Method and apparatus for reducing bandwidth limited noise in bar code scanner
First Claim
1. 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 laser pulser coupled to the laser light source and the demodulator circuit, that controls the duty cycle of the laser light source.
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Accused Products
Abstract
A bar code scanner system includes a laser light source that periodically produces a light beam that is swept across a bar code label. The laser light source is periodically turned "on" and "off" according to a duty cycle. A detector produces a first electric signal representative of received bar code label reflected light and ambient light when the laser 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, provides a first gain to the first electric signal and provides a second gain to the second electric signal. The gains applied are selected such that the signal and signal component produced solely as a result of the ambient light will significantly cancel out one another when the signals are combined. A filter, coupled to the demodulator circuit, receives the electric signals from the demodulator circuit and reduces out-of-band signal components such as noise. When the duty cycle of the laser light source is equal to 50%, the first gain is equal to the inverse of the second gain.
119 Citations
13 Claims
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1. A bar code scanner system comprising:
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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 laser pulser coupled to the laser light source and the demodulator circuit, that controls the duty cycle of the laser light source. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A bar code scanner system comprising:
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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.
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10. A bar code scanner system comprising:
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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.
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11. A bar code scanner system comprising:
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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.
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12. A bar code scanner system comprising:
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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. - View Dependent Claims (13)
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Specification