Those who play radio frequency amplifiers know that RF power amplifiers (RF PA) are an important part of a variety of wireless transmitters. In the transmitter pre-stage circuit, the modulation oscillator circuit generated by the RF signal power is very small, need to go through a series of amplification a buffer level, the middle amplifier stage, the final power amplifier level, get enough RF power before feeding To the antenna to radiate out. In order to obtain a sufficiently large RF output power, an RF power amplifier must be used. RF power amplifier is the main technical indicators of output power and efficiency, is the key to the study of RF power amplifier. The requirements of the power transistor, mainly to consider the breakdown voltage, the maximum collector current and maximum tube and other parameters. In order to achieve effective energy transfer, between the antenna and the amplifier need to use impedance matching network.
Recently, the platform has been open to the project, it is related to the RF amplifier, the employer's request "to see this demand, Xiaobian do not understand the knowledge of the RF amplifier, in order to brain up, specifically to find the relevant information, Mentioned earlier efficiency is one of the main indicators of RF power amplifier, then now talk about how to improve the efficiency of RF power amplifier.
Two ways to improve the power of the RF amplifier: to enhance the linearity, the use of different-phase power amplifier.
Improve linearity
Modern digital modulation technology requires the amplifier linearity is high enough, otherwise there will be intermodulation distortion and thus reduce the signal quality. Unfortunately, when the amplifier performance is optimal, they are close to the saturation level, and then they become non-linear, the RF power output decreases as the input power increases, and significant distortion begins to occur. This distortion can cause crosstalk of adjacent channels or services. As a result, the designer typically returns the RF output power back to a "safe area" to ensure linearity. When they do so, multiple RF transistors are necessary to achieve a given RF output power, which will increase the current consumption and lead to shorter battery life, or in the base station will cause higher operating costs. DPD effectively introduces "anti-distortion" at the input of the amplifier, eliminating the non-linearity of the amplifier. As a result, the amplifier does not need to fall back to the optimum operating point, eliminating the need for more RF power devices. As the amplifier becomes more efficient, the benefits are the reduction in cooling costs and the reduction of all significant power consumption. When CFR is operated, the distortion is continuously checked by reducing the peak-to-average ratio of the input signal. This reduces the peak of the signal so that no clipping or distortion occurs when the signal passes through the amplifier. When DPD and CFR are used together, a greater gain can be achieved.
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Method of out - of - phase power amplifier
Another technology, patented by Henri Chireix invented and held 80 years ago, is often referred to as "outphasing" (a member of the phase-locked power amplifier, a family of load modulation technologies) and is currently used by Fujitsu and NXP To enhance the efficiency of the amplifier. It combines two non-linear RF power amplifiers that drive two amplifiers from different phase signals. Since the phase is controlled so that the efficiency gains can be achieved using the Class B RF power amplifier when the output signal is coupled. Careful design techniques, especially the selection of appropriate reactance, can optimize the system to a specific output amplitude, which will bring twice the efficiency boost (at least in theory). Fujitsu announced last year that it has used an outphasing method in a power amplifier to integrate a compact, low-loss power-coupled circuit with a DSP-based phase error correction compensation circuit that is comparable to the conventional 65% transmission time of existing amplifiers , The amplifier transmission time can be more than 95%. The design of the test, the peak output of this power amplifier can reach 100 watts; average power efficiency from 50% to 70%. The input signal is divided into two signals with constant amplitude and phase change. The amplitude is set by the RF power device, and the power coupling circuit reconstructs the source signal waveform. Previously, when the source signal was reconstructed, the coupling accuracy loss required to determine the phase difference, preventing the commercialization of the technique. Fujitsu's coupler has a shorter signal path, reducing losses and increasing bandwidth.
As for the increase in power, multiple auxiliary amplifiers can be used in parallel with the main amplifier, and each auxiliary amplifier is biased to provide amplified output when the main amplifier is near saturation. The input signal is delivered to the main amplifier and the plurality of auxiliary amplifiers through the signal distributor, and the output terminal receiving the output signal amplified by the main amplifier and the plurality of auxiliary amplifiers includes the resistive load R / 2. The split signal is applied to the main amplifier via a 90 ° transformer, and the output of the auxiliary amplifier is applied to the output load via a 90 ° transformer. When the operating point is below saturation, the main amplifier delivers power to the load 2R, and the main amplifier delivers the load to the maximum power and half of the amplifier saturation.
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