> > I have something of a follow up question. How good is the isolation inside > these devices (74LVC, SOT-23 package) between gates? > Maybe it's just me ... but I wouldn't trust the isolation to be good. Apart from on-die coupling, they share the same power/ground leads, however short they are. So just getting power and ground from the board onto the die, they would be corrupted by what happens in the other gate and its load (L*di/dt). Andy

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@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@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@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@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

Hi The question is always “good isolation compared to what?”. If you are expecting 180 db of isolation on a SOT-23 package at 10’s of MHz, it’s not going to happen. It’s also not going to happen with a practical pc board layout even without the SOT-23 involved. If something around 120 db is “good isolation”, then yes you can do that with a pair of the SC-70 parts and a good layout. In this case the test was at 10 MHz. Bob > On Jun 9, 2015, at 12:26 AM, Andy <AI.egrps+tn@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? >> > > Maybe it's just me ... but I wouldn't trust the isolation to be good. > Apart from on-die coupling, they share the same power/ground leads, however > short they are. So just getting power and ground from the board onto the > die, they would be corrupted by what happens in the other gate and its load > (L*di/dt). > > Andy > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.