The invention relates to a device for reading coded information, comprising illumination means, means for picking-up a luminous signal diffused by an illuminated support containing coded information, means for detecting the luminous signal intended to generate an electrical signal that is proportional to said luminous signal (for example, an electrical signal with an amplitude variable, along at least one reading direction, between at least one maximum value Vmax and at least one minimum value Vmin), and means for processing said electrical signal, intended to extract the information content from it. The device further comprises means for varying, preferably point by point, the amplitude pattern of said electrical signal along said at least one reading direction so as to generate an electrical signal having a predetermined amplitude pattern, for example, substantially constant. Preferably, said means for varying the amplitude pattern of said first electrical signal comprises amplifying means with a gain variable according to a variation law substantially inverse with respect to the variation law of said first electrical signal. At each scan, such device compensates the typical amplitude variations of the detected electrical signal, caused by the intrinsic operation characteristic of the illumination and detection means, thus increasing the reliability of the performed reading.
A ramp generator includes a resistance ladder supplied with a constant current. Switches are closed in sequence by a shift register to provide a stepped ramp output. The constant current is controlled by referencing an on-chip bandgap voltage that is used as an input to a feedback circuit controlling current through a reference resistor ladder.
A method for processing a digital signal obtained in a barcode reading operation comprises a step of applying a wavelet transformation to the digital signal. The noise threshold at each level of the wavelet transformation is determined from a total transfer function in the analogue processing stage, and the coefficients are set to be zero if less than the noise threshold.
A barcode scanning system is provided, which comprises an amplitude compensation circuit to change the amplitude of signals corresponding to each location on the barcode such that all the signals have the same amplitude. The changing of the amplitude may be determined according to an angular position or an oscillating velocity of an mirror. Preferably, the cutoff frequency of a low pass circuit in the barcode scanning system is variable according to the oscillating velocity or the angular position of the mirror too.
A method and system used in the barcode sensing process are disclosed, in which at least two instances of an optical signal are obtained from the same barcode in different time periods, and digitized by a first digitizer with a first threshold. The digitized results from the at least two instances are then applied with an AND algorithm to eliminate the noise, whereby create a correct digitized output. Preferably, the instances of the signal are also digitized by a second digitizer with a second threshold, which are used to synchronize the timing of the digitized results created by the first digitizer. The second threshold is preferably larger than the first threshold.
