[time-nuts] Performance of 74LVC series ICs

Hal Murray hmurray at megapathdsl.net
Tue Jun 9 03:40:19 UTC 2015

watsondaniel3 at gmail.com said:
> Let's say I have a 20MHz TCXO. I want to square up the output signal and
> divide by two. Easy, just a buffer or inverter and a flip flop. But looking
> at the pinout of the 74LVC1G175 (D flip flop) it doesn't have a Q not
> output. So now I need a second inverter to make it toggle. The 74LVC2G14
> includes two schmitt inverters in the package, but will isolation inside the
> device be good enough to use it for two separate functions at 20 and 10 MHz?

The simple answer is to use the 74LVC1G74 which has the inverted output.

The complicated answer is more complicated.  What are you using the inverter 
for?  Clock or data?  If both halves are used for data and there is plenty of 
setup/hold time, then the timing through the chip doesn't matter.  If you are 
using it for a clock, then things get interesting.  Is there a fixed phase 
between the 2 signals?  If they never change at the same time, it probably 
doesn't matter.  (How close counts as "same" might get interesting.)  If they 
do, how nutty are you feeling?  If it mattered, I'd probably do something 
else.  The simplest something-else is to use 2 packages.

These are my opinions.  I hate spam.

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