Broadband large-backoff radio frequency Doherty power amplifier based on switch structure

Abstract

The invention discloses a broadband large-backoff radio frequency Doherty power amplifier based on a switch structure, which comprises a power distribution unit, a frequency band selection unit, a signal phase shift unit, a signal amplification unit and a signal synthesis unit, and is characterized in that the frequency band selection unit comprises a radio frequency switch, and the signal amplification unit comprises a main power amplifier and a plurality of auxiliary power amplifiers; the signal synthesis unit comprises an impedance inverter and an impedance converter. According to the Doherty power amplifier, the radio frequency switch structure is added to the auxiliary power amplifier branch, so that the auxiliary power amplifier can complete active load modulation on the main power amplifier in two adjacent narrow frequency bands, and the auxiliary power amplifier branch and the main power amplifier are asymmetrically constructed, so that the overall bandwidth of the Doherty power amplifier is expanded, and the bandwidth of the Doherty power amplifier is increased. And meanwhile, the rollback amount is increased.

Description

Technical Field

[0001] The invention belongs to the field of wireless communications, relates to a transmitter submodule of wireless communications technology, and in particular to a broadband large back-off radio frequency Doherty power amplifier based on a switch structure. Background Art

[0002] The traditional circuit of Doherty power amplifier and its various extended architectures are a common technology used in modern wireless communication technology to achieve efficiency improvement. The traditional circuit principle block diagram is as follows Figure 1 As shown, the RF signal is first input into the power divider 10, and the power divider 10 divides the input signal into two electrical signals of equal power and the same phase through power distribution; the phase shifter 1 21 and the phase shifter 2 22 respectively adjust the phase delay of the two electrical signals; the main power amplifier (carrier amplifier) ​​31 and the auxiliary power amplifier (peak amplifier) ​​32 respectively amplify the two RF signals; the impedance inverter 40 adjusts the load impedance of the main power amplifier under low power conditions to a high impedance state; the signal synthesizer 50 synthesizes the two in-phase signals after power amplification into an output signal. In the field of modern wireless communication systems, the Doherty power amplifier architecture is well known, so the various unit circuits in its architecture will not be described here.

[0003] The Doherty power amplifier achieves high efficiency at low power levels through active load modulation of two power amplifiers (main power amplifier and auxiliary power amplifier). When the input signal is at a low power level, the auxiliary power amplifier is not turned on due to the Class C bias, and the main power amplifier in Class B or deep Class AB bias works alone to amplify the power of the RF signal on the path. At this time, the load of the main power amplifier is in a high impedance state, so the working efficiency is relatively high. When the input signal power level increases, the auxiliary power amplifier is turned on, and the two paths amplify the RF signal together. The Doherty power amplifier can achieve high efficiency in the range of low power levels to high power levels, has the advantages of simple structure and easy implementation, and is therefore widely used.

[0004] However, for monolithic microwave integrated circuits, the Doherty power amplifier under the relevant technology has the characteristic of narrowband amplification of the large signal output of the auxiliary power amplifier in Class C bias, making it difficult to achieve effective active load modulation of the main power amplifier at low power levels and amplification of broadband signals at high power levels within a broadband range, thus affecting the overall broadband characteristics of the Doherty power amplifier; at the same time, the symmetrical architecture of the traditional Doherty carrier power amplifier and the auxiliary power amplifier makes the back-off amount of the traditional Doherty only 6dB, which affects the back-off range and is not conducive to the efficient amplification of higher peak-to-average ratio signals. Summary of the invention

[0005] The main technical problem to be solved by the present invention is to provide a new Doherty power amplifier architecture that can achieve high efficiency in a wide band and improve the back-off amount, under the premise that the known class C bias auxiliary power amplifier can only ensure high-efficiency amplification in a narrow band under large signal output.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A broadband large back-off radio frequency Doherty power amplifier based on a switch structure, comprising a power distribution unit, a frequency band selection unit, a signal phase shift unit, a signal amplification unit and a signal synthesis unit; the frequency band selection unit comprises a plurality of radio frequency switches; the signal phase shift unit comprises a plurality of phase shifters; the signal amplification unit comprises a main power amplifier and at least two auxiliary power amplifiers, the main power amplifier is biased in class AB, the auxiliary power amplifier is a power amplifier with class C bias adapted to adjacent different frequency bands, and the signal synthesis unit is composed of an impedance inverter and an impedance converter;

[0008] The input end of the power distribution unit receives a radio frequency input signal, and one output end is connected to a phase shifter, and the phase shifter is connected to a main power amplifier; the other output end is connected to the radio frequency switch, and the output end of the radio frequency switch is divided into a plurality of branches, each branch is connected to a phase shifter, and the phase shifters connected to each branch are respectively connected to an auxiliary power amplifier; that is, the number of phase shifters is equal to the sum of the number of main power amplifiers and auxiliary power amplifiers, and the number of auxiliary power amplifiers is equal to the sum of the number of branches into which the output of the radio frequency switch is divided;

[0009] The radio frequency switch selects a certain frequency band signal of the output signal of the power distribution unit, and inputs it to the auxiliary power amplifier adapted to the frequency band through the phase shifter;

[0010] The output of the main power amplifier is connected to the impedance inverter, and the output of the impedance inverter and the output of each auxiliary power amplifier are connected to the impedance converter, that is, the output signals of the main power amplifier and all the auxiliary power amplifiers finally enter the signal synthesis unit, and the signal amplified by the broadband RF Doherty power amplifier is output from the output end of the impedance converter.

[0011] In one embodiment, the power distribution unit decomposes the RF input signal into two signals with equal power and the same phase, and outputs them separately.

[0012] Obviously, in the present invention, in order to ensure the complete signal amplification function, the frequency band selection unit needs to complete the selection of the entire frequency range of its input signal, that is, the output signal of the power distribution unit, and input the selected frequency band signals into one of the auxiliary power amplifiers. For example, the operating frequency range of the broadband RF Doherty power amplifier of the present invention is f1-fn. In order to cooperate with the frequency band selection function of the frequency band selection unit, f1-fn is divided into n-1 frequency bands. Obviously, n≥3. The selection function of the n-1 frequency bands can be realized by using a number of RF switches. Accordingly, the number of auxiliary power amplifiers is n-1, and they work in the n-1 frequency bands respectively, while the main power amplifier works in the overall broadband frequency band of f1-fn.

[0013] In a specific embodiment, n=3 is used for description. At this time, the two divided frequency bands are f1-f2 and f2-f3. Obviously, f1<f2<f3. The two auxiliary power amplifiers are named the first auxiliary power amplifier and the second auxiliary power amplifier respectively. The first auxiliary power amplifier and the second auxiliary power amplifier are still biased in Class C respectively, but the two auxiliary power amplifiers are required to work in the two narrowband frequency bands f1-f2 and f2-f3 respectively, and the main power amplifier works in the overall broadband frequency band f1-f3. The RF switch can be set to 1, and its parameters are configured so that it can realize the selection function of the frequency bands f1-f2 and f2-f3. When the signal output by the power distribution unit received is the f1-f2 frequency band signal, the branch where the first auxiliary power amplifier is located is turned on, and the branch where the second auxiliary power amplifier is located is turned off; when the signal output by the power distribution unit received is the f2-f3 frequency band signal, the branch where the second auxiliary power amplifier is located is turned on, and the branch where the first auxiliary power amplifier is located is turned off, thereby completing the frequency band selection. The branch where the auxiliary power amplifier is located refers to the branch where the selected frequency band signal is input to the corresponding auxiliary power amplifier through a phase shifter; at the same time, the gate width of the two auxiliary power amplifiers is set to be larger than the gate width of the main power amplifier to ensure that the output current and output power of the auxiliary power amplifier branch are greater than those of the main power amplifier branch at saturation.

[0014] In another implementation, two RF switches may be set, named RF switch 1 and RF switch 2. When one signal output by the power distribution unit is a signal in the frequency band f1-f2, RF switch 1 is turned on, RF switch 2 is turned off, and the signal is amplified by the first auxiliary power amplifier of the branch where RF switch 1 is located; when one signal output by the power distribution unit is a signal in the frequency band f2-f3, RF switch 2 is turned on, RF switch 1 is turned off, and the signal is amplified by the second auxiliary power amplifier of the branch where RF switch 2 is located, thereby completing the frequency band selection.

[0015] The power amplifier under Class C bias uses the switching action of the transistor to amplify the signal, so the nonlinear amplification characteristics are significant, and it is only suitable for narrowband signal amplification and limited information transmission. Therefore, the RF switch of the present invention selects a certain frequency band signal of the power distribution unit output signal as a narrowband signal. The narrowband signal here refers to a signal with a relative bandwidth less than 1%. The relative bandwidth is the ratio of the signal bandwidth to the center frequency, which is expressed by the formula: ffoc=2(f H -f L ) / (f H +f L ), where f H and f L Represent the upper and lower frequency limits respectively.

[0016] The gate width of the auxiliary power amplifier of the present invention should be greater than that of the main power amplifier to meet the requirement that the output current and output power under large signals are greater than those of the main power amplifier, thereby ensuring the effect of back-off enhancement. After the input signal is amplified by the main power amplifier or each auxiliary power amplifier to obtain the output signal, the main power amplifier or each auxiliary power amplifier enters the nonlinear working area, and the power of the output signal is close to the input signal power amplitude of the saturated output power of the main power amplifier or each auxiliary power amplifier. The power amplifier has a maximum saturated output power. When the amplitude of the input signal is very small, the output power is significantly less than the output power, which can be called a small signal. When the amplitude of the input signal increases to the point where the output power is close to or even reaches the saturated output power, the input signal is a large signal.

[0017] The core idea of ​​the present invention is to achieve high-efficiency power amplification of the overall Doherty power amplifier with good characteristics in several adjacent narrowbands through the cooperation of the RF switch and several auxiliary power amplifiers, while increasing the back-off amount, and ultimately achieving broadband and large back-off amplification of RF signals.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] Without changing the narrowband amplification of the auxiliary power amplifier under Class C bias in the traditional Doherty power amplifier signal unit, a switch is integrated at the output end of the power divider to increase the auxiliary power amplifier branch. At the same time, an asymmetric architecture of the main power amplifier and the auxiliary power amplifier is introduced to achieve broadband and large back-off amplification of the RF signal, which has the advantages of simple structure and concise principle. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a block diagram of the structure principle of a traditional Doherty power amplifier.

[0021] Figure 2 It is a structural block diagram of a broadband large back-off RF Doherty power amplifier based on a switch structure in Example 1 of the present invention.

[0022] Figure 3 It is the specific working principle block diagram of the signal synthesizer in the broadband large-backoff Doherty power amplifier of the present invention.

[0023] Figure 4 It is the structural block diagram of the broadband radio frequency Doherty power amplifier based on the switch structure in Embodiment 2 of the present invention. Specific embodiments

[0024] The following will describe the embodiments of the present invention in detail with reference to the accompanying drawings and embodiments.

[0025] Embodiment 1

[0026] The broadband radio frequency Doherty power amplifier based on the switch structure provided by the present invention, as Figure 2 shown, includes a power distribution unit 100, a frequency band selection unit 200, a signal phase shift unit 300, a signal amplification unit 400, and a signal synthesis unit 500.

[0027] The power distribution unit 100 includes a power divider 101, which decomposes the radio frequency input signal S(t)=Acos(ωt + θ) into two signals S1(t) and S2(t) with equal power and the same phase: S1(t)=S2(t)=(A / 2)cos(ωt + θ), where A is the amplitude of the input signal S(t), ω is the angular frequency of the input signal, and θ is the phase of the two signals. The specific separation method of the power divider 101 is consistent with the traditional Wilkinson power distribution principle, which belongs to common knowledge and will not be elaborated here.

[0028] The frequency band selection unit 200 includes a radio frequency switch 201, and the radio frequency switch 201 is responsible for selectively outputting one of the received signals S2(t). Specifically, assume three frequencies f1, f2, f3 (f1 < f2 < f3). When S2(t) is a signal in the f1 - f2 frequency band, the radio frequency switch 201 turns on the branch where the first auxiliary power amplifier 402 is located and turns off the branch where the second auxiliary power amplifier 403 is located, and outputs the signal S 21 (t)=(A / 2)cos(ω2t + θ) on the branch where the first auxiliary power amplifier 402 is located; when S2(t) is a signal in the f2 - f3 frequency band, similarly, the radio frequency switch 201 turns on the branch where the second auxiliary power amplifier 403 is located and turns off the branch where the first auxiliary power amplifier 402 is located, and outputs the signal output S 22 (t)=(A / 2)cos(ω3t + θ) on the branch where the second auxiliary power amplifier 403 is located, where ω2 and ω3 respectively represent the angular frequencies of the signals in the f1 - f2 frequency band and the f2 - f3 frequency band.

[0029] The signal phase shift unit 300 is responsible for adjusting the signal phase of each path so that the subsequently processed signals can be synthesized in phase at the signal synthesis unit. The unit at least includes a first phase shifter 301, a second phase shifter 302 and a third phase shifter 303. 21 (t) and S 22 (t) is delayed to obtain RF signals X1(t), X2(t) and X3(t):

[0030] X1(t)=(A / 2)cos(ωt+θ+Φ1);

[0031] X2(t)=(A / 2)cos(ω2t+θ+Φ2);

[0032] X3(t)=(A / 2)cos(ω3t+θ+Φ3);

[0033] Among them, Φ1, Φ2, Φ3 are the delay phases of each channel respectively.

[0034] The signal amplification unit 400 includes three power amplifiers, namely a main power amplifier 401, a first auxiliary power amplifier 402 and a second auxiliary power amplifier 403, wherein the main power amplifier 401 is biased in class AB, that is, it starts working when there is an input signal, and is responsible for amplifying the signal X1(t) in the broadband range (f1-f3) to obtain a signal Y1(t); the first auxiliary power amplifier 402 and the second auxiliary power amplifier 403 are both biased in class C, that is, they are not turned on at low power, the first auxiliary power amplifier 402 is responsible for amplifying the signal X2(t) in the f1-f2 frequency band to obtain Y2(t), and the second auxiliary power amplifier 403 is responsible for amplifying the signal X3(t) in the f2-f3 frequency band to obtain Y3(t):

[0035] Y1(t)=G1(A / 2)cos(ωt+θ+Φ1+α1); Y2(t)=G2(A / 2)cos(ω2t+θ+Φ2+α2); Y3(t)=

[0036] G3(A / 2)cos(ω3t+θ+Φ3+α3); wherein G1, G2 and G3 are the power amplification gains of the main power amplifier 401, the first auxiliary power amplifier 402 and the second auxiliary power amplifier 403 respectively, and α1, α2 and α3 are the phase delays generated by each signal passing through the power amplifier.

[0037] The signal synthesis unit 500 is composed of an impedance inverter 501 and an impedance converter 502. The impedance inverter 501 is responsible for inverting the impedance at both ends. When the power is low, that is, when the two auxiliary power amplifiers are not turned on, the load is converted from low impedance to high impedance, so that the back end of the main power amplifier 401 is in a high impedance state, thereby obtaining high efficiency at a low power level.

[0038] When the input power is increased to a medium power level, one of the two auxiliary power amplifiers will be turned on according to the frequency band of the signal and perform active load modulation with the main power amplifier 401. The impedance converter 502 converts the impedance of the combined circuit to a standard 50 ohm terminal load.

[0039] Therefore, the present invention adds a radio frequency switch structure to the auxiliary power amplifier branch, so that the auxiliary power amplifier can complete active load modulation of the main power amplifier in two adjacent narrow frequency bands, thereby broadening the overall bandwidth of the Doherty power amplifier. At the same time, due to the use of an asymmetric architecture, the overall back-off amount of Doherty is improved.

[0040] Figure 3 This is a specific principle block diagram of the signal synthesis unit 500 in the structure block diagram of a broadband large back-off RF Doherty power amplifier based on a switch structure according to an embodiment of the present invention. The signal synthesis unit 500 is composed of an impedance inverter 501 and an impedance converter 502. The port impedance after the main power amplifier 401 is Z M , the port impedance Z after the impedance inverter 501 is located M’ The port impedance Z after the first auxiliary power amplifier 402 or the second auxiliary power amplifier 403 is P After being connected in parallel, they together form the combined impedance R of the signal combining unit 500. L , and then the impedance transformer 502 converts R L Transformed to 50 ohms (not shown in the figure). M is the output current of the impedance inverter 501, I P is the output current of the first auxiliary power amplifier 402 or the second auxiliary power amplifier 403 .

[0041] Example 2

[0042] In this embodiment, Figure 4As shown, the power distribution unit 100 includes a power distributor 101, which decomposes the RF input signal S(t) into two signals S1(t) and S2(t). S1(t) enters the branch where the main power amplifier 401 is located, and S2(t) enters the frequency band selection unit 200. In this embodiment, the frequency band selection unit 200 is composed of a RF switch 1 201 and a RF switch 2 202. The RF switches corresponding to different frequency bands are placed before the two auxiliary power amplifiers. When S2(t) is a signal in the f1-f2 frequency band, the RF switch 1 201 is turned on and the RF switch 2 202 is turned off. The signal is amplified by the first auxiliary power amplifier 402 of the branch where the RF switch 1 201 is located. Similarly, when S2(t) is a signal in the f2-f3 frequency band, the RF switch 2 202 is turned on and the RF switch 1 201 is turned off. The signal is amplified by the first auxiliary power amplifier 403 of the branch where the RF switch 2 202 is located. The remaining components and situations are the same as those in Example 1, so they are not repeated here.

Claims

1. A broadband large back-off RF Doherty power amplifier based on a switch structure, characterized in that: It includes a power distribution unit, a frequency band selection unit, a signal phase shift unit, a signal amplification unit and a signal synthesis unit; the frequency band selection unit includes a plurality of radio frequency switches; the signal phase shift unit includes a plurality of phase shifters; the signal amplification unit includes a main power amplifier and at least two auxiliary power amplifiers, the main power amplifier is biased in class AB, and the auxiliary power amplifier is a power amplifier with class C bias adapted to adjacent different frequency bands; the signal synthesis unit is composed of an impedance inverter and an impedance converter; The input end of the power distribution unit receives a radio frequency input signal, and one output end is connected to a phase shifter, and the phase shifter is connected to a main power amplifier; the other output end is connected to the radio frequency switch, and the output end of the radio frequency switch is divided into a plurality of branches, each branch is connected to a phase shifter, and the phase shifters connected to each branch are respectively connected to an auxiliary power amplifier; The radio frequency switch selects a certain frequency band signal of the output signal of the power distribution unit, and inputs it to the auxiliary power amplifier adapted to the frequency band through the phase shifter; The output of the main power amplifier is connected to the impedance inverter, the output of the impedance inverter and the output of each auxiliary power amplifier are connected to the impedance converter, and the impedance converter outputs the amplified signal.

2. According to claim 1, the broadband large back-off RF Doherty power amplifier based on the switch structure is characterized in that: The power distribution unit decomposes the radio frequency input signal into two signals with equal power and the same phase, and outputs them respectively.

3. The broadband large back-off RF Doherty power amplifier based on a switch structure according to claim 1, characterized in that: The gate width of the auxiliary power amplifier is greater than that of the main power amplifier, so as to ensure that the output current and output power under large signals are greater than those of the main power amplifier, thereby ensuring the effect of back-off boost.

4. The broadband large back-off RF Doherty power amplifier based on a switch structure according to claim 1, characterized in that: The operating frequency range of the broadband large back-off RF Doherty power amplifier is f1-fn, and f1-fn is divided into n-1 frequency bands, n≥3. The plurality of RF switches realize the selection function of the n-1 frequency bands. The number of the auxiliary power amplifiers is n-1, which respectively operate in the n-1 frequency bands, and the main power amplifier operates in the overall broadband frequency band of f1-fn.

5. The broadband large back-off RF Doherty power amplifier based on a switch structure according to claim 4, characterized in that: The n=3, the two divided frequency bands are f1-f2 and f2-f3, and there is one RF switch. When a signal output by the power distribution unit received by it is a signal of the f1-f2 frequency band, the branch where the first auxiliary power amplifier is located is turned on, and the branch where the second auxiliary power amplifier is located is turned off; when a signal output by the power distribution unit received by it is a signal of the f2-f3 frequency band, the branch where the second auxiliary power amplifier is located is turned on, and the branch where the first auxiliary power amplifier is located is turned off.

6. The broadband large back-off RF Doherty power amplifier based on a switch structure according to claim 4, characterized in that: When n=3, the two divided frequency bands are f1-f2 and f2-f3, and there are two RF switches. When a signal output by the power distribution unit is a signal in the f1-f2 frequency band, RF switch one is turned on and RF switch two is turned off, and the signal is amplified by a first auxiliary power amplifier of the branch where RF switch one is located; when a signal output by the power distribution unit is a signal in the f2-f3 frequency band, RF switch two is turned on and RF switch one is turned off, and the signal is amplified by a second auxiliary power amplifier of the branch where RF switch two is located.

7. The broadband large back-off RF Doherty power amplifier based on a switch structure according to claim 6, characterized in that: The RF switch 1 is turned on when the signal is in the f1-f2 frequency band, and the switching loss is less than 1dB; the RF switch 2 is turned on when the signal is in the f2-f3 frequency band, and the switching loss is less than 1dB.

8. The broadband large back-off RF Doherty power amplifier based on a switch structure according to any one of claims 1 to 7, characterized in that: The back-off amount of the Doherty power amplifier is greater than 6dB; the radio frequency switch selects a certain frequency band signal of the power distribution unit output signal as a narrowband signal, and the narrowband signal is a signal with a relative bandwidth of less than 10%.

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