HCTL-2032 Datasheet, PDF (14/21 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
CHA
filtered
CHB
filtered
CHI
filtered
t_E
t_E
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 resolu-
tion 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 transi-
tions 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 lead-
ing channel B results in counting up. Channel B leading
channel A results in counting down. Illegal state transi-
tions, 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
14