Re: 50 ohm termination

On Sun, 30 Mar 2025 03:59:47 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

Am 30.03.25 um 00:53 schrieb Phil Hobbs:

On 2025-03-19 10:41, john larkin wrote:> On Wed, 19 Mar 2025 06:23:25
-0400, Toaster <toaster@dne3.net> wrote:
 >
 >> On Tue, 18 Mar 2025 19:01:51 -0700
 >> john larkin <jlArbor.com> wrote:
 >>
 >>> On Tue, 18 Mar 2025 18:59:44 -0400, Toaster <toaster@dne3.net> wrote:
 >>>
 >>>> On Tue, 18 Mar 2025 16:02:45 -0700
 >>>> john larkin <jl@glen--canyon.com> wrote:
 >>>>
 >>>>> On Tue, 18 Mar 2025 18:29:42 -0400, Toaster <toaster@dne3.net>
 >>>>> wrote:
 >>>>>
 >>>>>> On Mon, 17 Mar 2025 19:17:13 -0700
 >>>>>> john larkin <jlArbor.com> wrote:
 >>>>>>
 >>>>>>> On Mon, 17 Mar 2025 19:50:17 -0400, Toaster <toaster@dne3.net>
 >>>>>>> wrote:
 >>>>>>>
 >>>>>>>> Thank you for the advice. In my case I have a 10Mhz signal with
 >>>>>>>> very sharp transitions (500ps, 5V) and wanted to make sure I
 >>>>>>>> did things properly.
 >>>>>>>
 >>>>>>> Interesting. What's generating the 5v signal? Lots of AC and
 >>>>>>> Tiny Logic chips are that fast, but might strain to drive 50
 >>>>>>> ohms. We use several tiny triple buffers in parallel sometimes.
 >>>>>>>
 >>>>>>> Regular thick-film surface-mount resistors are fine as
 >>>>>>> terminators at 500 ps.
 >>>>>>>
 >>>>>>> LVDS line receivers are great at the receive end.
 >>>>>>>
 >>>>>>>
 >>>>>>
 >>>>>> I used a THS3111CD. Split up my project into a timing and driver
 >>>>>> board, so i have some 50 ohm BNC cables between and wanted to be
 >>>>>> extra safe about reflections at these higher frequencies.
 >>>>>
 >>>>> Is the signal some analog thing, or a 10 MHz clock? The THS is an
 >>>>> opamp, but they can make good cable drivers too, even for clocks.
 >>>>>
 >>>>> Lately I'm enamored of BUF602, a unity-gain 1 GHz beast.
 >>>>>
 >>>>
 >>>> I had a really hard time finding a good line driver. I might look
 >>>> into this chip.
 >>>>
 >>>> Thank you!
 >>>
 >>> Is your signal analog or digital?
 >>>
 >>
 >> digital
 >
 > I use Tiny Logic triple buffers as line drivers, with all three
 > sections in parallel, and then sometimes two or three chips.
 >
 > NL37WZ16US costs 10 cents.
 >
 >
https://www.dropbox.com/scl/fi/gw7wetgtovqc04as2gxol/NL37WZ16_5V_Pulse.JPG?rlkey=2eqbyhds8l1myrzfjsrqwn5b3&raw=1
 >
 > That US8 package is nasty to solder or probe.
 >
Just rereading this.  John,  the prop delay spreads in the datasheet are
all over the place--almost a factor of 2 from typical to max over
temperature.
 
I'd expect the three sections to match OK, but paralleling packages
seems quite a lot sportier.  How well does that work in production?
 
Cheers
 
Phil Hobbs

>
This here are 2 single TI 74LVC inverters, 100 Ohms on each output,
RG174 / RG188-like Coax into the 50 Ohm of an Agilent 2.4GHz scope.
>
<
https://www.flickr.com/photos/137684711@N07/32245910240/in/album-72157662535945536/
     >    + 2 pics to the right.
>
Sorry for the blue on black trace; it is default for input 3 that
happened to be unused. Looks better if downloaded.
Having a GND/VCC pair for each output is friendlier to GND bounce
and temp rise is also smaller in comparison to multichannel gates.
>
Gerhard

What scope is that? The gate may be a tad faster.

Splitting the 50r source terminator into 100's has virtues.