CN108768305A - A kind of broadband Doherty power amplifier and design method - Google Patents

Abstract

The invention discloses a broadband Doherty power amplifier and a design method. The bandwidth of a conventional Doherty power amplifier is limited by the quarter-wavelength impedance transformer that achieves optimal impedance transformation at a specific frequency. The invention relates to a broadband Doherty power amplifier, comprising a power divider, a carrier amplifier, a peak amplifier, a first compensation line, a second compensation line, a third compensation line and a low-pass filter matching module. The low-pass filter matching module includes the first microstrip line, the second microstrip line, ..., the nth microstrip line, each of which has an electrical length of λ/8, and n is a multiple of three. One end of the first microstrip line is connected to the combination point of the peak amplifier and the second compensation line, and the other end is connected to one end of the second microstrip line and the third microstrip line. The other ends of the second microstrip line and the third microstrip line are suspended. The invention uses a low-pass filter matching method to increase the bandwidth of the power amplifier while maintaining high efficiency, and at the same time ensure that the back-off efficiency within the bandwidth meets the design requirements.

Description

A Broadband Doherty Power Amplifier and Its Design Method

technical field

The invention belongs to the technical field of power amplifiers, and in particular relates to a broadband Doherty power amplifier based on a novel low-pass matching combined circuit end structure and a design method.

Background technique

For more than half a century, radio frequency microwave technology has been developed rapidly and has been widely used in communication fields such as mobile phones, satellite communications, and WLAN. The RF power amplifier module is an important part of the wireless communication system. In order to meet the long-distance transmission of the signal and ensure the reliable reception of the signal, the power amplifier module must be used to amplify the signal in the wireless transceiver system. Therefore, the performance of the power amplifier module directly determines the working conditions of the entire transceiver system. There is no doubt that the power amplifier module is the core part of the RF front end.

With the rapid growth of mobile devices, the fifth generation mobile communication system (5G) is expected to be standardized and commercialized in 2020 and beyond. According to the new 5G standard, users' demand for data rate continues to increase, making the entire communication system have higher and higher requirements for signal bandwidth and peak-to-average power ratio. In this case, the power amplifier, as a key component of the transmitter, needs to improve efficiency in the wideband output back-off region. Doherty power amplifiers have become the mainstream form of power amplifiers used in today's wireless communications because they can amplify modulated signals with high efficiency and low cost. However, there are certain technical problems in the traditional Doherty power amplifier, and the quarter-wavelength impedance converter that realizes the best impedance transformation at a specific frequency limits the bandwidth of the traditional Doherty power amplifier.

Contents of the invention

The object of the present invention is to provide a kind of wide-band Doherty power amplifier and design method based on novel low-pass matching combination end structure

The invention relates to a broadband Doherty power amplifier, comprising a power divider, a carrier amplifier, a peak amplifier, a first compensation line, a second compensation line, a third compensation line and a low-pass filter matching module. The input terminal of the carrier amplifier is connected to the first output terminal of the power divider, and the load terminal is connected to one end of the first compensation line. The other end of the first compensation line is connected to one end of the second compensation line. One end of the third compensation line is connected to the second output end of the power divider, and the other end is connected to the input end of the peak amplifier. The load end of the peak amplifier is connected to the other end of the second compensation line.

The low-pass filter matching module includes the first microstrip line, the second microstrip line, ..., the nth microstrip line, the electrical length of which is λ/8, and n is a multiple of three. One end of the first microstrip line is connected to the combination point of the peak amplifier and the second compensation line, and the other end is connected to one end of the second microstrip line and the third microstrip line. The other ends of the second microstrip line and the third microstrip line are suspended.

The end of the 3i+1 microstrip line close to the peak amplifier is connected to the end of the 3i-2 microstrip line away from the peak amplifier, and the end far away from the peak amplifier is connected to the 3i+2 microstrip line and the 3i+3 One end of the microstrip line. The other ends of the 3i+2 microstrip line and the 3i+3 microstrip line are suspended, i=1, 2, . . . , n/3-1.

In the case of i=1,2,...,n/3, the characteristic impedance value of the 3i-2 microstrip line satisfies formula (1); the characteristic impedance value of the 3i-1 microstrip line and the 3i microstrip line Both satisfy formula (2).

Z _3i-1 ＝Z _3i ＝ω ₀ ·L _i Formula (2)

Wherein, ω ₀ =2πf; f is the center frequency of the signal to be amplified; the value of C _i and the value of L _i are at 0.5dB equal ripple Chebyshev normalized low-pass filter circuit parameter table (Science Press 2010 "Radio Frequency Communication Circuit Design" published in 2010, page 152). The retrieval method is as follows: find the target line in the ripple Chebyshev normalized low-pass filter circuit parameter table. target behavior The line corresponding to the order (the Row). The 2i-1th parameter of the target line is the value of C _i , and the 2ith parameter is the value of L _i .

Further, the carrier amplifier includes a first transistor, a carrier input matching network and a carrier output matching network. The input end of the first transistor is connected to the output end of the carrier input matching network, and the output end is connected to the input end of the carrier output matching network. The input terminal of the carrier input matching network is used as the input terminal of the carrier amplifier. The load end of the carrier output matching network is used as the load end of the carrier amplifier.

Further, the peak amplifier includes a second transistor, a peak input matching network and a peak output matching network. The input end of the second transistor is connected to the output end of the peak input matching network, and the output end is connected to the input end of the peak output matching network. The input terminal of the peak input matching network is used as the input terminal of the peak amplifier. The load end of the peak output matching network is used as the load end of the peak amplifier.

Further, the electrical lengths of the first compensation line, the second compensation line and the third compensation line are all λ/4.

The design method of the broadband Doherty power amplifier is as follows:

Step 1: Adjust the input voltage of the grid of the carrier amplifier in the ADS software, so that the carrier power amplifier works in the class AB mode. And design the carrier output matching network.

Step 2: Adjust the input voltage of the gate of the peak power amplifier in the ADS software, make the peak power amplifier work in the class C mode, and design the peak output matching network.

Step 3: Design a low-pass filter matching module in the ADS software.

Step 4: Combine the debugged carrier amplifier, peak amplifier, power divider and low-pass filter matching module in the ADS software to form a Doherty power amplifier. Get the schematic. Go to step five.

Step 5: Export the schematic diagram obtained in step 4 in the ADS software to form a layout. Then carry out the co-simulation of layout and schematic diagram. If the efficiency values of the Doherty power amplifier obtained by the co-simulation of the layout and the schematic diagram are greater than 60% within the design bandwidth, go directly to step six. If the efficiency value of the Doherty power amplifier obtained by joint simulation of the layout and schematic diagram is less than or equal to 60% within the design bandwidth, adjust the electrical length of the first compensation line of the Doherty power amplifier, and repeat step 4.

Step 6: Process the Doherty power amplifier according to the layout obtained in Step 5.

The beneficial effects that the present invention has are:

1. The technical solution of the present invention improves the post-matching network of the existing Doherty power amplifier and uses a low-pass filter matching method, so that the power amplifier can increase the bandwidth while maintaining high efficiency, and at the same time ensure the back-off within the bandwidth Efficiency meets design requirements.

2. The efficiency of the present invention reaches more than 60% in the bandwidth of 0.8GHz (1.8GHz-2.6GHz), which is obviously better than that of the existing Doherty power amplifier in the bandwidth of 0.2GHz (2.1GHz-2.3GHz). More than 60%.

3. The efficiency of the present invention within the bandwidth exceeds 60%, which is higher than the efficiency of the power amplifier used by the base station (the efficiency of the power amplifier of the base station in the prior art is generally about 50% within the bandwidth). It provides a new method for the construction of base station power amplifier in the future.

Description of drawings

Fig. 1 is a working principle diagram of the present invention;

Fig. 2 is an efficiency line diagram obtained by performing efficiency simulations on the present invention in a 6dB back state, the present invention in a saturated output state, an existing base station power amplifier, and an existing Doherty power amplifier in the ADS software.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

As shown in Figure 1, a wideband Doherty power amplifier includes a power divider 1, a carrier amplifier 2, a peak amplifier 3, a first compensation line 4, a second compensation line 5, a third compensation line 6 and a low-pass filter matching module 7. The electrical lengths of the second compensation line 5 and the third compensation line 6 are both λ/4. The carrier amplifier 2 includes a first transistor, a carrier input matching network and a carrier output matching network. The input end (gate) of the first transistor is connected to the output end of the carrier input matching network, and the output end (drain) is connected to the input end of the carrier output matching network. The input end of the carrier input matching network is used as the input end of the carrier amplifier 2 . The load end of the carrier output matching network is used as the load end of the carrier amplifier 2 . The peak amplifier 3 includes a second transistor, a peak input matching network and a peak output matching network. The input terminal (gate) of the second transistor is connected to the output terminal of the peak input matching network, and the output terminal (drain) is connected to the input terminal of the peak output matching network. The input end of the peak input matching network is used as the input end of the peak amplifier 3 . The load end of the peak output matching network is used as the load end of the peak amplifier 3 .

The input terminal of the carrier amplifier 2 is connected to the first output terminal of the power divider 1 . The load terminal of the carrier amplifier 2 is connected to one end of the first compensation line 4 . The other end of the first compensation line 4 is connected to one end of the second compensation line 5 . One end of the third compensation line 6 is connected to the second output end of the power divider 1 , and the other end is connected to the input end of the peak amplifier 3 . The load end of the peak amplifier 3 is connected (combined) with the other end of the second compensation line 5 .

The low-pass filter matching module 7 includes a first microstrip line T1 , a second microstrip line T2 , . One end of the first microstrip line T1 is connected to the junction point of the peak amplifier 3 and the second compensation line 5 , and the other end is connected to one end of the second microstrip line T2 and the third microstrip line T3 . The other ends of the second microstrip line T2 and the third microstrip line T3 are suspended

The end of the 3i+1 microstrip line T3i+1 close to the peak amplifier 3 is connected to the end of the 3i-2 microstrip line T3i-2 away from the peak amplifier 3, and the end far away from the peak amplifier 3 is connected to the 3i+2 microstrip line One end of the strip line T3i+2 and the 3i+3 microstrip line T3i+3. The other ends of the 3i+2 microstrip line T3i+2 and the 3i+3 microstrip line T3i+3 are suspended, i=1, 2, . . . , n/3−1. The end of the n-2th microstrip line Tn-2 away from the peak amplifier 3 is connected to the load 8 as the output end of the present invention.

In the case of i=1,2,...,n/3, the characteristic impedance value of the 3i-2 microstrip line satisfies formula (1); the characteristic impedance value of the 3i-1 microstrip line and the 3i microstrip line Both satisfy formula (2):

Z _3i-1 ＝Z _3i ＝ω ₀ ·L _i Formula (2)

Among them, ω ₀ =2πf; f is the center frequency of the signal that needs to be amplified by the Doherty power amplifier, and the value is 2.2 GHz; the value of C _i and the value of L _i are normalized by Chebyshev with equal ripples of 0.5 dB Low-pass filter circuit parameter table (page 152 of "RF Communication Circuit Design" published by Science Press in 2010). The retrieval method is as follows: find the target line in the ripple Chebyshev normalized low-pass filter circuit parameter table. target behavior The line corresponding to the order (the Row). The 2i-1th parameter of the target line is the value of C _i , and the 2ith parameter is the value of L _i .

The low-pass filter matching module 7 can filter the signal at the junction point of the peak amplifier 3 and the second compensation line 5, so that the input reflection coefficient (S11) of the power amplifier is reduced, and the forward transmission coefficient (S21) is increased. In turn, the bandwidth of the Doherty power amplifier is increased, and the efficiency is improved.

Under the condition that the input signal is a continuous wave of 1.8～2.6GHz and the input power is 28dBm, the present invention under the state of back-off 6dB, the present invention under the saturated output state, the existing base station power amplifier, and the existing Doherty Power amplifiers are simulated separately for efficiency simulation. The simulation result is shown in Fig. 2. It can be seen that the efficiency of the power amplifier of the existing base station can only reach about 50%. The design bandwidth of the existing Doherty power amplifier is only 200MHz, and the efficiency can only reach more than 60% in the frequency band of 2.1-2.3GHz, which cannot meet the requirements of modern base stations for power amplifier indicators. In the saturated output state, the efficiency of the present invention can reach more than 60% in the frequency band of 1.8-2.6 GHz. It can be seen that the present invention can greatly improve the video bandwidth while ensuring the high efficiency of the power amplifier. In addition, the efficiency of the present invention under the back-off state of 6dB can reach more than 30% in the frequency band of 1.8-2.6GHz, and can still work normally. It can be seen that the peak-to-average power ratio and bandwidth of the present invention are significantly better than those of the existing Doherty power amplifier.

The design method of the broadband Doherty power amplifier is as follows:

Step 1: Adjust the input voltage of the grid of the carrier amplifier 2 in the ADS software, so that the carrier power amplifier works in the class AB working mode. And design the carrier output matching network.

Step 2: Adjust the input voltage of the gate of the peak power amplifier in the ADS software, make the peak power amplifier work in the class C mode, and design the peak output matching network.

Step 3: Design the low-pass filter matching module 7 in the ADS software and perform simulation verification.

Step 4: Combine the debugged carrier amplifier 2, peak amplifier 3, power divider 1 and low-pass filter matching module 7 in the ADS software to form a Doherty power amplifier. Get the schematic. Go to step five.

Step 5: Export the schematic diagram obtained in step 4 in the ADS software to form a layout. Then carry out the co-simulation of layout and schematic diagram. If the efficiency values of the Doherty power amplifier obtained by the co-simulation of the layout and the schematic diagram are greater than 60% within the design bandwidth, go directly to step six. If the efficiency value of the Doherty power amplifier obtained by joint simulation of layout and schematic diagram is less than or equal to 60% within the design bandwidth, adjust the electrical length of the first compensation line 4 of the Doherty power amplifier, and repeat step 4.

Step 6: Process the Doherty power amplifier according to the layout obtained in Step 5.

Claims (5)

1. a kind of broadband Doherty power amplifier, including power splitter, carrier amplifier, peak amplifier, the first compensating line, Second compensating line and third compensating line；It is characterized in that：It further include low-pass filtering matching module；The input of the carrier amplifier Terminate the first output end of power splitter, one end of the first compensating line of load termination；Another termination second of first compensating line compensates One end of line；The second output terminal of one termination power splitter of third compensating line, the input terminal of another termination peak amplifier；Peak value The load end of amplifier is connected with the other end of the second compensating line；

The low-pass filtering matching module include electrical length be the 1st microstrip line of λ/8, the 2nd microstrip line ..., the n-th micro-strip Line, the multiple that n is three；The combining point of one termination peak amplifier and the second compensating line of the 1st microstrip line, it is another to terminate the One end of 2 microstrip lines and the 3rd microstrip line；The other end of 2nd microstrip line and the 3rd microstrip line is hanging；

That that end of termination 3i-2 microstrip lines far from peak amplifier of the close peak amplifier of the 3i+1 microstrip lines, One end of that termination 3i+2 microstrip line and 3i+3 microstrip lines far from peak amplifier；3i+2 microstrip lines and 3i+3 are micro- The other end with line is hanging, i=1,2 ..., n/3-1；

In the case of i=1,2 ..., n/3, the characteristic impedance value of 3i-2 microstrip lines meets formula (1)；3i-1 microstrip lines, The characteristic impedance value of 3i microstrip lines is satisfied by formula (2)；

Z_3i-1=Z_3i=ω₀·L_iFormula (2)

Wherein, ω₀=2 π f；F is the centre frequency for the signal for needing to amplify；C_iValue and L_iValue in ripples such as 0.5dB Chebyshev normalization low-pass filter circuit parameter list, which is looked into, to be taken；It looks into and takes the method to be：Low-pass filtering is normalized in ripple Chebyshev Target line is found in circuit parameter table；Goal behaviorThat corresponding row (of rankRow)；The 2i-1 ginseng of target line Number is C_iValue, the 2i parameter is L_iValue.

2. a kind of broadband Doherty power amplifier according to claim 1, it is characterised in that：The carrier wave amplification Device includes the first transistor, carrier wave input matching network and carrier wave output matching network；The input terminal of the first transistor with The output end of carrier wave input matching network is connected, and output end is connected with the input terminal of carrier wave output matching network；The carrier wave is defeated Enter input terminal of the input terminal as carrier amplifier of matching network；The load end of the carrier wave output matching network is as carrier wave The load end of amplifier.

3. a kind of broadband Doherty power amplifier according to claim 1, it is characterised in that：The peak value amplification Device includes second transistor, peak value input matching network and peak value output matching network；The input terminal of the second transistor with The output end of peak value input matching network is connected, and output end is connected with the input terminal of peak value output matching network；The peak value is defeated Enter input terminal of the input terminal as peak amplifier of matching network；The load end of the peak value output matching network is as peak value The load end of amplifier.

4. a kind of broadband Doherty power amplifier according to claim 1, it is characterised in that：First compensating line, The electrical length of second compensating line and third compensating line is λ/4.

5. a kind of design method of broadband Doherty power amplifier as described in claim 1, it is characterised in that：Step 1： The input voltage that carrier amplifier grid is adjusted in ADS softwares, makes Carrier Power Amplifier be operated in AB class operating modes；And Design carrier wave output matching network；

Step 2: adjusting the input voltage of peak power amplifier grid in ADS softwares, peak power amplifier operation is made to exist C class operating modes, and design peak value output matching network；

Step 3：Low-pass filtering matching module is designed in ADS softwares；

Step 4：The carrier amplifier debugged, peak amplifier, power splitter and low-pass filtering are matched into mould in ADS softwares Block, which combines, constitutes Doherty power amplifier；Obtain schematic diagram；Enter step five；

Step 5：It exports schematic diagram obtained by step 4 to form domain in ADS softwares；It is imitative that domain, schematic diagram joint are carried out again Very；If the efficiency value of Doherty power amplifier obtained by domain, schematic diagram associative simulation is all higher than 60% in design bandwidth, Then it is directly entered step 6；If the efficiency value of the Doherty power amplifier obtained by domain, schematic diagram associative simulation is in design band The case where wide interior appearance is less than or equal to 60%, then the electrical length of the first compensating line of Doherty power amplifier is adjusted, and repeat Step 4；

Step 6：Domain obtained by step 5 processes Doherty power amplifier.