HCTL-2032 Datasheet, PDF (13/20 Pages) Agilent(Hewlett-Packard) – Quadrature Decoder/Counter Interface ICs

3 t_CLK
CLK
CHA
t_E
t_E
t_ES
t_ES
t_ES
t_ES
CHB
Noise Spike
CHI
t_E
t_E
CHA
filtered
CHB
filtered
CHI
filtered
Figure 12. Signal Propagation through Digital Noise Filter
Quadrature Decoder
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.
The quadrature decoder samples
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.
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
down). Figure 14 shows the
valid state transitions for 2x
and 1x decoder modes. The 2x/
1x decoder will output a count
signal at respective state
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.
clk
state
chA
chB
1
2
3
4
Tes
Te
Telp
count up
1
4
Valid State
Transitions
2
3
count
down
13