The Design And Realization Of Transmitter Based On RF Communication System

With the arrival of "Information Age", Radio Frequency technology has increasingly become the focus of communication. It is urgently necessary to develop a laboratorial communication system of RF, because of increasingly lack of RF engineers. The system generally includes transceiver equipments, antenna equipments (including feeder), input and output equipments (such as speakers, headphones, etc.), and power equipment (such as DC power). The purpose of the paper is to solve the problem. The design and realization of the transmitter in RF communication laboratorial system are presented.According to the analysis of transmitter solutions, the paper proposes a transmitter solution based on the PLL direct-frequency modulation. The design uses discrete components and is divided into many independent modules according to the different function, which has solved the conflictions between systematization and modularization in the RF communication laboratorial system. So the experimenters have an intuitionistic understanding to the radio frequency circuit and the theory. This plan combines the frequency synthesizer and the PLL in a module, which meets the performance requirements and greatly reduces system complexity and cost. In order to reduce the influence of the temperature effect, the output of the PLL should be lowered. Therefore a pre-amplifier is placed in front of the power amplifier to achieve the input requirements of the power amplifier.The paper describes the hardware design of the two modules (the amplifiers and the PLL). In the period of the design, the circuits are simulated and optimized by ADS (Advanced Design System). Based on the theory of RF amplifier including gain, stability, non-linearity and bias network, the pre-amplifier and the power amplifier are realized by discrete components, using the ADS , according to the different performance requirement of pre-amplifier and the power amplifier. Using the advantage of the MB15E03SL chip in PLL design, multi-channels design is realized in the PLL system. The frequency modulation of audio signal in 880MHz～920MHz is realized by adjusting cut-off frequency of the loop filter, which has smaller distortion and ensures the realization of the communications system.