Research On Ultra-band Large Dynamic Range Automatic Level Control Technology

In recent years, with the frequency range and the power range of television, radio,communication, radar transmitter, signal source and varies of measuring apparatuses have been becoming larger and larger, the demand on automatic level control(ALC)system is more and more rigid. Based on the requirement of research, after comparing advantages and disadvantages of different kinds of ALC schemes, this thesis makes new research and exploration on ALC system.Firstly, the thesis introduces the concept, principle, application background and development situation of ALC system. Then the metrics the system is given. And after it is analyzed, a scheme of combination of analog ALC loop circuit and digital power extension circuit is proposed. The ALC loop circuit is designed with analog circuit, the control and the power extension circuit is designed with digital circuit. The devices of circuit are selected after the scheme is made. In order to validate the viability of the design, the power level of each node of system is estimated. Based on RF theory,simulation software, each stage of sub-circuit is simulated and devised, including an ultra-band low noise amplifier, a broadband MMIC amplifier, an ultra-band asymmetric multi-element coupler, a voltage variable attenuator, digital attenuators, a power detector,a voltage comparator, a phase inverter, an MCU, a level converter, an E2 PROM, a DAC and power source circuits. Besides, both the tabling program and the power setting program are written and compiled. For the purpose of minimizing the electromagnetic interference and leakage, a aluminum shielding box is also designed and processed.After the completion of the design and processing, every stage of sub-circuit is tested and debugged. Then the whole system is tested. Finally, this thesis designs a ultra-band large dynamic range automatic level control system rooted on combination of analog ALC loop circuit and digital power extension circuit. The system covers frequency of 500MHz~3GHz, with the input power dynamic range 0dBm~+13dBm,and the output power dynamic range-60dBm~+10dBm. The flatness is ±1dB, and the power resolution is 0.5dB. The tested results well satisfy the designing requirements,which proves that the theory analysis is basically correct, and the design is successful.