Dual-band power amplifier based on harmonic control circuit and its design method

Abstract

The present invention discloses a dual-band power amplifier based on a harmonic control circuit and a design method thereof, including a transistor, a dual-band bias circuit, a dual-band input matching circuit, a harmonic control circuit, and a dual-band fundamental matching circuit. The input end of the harmonic control circuit is connected to the drain of the transistor, and the output end is connected to the dual-band fundamental matching circuit. The present invention changes the output impedance condition of the traditional dual-band harmonic control network so that the power amplifier satisfies the characteristics of the inverse F class and the F class power amplifier at the low frequency point and the high frequency point, respectively, reduces the influence between the two frequency points, and improves the efficiency. At the same time, the third harmonic at the low frequency point and the second harmonic at the high frequency point are combined to reduce the calculation complexity of the harmonic circuit.

Description

Technical Field

[0001] The invention belongs to the technical field of radio frequency circuits and relates to a dual-band power amplifier based on a harmonic control circuit and a design method thereof. Background Art

[0002] As the core and front-end part of the RF transceiver system, the performance of the power amplifier has a great impact on the entire communication system, so high-efficiency, wide-bandwidth power amplifiers are key factors in improving communication quality. Nonlinear amplifiers have always been a hot topic in power amplifier research due to their effective improvement in efficiency and output power. Class F and inverse class F power amplifiers are widely used due to their excellent harmonic control capabilities and simple circuits.

[0003] Dual-band power amplifiers need to work at two different frequencies, and how to achieve high efficiency at both frequencies is a difficult problem. There are relatively few methods for improving the efficiency of dual-band power amplifiers, and most of them simply apply the harmonic control method of single-band power amplifiers directly to dual-band power amplifiers.

[0004] However, the traditional Class F or inverse Class F harmonic control method will cause problems when applied to dual-band. For example, if the second harmonic of two frequency points is simply short-circuited and the third harmonic is open-circuited, the third harmonic of the low frequency point and the second harmonic of the high frequency point will affect each other when the frequency difference is close, resulting in a decrease in efficiency. This shows that the traditional dual-band harmonic control method cannot control the harmonics of two frequency points at the same time. Instead, it will cause the two frequency points to affect each other, resulting in a decrease in efficiency.

[0005] Therefore, it is necessary to propose an improved harmonic control circuit to optimize dual-band harmonic control. Summary of the invention

[0006] In view of the shortcomings of the dual-band power amplifier in harmonic control, the present invention proposes a dual-band power amplifier based on a harmonic control circuit. The harmonic matching mode is changed by changing the output impedance condition of the power amplifier, so that the two frequency points work in different modes respectively, thereby reducing the mutual influence of the two frequency points in the harmonic matching process, effectively improving the efficiency while ensuring the bandwidth; at the same time, by combining the third harmonic of the low frequency point and the second harmonic of the high frequency point, the complexity of the calculation is simplified, and the invention has good application value.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A dual-band power amplifier based on a harmonic control circuit, comprising a transistor, a dual-band gate bias circuit, a dual-band input matching circuit, a harmonic control circuit, a dual-band drain bias circuit, and a dual-band fundamental matching circuit;

[0009] The input end of the dual-band input matching circuit is connected to a 50Ω impedance, and the output end is connected to a transistor gate, so that the 50Ω impedance is matched to the transistor impedance through reasonable impedance matching.

[0010] The gate bias circuit and the drain bias circuit are respectively connected to the transistor input and output terminals to provide a DC voltage to maintain the normal operation of the power amplifier.

[0011] The input end of the harmonic control circuit is connected to the drain of the transistor, and the output end is connected to the input end of the dual-band fundamental matching circuit.

[0012] The output end of the dual-band fundamental wave matching circuit is connected to a 50Ω load impedance, and the fundamental wave impedances of the two frequency points at its input end are matched to the load impedance.

[0013] The harmonic control circuit further comprises serial microstrip lines T1, T2, T3, T7, and parallel microstrip lines T4, T5, T6. Among them, one end of the third microstrip line (T3) is respectively connected to the sixth microstrip line (T6) and the second microstrip line (T2), and the sixth microstrip line (T6) and the third microstrip line (T3) jointly control the high-frequency third harmonic. The other end of the second microstrip line (T2) is respectively connected to the fifth microstrip line (T5) and the first microstrip line (T1), and the fifth microstrip line (T5) is respectively connected to the second, third microstrip lines (T2, T3) and the sixth microstrip line (T6) to jointly control the low-frequency third harmonic and the high-frequency second harmonic. The other end of the first microstrip line (T1) is connected to the fourth microstrip line (T4) and the transistor drain output end, and the fourth microstrip line (T4) is jointly controlled by the first, second, third microstrip lines (T1, T2, T3) and the fifth and sixth microstrip lines (T5, T6) to control the low-frequency second harmonic.

[0014] The seventh microstrip line (T7) is connected to the other end of the third microstrip line (T3), and finally realizes that the low-frequency second harmonic is open and the third harmonic is short-circuited at the OP point, and the high-frequency second harmonic is short-circuited and the third harmonic is open at the OP point through parameter tuning of the seventh microstrip line (T7), and satisfies the output impedance conditions of the inverse F class and the F class at the two fundamental frequencies (low frequency point and high frequency point) respectively.

[0015] The present invention also discloses a design method of a dual-band power amplifier based on a harmonic control circuit, comprising the following steps:

[0016] Step S1: Select the dual-band center frequency f H and f L , f H The second harmonic of f L The third harmonic of k is 2±0.1, called f a ;

[0017] Step S2: designing a gate bias circuit and a drain bias circuit to ensure the normal operation of the power amplifier, and matching the dual-band input circuit;

[0018] Step S3: Design a harmonic control circuit to make f L and f H It meets the inverse F and F output impedance conditions, the transmission line characteristic impedance Z is a free parameter, and the electrical length θ is a parameter to be determined; the electrical lengths of the microstrip lines T6, T5, and T4 are designed to be Make 3f H Short circuit at A, 3f L and 2f H Short circuit at B, 2f L Short circuit at C; design the electrical length of T3 Make 3f H Open the output terminal and use formulas (1)-(3) to make 3f L and 2f H When the output end is short-circuited, the electrical length of T2 is obtained, θ2, and 2f is obtained by using formulas (4)-(7). L The output end is open circuited, and the electrical length θ1 of T1 is obtained. T7 is tuned to meet the output impedance condition. Finally, the circuit parameters are converted into microstrip line parameters width W and length L through calculation.

[0019]

[0020]

[0021] Z' A (f a )=jZ2 tanθ2 (3)

[0022]

[0023]

[0024]

[0025] Z' B (2f L )=jZ1tanθ1 (7)

[0026] Where Z A (f a ), Z' A (f a ) is the 3f from the harmonic control output terminal to point A, A' L and 2f H The input impedance, Z B (2f L ), Z' B (2f L) is the 2f value from the harmonic control output end looking toward B, B' L The input impedance, Z n and θ n are the impedance and electrical length of the transmission line respectively;

[0027] Step S4: Design a fundamental wave output matching circuit by using harmonics to control the fundamental wave impedance at the output end; combine steps S1, S2, S3, and S4 and use ADS to perform schematic simulation and parameter adjustment to ensure maximum efficiency.

[0028] Compared with the prior art, the beneficial effects of the present invention are: realizing a high-efficiency power amplifier working in dual frequency bands, and the harmonic control circuit of the present invention successfully eliminates the influence between the low-frequency third harmonic and the high-frequency second harmonic by making the two frequency points work in different modes, thereby reducing the influence between the two frequency points. While ensuring the bandwidth, the efficiency of the dual-standby power amplifier is effectively improved, and the calculation is simple, which has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a principle block diagram of the present invention

[0030] Figure 2 Schematic diagram of the harmonic control circuit module of the present invention

[0031] Figure 3 This is a schematic diagram of the low-frequency third harmonic and high-frequency second harmonic circuit.

[0032] Figure 4 This is a schematic diagram of a low-frequency second harmonic circuit.

[0033] Figure 5 This is the Smith chart of a conventional dual-band power amplifier.

[0034] Figure 6 The Smith chart of the dual-band power amplifier based on harmonic control of the present invention is

[0035] Figure 7 Schematic diagram of efficiency simulation of a conventional dual-band power amplifier and a dual-band power amplifier of the present invention DETAILED DESCRIPTION

[0036] The specific implementation of the present invention is further described below in conjunction with the drawings and embodiments:

[0037] The Smith chart of the conventional dual-band inverse class F harmonic control circuit operating at 1.9 GHz and 2.6 GHz is shown in Figure 5We can see that the low-frequency third harmonic and the high-frequency second harmonic are not matched to open circuit and short circuit, but are matched to non-ideal impedance values ​​due to mutual influence. This is because when the frequency difference between the two is close, they will influence each other, which will have a greater impact on efficiency, especially at high frequencies, the efficiency is greatly reduced (the second harmonic has a greater impact than the third harmonic). In the harmonic control of dual-band power amplifiers, this situation where the efficiency is affected by the close frequency difference is very common.

[0038] In view of the problems caused by the traditional harmonic circuit, the applicant has proposed a solution. Under the premise that the low-frequency third harmonic and the high-frequency second harmonic are close to each other, the low-frequency third harmonic and the high-frequency second harmonic are combined to form a The value of the adjustment factor k is generally 2, and the error factor is plus or minus 0.1, so that both are matched to the vicinity of the short-circuit (R=0) point. Since the frequency difference between the low-frequency third harmonic and the high-frequency second harmonic is relatively close, the impact on the fundamental frequency is small. We can further reduce the impact on the fundamental frequency by adjusting the k value. At the same time, we match the low-frequency second harmonic and the high-frequency third harmonic to the vicinity of the open-circuit point (R=∞). Through the above scheme, it is finally achieved that at the input point (OP) of the fundamental dual-band matching circuit, the second harmonic is open-circuited and the third harmonic is short-circuited at the low-frequency point, and the second harmonic is short-circuited and the third harmonic is open-circuited at the high-frequency point. The power amplifier belongs to the inverse F and F class power amplifiers at the two frequency points, that is, different working modes, thereby solving the problem of mutual influence between the two frequency points in the traditional circuit.

[0039] See also Figure 1 , is a principle block diagram of the present invention, from which it can be seen that the power amplifier of the present invention comprises a transistor, a dual-band gate bias circuit, a dual-band input matching circuit, a harmonic control circuit, a dual-band drain bias circuit, and a dual-band fundamental matching circuit. The dual-band input matching circuit has an input end connected to a 50Ω impedance, and an output end connected to the transistor gate; the harmonic control circuit has an input end connected to the transistor drain, and an output end connected to the dual-band fundamental matching circuit; the dual-band fundamental matching circuit has an output end connected to a 50Ω impedance; the gate bias circuit and the drain bias circuit are connected to the transistor input and output ends, respectively.

[0040] See also Figure 2, is a harmonic control circuit diagram of the present invention, comprising series microstrip lines T1, T2, T3, T7, and parallel microstrip lines T4, T5, T6. One end of the third microstrip line (T3) is respectively connected to the sixth microstrip line (T6) and the second microstrip line (T2), the other end of the second microstrip line (T2) is respectively connected to the fifth microstrip line (T5) and the first microstrip line (T1), and the other end of the first microstrip line (T1) is connected to the fourth microstrip line (T4) and the transistor drain output terminal. Among them, the sixth microstrip line (T6) and the third microstrip line (T3) jointly control the high-frequency third harmonic, the fifth microstrip line (T5) and the second, third microstrip lines (T2, T3) and the sixth microstrip line (T6) respectively jointly control the low-frequency third harmonic and the high-frequency second harmonic, and the fourth microstrip line (T4) and the first, second, third microstrip lines (T1, T2, T3) and the fifth and sixth microstrip lines (T5, T6) jointly control the low-frequency second harmonic. Further, the seventh microstrip line (T7) is connected to the other end of the third microstrip line (T3), and the seventh microstrip line (T7) parameter tuning is finally achieved to meet the output impedance conditions of the inverse F class and the F class at the OP point at two fundamental frequencies (low frequency point and high frequency point).

[0041] Furthermore, the calculation method of the microstrip line parameters of the harmonic control circuit is explained:

[0042] The two parameters of the microstrip line are the electrical length θ n and characteristic impedance Z n , where the characteristic impedance Z n is a free parameter, the electrical length θ n is the parameter to be determined. At the same time, in order to simplify the explanation, the low frequency in the dual band is denoted by f L Indicates that high frequency is represented by f H express.

[0043] f H The third harmonic of The sixth microstrip line (T6) is short-circuited at point A, and then the electrical length The third microstrip line (T3) is open circuit at OP'. Figure 3 , f H The second harmonic of f L The third harmonic of Where k is generally 2, and the error factor is plus or minus 0.1. For convenience, we call it f a ,f a The electrical length is The fifth microstrip line (T5) with a length of 1000 mm is short-circuited at point B and finally at OP'. According to the impedance calculation formula, by selecting a suitable Z3, the input impedance from the output end OP of the harmonic control circuit to point A can be obtained as follows:

[0044]

[0045] By selecting a suitable Z6, the input impedance from OP to A' after the sixth microstrip line (T6) is connected in parallel is:

[0046]

[0047] Because at B a Short circuit, by selecting the appropriate Z2, the parameter θ2 of the second microstrip line (T2) can be determined

[0048] Z' A (f a )=jZ2tanθ2 (3)

[0049] For further information, see Figure 4 , f L The electrical length of the second harmonic is The fourth microstrip line (T4) is short-circuited at point C and open-circuited at OP'. The input impedance from OP to point A' and the input impedance from OP to points B and B' are

[0050]

[0051]

[0052]

[0053] Z' B (2f L )=jZ1tanθ1 (7)

[0054] By selecting an appropriate Z1, the parameter θ1 of the first microstrip line (T1) can be determined

[0055] Furthermore, the seventh microstrip line (T7) is tuned to make f L ,f H The harmonics of f at OP finally present L The second harmonic of open circuit, f H The third harmonic of open circuit, f a Short circuit, due to f a The frequency difference is close to f L The third harmonic and f H The second harmonic of is calculated, so it can be approximated to f L The third harmonic and f H The second harmonic of the signal is not affected by the fundamental matching. Thus, the low frequency f is achieved at the OP point. L Working in the inverse class F power amplifier working state, high frequency f HIt works in the Class F power amplifier working state, that is, it works at two frequency points and in different working states.

[0056] By improving the harmonic control network, the impact between the two frequency points was successfully reduced, and the efficiency was improved to a certain extent through accurate harmonic calculation. Figure 5 , Figure 6 The Smith chart shows that the influence of harmonics between the two frequency points is reduced, which solves the problem of the traditional harmonic control method that the low-frequency third harmonic and the high-frequency second harmonic affect each other and cannot be matched to the open circuit point and the short circuit point. In particular, the high-frequency second harmonic can be well matched to the short circuit state. Since the harmonics are well controlled, the efficiency is significantly improved.

[0057] The present invention also discloses a design method of a dual-band power amplifier based on a harmonic control circuit, which is implemented by the following steps:

[0058] Step S1: Select the dual-band center frequency f H and f L , f H The second harmonic of f L The third harmonic of k is 2±0.1, called f a .

[0059] Step S2: Design a gate bias circuit and a drain bias circuit to ensure the normal operation of the power amplifier, and design a dual-band input circuit.

[0060] Step S3: Design a harmonic control circuit to make f L and f H It meets the inverse F and F output impedance conditions, the transmission line characteristic impedance Z is a free parameter, and the electrical length θ is a parameter to be determined. The electrical lengths of the microstrip lines T6, T5, and T4 are designed to be Make 3f H Short circuit at A, 3f L and 2f H Short circuit at B, 2f L Short circuit at C. Design the electrical length of T3 Make 3f H Open the output terminal and use formulas (1)-(3) to make 3f L and 2f H When the output end is short-circuited, the electrical length of T2 is obtained, θ2, and 2f is obtained by using formulas (4)-(7). L The output end is open circuited, and the electrical length of T1 is obtained, θ1, and T7 is tuned to meet the output impedance condition. Finally, the circuit parameters are converted into microstrip line parameters width W and length L through calculation.

[0061]

[0062]

[0063] Z' A (f a )=jZ2 tanθ2 (3)

[0064]

[0065]

[0066]

[0067] Z' B (2f L )=jZ1tanθ1 (7)

[0068] Where Z A (f a ), Z' A (f a ) is the 3f from the harmonic control output terminal to point A, A' L and 2f H The input impedance, Z B (2f L ), Z' B (2f L ) is the 2f value from the harmonic control output end looking toward B, B' L The input impedance, Z n and θ n are the impedance and electrical length of the transmission line respectively.

[0069] Step S4: Design a fundamental output matching circuit using the fundamental impedance of the harmonic control output end, and match the fundamental impedance of the two frequency points at the circuit input end to the load impedance. Use ADS to perform schematic simulation and parameter adjustment to ensure maximum efficiency.

[0070] See also Figure 7 , which is the efficiency curve of a power amplifier with a certain bandwidth of 1.9 GHz and 2.6 GHz simulated by ADS using the present invention and traditional harmonic control technology. It can be seen that the efficiency at the low frequency point (1.9 GHz) is slightly improved, reaching more than 68%, and the efficiency at the high frequency point (2.6 GHz) is improved by more than 8% compared with the traditional structure, reaching more than 70%, which is consistent with the theory explained in the present invention.

[0071] The above embodiment is only an example to explain the principle of the present invention. The present invention is not limited to the above embodiment. Any other improvements that conform to the principle of the present invention are within the protection scope of the present invention.

Claims

1. A design method for a dual-band power amplifier based on a harmonic control circuit, characterized in that: The following steps are involved: Step S1: Select the dual-band center frequency and ,Will The second harmonic of The third harmonic of ,k take , called ; Step S2: designing a gate bias circuit and a drain bias circuit to ensure the normal operation of the power amplifier, and matching the dual-band input circuit; Step S3: Design a harmonic control circuit to make and It meets the inverse F and F output impedance conditions. The transmission line characteristic impedance Z is a free parameter, and the electrical length is the parameter to be determined; the electrical lengths of the microstrip lines T6, T5, and T4 are designed to be , , make Short circuit at A, and Short circuit at B, Short circuit at C; design the electrical length of T3 make With the output terminal open, use formulas (1)-(3) to make and When the output is short-circuited, the electrical length of T2 is obtained. , using formulas (4)-(7) to make With the output open, the electrical length of T1 is obtained , T7 is tuned to meet the output impedance condition; finally, the circuit parameters are converted into microstrip line parameters width W and length L by calculation; (1) (2) (3) (4) (5) (6) (7) in , The value of A and A' from the harmonic control output terminal. and The input impedance, , The harmonic control output terminal looks toward B, B' The input impedance, and are the impedance and electrical length of the transmission line respectively; Step S4: Designing a fundamental wave output matching circuit by using the fundamental wave impedance of the harmonic control output terminal to ensure maximum efficiency.

2. A dual-band power amplifier based on a harmonic control circuit according to the method of claim 1, characterized in that: It includes a transistor, a dual-band gate bias circuit, a dual-band input matching circuit, a harmonic control circuit, a dual-band drain bias circuit, and a dual-band fundamental matching circuit, wherein: The input end of the dual-band input matching circuit is connected to a 50Ω impedance, and the output end thereof is connected to a transistor gate, for impedance matching the 50Ω impedance to match the transistor impedance; The dual-band gate bias circuit and the dual-band drain bias circuit are used to provide a DC voltage to maintain the normal operation of the power amplifier; The input end of the harmonic control circuit is connected to the drain of the transistor, and the output end thereof is connected to the input end of the dual-band fundamental matching circuit; The output end of the dual-band fundamental wave matching circuit is connected to a 50Ω load impedance, and the fundamental wave impedance of the two frequency points at its input end is matched to the load impedance; The harmonic control circuit comprises a first microstrip line T1, a second microstrip line T2, a third microstrip line T3, a fourth microstrip line T4, a fifth microstrip line T5, a sixth microstrip line T6 and a seventh microstrip line T7, wherein T1, T2, T3 and T7 are series microstrip lines, and T4, T5 and T6 are parallel microstrip lines; one end of the third microstrip line T3 is connected to the sixth microstrip line T6 and one end of the second microstrip line T2, and the sixth microstrip line T6 and the third microstrip line T3 jointly control the high-frequency third harmonic; the second microstrip line T The other end of the first microstrip line T1 is connected to the fifth microstrip line T5 and one end of the first microstrip line T1, and the fifth microstrip line T5, the second microstrip line T2, the third microstrip line T3 and the sixth microstrip line T6 jointly control the low-frequency third harmonic and the high-frequency second harmonic; the other end of the first microstrip line T1 is connected to one end of the fourth microstrip line T4 and the drain output end of the transistor, and the fourth microstrip line T4, the first microstrip line T1, the second microstrip line T2, the third microstrip line T3, the fifth microstrip line T5 and the sixth microstrip line T6 jointly control the low-frequency second harmonic.

3. The dual-band power amplifier based on harmonic control circuit according to claim 2, characterized in that: The seventh microstrip line T7 is connected to the other end of the third microstrip line T3. Through parameter tuning of the seventh microstrip line T7, the low-frequency second harmonic is open and the third harmonic is short-circuited, and the high-frequency second harmonic is short-circuited and the third harmonic is open at the OP point, and the output impedance conditions of inverse class F and class F are met at the two fundamental frequencies respectively.

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