The Design Of The Large Range AGC Control Circuit In The Front-end Of Short-wave Receiver

AGC system is widely used in military radio, smart antennas, mobile terminals, multimedia, power system, digital cameras,hearing aids as a basis for component. The IF AGC circuit is the key module in wireless transceiver. This paper conducted a systematic summary of the existing AGC technology and the development process. For the short-wave receiver AGC system design requirements, it puts forward an expanded dynamic range method which uses analog tube and VGA chip cascade to achieve the wide range of the input’s signal dynamic controllability.The subject comes from a crosswise tasks "the design of module in the Front-end of short-wave receiver ",and the design of a large range of controllable AGC system is an important part of the research project,the author is responsible for the large-scale development of the AGC control circuit,in order to get a large range of input level which is controlled,the paper uses the cascade form of four FETs and a AD chip,the design reflects the innovative and unique.This paper firstly outlines the background of the thesis by describing the AGC research status of both home and abroad in this field, followed by the introduction of the principle of the AGC system and the design model of the AGC system, and then describes the structure of AGC as well as the requirements of the AGC control circuit designed for the receiver. It also conducts an AGC system structure modeling and simulation, and the system function gets a preliminary validation; Then it carries out analysis and design on each sub-circuit of the AGC system. In order to achieve short-wave receiver dynamic and enhance the stability of the system, the AGC IF amplifier adopts the cascade way by using four pairs of gate tube3SK223and a variable gain amplifier chip AD8367to increase the dynamic range of the input signal, thus enhancing its auto-gain control function. The detector circuit uses diode detectors and the voltage comparator uses the LM358M chip; then finalize the production of circuit boards, give the test methods of each indicator. Finally, it presents the test results of the AGC system modules and the whole index and analysis the test data.The test results show that:under the condition of that the receiver can receive a certain output voltage, the designed AGC circuit can get to80dB for the input signal dynamic range and lμV for sensitivity,101dBμV for receiver blocking,90dB for IF rejection radio,90dB for image rejection ratio, the test data has basically reached the design target,This designed AGC circuit basically achieves the desired results.