[time-nuts] Performance of 74LVC series ICs

[Bob Camp]

Hi

The isolation in the package is likely better than the (practical) layout you will
do to mate up with them. In fact, the single gate stuff probably does a better job
of isolation than the multi gate stuff, simply because you can spread it out on 
the board.

In the case of dividing by two, there are single gate flip-flops that are Q bar output 
rather than Q. That eliminates the second single gate package in this design. Yes, there
are far to many different numbering systems. Finding this or that can be a massive
pain. 

======

If power is an issue, the real trick is to find a family that is happy running on a low(er)
supply voltage. Some of this stuff will toggle at 20 MHz with very low supply. Often 
the inputs are “high voltage tolerant” even with those low supplies.

Bob

> On Jun 8, 2015, at 8:30 PM, Dan Watson <watsondaniel3 at gmail.com> wrote:
> 
> I have something of a follow up question. How good is the isolation inside
> these devices (74LVC, SOT-23 package) between gates?
> 
> 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?
> 
> Just from a layout perspective using three devices instead of two would be
> easier. However the thing will be battery powered, so I'd like to save the
> power if possible.
> 
> 
> Thanks
> 
> Dan
> 
> On Mon, Jun 1, 2015 at 6:13 PM, Andy <AI.egrps+tn at gmail.com> wrote:
> 
>> The gates on that page
>> 
>>   http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html
>> 
>> use bipolar transistors.  The 74LVC parts are CMOS.  There are various
>> effects caused by that difference.
>> 
>> And those examples have vastly inferior control over input switching
>> levels, compared to just about any well made digital IC from the last half
>> century.  (Funny to think that it has been half of a century!)
>> 
>> 2N2222 type transistors might have switching delays upwards of 100 ns
>> (depending on load), whereas the LVC parts switch in the 1-5 ns range.
>> 
>>   "On the other hand: A well designed discrete circuit can beat a general
>>    purpose integrated circuit in almost all performance measures."
>> 
>> Some performance metrics would be hard to beat with even a well designed
>> discrete circuit.  On-die capacitance and inductance tends to be much
>> smaller than any discrete circuit can achieve.
>> 
>> Andy
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.