| 摘要 |
An amplifier (5) within a bar code reading system provides a plurality of selectable amplification gain levels for increasing the size of the signal received by a digitizing element (6). A processor (10) is programmed to select the gain level. The system has a light source, preferably a laser diode, and a laser diode circuit (1), which provides accurate setting by the processor of the laser optical power output. The laser diode is calibrated according to each selected gain level of the amplifier such that the system can scan within a desired range of distances from the system to a bar code. The system successively scans a bar code, with each scan being at a different amplification level. In the aternative, a signal size detector (16) provides a signal representative of the size of the signal to the digitizer.
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