[time-nuts] 50 ohm Driver

John Ackermann N8UR jra at febo.com
Wed Mar 4 08:54:21 EST 2015

One comment on the parallel AC gate approach.  It may not be directly 
applicable to Martyn's issue, but there is a common confusion about the 
value of the summing resistors.

Per Tom Clark, who came up with the idea, they are *not* intended to 
provide a near-end line termination to 50 ohms, but are simply there to 
protect the paralleled devices if the gates have slightly different 
delays (in which case one gate could end up sinking the other two).

So, the commonly used 47 ohm value isn't magic.  You can use a lower 
value, and thus get more voltage at the far end.  I haven't experimented 
to see how far you can take that idea before destroying gates.

On 3/4/2015 5:26 AM, Martyn Smith wrote:
> Hello,
> A quick question.
> My output driver for a simple amplifier.
> I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm.
> I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms.
> Can anyone recommend an IC that can delivery this.
> But it needs to have similar jitter performance to the 74AC14.
> I use it up to 10 MHz.
> Best Regards
> Martyn
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