1) I like Doug Smith's approach, with appropriate amp even larger than
1k resistor could be used -- watch your input RC time constant
2) an alternative -- treat your LVDS line as a transmission line and use
an RF "tap" -- this is a quarter wavelength conductor parallel, nearby
-- which couples by the E&M field -- although this is best suited to
narrow-band analog signals, it could work well for a clock line -- the
dis-advantage - more complicated -- the advantage - you can separate
forward going and backward going signals and check both
The tap approach has been used by HAMs &c for decades -- there should be
plenty of design info freely available -- but the complication is
unnecessary unless you need to separate the signals propagating in the
two directions ...
Sincerely
Kevin G. Rhoads
On 2/12/2016 4:18 PM, Doug Smith wrote:
Hi Charles and the group,
Could you use a 1000 Ohm resistor to tap the signal and feed it to the
input of a gate where you have biased the gate so a small variation
(attenuated signal from resistor) will get "amplified" to a digital
signal. I call this "digilog" design. You would be, in some sense, be
building a ~20X scope probe.
BTW, LVDS is very prone to corruption from ESD like noise. Balanced
signals from solid state devices provide no protection for impulse
immunity, just emissions help, small amplitude noise help, and small DC
offset help.
Doug
On Fri, 12 Feb 2016 20:45:29 +0000, "Grasso, Charles"
<Charles.Grasso@xxxxxxxxxxxx> wrote:
Hello,
We need to use a high speed clock from our mother board to enable------------------------------------------------------------------
a functional check circuit. One of the obvious constraints is that
the signal "tap" is not permitted to change the signal in any way.
One solution would be to use opamps (which have a high z input) however
I cannot seem to find a solution that is fast enough. (The signal is LVDS
based and the spec says the 20-80 rise time min is 500ps running at 200MHz)
My initial thought is that I would need a gain/bw product of around 1GHz.
Does this august body agree?
That being the case - would someone be so kind as to point me at a part that
might work?
Best Regards
Charles Grasso
Compliance Engineer
Echostar Communications
(w) 303-706-5467
(c) 303-204-2974
(t) 3032042974@xxxxxxxxx<mailto:3032042974@xxxxxxxxx>
(e) charles.grasso@xxxxxxxxxxxx<mailto:charles.grasso@xxxxxxxxxxxx>
(e2) chasgrasso@xxxxxxxxx<mailto:chasgrasso@xxxxxxxxx>
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