what is the output drive circuit and what is the drive
level / source impedance from the Thunderbolt?
Greg
On 3/24/2011 2:10 PM, Hal Murray wrote:
I'm not sure everything can handle the 10Mhz signal.
Bingo.
LM339 (National data sheet)
Response time: 0.5 us
CD4049B/CD405B (from TI data sheet)
Rise time is 80 ns
Fall time is 30 ns
Those are typicals at 5 V with a 5V input signal.
The LM399 says "low power" which usually means low speed.
I occasionally go "oops" when I sanity check the speed on a circuit I'm about
to build using HC/LS parts. They aren't very fast, and the old 4000 logic is
even slower.
10 MHz is about the corner for HC. I use the HC163 (4 bit binary counter) as
an example. It has a max clock frequency of 25 MHz, so you think "no
problems" at 10 MHz. But the setup times are 30-40 ns and the clock-out are
40-50 ns so doing anything interesting at 10 MHz gets tight.
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