Adopt the Doherty power amplifier of multistage bypass amplifierTechnical field
The present invention relates to communication technical field, specifically, relate to a kind of Doherty power amplifier adopting multistage bypass amplifier.
Background technology
Along with environmental protection and energy-saving and emission-reduction come into one's own day by day, common carrier is also more and more higher for the requirement of wireless communication system lower power consumption.Power amplifier is as the final block in radio communication emission system, and the efficiency of himself is huge for the impact of whole communication system efficiency index.In general commercial mobile communication base station, the power consumption of final power amplifier accounts for more than 60% of whole system.As can be seen here, if final power amplifier efficiency is too low, not only increase the power consumption of whole mobile base station system, but also create too much heat, the cooling measure brought thus also will consume mass energy.Therefore, the efficiency improving power amplifier has become the hot subject of nowadays wireless communication field.
In addition, along with developing rapidly of mobile communication technology, especially the development of the universal and forth generation mobile communication technology (4G) of G mobile communication (3G), the amount of information that mobile communication is transmitted is increasing, and the performance for Wireless communication transceiver system is had higher requirement.The signal peak-to-average ratio that signal peak-to-average ratio due to 4G mobile communication system compares former mobile communication system is larger, progressively to enter the 4G mobile communication system such as commercial test stage LTE system at present, its signal peak-to-average ratio is at about 10dB, so power amplifier is when amplifying this type of high peak-to-average power ratio signal, in order to ensure the linearity of signal, must operate at a power points more much lower than saturation power, bring the sharply decline of efficiency thus.Therefore, the design for high efficiency power amplifier has been not only require near saturation power, realize higher efficiency, but requires also can provide higher efficiency within the scope of a larger back-off.
Doherty power amplifier is widely used a kind of high efficiency power amplifier technology in current commercial mobile communication base station, tradition Doherty power amplifier, as shown in Figure 1, comprise 3dB power divider, main road amplifier, bypass amplifier and mixer, its general principle is: when input signal is less, be biased in the main road amplifier of AB class prior to being biased in the conducting of C class bypass amplifier, under the effect of the λ/4 impedance transformation line of main road amplifier in mixer, reach capacity in advance and realize high efficiency; Along with input signal increases further, bypass amplifier starts conducting, by the effect of Doherty active load modulation, make main road and bypass amplifier all be operated in saturation region, thus make whole Doherty power amplifier all keep high efficiency within the scope of larger back-off.
But, inventor finds under study for action, for traditional Doherty power amplifier, when identical input power, the ratio of gains AB class main road amplifier of C class bypass amplifier is low, make bypass amplifier output current lower than main road amplifier, result in Doherty active load modulation abundant not, reduce power output and the rollback efficiency of whole Doherty power amplifier.Therefore, how to strengthen the load-modulate of Doherty power amplifier, and then improve power output and rollback efficiency for raising base station system performance and reduce costs, tool is of great significance.
Summary of the invention
Technical problem: technical problem to be solved by this invention is: a kind of Doherty power amplifier adopting multistage bypass amplifier is provided, this Doherty power amplifier is while guarantee main road amplifier has higher gain, the power output of bypass amplifier can be made to be improved, thus enhancing active load modulation, improve power output and the rollback efficiency of Doherty power amplifier.
Technical scheme: for solving the problems of the technologies described above, the technical solution used in the present invention is:
Adopt a Doherty power amplifier for multistage bypass amplifier, comprise asymmetric power divider, main road amplifying unit, bypass amplifying unit and mixer.Described main road amplifying unit comprises main road delay line phase, main road amplifier and main road compensating wire.Described bypass amplifying unit comprises bypass delay line phase, bypass prime amplifier, bypass amplifier and bypass compensating wire.Described mixer comprises the λ/4 impedance transformation line that characteristic impedance is 35 ohm, and wherein, λ is wavelength corresponding to Doherty power amplifier operating frequency.
Further, described asymmetric power divider exports the first via signal of relatively high power to main road amplifying unit, exports the second road signal of smaller power to bypass amplifying unit.
Further, described bypass prime amplifier exports bypass amplifier to by after the second road signal pre-amplification.
Further, described bypass prime amplifier can be made up of one or more amplifier.
Further, described main road amplifier is connected by the λ/4 impedance transformation line of main road compensating wire and 35 in mixer ohm.
Further, described main road delay line phase and bypass delay line phase, for adjusting the phase place of first via signal and the second road signal, make both keep same-phase at the input of mixer.
Beneficial effect: compared with prior art, technical scheme of the present invention has following beneficial effect:
(1) improve power output and rollback efficiency.In tradition Doherty power amplifier, because bypass amplifier biasing is in C class, its gain is lower than the main road amplifier being biased in AB class, thus make bypass amplifier saturation output current lower than main road amplifier, the active load modulation that cannot realize ideal and due saturation power, and then had influence on rollback efficiency.The present invention added prime amplifier before bypass amplifier, improve the gain of bypass amplifier, make it export the saturation current corresponding with main road amplifier, realize effective active load modulation, improve saturation output power and the rollback efficiency of power amplifier.
(2) improve gain.For the entire gain of power amplifier, when input signals are small, bypass amplifier does not temporarily work, and the gain of Doherty power amplifier is determined by main road amplifier.The 3dB power divider that in tradition Doherty power amplifier, the merit such as power divider employing is divided, makes the entire gain of Doherty power amplifier have dropped 3dB like this.Have employed asymmetric power divider in the present invention, relatively high power is exported to main road amplifier, the reduction of Doherty power amplifier entire gain can be made to be reduced to about 1dB.
(3) exit loss is reduced.50 ohm of λ/4 impedance transformation lines required for traditional Doherty power amplifier output are eliminated in the present invention, the state of Doherty load-modulate is reached by the length of adjustment main road compensating wire, shorten the length of transmission line of output as far as possible, thus reduce the loss of output, improve power output and the efficiency of power amplifier.
Accompanying drawing explanation
The structured flowchart of the Doherty power amplifier that Fig. 1 is traditional.
The structured flowchart of Fig. 2 Doherty power amplifier of the present invention.
The Doherty power amplifier gain of Fig. 3 embodiment of the present invention and the graph of a relation of power output.
The Doherty power amplifier efficiency of Fig. 4 embodiment of the present invention and the graph of a relation of power output.
Have in figure: asymmetric power divider 10, main road amplifying unit 20, main road delay line phase 201, main road amplifier 202, main road compensating wire 203, bypass amplifying unit 30, bypass delay line phase 301, bypass prime amplifier 302, bypass amplifier 303, bypass compensating wire 304, mixer 40,35 ohm of λ/4 impedance transformation lines 401.
Embodiment
Below in conjunction with accompanying drawing, technical scheme of the present invention is described in detail.
As shown in Figure 2, a kind of Doherty power amplifier adopting multistage bypass amplifier of the present invention, comprises asymmetric power divider 10, main road amplifying unit 20, bypass amplifying unit 30 and mixer 40.Described main road amplifying unit 20 comprises main road delay line phase 201, main road amplifier 202 and main road compensating wire 203.Described bypass amplifying unit 30 comprises bypass delay line phase 301, bypass prime amplifier 302, bypass amplifier 303 and bypass compensating wire 304.Described mixer 40 comprises λ/4 impedance transformation line 401, and wherein, λ is wavelength corresponding to Doherty power amplifier operating frequency.The characteristic impedance of main road delay line phase 201, bypass delay line phase 301, main road compensating wire 203, bypass compensating wire 304 is 50 ohm, and the characteristic impedance of λ/4 impedance transformation line 401 is 35 ohm.
In above-mentioned Doherty power amplifier, the input signal of Doherty power amplifier is asymmetricly assigned as two paths of signals by asymmetric power divider 10, i.e. first via signal and the second road signal.The power ratio of first via signal and the second road signal is greater than 1.First via signal exports main road amplifier 202 to after adjusting phase place by main road delay line phase 201, after main road amplifier 202 amplifies, is exported to the first input end of mixer 40 by main road compensating wire 203.Second road signal exports bypass prime amplifier 302 to after adjusting phase place by bypass delay line phase 301, after bypass prime amplifier 302 pre-amplification, export bypass amplifier 303 to, after amplifying, exported to the second input of mixer 40 by bypass compensating wire 304.Main road compensating wire 203 for compensating the parasitic parameters such as main road power tube endophyte inductance, electric capacity, and with 35 ohm of λ/4 impedance transformation line 401 actings in conjunction to ensure that amplifier reaches capacity when back-off efficiency.Bypass compensating wire 304 act as parasitic parameters such as compensating bypass power tube endophyte inductance, electric capacity with ensure its when not opening output for open circuit.The effect of main road delay line phase 201 and bypass delay line phase 301 is phase places of adjustment first via signal and the second road signal, makes two paths of signals realize homophase at the first and second inputs of mixer 40.
In above-mentioned Doherty power amplifier, bypass prime amplifier 302 exports bypass amplifier 303 to by after the second road signal pre-amplification, overcomes the problem that when bypass amplifier 303 is biased in C class, gain is lower.
In above-mentioned Doherty power amplifier, bypass prime amplifier 302 can be made up of one or more amplifier.
In above-mentioned Doherty power amplifier, main road amplifier 202 is directly connected with the λ/4 impedance transformation line 401 of 35 in mixer 40 ohm by main road compensating wire 203, reduces the length of output transmission line, thus reduces the loss of output.
In above-mentioned Doherty power amplifier, described main road delay line phase 201 and bypass delay line phase 301, for adjusting the phase place of first via signal and the second road signal, make both keep same-phase at the input of mixer 40.
Operation principle of the present invention is: export the first via signal of relatively high power to main road amplifying unit 20 by asymmetric power divider 10, thus reduce the loss of main road amplifying unit 20 gain, improve the entire gain of Doherty power amplifier.Second road signal of the smaller power that asymmetric power divider 10 exports exports bypass amplifying unit 30 to, export to again in bypass amplifier 303 after bypass prime amplifier 302 pre-amplification and amplify, overcome the problem that when bypass amplifier 303 is biased in C class, the lower active load modulation brought of gain is insufficient, thus make the saturation current that bypass amplifier 303 reaches identical with main road amplifier 202, the active load modulation of realizing ideal, thus improve the overall power output of Doherty power amplifier and rollback efficiency.
Exemplify an embodiment below.
Doherty power amplifier operating frequency in the present embodiment is 2550MHz, the power tube of main road amplifier 202 and bypass amplifier 303 all adopts the HEMT power tube CGH27060 of CREE, and the power tube of bypass prime amplifier 302 adopts the HEMT power tube CGH40010 of CREE.Main road amplifier 202 is biased in AB class, and bypass prime amplifier 302 is biased in C class, and bypass amplifier 303 is biased in category-B.The power ratio of the first via signal that asymmetric power divider exports and the second road signal is 3.5:1.
Fig. 3 is gain and the power output graph of a relation of the Doherty power amplifier of the present embodiment.As can be seen from the figure, the Doherty power amplifier small signal gain of the present embodiment is about 13dB, less relative to single channel amplifier gain reduction, is about about 1dB.Saturation output power is about 51dBm, and the power tube power capacity in main road amplifier 202 and bypass amplifier 303 is fully utilized.Fig. 4 is efficiency and the power output graph of a relation of the Doherty power amplifier of the present embodiment.As can be seen from Figure 4, the saturation efficiency of the Doherty power amplifier of the present embodiment is 55%.As back-off 9dBm, the efficiency of the Doherty power amplifier of the present embodiment is 41%, achieves the rollback efficiency higher when high-power rollback.