Reseach On Ultra-wideband Large Dynamic Range Automatic Level Control System

To meet the diverse requirements of power and stability in electronic systems, the automatic level control(ALC) systems have been widely used. Based on platforms and equipment requirements of department, this thesis designs the scheme of a broadband, large dynamic ALC system for frequency synthesizer, and complete the relevant circuit design andimplementation.In this thesis, the development and application of ALC system is briefly described. After a detail analysis of system metrics and comparing a variety of circuit structure, a wideband high dynamic ALC system solution is proposed and calculated carefully. For the system requirements, a wide range of device selection is done, then those devices is specifically designed and manufactured to achieve the various system components, to complete the operating bandwidth of 0.5~4GHz, output power of +10 dBm ~-60 dBm, flatness of ± 0.5dB, the power resolution of 0.5dB systems. After all, the improvements method is proposed based on tested information.Main work of this thesis: for the closed-loop and open-loop control, analyzing their strengths and weaknesses, while the closed-loop achieves the stability, and open-loop achieves large dynamic range. With the use of linear interpolation algorithm, building the reference table, it would be able to meet a wideband, precise control of large dynamic range signal, and make the circuit component performance requirements flexible. Based on amplifier theory, simulation software, designing a wideband low noise amplifier with FET, its structure is combining negative feedback with lossy matching. This structure provides an extended operating bandwidth of the circuit and stability. Within the operating band, amplifier gain is 10 dB, gain flatness <± 1dB, noise figure <2.8dB. Based on microstrip line theory and simulation software, designing a 20 dB wideband coupler, and a variety of coupler structure and design methods are compared and discussed, by using an algorithm, a rapid design method of cascaded coupler is presented. Referring to the device manual, programmable attenuators, broadband MMIC amplifier, power detector, large step attenuator is designed, all components meet the design goals.