"Mini Air Cooling Fan" in the master chip SPCE061A speech signal A / D converter with a dedicated conversion channels - voice analog - digital conversion channels. And set SPCE061A internal microphone and AGC amplifier section. Automatic gain control limiting section may automatically adjust the microphone volume received, such that the system will not be sending a command location of people. "Mini Air Cooling Fan" SPCE061A internal microphone preamplifier circuit mainly by the input stage, the intermediate stage, the output stage consists of three parts, the input stage uses a differential amplifier circuit, it is a microphone preamplifier major component, the difference amplifier input stage has a great advantage, can effectively suppress common mode interference input terminal, for the effective input differential signal is not generated any interference. Speech recognition signal input circuit "Mini Air Cooling Fan" of the system is shown below. C23, C24 are used as decoupling capacitors to reduce noise on speech recognition signal interference.