CN104579178A - Broadband input matching based improved doherty power amplifier - Google Patents
Broadband input matching based improved doherty power amplifier Download PDFInfo
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Abstract
The invention discloses an improved doherty power amplifier. The improved doherty power amplifier comprises a hybrid coupler, a carrier amplifier, a broadband input matching peak value amplifier, a phase compensator, second lambda/ 4 impedance transformation line and a combiner; the first signal output end of the hybrid coupler is connected with the signal input end of the carrier amplifier; the signal output end of the carrier amplifier is connected with the first signal input end of the combiner; the second signal output end of the hybrid coupler is connected with the signal input of the phase compensator; the signal output end of the phase compensator is connected with the signal input end of the peak value amplifier; the signal output end of the peak value amplifier is connected with the second signal input end of the combiner. With the adoption of the improved doherty power amplifier, the efficiency is increased, the uniformity and consistency of load modulation effect and efficiency characteristics of a broadband modulation signal belt are improved, and the broadband modulation signal transmission system applies. The invention further discloses a design method of the doherty power amplifier; the starting characteristics of the peak value amplifier are consistent under relatively wide frequency band.
Description
Technical field
The present invention relates to wireless communication technology field, be particularly applicable to the Doherty power amplifier of Broad-band Modulated Signal system.
Background technology
Along with the develop rapidly of wireless communication technology, 3G, 4G or even 5G mechanics of communication has been applied in periodic traffic gradually.In order to pursue higher message transmission rate and more jumbo business need, the signal modulation technique of high spectrum utilization is widely adopted in a communications system.Such signal modulation technique brings the signal of broadband high peak-to-average power ratio in receive-transmit system, is compressed and lose in order to avoid signal in transmitting procedure, and power amplifier must be allowed to return back to low power state work.As the parts that power consumption in whole wireless communication system is maximum, the energy consumption ratio of power amplifier in communication base station system reaches 50%, and the inefficient state therefore under low-power will cause whole wireless communication system efficiency greatly to reduce.In addition, also have higher requirement to the bandwidth of operation of power amplifier up to the application of 100MHz modulation signal in 4G communication system, the efficiency under instant bandwidth 100MHz operating state, the linearity and the power amplifier characteristic in this bandwidth all makes the research of high efficiency wideband power amplifer become the hot subject of current power amplifier field.
Doherty (corresponding English is: Doherty) is a kind of high efficiency linear power amplifiers for non-constant envelope modulation signal proposed first in 1936 by U.S. bell laboratory Radio Frequency Engineer W.H.Doherty.Also be most popular a kind of power amplifier techniques in current communication base station.Conventional Doherty power amplifier comprises carrier amplifier, peak amplifier, its general principle is: carrier amplifier is operated in AB class (Class AB), peak amplifier is operated in C class (Class C), input signal is divided into two paths of signals incoming carrier amplifier and peak amplifier respectively through power splitter, carrier amplifier is prior to peak amplifier conducting, and under the transmission line impedance change action of output λ/4, reach capacity in advance, realize high efficiency; Along with input signal increases further, peak amplifier is started working, its effect is equivalent to an active load and modulates carrier amplifier, make carrier wave and peak amplifier all be operated in respective saturation region as much as possible, make whole power amplifier also keep higher efficiency in high level input reference signal.
But find under study for action through inventor, as shown in Figure 1, traditional Doherty power amplifier uses identical match circuit in carrier amplifier and peak amplifier, although this can the design cost of step-down amplifier and design difficulty, but, because the AB class that the C class of peak amplifier is biased lower than carrier amplifier is biased, the gain characteristic of peak amplifier in frequency band is lower than the gain characteristic of AB class and opening feature also produces skew in band, cause the output current of peak amplifier uneven in band, so will be inconsistent to the load-modulate of carrier amplifier.The variation tendency that the efficiency curve of such Doherty power amplifier is inconsistent along with frequency change presents.The method of the common inconsistent characteristic of reduction peak amplifier additionally adjusts the input circuit of peak amplifier, adds extra cost and time.Therefore, how ensureing that Doherty power amplifier is while the interval internal efficiency of back-off, improves consistency in power amplifier band by simple method, for raising Broad-band Modulated Signal communication system, tool is of great significance.
Summary of the invention
The technical problem solved: for the deficiencies in the prior art, the present invention proposes a kind of modified model Doherty power amplifier based on broadband Input matching, and for solving, efficiency that is inconsistent and that bring thus in power amplifier band is low, the technical problem of poor linearity.
Technical scheme: for solving the problems of the technologies described above, the present invention by the following technical solutions:
Based on a modified model Doherty power amplifier for broadband Input matching, comprise the hybrid coupler, first phase compensator, carrier amplifier, broadband input matching network, peak amplifier, second phase compensator, third phase compensator, a λ/4 impedance transformation line and the mixer containing the 2nd λ/4 impedance transformation line that are connected to 50 Ω matched loads; Wherein, λ is wavelength corresponding to Doherty power amplifier operating frequency centre frequency, and the characteristic impedance of a λ/4 impedance transformation line is 50 ohm, and the characteristic impedance of the 2nd λ/4 impedance transformation line is 35 ohm;
Described mixer has the first signal input part and secondary signal input, first signal input part and secondary signal input are all connected with the input of the 2nd λ/4 impedance transformation line in mixer, and the output of the 2nd λ/4 impedance transformation line is the output of Doherty power amplifier;
Described hybrid coupler has the first signal output part and secondary signal output, and hybrid coupler is assigned as two paths of signals and exports from above-mentioned two signal output parts respectively after receiving input signal; Wherein the first signal output part is connected with the signal input part of carrier amplifier, and the signal output part of carrier amplifier is in series with first phase compensator and a λ/4 impedance transformation line, is finally connected on the first signal input part of mixer; Secondary signal output is connected with the signal input part of first phase compensator, the signal output part of first phase compensator is connected with the signal input part of broadband input matching network, the signal output part of broadband input matching network is connected with the signal input part of peak amplifier, the signal output part of peak amplifier is connected with the signal input part of third phase compensator, and the signal output part of third phase compensator is connected with the secondary signal input of mixer.
Further, in the present invention, described broadband input matching network comprises broadband matching circuit and stability circuit, the input of broadband matching circuit is as the input of whole broadband input matching network, the output of broadband matching circuit is connected to the input of stability circuit, and the output of stability circuit is as the output of whole broadband input matching network.
Further, in the present invention, first phase compensator, second phase compensator and third phase compensator have identical structure; In above-mentioned each phase compensator, comprise output line, input line and decoupling capacitor, and output line and input line are parallel to each other, decoupling capacitor is overlapped between output line and input line.By changing the link position of decoupling capacitor, obtaining different phase lengths, the phase place of two paths of signals is compensated.
Further, in the present invention, described broadband input matching circuit is made up of the microstrip transmission line of the different qualities impedance of mutually connecting, and the input of first microstrip transmission line is connected with the output of first phase compensator, the output of last microstrip transmission line is connected with the input of stability circuit.The peak amplifier Input matching used in the present invention is different from carrier amplifier Input matching, and uses wider broadband Input matching and mate based on simple and easy real interpolation.
Further, in the present invention, described stability circuit comprises microstrip transmission line and the capacitor-resistor circuit of series connection mutually, described capacitor-resistor circuit is the parallel-connection structure of electric capacity and resistance, capacitor-resistor circuit is as the input of stability circuit, the output of capacitor-resistor circuit is connected to microstrip transmission line input, and the output of microstrip transmission line is connected with peak amplifier input.Above-mentioned capacitance resistance is built by the Surface Mount components and parts with centrifugal pump, and easily design, making and replacing use.Although stability circuit itself belongs to conventional design, be placed on inconsistent opening feature in bandwidth of operation to effectively reduce its peak work in the present invention, and the matched design combined by the simple and easy real interpolation of stability circuit and broadband belongs to non-conventional design.
Based on a method for designing for the modified model Doherty power amplifier of broadband Input matching, comprise the following steps:
Step one, design carrier amplifier, make the power efficiency of carrier amplifier require to meet AB class; As long as use general method for designing to get final product complete design here, this belongs to the technological know-how that those skilled in the art in this area know;
Step 2, except the input matching network of broadband, according to circuit structure, all the other each components and parts to be overlapped, be wherein directly connected between the input of peak amplifier and the output of first phase compensator;
Step 3, between input stability circuit being connected to peak amplifier and the output of first phase compensator, capacitance resistance component value in microstrip transmission line width, length and capacitor-resistor circuit in modification stability circuit, makes peak amplifier in whole work strip, keep stable;
Step 4, circuit structure in step 3 is emulated to the input impedance obtaining this circuit structure, bring in simple and easy real interpolation algorithm routine by emulating the input impedance obtained, according to input circuit bandwidth needs, the parameters such as the cut-off frequency in given simple and easy real interpolation algorithm routine and transmission line exponent number, run simple and easy real interpolation algorithm routine thus carry out Broadband Matching, the structure obtaining broadband input matching circuit comprises the characteristic impedance parameter of physical length and every section of microstrip transmission line, determine to use several sections of microstrip transmission lines to produce several rank transfer function, general wider coupling bandwidth needs multistage microstrip transmission line to produce, here simple and easy real interpolation algorithm routine is the algorithm for Broadband Matching common in this area, general simple and easy real interpolation algorithm routine can carry out the Circuit Matching of 50 Ω true impedances to any complex impedance, the plural form input impedance that emulation obtains directly is inputted algorithm routine and can complete Broadband Matching.
Step 5, the broadband input matching circuit obtained to be connected between the input of stability circuit structure and the output of first phase compensator, to complete the design of whole amplifier.
Beneficial effect: the present invention, compared with existing power amplifier, has the following advantages:
(1) efficiency is high.In Doherty power amplifier of the present invention, by giving the input circuit design that peak amplifier is different from carrier amplifier, peak amplifier output current under adjustment C class state.Utilize broadband input matching network, effectively reduction its peak work is placed on the inconsistent opening feature in bandwidth of operation.In peak amplifier band, output current is more even, more consistent to the load-modulate effect of carrier amplifier.Avoid because inconsistent unlatching causes the load-modulate of low frequency place to carrier amplifier in bandwidth of operation more late, carrier amplifier compression is serious, and to the load-modulate of carrier amplifier in advance, whole efficiency is low for high frequency treatment, and whole bandwidth of operation internal efficiency fluctuation is violent.By improving the output current of peak amplifier, making the load-modulate of power amplifier in bandwidth of operation mechanism more consistent with efficiency characteristic, improving efficiency during Broad-band Modulated Signal application.When identical power output, the Doherty power amplifier 100MHz bandwidth of operation internal efficiency fluctuation 10% of the identical input circuit of tradition two-way, and broadband of the present invention Input matching peak amplifier Doherty power amplifier 100MHz bandwidth of operation internal efficiency fluctuation 2%.
(2) linearity is high.By the opening feature under improving peak amplifier C class and being biased, in bandwidth of operation, the input current of peak amplifier is more even.So low frequency place in bandwidth of operation, the output current of peak amplifier increases, and avoids carrier amplifier to enter saturation condition too early.Bandwidth of operation is high to occur frequently, and the output current of peak amplifier reduces, and avoids carrier amplifier to enter load-modulate state in advance.When Broad-band Modulated Signal uses, the carrier amplifier reducing low frequency place is saturated in advance, and high frequency treatment carrier amplifier shifts to an earlier date load-modulate, and in unitary strip, consistency increases, so can improve the linearity.When identical power output, ACLR-35.9/-31.0dBc is recorded during the Doherty power amplifier 100MHz signal 40dBm power output of tradition two-way identical input circuit, carry out linearisation in conjunction with digital pre-distortion and improve that to obtain ACLR be-45.3/-43.0dBc, and broadband Input matching peak amplifier Doherty power amplifier is improved to-45.1/-44.9dBc from-33.9/-33.4dBc, 2dB before and after DPD, is all had to improve.
(3) realize simply.Compare other carry out extra post debugging design to peak amplifier, the present invention is without the need to additional devices, by means of only carrying out efficiency and the linearity that broadband Input matching just can improve Doherty power amplifier to peak amplifier inlet circuit, improve the efficiency of the production of power amplifier.
(3) low cost.Comparing other uses complex digital and radio circuit to improve the technology of power amplifier linearity and efficiency, and the present invention does not need to use additional devices, thus considerably reduces product cost and the production cost of power amplifier.
(4) volume is little.Comparing other uses complex digital and radio circuit to improve the technology of power amplifier linearity and efficiency, and the present invention, based on the circuit of Doherty power amplifier own, takies volume much smaller.
Accompanying drawing explanation
The structural representation of the Doherty power amplifier that the two-way input circuit that Fig. 1 is traditional is identical;
The structural representation of Fig. 2 improvement Doherty power amplifier based on broadband Input matching of the present invention;
Fig. 3 is that input impedance under power tube AB class and C class are biased is with frequency variation curve figure;
Fig. 4 is normalized voltage current diagram when there is not mismatch in the desirable unlatching situation of peak amplifier;
Normalized voltage current diagram when Fig. 5 is actual generation mismatch in peak amplifier band in inconsistent unlatching situation;
Fig. 6 is the structural representation of middle width strip input matching network of the present invention;
The structural representation of phase compensator in Fig. 7 the present invention;
Fig. 8 is the graph of a relation of traditional Doherty power amplifier gain, efficiency and power output;
The graph of a relation of the Doherty power amplifier gain in Fig. 9 the present invention, efficiency and power output;
Figure 10 is that traditional peak amplifier uses result figure before and after the identical input matching circuit digital pre-distortion of two-way;
The peak amplifier that Figure 11 embodiment of the present invention provides uses result figure before and after the input matching circuit digital pre-distortion of broadband.
Embodiment
Below in conjunction with accompanying drawing, the present invention is further described.
As shown in Figure 2, a kind of modified model Doherty power amplifier based on broadband Input matching of the present invention, comprises the hybrid coupler 2, first phase compensator 3, carrier amplifier 5, broadband input matching network 4, peak amplifier 6, second phase compensator 7, third phase compensator 8, a λ/4 impedance transformation line 9 and the mixer 10 containing the 2nd λ/4 impedance transformation line 101 that are connected to 50 Ω matched loads 1; Wherein, λ is wavelength corresponding to Doherty power amplifier operating frequency centre frequency, and the characteristic impedance of a λ/4 impedance transformation line 9 is 50 ohm, and the characteristic impedance of the 2nd λ/4 impedance transformation line 101 is 35 ohm;
First signal output part of hybrid coupler 2 is connected with the signal input part of carrier amplifier 5, and the signal output part of carrier amplifier 5 is connected with the first signal input part of mixer 10 by first phase compensator 7, a λ/4 impedance transformation line 9; The secondary signal output of hybrid coupler 2 is connected with the signal input part of first phase compensator 3, the signal output part of first phase compensator 3 is connected with the input of broadband input matching network 4, the signal output part of broadband input matching network 4 is connected with the signal input part of peak amplifier 6, the signal output part of peak amplifier 6 is connected with the signal input part of third phase compensator 8, and the signal output part of third phase compensator 8 is connected with the secondary signal input of mixer 10; First signal input part of mixer 10 is connected with the input of the 2nd λ/4 impedance transformation line 101 in mixer 10 respectively with secondary signal input, and the output of the 2nd λ/4 impedance transformation line 101 is the output of Doherty power amplifier.
In above-mentioned Doherty power amplifier, described broadband input matching network 4 comprises broadband matching circuit and stability circuit; The input of broadband matching circuit is as the input of whole broadband input matching network 4, be made up of the microstrip transmission line of n the different qualities impedance of mutually connecting, and the input of first microstrip transmission line is connected with the output of first phase compensator 3, the output of last microstrip transmission line is connected with the input of stability circuit; Described stability circuit comprises microstrip transmission line and the capacitor-resistor circuit of series connection mutually, described capacitor-resistor circuit is the parallel-connection structure of electric capacity and resistance, capacitor-resistor circuit is as the input of stability circuit, the output of capacitor-resistor circuit is connected to microstrip transmission line input, and the output of microstrip transmission line is connected with peak amplifier input.
In above-mentioned Doherty power amplifier, first phase compensator 3, second phase compensator 7 and third phase compensator 8 have identical structure; In above-mentioned each phase compensator, comprise output line, input line and decoupling capacitor, and output line and input line are parallel to each other, decoupling capacitor is overlapped between output line and input line.
In above-mentioned Doherty power amplifier, hybrid coupler 2 for the input signal constant power of Doherty power amplifier is assigned as two paths of signals, i.e. first via signal and the second road signal.First via signal is connected with the signal input part of carrier amplifier 5 by the first signal output part of hybrid coupler 2, the signal output part of carrier amplifier 5 is connected with the first signal input part of mixer 10 by second phase compensator 7, a λ/4 impedance transformation line 9, and second phase compensator 7 is for adjusting the high efficiency state under carrier amplifier 5 low power state.Second road signal is connected with the signal input part of first phase compensator 3 by the secondary signal output of hybrid coupler 2, the signal output part of first phase compensator 3 is connected with the input of broadband input matching network 4, the signal output part of broadband input matching network 4 is connected with the signal input part of peak amplifier 6, the signal output part of peak amplifier 6 is connected with the signal input part of third phase compensator 8, and the signal output part of third phase compensator 8 is connected with the secondary signal input of mixer 10.First phase compensator 3 is for the adjustment of two paths of signals phase place, and third phase compensator 8, for adjusting the phase place of peak amplifier when low-power, makes to present high resistant open-circuit condition at the secondary signal input of mixer 10.Carrier amplifier 5 is for amplifying first via signal.Peak amplifier 6 is for amplifying the second road signal.Broadband input matching network adds stability circuit by the broadband matching circuit on n rank and forms, and provides stable broadband Input matching.The second road signal that mixer 10 exports for the first via signal that exported by a λ/4 impedance transformation line 9 and third phase compensator 8 closes road, and by impedance transformation by the load impedance of Doherty power amplifier with close road after impedance mate.
Operation principle of the present invention is: in Doherty power amplifier, and carrier amplifier 5 is biased in AB class usually, and peak amplifier 6 is biased in C class.From the equivalent-circuit model of GaN device, its input admittance can be expressed as
y
inrepresent the admittance value of input impedance, G represents the electric conductivity value of input admittance, and
represent the susceptance value of input admittance,
equal angular frequency.Input capacitance C
incomposition component can reduce gradually with biased reduction, cause imaginary part to diminish.But when frequency raises, admittance imaginary part but can become large.When height is biased to offsetting low-voltage during a certain characteristic frequency the imaginary part reduction effect brought, produce and low-frequency phase input admittance together, as shown in the formula (1).
(1), in formula, G represents the electric conductivity value of input admittance, C
in_class aBrepresent the input capacitance of power amplifier element under AB class is biased, C
in_class crepresent the input capacitance of power amplifier element under being biased with C class, f
lowand f
highrepresent high-frequency and low frequency value respectively.
As shown in Figure 3, f
0represent the centre frequency of designed many He Erdi power amplifier, Smith circle diagram upper frequency growing direction is clockwise, and the low frequency input impedance (in figure, solid line represents) under the high frequency input impedance (in figure, dotted line represents) under C class is biased and AB class are biased is overlapping, equal on Smith circle diagram.Therefore, for the AB class carrier amplifier matched, if be biased to C class as peak amplifier, the input impedance occured frequently low with AB class is identical in fact to mate the input impedance pointed out, and in former frequency generation mismatch.Equation (2) and (3) are had according to GENERALIZED REFLECTION COEFFICIENT and injecting power computing formula.
(2) in formula, Γ represents GENERALIZED REFLECTION COEFFICIENT, Z
fixrepresent the impedance needing coupling, and Z
inrepresent practical impedance,
represent Z
fixconjugate impedance
(3) in formula, P
peaking_inputrepresent the injecting power of peak power amplifier, P
inrepresent the input power injecting many He Erdi power amplifier, Γ represents broad sense input reflection coefficient.
Known owing to there is mismatch by formula (3), the power that peak amplifier 6 is injected at former frequency place can reduce thus output current is reduced.Fig. 4 represents desirable and mismatch does not occur, and peak amplifier 6 is with the interior unified schematic diagram opened, and the output current of final peak amplifier 6 is all equal in whole frequency band with the output current of carrier amplifier 5.Fig. 5 represents actual, in band, mismatch occurs, peak amplifier 6 has the unlatching scope of Δ ε (f)=0.2 centered by 0.5 times of normalization incoming level, input power generation mismatch, output current and the output current of carrier amplifier 5 in frequency band of peak amplifier 6 misplace, and produce inconsistent load-modulate effect and efficiency impact to carrier amplifier 5.
Open when peak value power amplifier is different and the reason that carrier power amplifier produces insufficient load-modulate be mainly biased to skew and the mismatch of lower input impedance from C class.Analyzed from equation (1), the resistance value Z at design frequency place under C class bias state
design_Cwith the impedance Z at low frequency place
lower_ABidentical, open to realize peak value power amplifier, the impedance that the while that just needing under AB class state, matched design frequency goes out and the impedance at low frequency place, could reduce the skew under C class state simultaneously.For whole planned network, just need to produce such frequency response F (Z
design_AB)=F (Z
lower_AB), F (Z
design_AB) represent the input circuit frequency response that the input impedance of design frequency place is corresponding under AB class state, F (Z
lower_AB_) represent the frequency response that the input impedance of low frequency place is corresponding under AB class state, because of by obtaining Z above
lower_AB=Z
design_C, input matching network mates AB class low frequency and design frequency two place simultaneously, also can obtain good coupling under just ensureing C class state, opens when preventing peak value power amplifier different, reduces its insufficient modulation to carrier power amplifier.
Therefore use simple and easy real interpolation to carry out Broadband Matching, combination stability circuit structure here, realize broadband Input matching, reduce inconsistent opening feature, reduce the fluctuation of band internal efficiency curve, make peak amplifier more consistent to the load-modulate of carrier amplifier.
The method for designing of above-mentioned Doherty power amplifier broadband Input matching peak amplifier, comprises the following steps:
Step one, use general matching process design carrier amplifier 5, make the power efficiency of carrier amplifier 5 require to meet AB class;
Wen Zhong, category-A, category-B, C class and AB class refer to according to the bias state of amplifier to the classification of amplifier, are the common practise of the art.Specifically can see MAG row Bie Nikefu work, Zhang Yuxing, Zhao Hongfei translate, RF and microwave Designing power amplifier, Electronic Industry Press, 2006.
Step 2, except broadband input matching network 4, according to circuit structure, all the other each components and parts to be overlapped, be wherein directly connected between the input of peak amplifier 6 and the output of first phase compensator 3;
Step 3, between input stability circuit being connected to peak amplifier 6 and the output of first phase compensator 3, capacitance resistance component value in microstrip transmission line width, length and capacitor-resistor circuit in modification stability circuit, makes peak amplifier 6 in whole work strip, keep stable;
Step 4, the circuit structure in step 3 is emulated to the input impedance obtaining this circuit structure, bring in simple and easy real interpolation algorithm routine by emulating the input impedance obtained, according to the cut-off frequency in the given simple and easy real interpolation algorithm routine of circuit needs and transmission line exponent number, run simple and easy real interpolation algorithm routine thus carry out Broadband Matching, the structure obtaining broadband input matching circuit comprises physical length and characteristic impedance parameter;
Step 5, the broadband input matching circuit obtained to be connected between the input of stability circuit structure and the output of first phase compensator 3, to complete the design of whole amplifier.
In involved simple and easy real interpolation algorithm routine, various parameter can with reference to " Design of Ultra WidebandAntenna Matching Networks via Simplified Real Frequency Technique " chapter 9 and chapter 10.BinbogaSiddik Yarman work, " Design of Ultra Wideband Antenna Matching Networks via Simplified RealFrequency Technique " Springer publishing house, the first edition, 2008; And " Design of Ultra WidebandPower Transfer Networks " chapter 4 and chapter 11.Binboga Siddik Yarman work, " Design of UltraWideband Power Transfer Networks ", Wiley publishing house, the first edition, 2010.
Enumerate an embodiment below.
Doherty power amplifier operating frequency in the present embodiment is 2.15GHz, the power tube of carrier amplifier 5 and peak amplifier 6 all adopts the corresponding English of the GaN high electron mobility transistor of Cree company to be: GaN HEMTCGH27060, CGH27060 are power tube model.
As shown in Figure 6, broadband input matching network 4 comprises: stability circuit and broadband input matching network.Wherein stability circuit comprises microstrip transmission line and the capacitor-resistor circuit of series connection, wherein microstrip transmission line resistance 13 Ω, electrical length 46 °, electric capacity 4.7pF, resistance 150 Ω in capacitor-resistor circuit; Following 22.8 Ω/37.2 of parameter of 3 microstrip transmission lines in the broadband input matching network on n=3 rank °, 37.6 Ω/40.9 °, 49.5 Ω/12.8 °, wherein frequency 2.15GHz centered by electrical length respective frequencies, also has the decoupling capacitor 220pF playing stopping direct current effect existed in conventional design in addition.
As shown in Figure 7, the first phase compensator 3 that the present embodiment adopts, second phase compensator 7 and third phase compensator 8 all realize based on microstrip transmission line and decoupling capacitor, in figure, both sides long line preset length excursion is the microstrip transmission line of 42mm, phase place excursion is-90 ° ~+90 °, in debug process, by moving the position of decoupling capacitor, realize ± 90 ° of range-phase continuously adjustabe.
In Fig. 8, lines with circle represent the relation lines of the gain of the conventional Doherty power amplifier of 2.1GHz, efficiency and power output, represent the relation lines of the gain of 2.2GHz routine Doherty power amplifier, efficiency and power output with an angle leg-of-mutton lines upward; In Fig. 9, in the working frequency range 2.1GHz ~ 2.2GHz of design, lines with circle represent the gain efficiency of the Doherty power amplifier of 2.1GHz the present embodiment and the relation lines of power output, represent the relation lines of the efficiency of the Doherty power amplifier of the present embodiment 2.2GHz, gain and power output with an angle leg-of-mutton lines upward.
Second phase compensator in conventional Doherty power amplifier after carrier amplifier, after adjustment, optimum efficiency power corresponding phase is-42 °, third phase compensator corresponding phase after peak amplifier is-55 °, first phase compensator before peak amplifier Input matching, the phase lengths of corresponding optimum phase superposition is-163 °; Second phase compensator in the Doherty power amplifier of the present embodiment after carrier amplifier, after adjustment, corresponding phase is-70 °, third phase compensator after peak amplifier, after adjustment, under best open-circuit condition, corresponding phase is-90 °.First phase compensator before peak amplifier, after adjustment, corresponding phase is-170 °.
As can be seen from Figure 8, the maximum saturation power 49dBm that conventional Doherty power amplifier exports, saturation efficiency is 60%.As back-off 7dBm, when power output is 42.5dBm, 2.1 ~ 2.2GHz peak efficiency 47% of conventional Doherty power amplifier, minimum efficiency is that 37%, 100MHz is with internal efficiency fluctuation to be 10%.As can be known from Fig. 9, the maximum full power 49.7dBm of the Doherty power amplifier output of the present embodiment, saturation efficiency is 64%.As back-off 7dBm, during power output 42.5dBm, 2.1 ~ 2.2GHz peak efficiency 45% of the Doherty power amplifier of the present embodiment, minimum efficiency is 43%.Compared with conventional Doherty power amplifier, the Doherty power amplifier of the embodiment of the present invention promotes all to some extent on saturation output power and efficiency index, this method is described to Doherty power amplifier by improving peak amplifier 6 Input matching, improve peak amplifier 6 output current, have increase for the saturation output power of Doherty power amplifier and delivery efficiency.Also illustrate simultaneously, utilize after method provided by the invention adjusts the peak amplifier output current in Doherty power amplifier, load-modulate effect in whole band is improved, passband fluctuation is reduced to 2% from original 10%, for Broad-band Modulated Signal, ensemble average efficiency gets a promotion.
Represent conventional Doherty power amplifier power output 40.3dBm shown in Figure 10, power spectral density plot during efficiency 39.5% measured by 100MHz Broad-band Modulated Signal, the adjacent channel leakage power that can obtain now is-35.9/-31.0dBc than ACLR.Represent the Doherty power amplifier power output 40.6dBm of the present embodiment as shown in figure 11, the power spectral density plot recorded during efficiency 40.5%, ACLR is now-33.9/-33.4dBc.Carry out digital pre-distortion to two kinds of Doherty power amplifiers, obtain result and be respectively, conventional Doherty power amplifier ACLR is-45.3/-43.0dBc, and the present embodiment Doherty power amplifier ACLR is-45.1/-44.9dBc.As can be seen from Figure 10, no matter really before and after digital pre-distortion, the linear measurement index of Broad-band Modulated Signal, all good than the conventional Doherty power amplifier ACLR index 2dB of the present embodiment Doherty power amplifier, the improvement of the adjacent channel leakage power ratio before digital pre-distortion shows that this broadband Input matching strategy can improve the linearity from circuit design, and the result after digital pre-distortion also shows that this routine Doherty power amplifier reaches the requirement of LTE-Advanced for adjacent channel leakage power ratio≤-45dBc substantially.The present embodiment Doherty power amplifier is described, through improving peak amplifier output current, in Broad-band Modulated Signal band, the gain of Doherty power amplifier, efficiency, load-modulate effect is more consistent.So the linearity is more excellent.
The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.
Claims (6)
1., based on a modified model Doherty power amplifier for broadband Input matching, it is characterized in that: comprise be connected to 50 Ω matched loads (1) hybrid coupler (2), first phase compensator (3), carrier amplifier (5), broadband input matching network (4), peak amplifier (6), second phase compensator (7), third phase compensator (8), λ/4 impedance transformation line (9) and containing the mixer (10) of the 2nd λ/4 impedance transformation line (101); Wherein, λ is wavelength corresponding to Doherty power amplifier operating frequency centre frequency, and the characteristic impedance of λ/4 impedance transformation line (9) is 50 ohm, and the characteristic impedance of the 2nd λ/4 impedance transformation line (101) is 35 ohm;
Described mixer (10) has the first signal input part and secondary signal input, first signal input part and secondary signal input are all connected with the input of the 2nd λ/4 impedance transformation line (101) in mixer (10), and the output of the 2nd λ/4 impedance transformation line (101) is the output of Doherty power amplifier;
Described hybrid coupler (2) has the first signal output part and secondary signal output, the input of hybrid coupler (2) is the input of Doherty power amplifier, is assigned as two paths of signals and exports from above-mentioned two signal output parts respectively after the input of hybrid coupler (2) receives input signal; Wherein the first signal output part is connected with the signal input part of carrier amplifier (5), the signal output part of carrier amplifier (5) is in series with first phase compensator (7) and λ/4 impedance transformation line (9), is finally connected on the first signal input part of mixer (10); Secondary signal output is connected with the signal input part of first phase compensator (3), the signal output part of first phase compensator (3) is connected with the signal input part of broadband input matching network (4), the signal output part of broadband input matching network (4) is connected with the signal input part of peak amplifier (6), the signal output part of peak amplifier (6) is connected with the signal input part of third phase compensator (8), and the signal output part of third phase compensator (8) is connected with the secondary signal input of mixer (10).
2. the modified model Doherty power amplifier based on broadband Input matching according to claim 1, it is characterized in that: described broadband input matching network (4) comprises broadband matching circuit and stability circuit, the input of broadband matching circuit is as the input in whole broadband input matching network (4), the output of broadband matching circuit is connected to the input of stability circuit, and the output of stability circuit is as the output in whole broadband input matching network (4).
3. the modified model Doherty power amplifier based on broadband Input matching according to claim 1, is characterized in that: first phase compensator (3), second phase compensator (7) and third phase compensator (8) have identical structure; In above-mentioned each phase compensator, comprise output line, input line and decoupling capacitor, and output line and input line are parallel to each other, decoupling capacitor is overlapped between output line and input line.
4. the modified model Doherty power amplifier based on broadband Input matching according to claim 2, it is characterized in that: described broadband input matching circuit is made up of the microstrip transmission line of the different qualities impedance of mutually connecting, and the input of first microstrip transmission line is connected with the output of first phase compensator (3), the output of last microstrip transmission line is connected with the input of stability circuit.
5. the modified model Doherty power amplifier based on broadband Input matching according to claim 2, it is characterized in that: described stability circuit comprises microstrip transmission line and the capacitor-resistor circuit of series connection mutually, described capacitor-resistor circuit is the parallel-connection structure of electric capacity and resistance, capacitor-resistor circuit is as the input of stability circuit, the output of capacitor-resistor circuit is connected to microstrip transmission line input, and the output of microstrip transmission line is connected with peak amplifier input.
6., based on a method for designing for the modified model Doherty power amplifier of broadband Input matching, it is characterized in that:
Step one, design carrier amplifier (5), make the power efficiency of carrier amplifier (5) require to meet AB class;
Step 2, except broadband input matching network (3), according to circuit structure, all the other each components and parts to be overlapped, be wherein directly connected between the input of peak amplifier (6) and the output of first phase compensator (3);
Step 3, between input stability circuit being connected to peak amplifier (6) and the output of first phase compensator (3), capacitance resistance component value in microstrip transmission line width, length and capacitor-resistor circuit in modification stability circuit, makes peak amplifier in whole work strip, keep stable;
Step 4, the circuit structure in step 3 is emulated to the input impedance obtaining this circuit structure, bring in simple and easy real interpolation algorithm routine by emulating the input impedance obtained, according to the cut-off frequency in the given simple and easy real interpolation algorithm routine of input circuit bandwidth needs and transmission line exponent number, run simple and easy real interpolation algorithm routine thus carry out Broadband Matching, obtaining the structure of broadband input matching circuit: comprising the characteristic impedance parameter of physical length and every section of microstrip transmission line;
Step 5, the broadband input matching circuit obtained to be connected between the input of stability circuit structure and the output of first phase compensator (3), to complete the design of whole amplifier.
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