Filtering power amplifier with high rectangular coefficient

Abstract

This invention discloses a power amplifier with a high rectangular coefficient filter. The gate DC bias network provides the gate bias voltage required for the power amplifier transistor to operate; the drain DC bias network provides the drain bias voltage required for the power amplifier transistor to operate; the broadband filter input matching network includes a stepped impedance low-pass filter, a filter network composed of two pairs of cascaded open-circuit stubs, a DC blocking capacitor, and an RC parallel stabilizing circuit; the broadband filter output matching network includes a fundamental frequency matching network and a cascaded stub filter network, wherein the cascaded filter network includes a tuning stub and a T-shaped composite cascaded bandpass filter stub. Compared with existing methods of directly cascading filters and power amplifiers, this invention integrates the filter into the overall circuit through a multi-zero controllable mechanism of cascaded stubs, achieving steep out-of-band rejection and miniaturizing the overall circuit while ensuring broadband performance and high efficiency.

Description

Technical Field

[0001] This invention belongs to the field of power semiconductor device technology and relates to a filter power amplifier with a high rectangular coefficient. Background Technology

[0002] With the rapid development of wireless communication technology, radio frequency (RF) transmitters face increasingly stringent performance requirements in system standards. As a core component of the RF front-end, the performance of the power amplifier directly impacts the overall performance of the transmitter. Especially in today's information age, RF modules not only need to support multi-band or wideband operation within their operating frequency band, but also require miniaturized design. In traditional implementations, the power amplifier is typically cascaded directly with a filter. This architecture often introduces additional insertion loss and increases the overall circuit size. Therefore, some research attempts to integrate the filter into the input-output matching network of the amplifier circuit. However, such designs often face bandwidth limitations or low efficiency, making it difficult to fully cover the operating requirements of the target frequency band.

[0003] To address the aforementioned technical limitations, it is necessary to conduct further research and design a novel broadband filtered power amplifier that maintains high efficiency while also achieving a miniaturized structure and effective coverage of the target frequency band. Summary of the Invention

[0004] To address the problems existing in the aforementioned technologies, this invention provides a filtered power amplifier with a high rectangular coefficient. The traditional two-stage structure of "matching network + filtering network" is integrated into a single-stage multi-functional integrated network. By cascading open-circuit stubs, multi-resonant coupling is achieved at a single parallel node, thereby simultaneously completing impedance transformation, harmonic suppression, and broadband matching without increasing the complexity of the main circuit or introducing additional components. This overcomes the traditional contradiction between "broadband matching" and "steep roll-off" in power amplifier design. Through the multi-zero controllable mechanism of cascaded stubs, good return loss can be maintained over a wide bandwidth while achieving steep out-of-band rejection characteristics, effectively improving the rectangular coefficient of the frequency response and significantly enhancing the spectral purity and overall system stability of the power amplifier.

[0005] To achieve the above objectives, the present invention provides a high rectangular coefficient filtered power amplifier, comprising a gate DC bias network, a drain DC bias network, a broadband filter input matching network, a power amplifier transistor, and a broadband filter output matching network, wherein...

[0006] The gate DC bias network is used to provide the gate bias voltage required for the power amplifier transistor to operate;

[0007] The drain DC bias network is used to provide the drain bias voltage required for the power amplifier transistor to operate;

[0008] The broadband filter input matching network includes a stepped impedance low-pass filter, a filter network composed of two pairs of cascaded open-circuit stubs, a DC blocking capacitor, and an RC parallel stabilizing circuit.

[0009] The broadband filter output matching network includes a fundamental matching network and a cascaded stub filter network, wherein the cascaded filter network includes a tuned stub and a T-shaped composite cascaded bandpass filter stub.

[0010] Preferably, both the gate DC bias network and the drain DC bias network include microstrip lines and several filter capacitors. The gate DC bias network is connected in parallel at the connection point of microstrip lines TL5 and TL9, and the drain DC bias network is connected in parallel at the connection point of the transistor drain and microstrip line TL14.

[0011] Preferably, the broadband filter input matching network includes microstrip lines TL1, TL2, TL3, TL4, TL5, TL7, TL8, TL9, TL10, TL11, TL12, TL13, a DC blocking capacitor C1, and an RC parallel stabilizing circuit; one end of microstrip line TL1 is connected to the input signal, and the other end is connected to the DC blocking capacitor C1. The other end of the DC blocking capacitor is connected to microstrip line TL2. Microstrip line TL2 is connected in series with microstrip lines TL3, TL4, TL5, TL9, and TL12 in sequence. Microstrip line TL12... The other end is connected to an RC parallel stabilizing circuit, the other end of which is connected to microstrip line TL13. The other end of microstrip line TL13 is connected to the gate of the power amplifier transistor. Microstrip line TL7 is connected in parallel with microstrip lines TL5 and TL9 at their connection points. The other end of microstrip line TL7 is connected to microstrip line TL8, and the other end of microstrip line TL8 is open. Microstrip line TL10 is connected in parallel with microstrip lines TL9 and TL12 at their connection points. The other end of microstrip line TL10 is connected to microstrip line TL11, and the other end of microstrip line TL11 is open.

[0012] Preferably, the broadband filter output matching network consists of microstrip lines TL14, TL15, TL16, TL17, TL18, TL19, TL20, TL21, TL22 and a DC blocking capacitor C3. One end of microstrip line TL14 serves as the input terminal of the output matching circuit and is connected to the drain of the power amplifier transistor. The other end of microstrip line TL14 is connected in series with microstrip lines TL15, TL20, and TL21 in sequence. The other end of microstrip line TL21 is connected to DC blocking capacitor C3. The other end of DC blocking capacitor C3 is connected to microstrip line TL22. The other end of microstrip line TL22 is connected to the output terminal. Microstrip line TL16 is connected in parallel with the connection point of microstrip lines TL15 and TL20. The other end of microstrip line TL16 is open. Microstrip line TL17 is connected in parallel with the connection point of microstrip lines TL15 and TL20. The other end of microstrip line TL17 is connected to microstrip lines TL18 and TL19 respectively. The other ends of microstrip lines TL18 and TL19 are open.

[0013] Preferably, the power amplifier transistor is a GaN HEMT CGH40010F transistor.

[0014] The beneficial effects of this invention include at least the following: the gate DC bias network and drain DC bias network include microstrip lines and several filter capacitors; the input impedance matching network includes a stepped impedance low-pass filter and a band-pass filter composed of a pair of cascaded open-circuit stubs, as well as a DC blocking capacitor and an RC parallel circuit; the output impedance network includes a fundamental impedance matching network and a second harmonic control branch connected in parallel thereon, and a T-shaped composite cascaded band-pass filter stub network. Compared with the traditional design of cascading power amplifiers and filters, this invention integrates the band-pass filter into the output matching network, achieving both circuit miniaturization and high bandwidth and high efficiency. Furthermore, by precisely adjusting the electrical parameters of the cascaded open-circuit stubs, the position of the transmission zero can be effectively controlled, thereby ensuring a high roll-off factor in the frequency response. Attached Figure Description

[0015] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration:

[0016] Figure 1 This is a schematic diagram of the structure of a filter power amplifier with a high rectangular coefficient according to an embodiment of the present invention;

[0017] Figure 2 This is a diagram of the input impedance matching network topology of a filtered power amplifier with a high rectangular coefficient according to an embodiment of the present invention.

[0018] Figure 3 This is a diagram of the output impedance matching network topology of a filtered power amplifier with a high rectangular coefficient according to an embodiment of the present invention.

[0019] Figure 4 The S-parameter diagram of a filtered power amplifier with a high rectangular coefficient according to an embodiment of the present invention is shown.

[0020] Figure 5 This is an output power diagram of a filter power amplifier with a high rectangular coefficient according to an embodiment of the present invention;

[0021] Figure 6 This is a drain efficiency diagram of a filter power amplifier with a high rectangular coefficient according to an embodiment of the present invention. Detailed Implementation

[0022] The following are specific embodiments of the present invention, described in conjunction with the accompanying drawings, to further illustrate the technical solution of the present invention. Furthermore, the aspects described in connection with specific embodiments of the present invention are not necessarily limited to those embodiments, but can be practiced in any other embodiments of the present invention.

[0023] See Figure 1 The diagram shows the overall structure of a high rectangular coefficient filtered power amplifier according to the present invention, including a gate DC bias network 5, a drain DC bias network 10, a broadband filter input matching network 15, a power amplifier transistor 20, and a broadband filter output matching network 25. The gate DC bias network 5 provides the gate bias voltage required for the power amplifier transistor 20 to operate, and the drain DC bias network 10 provides the drain bias voltage required for the power amplifier transistor 20 to operate. For the power amplifier transistor 20, Cree's CGH40010F is selected, which has a small-signal gain of 14-16dB, a saturation gain of 10dB, and a saturated output power exceeding 10W, thus meeting the functional requirements of the present invention.

[0024] See Figure 2 The diagram shows the network topology of the input terminal in this invention. One end of microstrip line TL1 is the signal input port, and the other end is connected to one end of DC blocking capacitor C1. The other end of DC blocking capacitor C1 is connected to microstrip line TL2. Microstrip lines TL2, TL3, TL4, TL5, TL7, TL8, TL9, TL10, TL11, TL12, and TL13 constitute the input matching network of the broadband filter power amplifier. The design of the input matching network is divided into two steps: the first step is the design of the low-frequency broadband network, which is implemented by a stepped impedance low-pass filter composed of microstrip lines TL2, TL3, TL4, TL5, TL9, TL12, and TL13. This filter lays the foundation for the broadband performance of the power amplifier by providing a wide bandpass response within the target frequency band. In the stepped impedance structure, the high characteristic impedance microstrip line can be equivalent to a series inductor with an inductance value L. eq The capacitance can be calculated using Equation 1 based on the electrical length and characteristic impedance of the microstrip line; correspondingly, a microstrip line with low characteristic impedance is equivalent to a parallel capacitor, with a capacitance value C. eq It can be obtained from Formula 2.

[0025] (1)

[0026] Where θ h Z is the electric length. h This is the characteristic impedance.

[0027] (2)

[0028] Where θ l Z is the electric length. l This is the characteristic impedance.

[0029] Based on this equivalence, the entire distributed filter can be transformed into a corresponding lumped-parameter LC low-pass prototype network, thus facilitating subsequent circuit analysis and synthesis. To achieve effective matching with the transistor input, a microstrip line TL13 is first used to convert the complex input impedance Z of the transistor at its center frequency f0. S,f0 The impedance is transformed to an intermediate value (20 + j * 4 Ω). Based on this, a third-order LC low-pass matching network with a center frequency of 2.5 GHz and an impedance transformation ratio of 5:2 is constructed. This network not only completes the transformation from real impedance to complex impedance, but also further shapes the passband frequency response. By optimizing the values ​​of each capacitor and inductor component in this LC network, the impedance matching conditions can be met while also taking into account key indicators such as bandwidth, insertion loss, and out-of-band roll-off. The optimized lumped parameter values ​​are converted into the physical lengths of the corresponding microstrip lines TL2, TL3, TL4, TL5, TL9, TL12, and TL13 using Equations 3 and 4, completing the full mapping from circuit topology to actual planar circuit structure.

[0030] (3)

[0031] (4)

[0032] Where λ gL and λ gC It is the waveguide wavelength, Z n 0L and Z n 0C It is the characteristic impedance of the microstrip line, ω c It is the cutoff frequency.

[0033] The second step is to design a bandpass filter consisting of two pairs of cascaded open-circuit stubs, TL7 and TL8, and TL10 and TL11, respectively. Let the characteristic admittance of TL8 be Y8 and its electrical length be θ8, and the characteristic admittance of TL7 be Y7 and its electrical length be θ7. For the open-circuit microstrip line TL8, its input admittance is:

[0034] (5)

[0035] The microstrip line TL7 is a segment based on Y... in,8 The transmission line is the load. According to transmission line theory, its input admittance is:

[0036] (6)

[0037] Similar to parallel simple branches, when the real part of the input admittance of a cascaded branch approaches zero and the imaginary part approaches infinity (Y in,stub →∞), which will create an approximate short circuit to ground on the main road, thus generating a transmission zero. Its mathematical condition is given by letting Y...in,stub The expression is derived by setting the denominator to zero (i.e., the input impedance is zero), and the condition is:

[0038] (7)

[0039] You will then receive:

[0040] (8)

[0041] (9)

[0042] Where θ is the electric length of the microstrip line, f Z denoted by 'l', where 'l' represents the physical length of the microstrip line and 'v' represents the wave velocity in the microstrip line.

[0043] Therefore, by adjusting θ7, θ8, and the ratio of Y7 / Y8, the location of the zeros can be precisely controlled. Microstrip lines TL7 and TL8, along with another pair of microstrip lines TL10 and TL11, each form a transmission zero outside the high-frequency and low-frequency bands, respectively. Furthermore, because the transmission zeros are precisely designed at frequencies close to the passband edge, the network achieves an extremely steep transition band characteristic between the passband and stopband, resulting in an excellent roll-off factor. This design significantly improves the frequency selectivity of the filter, effectively suppresses out-of-band spurious and harmonic components, and simultaneously ensures low-loss signal transmission within the passband.

[0044] See Figure 3 The output impedance matching network mainly includes a fundamental impedance matching network and a second harmonic control branch connected in parallel thereon, as well as a T-shaped composite cascaded bandpass filter stub. The fundamental impedance matching network is composed of microstrip lines TL14, TL15, TL20, and TL21, and is used to reduce the transistor's output impedance Z at the fundamental frequency f0. L，f0 Matched to a 50Ω load. The second harmonic control branch is constructed from microstrip line TL16 and connected in parallel to the main circuit to suppress second harmonics and improve power amplifier efficiency. The T-shaped composite cascaded bandpass filter stub is constructed from two open-circuit stub microstrip lines TL18 and TL19 sharing a single series stub microstrip line TL17, cascaded and connected in parallel to the main circuit to further enhance filtering performance. Let the characteristic admittances of microstrip lines TL17, TL18, and TL19 be Y... 17 Y 18 Y 19 The electric length is θ 17 θ 18 θ 19 The total load admittance Y at the end of the microstrip line TL17 L for:

[0045] (10)

[0046] Looking in from the main parallel connection point, the input admittance Y of the entire T-shaped composite branch... in,stub It is a characteristic admittance of Y 17 Electric length is θ 17 Terminal load is Y L The input admittance of the transmission line. According to the formula for the input admittance of a transmission line:

[0047] (11)

[0048] Substitute Y L have to:

[0049] (12)

[0050] By setting the denominator to zero and simplifying based on the condition for generating zero, we can obtain the following:

[0051] (13)

[0052] By adjusting the characteristic impedance and electrical length of these three microstrip lines, the zero-point position can be precisely controlled at multiple frequency points. The transmission network of this T-shaped composite stub can be represented by Equation 14. Since the zero-point position can be precisely controlled, two zeros can be set to be closely adjacent to each other to achieve an extremely steep roll-off.

[0053] (14)

[0054] Where f zm It is the transmission zero point generated by the T-shaped composite stub.

[0055] See Figures 4 to 6 The figure shows the S-parameters, drain efficiency, and output power of the high rectangular coefficient filtered power amplifier of the present invention after ADS simulation. The results show that the designed power amplifier operates in the 1.6-3.4 GHz frequency band, with S21 > 14.1 dB within the band, exhibiting good in-band flatness. It also has five out-of-band zeros, three of which are less than -20 dB, demonstrating excellent out-of-band filtering performance. Furthermore, due to the controllable zero-point positions, it exhibits a very high roll-off factor, achieving 30 dB attenuation within a 100 MHz bandwidth, demonstrating excellent out-of-band rejection performance. Within the operating frequency band, the drain efficiency reaches 55.7-75%, exhibiting good power conversion efficiency. Within the frequency band, the output power is above 40 dBm, with a maximum output power of 41.8 dBm.

[0056] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A filtered power amplifier with a high rectangular coefficient, characterized in that, This includes a gate DC bias network, a drain DC bias network, a broadband filter input matching network, a power amplifier transistor, and a broadband filter output matching network, among which... The gate DC bias network provides the gate operating bias voltage for the power amplifier transistor; The drain DC bias network provides a drain operating bias voltage for the power amplifier transistor; The broadband filter input matching network specifically includes: a stepped impedance low-pass filter, formed by microstrip lines TL2, TL3, TL4, TL5, TL9, and TL12 connected in series, used to achieve broadband fundamental frequency matching; a first cascaded open-circuit stub pair, composed of microstrip lines TL7 and TL8, connected in parallel to the nodes of the stepped impedance low-pass filter, at the connection point of microstrip lines TL5 and TL9, used to generate a transmission zero at a first specific frequency; a second cascaded open-circuit stub pair, composed of microstrip lines TL10 and TL11, connected in parallel to the nodes of the stepped impedance low-pass filter, at the connection point of microstrip lines TL9 and TL12, used to generate another transmission zero at a second specific frequency; and an RC parallel stabilizing circuit, connected in series between the stepped impedance low-pass filter and microstrip line TL13; wherein the first specific frequency and the second specific frequency are located on both sides outside the passband to achieve out-of-band suppression; The broadband filter output matching network specifically includes: a fundamental matching network, composed of microstrip lines TL14, TL15, TL20, and TL21 connected in series, used to transform the optimal load impedance of the transistor drain to a 50Ω load; and a cascaded filter stub network, connected in parallel to the nodes of the fundamental matching network, at the connection point of microstrip lines TL15 and TL20. This cascaded filter stub network includes: a tuning stub, an open-circuit stub composed of microstrip line TL16, used to suppress the second harmonic generated by the circuit to improve efficiency; and a T-shaped composite cascaded bandpass filter stub, a T-shaped open-circuit composite structure composed of microstrip lines TL17, TL18, and TL19, used to generate a zero on each side outside the passband, thereby achieving a high rectangular coefficient filter response together with the zeros generated by the broadband filter input matching network.

2. The filtered power amplifier with a high rectangular coefficient according to claim 1, characterized in that, The gate DC bias network includes a microstrip line and a decoupling capacitor Cg; wherein, one end of the microstrip line is connected to the common connection point of the cascaded open stub in the broadband filter input matching network used to generate the first transmission zero, and the other end is grounded through the decoupling capacitor Cg; and a -2.7V DC bias voltage is applied to make the power amplifier transistor operate in class AB mode.

3. The filtered power amplifier with a high rectangular coefficient according to claim 1, characterized in that, The drain DC bias network includes a microstrip line and a decoupling capacitor Cd; wherein, the microstrip line is connected to the connection between TL14 and the transistor drain, and the other end is grounded through the decoupling capacitor Cd and connected to a 28V DC bias voltage.

4. The filter power amplifier with high rectangular coefficient according to claim 1, characterized in that, The power amplifier transistor is a GaN HEMT CGH40010F transistor.

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