Re: 50 ohm termination

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
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com