01-05-2012, 10:36 AM
Pseudo-Random Sequence Generator
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The use of a shift-register with XNOR feedback will yield a pseudo random sequence of numbers. If an n-bit shift register is used, the sequence is 2n-1 where the state of all one’s is excluded.
The schematic for this pseudo random sequence generator is shown in Figure 1. This diagram shows the most common configuration with two taps. To reach a maximal length sequence sometimes 3, 4 or 5 taps are required. See Table 1 for the taps that give maximal length pseudo random sequences. Note when the shift register is powered up the content is all zeros. By using the exclusive-NOR the sequence is self starting.