V
I
50%
INPUTS
DATA
V
O
2.5 V,
CMOS
t
PSK
CLOCK
V
I
50%
DATA
OUTPUTS
2.5 V,
CMOS
CLOCK
t
PSK
t
PSK
V
O
Figure 14. Propagation Delay Skew Waveform.
Figure 15. Parallel Data Transmission Example.
Propagation delay skew repre-
sents the uncertainty of where an
edge might be after being sent
through an optocoupler.
Figure 15 shows that there will be
uncertainty in both the data and
clock lines. It is important that
these two areas of uncertainty not
overlap, otherwise the clock
signal might arrive before all of
the data outputs have settled, or
some of the data outputs may
start to change before the clock
signal has arrived. From these
considerations, the absolute
minimum pulse width that can be
sent through optocouplers in a
parallel application is twice t
PSK
.
A cautious design should use a
slightly longer pulse width to
ensure that any additional
uncertainty in the rest of the
circuit does not cause a problem.
The HCPL-0710 optocoupler
offers the advantage of
guaranteed specifications for
propagation delays, pulse-width
distortion, and propagation delay
skew over the recommended
temperature and power supply
ranges.
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
