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SBAS253E − MAY 2003 − REVISED JULY 2006
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3.8.2 Digital Noise Filter
A digital noise filter rejects noise on the incoming quadrature signal. The digital noise filter rejects large, short
duration, noise spikes; false counts, triggered by noise or spikes, are also significantly suppressed. See
Figure 1−24.
CNTA1
Clk
QD QD QD QD
Clk Clk Clk
Clk
FiltA1
CNTB1
Clk
QD QD QD QD
Clk Clk Clk
Clk
FiltB1
CLK
CLK
Figure 1−24. Digital Noise Filter Block Diagram
The input signals, Cnt
XY
, are sampled on the rising clock edge. Before the signals are passed to the state
machine, the signals must be stable for a minimum of three consecutive rising clock edges. Pulses shorter
than two clock periods are rejected; glitches between rising clock edges are also ignored. See Figure 1−25.