The Research For RF Circuits In Adaptive Feedforward Power Amplifier

In mobile wireless communication system, as the last part of the base-station transmitter, RF power amplifier is an important aspect which not only can decide the system index but also can bring the distortion while supply the full power to the transmitter. Especially in model wireless communication system, with the development of digital modulation technology, the system is very sensitive to the linearity characteristic of the PA (power amplifier) due to using the non-constant envelope signal. So it is a new emergency subject for how to reduce IMD, increase linearity and improve the efficiency of PA.In this thesis, the nonlinear principle and distortion, both and the nonlinear technology index of the amplifier was firstly researched. In reality, all of the amplifiers are nonlinear, thus the received signals out from these amplifiers will distort. Single wave generate harmonious distortion, and multi-wave generate both harmonious distortion and intermodulation distortion. Amplifier will arise many affects such as block and intermodulation due to the nonlinear distortion. IMD3 and ACPR are the key indexes while describe the nonlinear PA.Secondly, the development of linear PA of both the domestic and foreign was summarized in the paper. The mainly linear technologies widely used in nowadays conclude as fellows: feedforward, analog predistortion, digital predistortion, negative feedback, power back and so on. Based on the compare, adaptive feedforward technology can fulfill the high linear request, and it is one of the best methods. Based on this, the system scheme of the adaptive feedforward technology was designed, which contained the gain, phase and delay match.The ADS simulation design of Main PA and error PA was mainly introduced, which as the key elements to construct the adaptive feedback linear PA. PA was composed by three parts. These are: balance amplifier, FET amplifier and LDMOS amplifier. Through ADS simulation, the gain index can meet the requirement, the input VSWR was good while the output VSWR not idea. So, an isolator was added at the output port.Finally, both main PA and error PA can fulfill the requirements of the anticipation based on the test. The gain of main PA and error PA were 47dB and 48dB. System test which connected the PA, loop and downconverter indicated that, IMD3 was improved 14.1dB, and ACPR was improved about 10dB. Therefore, the nonlinear of PA was improved greatly through feedforward linear technology. In conclusion, the feedforward scheme was right and this technology is valuable in practicality.This article aimed to research the circuit design and simulation of adaptive feedforward PA in base station, which applies to various kinds of mobile communication transmission systems. The test result testified the correctness of the principle, and the effect was obvious. But, there still exist some difference from test index to simulation result.