Re: 50 ohm termination

On Sat, 29 Mar 2025 19:53:04 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

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

I have one product with three chips, nine gates, in parallel. But each
package has its own output resistor, so they sorta share nicely.

Seems to work. Maybe parts on the same reel match pretty well.

I'd love to have a chip that was specifically a brutal fast driver.