| 摘要 |
<p>An optical target is acquired by an optical scanning system according to an in-band target frequency in an input signal from an optical scanning device. Both the in-band energy level and the out-of-band energy level of the input signal from the optical scanning device are determined. These two energy levels are compared and a possible detection of the target is determined according to this comparison. A minimum threshold of in-band energy is required in order for the possible detection to be confirmed. The input signal may have various frequencies due to various amounts of magnification of the acquisition target as scanned by the optical scanning device. Thus the input signal may represent the target as various frequencies due to the various amounts of magnification. The various amounts of magnification of the acquisition target are due to various scanning distances between the scanning device and the acquisition target. Magnification compensation is therefore performed by providing an amount of frequency shifting of either the center frequency of a filter or the input signal frequency. The amount of frequency shifting is determined according to scanning distance. The frequency shifting is accomplished by performing digital-to-analog conversion on the digital input signal at a fiexed frequency. The output of the digital-to-analog converter is applied to an analog-to-digital converter where the analog signal is resampled at a varying resampling frequency. When the resampling frequency differs from the sampling frequency the signal is frequency shifted. Alternately, the resampled signal may be buffered and clocked out, in which case the frequency of the input signal is effectively shifted. In order to vary the amount of frequency shift according to the scanning distance, the resampling frequency applied to the analog-to-digital converter is varied according to the scanning distance. The relationship between the various resampling frequency and the varying scanning distances may be selected to cause the various input frequencies representative of a scanned acquisition target to be shifted to a single predetermined fundamental frequency.</p> |
