A novel impedance transformation network broadband Doherty power amplifier and its design method

Abstract

The present invention discloses a novel impedance transformation network broadband Doherty power amplifier and a design method thereof, wherein a power divider is used to divide the radio frequency input power equally, one end output is connected to a carrier power amplifier circuit, and the other end is connected to a peak power amplifier circuit; the carrier power amplifier circuit includes a carrier power amplifier input and output bias / matching circuit and a carrier power amplifier; the peak power amplifier circuit includes a phase compensation line, a peak power amplifier input and output bias / matching circuit and a peak power amplifier; the input end of the impedance transformation network is connected to the output ends of the carrier power amplifier circuit and the peak power amplifier circuit, and the output end of the impedance transformation network is connected to a load. The present invention utilizes the principle of active load traction to ensure that the load in the Doherty power amplifier is always kept at an optimal impedance value for the carrier power amplifier, and the dispersion effect of the frequency is weakened to expand the bandwidth.

Description

Technical Field

[0001] The invention belongs to the technical field of radio frequency communication, and in particular relates to a novel impedance transformation network broadband Doherty power amplifier and a design method thereof. Background Art

[0002] With the rapid development of wireless communication technology, communication speed and data volume are gradually increasing, and spectrum resources are becoming increasingly scarce. Communication operators usually adopt more complex modulation methods to increase the amount of data carried per unit bandwidth, but this will also increase the peak-to-average ratio of the signal, and the current communication system works in a low-power state most of the time, which puts higher requirements on the back-off efficiency of the RF power amplifier as an important component of the communication system. However, the drain efficiency of traditional power amplifiers such as Class A and Class AB in the back-off state is too low to meet the requirements of the communication system. The Doherty power amplifier is widely used in wireless communication systems due to its simple structure and high back-off efficiency. However, the traditional Doherty power amplifier has the problem of limited bandwidth. The main reason is that when the frequency deviates from the center frequency due to the dispersion effect of the frequency, the post-matching circuit and the 1 / 4 wavelength microstrip line in the Doherty power amplifier deviate from the set optimal impedance value.

[0003] In view of the defects in the current technology, it is necessary to conduct research to provide a comprehensive impedance transformation network. Based on this impedance transformation network, a broadband Doherty power amplifier that can still work in the optimal impedance state when the output power is backed off is proposed. Summary of the invention

[0004] In order to overcome the defects of the prior art, the present invention proposes a novel impedance transformation network broadband Doherty power amplifier, which adopts a sixth-order low-pass filter to realize a broadband impedance matching network. The impedance transformation network composed of a 1 / 4 wavelength microstrip line, a 1 / 2 wavelength line with an open terminal and two impedance transformation lines enables the power amplifier to always operate in the optimal impedance state at different frequencies.

[0005] To achieve the above object, the present invention provides a novel impedance transformation network broadband Doherty power amplifier, comprising a power divider, a carrier power amplifier circuit, a peak power amplifier circuit and an impedance transformation network, wherein:

[0006] The power divider is used to divide the RF input power into equal parts, one end of the output is connected to the carrier power amplifier circuit, and the other end is connected to the peak power amplifier circuit;

[0007] The carrier power amplifier circuit includes a carrier power amplifier input and output bias / matching circuit and a carrier power amplifier, and the carrier power amplifier input and output bias / matching circuit includes a carrier power amplifier input bias / matching circuit and a carrier power amplifier output bias / matching circuit; the peak power amplifier circuit includes a phase compensation line, a peak power amplifier input and output bias / matching circuit and a peak power amplifier, and the peak power amplifier input and output bias / matching circuit includes a peak power amplifier input bias / matching circuit and a peak power amplifier output bias / matching circuit;

[0008] The input end of the impedance transformation network is connected to the output ends of the carrier power amplifier circuit and the peak power amplifier circuit, and the output end of the impedance transformation network is connected to the load.

[0009] Preferably, the carrier power amplifier input and output bias / matching circuit and the peak power amplifier input and output bias / matching circuit are both implemented by sixth-order low-pass filters to achieve broadband matching.

[0010] Preferably, the carrier power amplifier input and output bias / matching circuit and the peak power amplifier input and output bias / matching circuit are both composed of a distributed parameter matching network consisting of six series microstrip lines to achieve broadband matching, the inductors in the lumped parameter matching network are equivalent to high characteristic impedance transmission lines TL1, TL3 and TL5, and the capacitors are equivalent to low characteristic impedance terminal open-circuit transmission lines TL2, TL4 and TL6, thereby being equivalent to a distributed parameter matching network.

[0011] Preferably, the output of the carrier power amplifier circuit is matched to 2Z L , the peak power amplifier output is matched to Z L , Z L is the load impedance.

[0012] Preferably, the impedance transformation network is composed of two 1 / 4 wavelength impedance transformation lines TL7 and TL8 connected in series, and an open-ended 1 / 2 wavelength microstrip line TL9 is connected in parallel at the junction of the carrier power amplifier circuit and the peak power amplifier circuit, and finally output to the load through the 1 / 4 wavelength impedance transformation line TL10.

[0013] Preferably, the phase compensation line is the same as the microstrip lines TL7 and TL8 in the impedance transformation network or adjusts the phase difference between the carrier power amplifier circuit and the peak power amplifier circuit to keep consistent.

[0014] Preferably, the impedance transformation network keeps the equivalent load impedance of the carrier power amplifier circuit at 2Z when the power is backed off by 6 dB within the frequency band. L .

[0015] Based on the above purpose, the present invention also provides a design method for the novel impedance transformation network broadband Doherty power amplifier, comprising the following steps:

[0016] S1, design a broadband equal power divider;

[0017] S2, performing source pulling and load pulling on the power amplifier within the selected frequency band to obtain the optimal source impedance curve and load impedance curve;

[0018] S3, according to the optimal impedance requirements obtained in S1, a sixth-order lumped parameter low-pass filter matching circuit is designed to match the input end to the impedance value on the optimal source impedance curve, and the impedance value on the optimal load impedance curve of the carrier power amplifier circuit is matched to 2Z L , the impedance value on the peak power amplifier circuit's optimal load impedance curve is matched to Z L ;

[0019] S4, converting the lumped parameter low-pass filter obtained in S2 into a distributed parameter low-pass filter, the inductor in the lumped parameter matching network is equivalent to a high characteristic impedance transmission line, and the capacitor is equivalent to a low characteristic impedance terminal open circuit transmission line;

[0020] S5, designing a bias network, integrating and building the designed impedance matching and bias networks, designing a class AB power amplifier as a carrier power amplifier circuit, and designing a class C power amplifier as a peak power amplifier circuit;

[0021] S6, using three sections of 1 / 4 wavelength microstrip lines and one section of open-ended 1 / 2 wavelength microstrip line to design an impedance transformation network, so that the equivalent load of the carrier power amplifier circuit remains in an ideal condition when the power is backed off;

[0022] S7, placing a phase compensation line at the input end of the peak power amplifier to ensure that the phases of the peak power amplifier circuit and the carrier power amplifier circuit are consistent;

[0023] S8, integrate and debug the designed broadband equal power divider, carrier power amplifier circuit, peak power amplifier circuit and impedance transformation network to build a new impedance transformation network broadband Doherty power amplifier.

[0024] The beneficial effects of the present invention include at least:

[0025] 1. The present invention implements the input and output matching network in the traditional Doherty power amplifier with a sixth-order low-pass filter, wherein the inductor is equivalent to a high characteristic impedance microstrip transmission line, and the capacitor is equivalent to a low characteristic impedance microstrip transmission line, thereby achieving broadband matching to improve efficiency;

[0026] 2. The present invention uses a new impedance transformation network to replace the 1 / 4 wavelength microstrip line and post-matching circuit at the output end of the carrier power amplifier of the traditional Doherty power amplifier, thereby weakening the frequency dispersion effect and ensuring that the power amplifier works in the optimal impedance state to achieve broadband high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0028] Figure 1 It is a structural block diagram of a novel impedance transformation network broadband Doherty power amplifier according to an embodiment of the present invention;

[0029] Figure 2 A schematic diagram of the input and output matching network structure of a novel impedance transformation network broadband Doherty power amplifier according to an embodiment of the present invention;

[0030] Figure 3 A schematic diagram of the impedance transformation network structure of a broadband Doherty power amplifier with a novel impedance transformation network according to an embodiment of the present invention;

[0031] Figure 4 This is a simulation result diagram of the variation of the equivalent load of the carrier power amplifier circuit of the novel impedance transformation network broadband Doherty power amplifier according to an embodiment of the present invention with respect to the frequency;

[0032] Figure 5 It is a simulation result diagram of the drain efficiency and saturated output power of the novel impedance transformation network broadband Doherty power amplifier according to the embodiment of the present invention changing with the frequency;

[0033] Figure 6 This is a simulation result diagram of the drain efficiency and gain of the novel impedance transformation network broadband Doherty power amplifier according to an embodiment of the present invention as a function of output power. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0035] See Figure Figure 1 A novel impedance transformation network broadband Doherty power amplifier comprises a power divider 10, a carrier power amplifier circuit 20, a peak power amplifier circuit 30 and an impedance transformation network 40, wherein:

[0036] The power divider 10 is used to divide the RF input power into equal parts, one end of the output is connected to the carrier power amplifier circuit 20, and the other end is connected to the peak power amplifier circuit 30;

[0037] The carrier power amplifier circuit 20 includes a carrier power amplifier input and output bias / matching circuit and a carrier power amplifier 22, wherein the carrier power amplifier input and output bias / matching circuit includes a carrier power amplifier input bias / matching circuit 21 and a carrier power amplifier output bias / matching circuit 23; the peak power amplifier circuit 30 includes a phase compensation line 31, a peak power amplifier input and output bias / matching circuit and a peak power amplifier 33, wherein the peak power amplifier input and output bias / matching circuit includes a peak power amplifier input bias / matching circuit 32 and a peak power amplifier output bias / matching circuit 34;

[0038] An input end of the impedance transformation network 40 is connected to output ends of the carrier power amplifier circuit 20 and the peak power amplifier circuit 30 , and an output end of the impedance transformation network 40 is connected to a load 41 .

[0039] The carrier power amplifier input and output bias / matching circuit and the peak power amplifier input and output bias / matching circuit are both implemented with a sixth-order low-pass filter to achieve broadband matching.

[0040] The carrier power amplifier input and output bias / matching circuit and the peak power amplifier input and output bias / matching circuit are both composed of a distributed parameter matching network consisting of six series microstrip lines to achieve broadband matching. The inductors in the lumped parameter matching network are equivalent to high characteristic impedance transmission lines TL1, TL3 and TL5, and the capacitors are equivalent to low characteristic impedance terminal open-circuit transmission lines TL2, TL4 and TL6, thus being equivalent to a distributed parameter matching network.

[0041] The output of the carrier power amplifier circuit 20 is matched to 2Z L , the peak power amplifier circuit 30 output is matched to Z L , Z L is the load impedance.

[0042] The impedance transformation network 40 is composed of two 1 / 4 wavelength impedance transformation lines TL7 and TL8 connected in series, and an open-ended 1 / 2 wavelength microstrip line TL9 is connected in parallel at the junction of the carrier power amplifier circuit 20 and the peak power amplifier circuit 30, and finally output to the load 41 through the 1 / 4 wavelength impedance transformation line TL10.

[0043] The phase compensation line 31 is the same as the microstrip lines TL7 and TL8 in the impedance transformation network 40 or adjusts the phase difference between the carrier power amplifier circuit 20 and the peak power amplifier circuit 30 to keep consistent.

[0044] The impedance transformation network 40 keeps the equivalent load impedance of the load 41 at 2Z when the carrier power amplifier circuit 20 has a 6dB power back-off within the frequency band. L .

[0045] See also Figure 2The schematic diagram of the input and output matching network structure in the present invention is shown. The carrier power amplifier input and output bias / matching circuit and the peak power amplifier input and output bias / matching circuit are both distributed parameter matching networks composed of six series microstrip lines to achieve broadband matching. The inductors in the lumped parameter matching network are equivalent to high characteristic impedance (96Ω) transmission lines TL1, TL3 and TL5, and the capacitors are equivalent to low characteristic impedance (36Ω) terminal open-circuit transmission lines TL2, TL4 and TL6, thereby equivalent to a distributed parameter matching network. Among them, the formula for the lumped parameter element to be equivalent to the distributed parameter element is:

[0046]

[0047]

[0048] Among them, l L is the length of the inductor after it is equivalent to the transmission line, l C is the length of the capacitor equivalent to the transmission line, ω is the angular velocity, v p is the phase velocity of the transmission line, L is the inductance value, C is the capacitance value, and Z l is the high characteristic impedance of the transmission line, Z Cap is the low characteristic impedance of the transmission line, and β is the phase constant.

[0049] See also Figure 3 The figure shows the structure of the impedance transformation network 40 in the present invention, which is composed of two 1 / 4 wavelength impedance transformation lines TL7 and TL8 connected in series, and a terminal open circuit 1 / 2 wavelength microstrip line TL9 is connected in parallel at the junction of the carrier power amplifier and the peak power amplifier, and finally output to the load end through the 1 / 4 wavelength impedance transformation line TL10. The impedance of the junction point is recorded as Z″ C , through transmission line theory, we have

[0050]

[0051]

[0052]

[0053] in, is the normalized frequency,

[0054] Then, the impedance of the junction point is transformed into the equivalent load ZC of the carrier amplifier through two microstrip lines TL7 and TL8. According to the transmission line theory,

[0055]

[0056]

[0057] See also Figure 4The equivalent load impedance Z obtained from the above formula is C By extracting the real part (Re) and imaginary part (Im), we can get Figure 4 ,Depend on Figure 4 It can be seen that compared with the traditional (Conv) Doherty power amplifier, the present invention (New) transforms the imaginary part of the equivalent load of the carrier power amplifier into an ideal state (Ideal) while the real part of the equivalent load is basically close to the ideal state, which solves the dispersion effect of the load network to a certain extent, thereby improving the bandwidth.

[0058] See also Figure 5 The figure is a simulation result of the drain efficiency and saturated output power of a novel impedance transformation network broadband Doherty power amplifier in the present invention. The designed novel impedance transformation network broadband Doherty power amplifier has a drain efficiency of 65-73% in the saturated state and a saturated output power of 42.5-44dBm in the frequency band of 2.5-3.5GHz.

[0059] See also Figure 6 The figure is a simulation result of the drain efficiency and gain of a novel impedance transformation network broadband Doherty power amplifier according to the present invention. The designed novel impedance transformation network broadband Doherty power amplifier has a drain efficiency of 44-50% when the output power is backed off by 6dB in the frequency band of 2.5-3.5GHz.

[0060] Based on the above purpose, the present invention also provides a design method for the novel impedance transformation network broadband Doherty power amplifier, comprising the following steps:

[0061] S1, design a broadband equal power divider;

[0062] S2, performing source pulling and load pulling on the power amplifier within the selected frequency band to obtain the optimal source impedance curve and load impedance curve;

[0063] S3, according to the optimal impedance requirements obtained in S1, a sixth-order lumped parameter low-pass filter matching circuit is designed to match the input end to the impedance value on the optimal source impedance curve, and the impedance value on the optimal load impedance curve of the carrier power amplifier circuit is matched to 2Z L , the impedance value on the peak power amplifier circuit's optimal load impedance curve is matched to Z L ;

[0064] S4, converting the lumped parameter low-pass filter obtained in S2 into a distributed parameter low-pass filter, the inductor in the lumped parameter matching network is equivalent to a high characteristic impedance transmission line, and the capacitor is equivalent to a low characteristic impedance terminal open circuit transmission line;

[0065] S5, designing a bias network, integrating and building the designed impedance matching and bias networks, designing a class AB power amplifier as a carrier power amplifier circuit, and designing a class C power amplifier as a peak power amplifier circuit;

[0066] S6, using three sections of 1 / 4 wavelength microstrip lines and one section of open-ended 1 / 2 wavelength microstrip line to design an impedance transformation network, so that the equivalent load of the carrier power amplifier circuit remains in an ideal condition when the power is backed off;

[0067] S7, placing a phase compensation line at the input end of the peak power amplifier to ensure that the phases of the peak power amplifier circuit and the carrier power amplifier circuit are consistent;

[0068] S8, integrate and debug the designed broadband equal power divider, carrier power amplifier circuit, peak power amplifier circuit and impedance transformation network to build a new impedance transformation network broadband Doherty power amplifier.

[0069] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than 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 in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A novel impedance transformation network broadband Doherty power amplifier, characterized in that: It includes a power divider, a carrier power amplifier circuit, a peak power amplifier circuit and an impedance transformation network, wherein: The power divider is used to divide the RF input power into equal parts, one end of the output is connected to the carrier power amplifier circuit, and the other end is connected to the peak power amplifier circuit; The carrier power amplifier circuit includes a carrier power amplifier input and output bias / matching circuit and a carrier power amplifier, and the carrier power amplifier input and output bias / matching circuit includes a carrier power amplifier input bias / matching circuit and a carrier power amplifier output bias / matching circuit; the peak power amplifier circuit includes a phase compensation line, a peak power amplifier input and output bias / matching circuit and a peak power amplifier, and the peak power amplifier input and output bias / matching circuit includes a peak power amplifier input bias / matching circuit and a peak power amplifier output bias / matching circuit; The input end of the impedance transformation network is connected to the output ends of the carrier power amplifier circuit and the peak power amplifier circuit, and the output end of the impedance transformation network is connected to the load; The carrier power amplifier input and output bias / matching circuit and the peak power amplifier input and output bias / matching circuit are both implemented with a sixth-order low-pass filter to achieve broadband matching; The carrier power amplifier input and output bias / matching circuit and the peak power amplifier input and output bias / matching circuit are both distributed parameter matching networks composed of six series microstrip lines to achieve broadband matching. The inductors in the lumped parameter matching network are equivalent to high characteristic impedance transmission lines TL1, TL3 and TL5, and the capacitors are equivalent to low characteristic impedance terminal open-circuit transmission lines TL2, TL4 and TL6, thereby being equivalent to a distributed parameter matching network.

2. The novel impedance transformation network broadband Doherty power amplifier according to claim 1 is characterized in that: The carrier power amplifier circuit output is matched to 2 Z L , the peak power amplifier circuit output is matched to Z L , Z L is the load impedance.

3. The novel impedance transformation network broadband Doherty power amplifier according to claim 1 is characterized in that: The impedance transformation network is composed of two 1 / 4 wavelength impedance transformation lines TL7 and TL8 connected in series, a terminal open-circuit 1 / 2 wavelength microstrip line TL9 is connected in parallel at the junction of the carrier power amplifier circuit and the peak power amplifier circuit, and finally output to the load through the 1 / 4 wavelength impedance transformation line TL10.

4. The novel impedance transformation network broadband Doherty power amplifier according to claim 3 is characterized in that: The phase compensation line is the same as the microstrip lines TL7 and TL8 in the impedance transformation network or adjusts the phase difference between the carrier power amplifier circuit and the peak power amplifier circuit to keep them consistent.

5. The novel impedance transformation network broadband Doherty power amplifier according to claim 1 is characterized in that: The impedance transformation network keeps the equivalent load impedance of the carrier power amplifier circuit at 2 dB when the power is backed off by 6 dB within the frequency band. Z L .

6. A design method for the novel impedance transformation network broadband Doherty power amplifier according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, design a broadband equal power divider; S2, performing source pulling and load pulling on the power amplifier within the selected frequency band to obtain the optimal source impedance curve and load impedance curve; S3, according to the optimal impedance requirements obtained in S1, a sixth-order lumped parameter low-pass filter matching circuit is designed to match the input end to the impedance value on the optimal source impedance curve, and the impedance value on the optimal load impedance curve of the carrier power amplifier circuit is matched to 2 Z L , the impedance value on the peak power amplifier circuit's optimal load impedance curve matches Z L ; S4, converting the lumped parameter low-pass filter obtained in S2 into a distributed parameter low-pass filter, the inductor in the lumped parameter matching network is equivalent to a high characteristic impedance transmission line, and the capacitor is equivalent to a low characteristic impedance terminal open circuit transmission line; S5, designing a bias network, integrating and building the designed impedance matching and bias networks, designing a class AB power amplifier as a carrier power amplifier circuit, and designing a class C power amplifier as a peak power amplifier circuit; S6, using three sections of 1 / 4 wavelength microstrip lines and one section of open-ended 1 / 2 wavelength microstrip line to design an impedance transformation network, so that the equivalent load of the carrier power amplifier circuit remains in an ideal condition when the power is backed off; S7, placing a phase compensation line at the input end of the peak power amplifier to ensure that the phases of the peak power amplifier circuit and the carrier power amplifier circuit are consistent; S8, integrate and debug the designed broadband equal power divider, carrier power amplifier circuit, peak power amplifier circuit and impedance transformation network to build a new impedance transformation network broadband Doherty power amplifier.

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