[time-nuts] 50 ohm drivers

[Bob kb8tq]

Hi

We have gone over CMOS 50 ohm line driving a bunch of times. Check the archives for all
of the various opinions. A quick summary:

If you are driving CMOS, the output swing does not have to hit 99% of the supply. You
can do a pretty good job with gates in parallel and no source termination. 

If you want both source and load termination *and* want 5V p-p on the load, you will
need a 10V p-p source. Good luck if that source ever gets tied to a “normal” CMOS 
input. Something made from 2N3904’s and 2N3906’s is probably your best bet (along 
with dual supplies) if *really* want to do this.

Source termination (open load) is the low power approach. Cable reflections are minimized
and you don’t use a lot of power.

===

If all you are after is sine wave signals, a pair of gates running on 5V will give you 20 dbm 
without a lot of effort. There aren’t many applications in the timing world that need more
power than that. 

Bob

> On Mar 3, 2018, at 9:17 PM, David C. Partridge <david.partridge at perdrix.co.uk> wrote:
> 
> Brice said:
> 
>> . Some fast CMOS devices (esp clock drivers) have an output R close to 50
> ohms as they are intended to drive 50 ohm source terminated transmission
> lines.
> 
> Any in particular that you'd recommend?   I need to drive a 50ohm line and a
> single gate inverter doesn't have the grunt to do so ...
> 
> Thanks
> David
> 
> 
> 
> 
> _______________________________________________
> 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.