阅读说明：本技术 一种class-AB驱动的Doherty功率放大器、基站和移动终端 (class-AB driven Doherty power amplifier, base station and mobile terminal ) 是由 吕关胜 陈文华 陈晓凡 黄飞 周航 于 2020-05-18 设计创作，主要内容包括：本发明公开一种class-AB驱动的Doherty功率放大器、基站和移动终端,其中Doherty功率放大器包括输入功分器、主功放支路和辅功放支路,在输入功分器前包括一class-AB驱动结构,该class-AB驱动结构包括一class-AB功率放大器和作为其输出匹配网络的一段λ/4线,主功放支路的输入端口与输入功分器的输入端口的相位差为0,辅功放支路的输入端口与输入功分器的输入端口的相位差为90°。本发明与传统class-AB驱动Doherty功放相比,回退效率有明显改善；与Doherty驱动Doherty功放相比,在实现高效率的同时,保持了高增益和高线性度。(The invention discloses a class-AB driven Doherty power amplifier, a base station and a mobile terminal, wherein the Doherty power amplifier comprises an input power divider, a main power amplifier branch and an auxiliary power amplifier branch, a class-AB driving structure is arranged in front of the input power divider, the class-AB driving structure comprises a class-AB power amplifier and a section of lambda/4 line serving as an output matching network of the class-AB power amplifier, the phase difference between an input port of the main power amplifier branch and an input port of the input power divider is 0, and the phase difference between an input port of the auxiliary power amplifier branch and the input port of the input power divider is 90 degrees. Compared with the traditional class-AB driven Doherty power amplifier, the backspacing efficiency is obviously improved; compared with a Doherty-driven Doherty power amplifier, the high efficiency is realized, and meanwhile, the high gain and the high linearity are kept.)

1. A class-AB driven Doherty power amplifier comprises an input power divider, a main power amplifier branch and an auxiliary power amplifier branch, and is characterized in that a class-AB driving structure is arranged in front of the input power divider, the class-AB driving structure comprises a class-AB power amplifier and a section of lambda/4 line serving as an output matching network of the class-AB power amplifier, the phase difference between an input port of the main power amplifier branch and an input port of the input power divider is 0, and the phase difference between an input port of the auxiliary power amplifier branch and the input port of the input power divider is 90 degrees.

2. The class-AB driven Doherty power amplifier of claim 1, wherein the input power divider is a coupler.

3. A class-AB driven Doherty power amplifier according to claim 1 and wherein the λ/4 lines are lumped parameter λ/4 lines.

4. The class-AB driven Doherty power amplifier of claim 1, wherein the main power amplifier branch comprises a main power amplifier input matching network, a main power amplifier transistor and a main power amplifier output matching network which are connected in sequence, the auxiliary power amplifier branch comprises an auxiliary power amplifier input matching network, an auxiliary power amplifier transistor and an auxiliary power amplifier output matching network which are connected in sequence, and the gate input impedances of the main power amplifier transistor and the auxiliary power amplifier transistor are respectively

Wherein R is_g1And R_g2The gate resistance values of the main power amplifier transistor and the auxiliary power amplifier transistor, C_in1And C_in2The equivalent input capacitors of the main power amplifier transistor and the auxiliary power amplifier transistor are respectively.

5. The class-AB driven Doherty power amplifier of claim 4, wherein the phase shift of both the main and auxiliary power amplifier input matching networks is close to 0 degrees.

6. A base station comprising a class-AB driven Doherty power amplifier as claimed in any one of claims 1 to 5.

7. A mobile terminal comprising a class-AB driven Doherty power amplifier as claimed in any one of claims 1 to 5.

Technical Field

The invention relates to the technical field of microwave power amplifiers, in particular to a class-AB driven Doherty power amplifier, a base station and a mobile terminal.

Background

In order to improve the spectrum efficiency, modern communication signals often use complex modulation schemes such as OFDM, which brings a problem of high peak-to-average ratio (PAPR). The high PAPR brings difficulties to the design of the radio frequency power amplifier (hereinafter referred to as power amplifier), especially brings adverse effects to the efficiency index of the power amplifier. The traditional AB linear power amplifier has higher efficiency near saturation power, and when the output power is reduced, the efficiency is sharply reduced. Under high PAPR, the power amplifier works in a backspacing power region most of the time, so the average efficiency of the AB class power amplifier is far lower than the saturation efficiency of the AB class power amplifier. In order to improve the average efficiency, a Doherty power amplifier with high back-off efficiency is commonly used in the communication base station at present.

The gain of the Doherty power amplifier is limited, and the actual communication system has strict requirements on the gain of the power amplifier, so that a driving stage needs to be inserted before the Doherty power amplifier. The additional power consumption introduced by the driver stage results in a reduction in overall efficiency, and the lower the efficiency of the driver stage, the more the overall efficiency is reduced. Fig. 1 shows the most common class-AB driver structure, i.e. the driver stage is a simple class-AB amplifier. This driving structure has a high gain and good linearity, but has a problem of low efficiency. In a saturation region, the efficiency of the class-AB power amplifier is high, and the influence on the overall efficiency is small, but in a backspacing region, the efficiency of the class-AB power amplifier is rapidly reduced, so that the overall backspacing efficiency is seriously deteriorated. In order to reduce the influence of the driving stage on the efficiency, a Doherty driving structure is proposed in patent application with the patent number of 201821696748.X and the invention name of "a Doherty-driven Doherty power amplifier", that is, the driving stage is a Doherty power amplifier, as shown in fig. 2. This driving structure has a great advantage in efficiency, but has problems of low gain and poor linearity. The gain of the Doherty drive structure is typically at least 3dB lower than the class-AB drive structure due to gain loss caused by input power distribution and the auxiliary power amplifier class-C bias. In addition, the linearity of the Doherty power amplifier is relatively poor, and after the drive-stage Doherty power amplifier and the final-stage Doherty power amplifier are cascaded, the linearity is further deteriorated, and it may be difficult to calibrate by using Digital Predistortion (DPD), so the Doherty drive structure shown in fig. 2 is not applied in practice. In summary, the driving stage of the Doherty power amplifier has a great influence on the overall performance, but the current driving structure has difficulty in achieving high gain, high linearity and high efficiency at the same time.

Disclosure of Invention

Aiming at the problem of efficiency deterioration of the traditional class-AB driven Doherty power amplifier, the invention provides the class-AB driven Doherty power amplifier, a base station and a mobile terminal, which can simultaneously realize the performances of high gain, high linearity and high efficiency.

The invention provides a class-AB driven Doherty power amplifier, which comprises an input power divider, a main power amplifier branch and an auxiliary power amplifier branch, wherein a class-AB driving structure is arranged in front of the input power divider, the class-AB driving structure comprises a class-AB power amplifier and a section of lambda/4 line serving as an output matching network of the class-AB power amplifier, the phase difference between an input port of the main power amplifier branch and an input port of the input power divider is 0, and the phase difference between an input port of the auxiliary power amplifier branch and the input port of the input power divider is 90 degrees.

Preferably, the input power divider is a coupler.

Preferably, the lambda/4 lines are lumped parameter lambda/4 lines.

The main power amplifier branch comprises a main power amplifier input matching network, a main power amplifier transistor and a main power amplifier output matching network which are connected in sequence, the auxiliary power amplifier branch comprises an auxiliary power amplifier input matching network, an auxiliary power amplifier transistor and an auxiliary power amplifier output matching network which are connected in sequence, and the main power amplifier transistor and the auxiliary power amplifier transistor have gate input impedance respectively

Wherein R is_g1And R_g2The gate resistance values of the main power amplifier transistor and the auxiliary power amplifier transistor, C_in1And C_in2The equivalent input capacitors of the main power amplifier transistor and the auxiliary power amplifier transistor are respectively.

The phase shift of the main power amplifier input matching network and the auxiliary power amplifier input matching network is close to 0 degree.

In a second aspect of the present invention, a base station is provided, which includes a class-AB driven Doherty power amplifier according to any of the above technical solutions.

In a second aspect of the present invention, a mobile terminal is provided, which includes a class-AB driven Doherty power amplifier according to any of the above technical solutions.

The high-efficiency class-AB driven Doherty power amplifier has the following advantages: firstly, compared with the traditional class-AB driven Doherty power amplifier, the backspacing efficiency of the invention is obviously improved; second, compared with a Doherty-driven Doherty power amplifier, the invention maintains high gain and high linearity while realizing high efficiency.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of a prior art class-AB driven Doherty power amplifier;

FIG. 2 is a schematic diagram of a prior art Doherty-driven Doherty power amplifier;

FIG. 3 is a schematic diagram of a Doherty power amplifier driven by class-AB according to an embodiment of the present invention;

FIG. 4(a) is a diagram of an equivalent circuit model of the field effect transistor used as the main power amplifier and the auxiliary power amplifier in the embodiment of FIG. 3; FIG. 4(b) is a diagram of an equivalent circuit model of a field effect transistor after Miller conversion;

fig. 5 is a circuit diagram of several lumped parameter lambda/4 lines in the embodiment of fig. 3.

Detailed Description

In order to make the technical solutions of the present invention better understood, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention. As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

As shown in fig. 3, this embodiment provides a class-AB driven Doherty power amplifier, which includes an input power divider, a main power amplifier branch, and an auxiliary power amplifier branch, and further includes a class-AB driving structure in front of the input power divider, where the class-AB driving structure includes a class-AB power amplifier and a λ/4 line serving as an output matching network of the class-AB power amplifier, a phase difference between an input port of the main power amplifier branch and an input port of the input power divider is 0, and a phase difference between an input port of the auxiliary power amplifier branch and an input port of the input power divider is 90 °. The phase shift of the input matching network of the main power amplifier and the auxiliary power amplifier is close to 0 degree.

The Doherty power amplifier of the embodiment utilizes the feedback capacitance of the transistor, and firstly needs to know the equivalent circuit model of the transistor. FIG. 4(a) shows a raw equivalent circuit model of a Field Effect Transistor (FET), where C_gdI.e., the feedback capacitance, the presence of the feedback capacitance can cause the transistor input impedance to be affected by the load impedance. According to Miller's principle, feedback capacitor C_gdCan be decomposed into two parts and C_gsAnd C_dsCapacitors connected in parallel to obtain an equivalent input capacitor C_inAnd an equivalent output capacitor C_outAs shown in fig. 4 (b). Hypothesis C_outQuilt susceptance jB_LComplete neutralization, then C_inCan be expressed as

C_in＝C_gs+C_gd(1+g_mR_L) (1)

Wherein g is_mR_LRepresenting the voltage gain. C_gdIs much less than C_gsBut due to higher voltage gain, C_gd(1+g_mR_L) A large proportion of the input capacitance is occupied.

In the high-efficiency class-AB driven Doherty power amplifier provided by this embodiment, both the main power amplifier transistor and the auxiliary power amplifier transistor are represented by equivalent circuit models thereof, as shown in fig. 3. The gate input impedance of the main and auxiliary power amplifier transistors can be calculated as

Assuming that the Doherty power amplifier has a symmetrical structure, the optimal load impedance of the main power amplifier is R_opt. In the load modulation process of the Doherty power amplifier, the load impedance R of the main power amplifier transistor_L1Gradually from 2R_optReduced to R_optAccording to the formula (1), the input capacitor C of the main power amplifier transistor_in1It will be significantly reduced. The auxiliary power amplifier is biased in a class-C state and starts to work after a backspacing point, and the voltage gain g_m2R_L2Gradually increased according to equation (1) with auxiliary amplifier transistor input capacitance C_in2It will also be significantly elevated. According to the formula (2), the input impedance Z of the main power amplifier transistor_g1And auxiliary power amplifier transistor input impedance Z_g2Will rise and fall, respectively. Because the phase shift of the input matching network of the main power amplifier and the auxiliary power amplifier is close to 0 degree, the matched input impedance Z_in1And Z_in2Are each independently of Z_g1And Z_g2The trend of the change is the same.

The Doherty power amplifier in fig. 3 adopts a coupler as an input power divider, and the phase difference between the main power amplifier port and the auxiliary power amplifier port and the input port of the coupler is 0 degree and 90 degrees respectively, so that the input impedance Z of the Doherty power amplifier_{in_dpa}The trend of change and Z_in1Same as Z_in2On the contrary, this means Z_in1Rising sum Z of_in2All result in Z_{in_dpa}Is increased.

In this embodiment, a quarter-wavelength (λ/4) line is used as the output matching network of the class-AB power amplifier, so as to drive the load impedance Z of the power amplifier_{L_driver}The impedance value in the back-off region is higher than that in the saturation region, so that the back-off efficiency similar to that of the Doherty power amplifier is improved, and the overall back-off efficiency of the driving power amplifier and the final-stage Doherty power amplifier after cascade connection is improved. In the conventional class-AB driven Doherty power amplifier, the input impedance of the final Doherty power amplifier also changes with the output power, but the change is random, and the design of the driven power amplifier does not consider the influence, which may cause further deterioration of the backoff efficiency.

The input power divider is a coupler.

It should be noted that although the above analysis is based on a symmetric Doherty structure and FET transistors, the class-AB driven Doherty amplifier proposed in the present embodiment is applicable to any structure of Doherty power amplifier and any type of transistor. In addition, during the integrated design, in order to reduce the chip size, the λ/4 line used for driving the power amplifier output matching network in fig. 3 can be equivalently implemented by a lumped parameter network, and fig. 5 shows several common lumped parameter λ/4 lines, but the actual matching network is not limited to the circuit shown in fig. 5, and any matching network which exhibits a phase shift close to 90 degrees in the working frequency band can achieve similar effects.

The embodiment further provides a base station, which includes the class-AB driven Doherty power amplifier described in any of the above technical solutions.

The embodiment further provides a mobile terminal, which includes the class-AB driven Doherty power amplifier in any technical scheme.

The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the various embodiments can be referred to each other, and each embodiment focuses on the differences from the other embodiments. The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.