Appeal No. 1999-1345 Page 2
Application No. 08/482,556
the dark bars, a detector in the reader can discriminate
between the two types of bars. Information contained in the
symbol is then extracted by a signal processor in the reader.
In a bar code reader, discriminating automatically
between detected signals of higher and lower frequency is
desirable. Figure 10 of the appellants’ specification shows
two bar code symbols, one above the other. The bars of the
upper symbol are narrower and more closely spaced than those
of the lower symbol. Given the same scanning speed for both
symbols, transitions from light to dark occur at a higher
frequency in a signal detected from the upper symbol than in a
signal detected from the lower symbol. Consequently, the
upper symbol produces a higher frequency detected signal than
the lower symbol.
The invention at issue automatically discriminates
between the higher and lower detected frequencies. Between a
detector and processor, a differentiator is coupled to a low-
pass filter of a selectable bandwidth. The bandwidth is
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