An Audio Amplifier Circuit Applied To Security&Defending System

With the development of social economy, the demand for personal safety andproperty safety is becoming increasingly prominent. The security&defending industryhas expanded in a rapid speed as a sunrise industry. It is estimated that the industry willsustainedly grow in an average speed of15%-30%in the next few years, andindustry-wide GDP will reach300billion yuan in2020. Video surveillance has beenwidely used in the people’s production and life, and occupys a very large market sharein the security&defending industry. The integration of audio and video of surveillance isan important trend for monitor products development. Audio surveillance will bringmore extensive application, and create new value growth.In this paper, an audio amplifier circuit which can be used for audio surveillance isdesigned. The circuit has integrated automatic gain adjustment function and sounddetection function on the basis of Class AB Power Amplifier. It will easily achieve thebidirectional application, i.e. the recepted sound amplified to the digital memory, andthe signal of digital memory amplified to the speaker. At the same time it canautomatically adjust the loop-gain according to the signal to prevent the cutoff distortionand to optimize sound quality. Combination of sound detection can meet the multi-levelneeds of audio monitoring. It has characteristics of high fidelity, multi-function, widescope of application, and can adapt to the development trend of the security industryintelligence, integration and generalization.The thesis firstly introduces the research background and the developmentdirection of the audio monitoring, secondly, it reviewes the relevant knowledge of theaudio amplifiers, which is mainly about the basic principles and topology, and comparesthe advantages and disadvantages and the application range. It analyzes severalimportant indexes of power amplifier, including total harmonic distortion and powersupply rejection ratio. Then the overall function of the circuit, the topology, thesub-module functions and expected parameters for different applications are described.The four major sub-module circuit designs are completed, including preamplifier, poweramplifier, automatic gain adjustment module and sound detection module, and their functions and principles are analyzed. The simulation and verification of the circuit usedthe technologe of2um Bipolar. Finally the Hspice simulation software was applied toexam sub-circuit module as well as the overall circuit functional verification andindicator parameters, which is proved to be appropriate.