. Precise impedance matching is achieved through subsequent on-chip debugging, ensuring that the chip performance meets theoretical design specifications. Furthermore, in the layout design of the test chip, in addition to configuring necessary power interfaces, ground interfaces, RF input and output interfaces, and basic circuit modules such as power-side decoupling capacitors and RF port decoupling capacitors, debugging grounding inductor interfaces are reserved at key nodes of the matching network, providing a hardware foundation for subsequent integrated circuit performance debugging. Moreover, in the matching circuit of this invention, all inductors are replaced with on-chip cascaded bonding gold wires, and circuit debugging is completed during board-level debugging and verification steps. Further debugging of the gold wires can also be performed during final packaging and testing to optimize the power amplifier performance. This effectively saves chip layout area and increases the tunability of the circuit through the reconfigurable characteristics of the gold wires. During the debugging process, technicians can precisely control the equivalent impedance parameters of the matching network by changing the length, curvature, and bonding position of the gold wire, ultimately achieving the optimal impedance matching state of the power amplifier.

[0035] In summary, the small-area matching circuit for RF power amplifiers of the present invention not only achieves optimal impedance matching with the RF power amplifier, improving the output power and linearity of the RF power amplifier; but also significantly reduces the area of ​​the matching circuit and improves the circuit integration by reusing the capacitor of the RF power amplifier and avoiding the use of a resonant network.

[0036] The present invention has been described above in conjunction with the preferred embodiments, but the present invention is not limited to the embodiments disclosed above, but should cover various modifications and equivalent combinations made in accordance with the essence of the present invention.

Claims

1. A small-area matching circuit for an RF power amplifier, connected to the output terminal of the RF power amplifier, for matching the impedance between the RF amplifier and the load; characterized in that, It includes at least one first capacitor and at least one first inductor, the first inductor and the first capacitor are connected in series or in parallel, the first first capacitor is reused as a capacitor on the radio frequency power amplifier; and the first first inductor and the first first capacitor form a two-stage cascaded structure.

2. The small-area matching circuit for an RF power amplifier as described in claim 1, characterized in that, The matching unit further includes a second inductor, one end of which is connected to the first first capacitor or the first first inductor, and the other end of which is grounded.

3. The small-area matching circuit for an RF power amplifier as described in claim 2, characterized in that, The second inductor is reused as an inductor in the radio frequency power amplifier.

4. The small-area matching circuit for an RF power amplifier as described in claim 2, characterized in that, Each of the first and second inductors is replaced with bonding wire.

5. The small-area matching circuit for an RF power amplifier as described in claim 4, characterized in that, The length of the bonding gold wire is 300-1200um.

6. The small-area matching circuit for an RF power amplifier as described in claim 1, characterized in that, When the quality factor of the matching circuit is less than or equal to 3, the matching circuit includes 3 first inductors and 4 first capacitors, and the 3 first inductors and 4 first capacitors form a seven-stage cascaded structure.

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