Research And Application Of Ultra-Wideband High Precision ALC System RF Front-end

Signal generator is an indispensable part in the field of microwave system,which has an important impact on the performance of microwave system.However,the automatic level control system plays a major role in the signal generator,which is inextricably linked to its operating bandwidth,power accuracy,power flatness,and dynamic modulation range.In recent years,as the market puts forward higher requirements for the performance of microwave signal generator,automatic level control system has attracted more and more attention.Aiming at the needs of teaching and research project,this paper proposes an ultrawideband high-precision large dynamic digital ALC system scheme based on a new circuit architecture of "dual-coupled and dual-mixed IF signal power feedback loop".Then,the production of printed circuit board and the design of host programs are completed.Finally,the feasibility of the scheme is demonstrated through the test results.Firstly,this paper introduces the application field and classification structure of ALC system,and gives a brief overview of some typical examples.Then,according to the requirements of the project,the design specifications of the system are analyzed in detail,and various circuit structures are compared in many aspects.A scheme of ultra-wideband high precision large dynamic digital ALC system is proposed,and the rationality of the scheme is demonstrated by simulation verification and physical test of the new circuit structure and calculation of the overall signal link gain of the scheme.In addition,important components of the ALC system,like Digital attenuator,analog attenuator,power detector,amplification channel link,switch filter module,fixed attenuation network,control circuit and power supply circuit are specifically designed and deviceselected.After that,schematic diagram of the ALC system and the design of printed circuit board(PCB)are completed,as well as the design of cavity structure and the preparation of test program are completed.Finally,individual functional tests are operated on each component,and then joint function test is performed on the entire system,and analyzes the test results and offers some relevant improvement suggestions.The new circuit structure of dual-coupled and dual-mixed improves the power feedback detection mechanism.At the same time,the tacit cooperation of digital attenuator and analog attenuator greatly improves the power accuracy of output signal.Tested,the ALC system achieves the selection of output signal level in the range of-85 ~ +20 dBm,the dynamic range is extended to 105 dB,and the power flatness is ±1 dB in the frequency range of 750 MHz~6 GHz.