3 tCLK
CLK
CHA
tE
tE
tES
tES
tES
tES
CHB
CHI
tE
tE
Noise Spike
CHA
filtered
CHB
filtered
CHI
filtered
Figure 12. Signal Propagation through Digital Noise Filter
Quadrature Decoder
The quadrature decoder samples down). Figure 14 shows the
the outputs of the CHA and
CHB filters. Based on the past
binary state of the two signals
and the present state, it outputs
a count signal and a direction
signal to the integral position
counter.
valid state transitions for 2x
and 1x decoder modes. The 2x/
1x decoder will output a count
signal at respective state
The quadrature decoder decodes
the incoming filtered signals
into count information. This
circuitry multiplies the
resolution of the input signals
by a factor of one, two or four
(1X, 2X, 4X decoding)
depending on the resolution
mode. When using an encoder
for motion sensing, the user
benefits from the selectable
resolution by being able to
provide better system control.
transition, depending on the
counting direction. Channel A
leading channel B results in
counting up. Channel B leading
channel A results in counting
down. Illegal state transitions,
caused by faulty encoders or
noise severe enough to pass
through the filter, will produce
an erroneous count.
Figure 13 shows the quadrature
states of Channel A and
Channel B signals. The 4x
decoder mode will output a
count signal for every state
transition (count up and count
clk
count up
1
2
3
4
1
state
chA
Valid State
Transitions
4
2
chB
Tes
Te
3
count
down
Telp
13
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