Re: LVDS line receiver with an unencrypted SPICE model?

john larkin <jlarkin_highland_tech> wrote:

On Thu, 4 Jul 2024 21:10:20 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

boB <boB@K7IQ.com> wrote:

On Wed, 3 Jul 2024 21:49:10 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

So I have this new gig making a very low cost TDR system for soil
moisture and conductivity, for use in agriculture.  All very interesting
and topical, what with droughts and low aquifers and all.
 
As one does, I'm planning to use a fast ramp and two comparators to
generate the TX pulse and the sampling gate.  One will have a fixed
comparison voltage, and the other one's will be set by a DAC, or
possibly by a slower ramp, depending on the BOM vs performance tradeoff
we wind up with.
 
Sooo, naturally I pulled out my fave LVDS line receiver, the FIN1002.
It has nice 250-300 ps edges and pretty low jitter, comes in SOT23, and
and costs 30 cents on LCSC.
 
It even has SPICE models, but of course they're nasty encrypted HSPICE
things.
 
TI's seem to be the same.
 
Anybody got a nice LVDS receiver with a real SPICE model that mere
mortals are allowed to use?
 
Thanks
 
Phil Hobbs

 
 
Does the spec sheet say anything about how it works so that a model
could be made ?  Block diagram or something ?
 
boB
 
 

 
Too much like work—it’ll be much easier to build the circuit and measure
it. I can simulate most of the fast stuff, because it’s all discrete.
 
Thanks
 
Phil Hobbs

 
What sorts of risetimes and swings do you want?
 
I haven't used the FIN1002, but we've used several similar LVDS
receivers and all seem to work like decent RRIO comparators. You can
put an RC ramp into one input and a DAC into the other and make a
ps-resolution programmable delay.
 
I've given up on fast linear ramps... too much work. An RC with a bit
of polynomial DAC correction works great.

I’m planning to use some fast gain to sharpen up the edge, probably a
BFP740. It won’t have much chance to oscillate, so it should be fine.

You have to be a bit careful, because the prop delay depends some on the CM
voltage. It’s a bit like the offset voltage of a RRIO op amp—squirrely
things happen within a couple of V_BEs of one rail.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics