Laser scanner having analog digitizer with increased noise immunity

A digitizer for a laser scanner utilized for reading a bar code having a plurality of bar code elements, the digitizer comprising:

• a) circuitry for receiving an analog signal representative of the pattern of a target bar code;
• b) circuitry for analyzing the analog signal and generating a digital bar code pattern signal toggling between a first state and a second state, the digital bar code pattern signal being switched to the first state when a positive polarity edge of the analog signal is sensed having a magnitude exceeding a first threshold and switching to the second state when a negative polarity edge of the analog signal is sensed having a magnitude exceeding a second threshold;
• and
• c) impulse generation circuitry for generating a short duration correction impulse when a second edge is sensed wherein the second edge has the same polarity as an immediately preceding first edge and further wherein a magnitude of the second edge is greater than a magnitude of the first edge, the impulse signal being imposed on the digital bar code pattern signal and having a state opposite of a present state of digital bar code pattern signal.

A method of reading a bar code having a plurality of bar code elements utilizing a laser scanner having a laser, photodetector circuitry, a digitizer and a decoder, the steps of the method comprising:

• a) generating a laser beam by energizing the laser and scanning the beam over a target bar code;
• b) directing light reflected from the target bar onto the photodetector circuitry, the photodetector circuitry generating time-varying analog signal representative of the target bar code;
• c) inputting the time-varying analog signal of the photodetector circuitry to the digitizer, the digitizer generating:
• 1) a digital bar code pattern signal toggling between a first state and a second state, the digital bar code pattern signal being switched to the first state when a positive polarity edge of the analog signal is sensed having a magnitude exceeding a first threshold and switching to the second state when a negative polarity edge of the analog signal is sensed having a magnitude exceeding a second threshold;
• and
• 2) a short duration correction impulse generated when a second edge is sensed wherein the second edge has the same polarity as an immediately preceding first edge and further wherein a magnitude of the second edge is greater than a magnitude of the first edge, the impulse signal being imposed on the digital bar code pattern signal and having a state opposite of a present state of digital bar code pattern signal;
• and
• d) inputting the digital bar code pattern signal with imposed correction impulses to the digitizer, the digitizer determining widths of successive bar code elements of the target bar code and decoding the target bar code wherein a width of a bar code element corresponding to a duration of an interval when the digital bar code pattern signal remains in a given one of the first and second states, except that when a short duration impulse is sensed on the digital bar code pattern signal, a state of an interval immediately prior to the impulse is interpreted by the decoder to be an opposite state of the state of the interval and a duration of the interval is added to a duration of an interval immediately preceding the interval.