Signal conditioning for variable focus optical reader
US6047894A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Oct 26, 1995 |
| Grant date | Apr 11, 2000 |
| Priority date | — |
| Expiry date | Oct 26, 2015 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06K7/10851
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
A method and apparatus for conditioning an input signal from an optical detector includes a controller for dynamically modifying adjustable delay elements connected to the input signal, thereby modifying characteristics of the signal conditioning circuitry. The method and apparatus determines the transitions between binary levels of an input signal such as a scanned bar code label by detecting zero crossings of an approximated second derivative of the input signal. Samples of the input signal are obtained by using delay lines, sample-and-hold circuits, an analog shift register or similar device. The first derivative of the signal is approximated by the slope of a straight line between two sampled points on the waveform. The second derivative is approximated by the difference between two first derivatives. Zero crossings of the second derivative indicating transitions of the input signal may be determined either by detecting a signal peak on both sides of the zero crossing, or by comparing the second derivative signal to zero when the first derivative exceeds a positive or negative threshold. The amount of shift in the zero crossings may be estimated by measuring relative amplitudes…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.