Digitizer for barcode scanner

A method of operating a bar code scanner for digitizing an analog signal produced in the bar code scanner, comprising the steps of, in said bar code scanner:

• a) differentiating said analog signal and determining zero-crossing of the differential of said analog signal to produce a pulse output representing peaks of said analog signal;
• b) sampling said analog signal in response to said pulse output and holding the level of said sample to produce a sample-and-hold signal;
• c) subtracting said sample-and-hold signal from said analog signal to produce a first signal;
• d) comparing said first signal to a selected first threshold to produce a representation of when said analog signal has changed by an amount of said first threshold since its last high or low peak;
• e) generating a second derivative of said analog signal and detecting zero crossings of said second derivative to produce a gating signal;
• f) generating an output having transitions when said representation is active and said gating signal is active.

A method of digitizing an analog signal comprising the steps of:

• a) generating a pulse output representing peaks of said analog signal;
• b) generating a hold signal representing the level of said analog signal when said pulse output is active;
• c) comparing a selected threshold to the difference between said analog signal and said hold signal, to produce a representation of when said analog signal has changed by an amount of said selected threshold since its last high or low peak;
• d) generating a gating signal corresponding to inflections of said analog signal;
• e) generating an output having transitions when said representation is active and said gating signal is active.

A circuit for digitizing a bar code scanner signal comprising:

• a) means for generating a pulse output representing peaks of said scanner signal;
• b) means for generating a hold signal representing the level of said scanner signal when said pulse output is active;
• c) means for comparing a selected threshold to the difference between said scanner signal and said hold signal, to produce a representation of when said scanner signal has changed by an amount of said selected threshold since its last high or low peak;
• d) means for generating a gating signal corresponding to inflections of said scanner signal;
• e) means for generating an output having transitions when said representation is active and said gating signal is active.

A bar code scanner comprising:

• a) a photodetector producing an electrical signal responsive to light reflected from a bar code symbol scanned by a light beam;
• b) a digitizer circuit receiving said electrical signal and producing an output switching between a first level and a second level, the digitizer circuit generating said first level then maintaining said first level until exhibiting a change of state to produce said second level when said electrical signal exhibits an inflection after having changed in value by at least a selected threshold amount from a positive or negative peak;
• said digitizer circuit having means including a peak detector and a sample-and-hold circuit for producing an indication of said electrical signal having changed in value by at least said selected threshold amount from a positive or negative peak;
• c) a decoder responsive to said first and second outputs to recognize said bar code symbol.