Method and apparatus for reducing bandwidth limited noise in bar code scanner

A bar code scanner system comprising:

• a laser light source that periodically produces a light beam that is swept across a bar code label, the laser light source being periodically turned "on" and "off" according to a duty cycle;
• a detector that produces a first electric signal representative of received ambient light and light reflected from the bar code label when the light source is "on" and produces a second electric signal representative of received ambient light when the light source is "off";
• a demodulator circuit, coupled to the detector, that provides a first gain to the first electric signal and provides a second gain to the second electric signal;
• and
• a filter, coupled to the demodulator circuit, that receives the electric signals from the demodulator circuit and reduces out-of-band-signal components,
• wherein the demodulator circuit includes first and second amplifiers, connected in parallel, respectively having first and second gains.

A bar code scanner system comprising:

• a laser light source that periodically produces a light beam that is swept across a bar code label, the laser light source being periodically turned "on" and "off" according to a duty cycle;
• a detector that produces a first electric signal representative of received ambient light and light reflected from the bar code label when the light source is "on" and produces a second electric signal representative of received ambient light when the light source is "off";
• a demodulator circuit, coupled to the detector, that provides a first gain to the first electric signal and provides a second gain to the second electric signal;
• and
• a filter, coupled to the demodulator circuit, that receives the electric signals from the demodulator circuit and reduces out-of-band-signal components,
• wherein the demodulator circuit includes a digital circuit, and
• wherein the demodulator circuit includes first and second digital gain elements respectively having the first and second gains.

A bar code scanner system comprising:

• a laser light source that periodically produces a light beam that is swept across a bar code label, the laser light source being periodically turned "on" and "off" according to a duty cycle;
• a detector that produces a first electric signal representative of received ambient light and light reflected from the bar code label when the light source is "on" and produces a second electric signal representative of received ambient light when the light source is "off";
• a demodulator circuit, coupled to the detector, that provides a first gain to the first electric signal and provides a second gain to the second electric signal;
• a filter, coupled to the demodulator circuit, that receives the electric signals from the demodulator circuit and reduces out-of-band-signal components;
• and
• a transimpedance amplifier, coupled between the detector and the demodulator circuit, that converts current of the electric signals to voltage.

A bar code scanner system comprising:

• a laser light source that periodically produces a light beam that is swept across a bar code label, the laser light source being periodically "on" and "off" according to a duty cycle;
• a detector that produces a first electric signal representative of received ambient light and light reflected from the bar code label when the light source is "on" and produces a second electric signal representative of received ambient light when the light source is "off";
• an ADC, coupled to the detector, that respectively converts the first and second electric signals to the first and second digital words;
• a digital circuit, coupled to the ADC, that provides a first gain to the first digital word and provides a second gain to the second digital word;
• a digital filter, coupled to the digital circuit, reduces out-of-band signal components of the digital words;
• and
• a DAC, coupled to the digital filter, that converts the filtered words to an analog signal.