Instant synchronous automatic gain control apparatus

An instant synchronous automatic gain control apparatus for a barcode reading device, comprising:

• a sensor unit for receiving reflected light from a barcode image resulting from projecting a light source on a barcode of an object by the barcode reading device and generating a first output signal;
• a current amplification unit for amplifying the first output signal and generating a second output signal;
• a first stage amplification unit for amplifying a voltage of the second output signal;
• a buffer stage amplification unit to control signal and gain control for synchronous processing,
• a signal pickup amplification unit for receiving the amplified signal from the first stage amplification unit to make an output variation value thereof matching a variation curve of a gain adjustment unit for achieving desired automatic gain control;
• a second stage amplification unit including the gain adjustment unit which has equivalent characteristics of a controllable resistance and uses resistance variance to adjust the amplified gain value of the second stage amplification unit for achieving desired automatic gain control;
• a third stage amplification unit for amplifying a signal output by the second stage amplification unit for getting a desired level and amplitude and output a third signal;
• a signal output amplification unit for amplifying the third signal to a desired digital signal level;
• a signal rectification unit for rectifying the digital signals amplified by the signal output amplification unit to have better up and low rim wave forms for transmitting to a microprocessor or decoder to process;
• and
• a signal isolation match unit for isolating the signal output amplification unit and signal rectification unit for preventing the signals of the two loops of the match unit and rectification unit thereof from interfering with each other.