[time-nuts] Achieving maximum performance when driving 5370A/B inputs

Glenn Little WB4UIV glennmaillist at bellsouth.net
Sun Feb 28 03:55:33 UTC 2010


These were used on some measuring instruments to provide a balance 
'guarded' input.
The shield around the balanced conductors provided a ground between 
the DUT and the measuring equipment that was not connected to the input.
IIRC this was for very low level signals.

73
Glenn
WB4UIV


At 10:06 PM 2/27/2010, you wrote:
>Hi
>
>Sure never seen any of them on any gear in my junk pile.
>
>I also never seen a customer ask for them as an output connector on 
>an oscillator. I wonder how common they actually are.
>
>Bob
>
>
>On Feb 27, 2010, at 9:59 PM, Bruce Griffiths wrote:
>
> > Actually there are miniature twinax style connectors, for example:
> > 
> http://www.amphenolrf.com/products/twinbnc.asp?N=0&sid=4B8860805409E17F& 
> <http://www.amphenolrf.com/products/twinbnc.asp?N=0&sid=4B8860805409E17F&>
> >
> > Bruce
> >
> > Bob Camp wrote:
> >> Hi
> >>
> >> I don't even have the counter and already we're butchering it....
> >>
> >> The big issue is suitable twin-ax connectors and cable. I have 
> both, but they are *big*. They never really made it into the world 
> of miniature connectors and miniature cable.
> >>
> >> Shielded twisted pair would be another option. That eliminates 
> the cable as an issue. Small connectors (BNC drop in) are still an 
> issue though.
> >>
> >> Bob
> >>
> >>
> >> On Feb 27, 2010, at 9:48 PM, Bruce Griffiths wrote:
> >>
> >>
> >>> Since the input amplifier and trigger circuit are located on a 
> small daughter board it wouldn't be too difficult to replace this 
> with an LVDS to CML stage.
> >>> The only remaining isue would be what input connector to use 
> (twinax??, SATA??).
> >>>
> >>> Bruce
> >>>
> >>> Bob Camp wrote:
> >>>
> >>>> Hi
> >>>>
> >>>> Gee, LVDS what an unusual approach :)....
> >>>>
> >>>> It would be nice if these instruments had a balanced input. 
> Common mode noise is indeed an issue in a lot of cases.
> >>>>
> >>>> Of course wrapping the coax headed to the counter 10X around a 
> fairly large core can help things a bit.
> >>>>
> >>>> Bob
> >>>>
> >>>>
> >>>> On Feb 27, 2010, at 9:32 PM, Bruce Griffiths wrote:
> >>>>
> >>>>
> >>>>
> >>>>> If one is feeling paranoid about ground loop noise (and 
> wishes to avoid transformers, optoisolators , or fibre optics), etc 
> one could always use an LVDS driver with a batter powered(?) LVDS 
> to CMOS receiver/translator right at the 5370A/B input BNC connector.
> >>>>> This may be useful for a DMTD system that uses a 5370A/B.
> >>>>>
> >>>>> Bruce
> >>>>>
> >>>>> Bob Camp wrote:
> >>>>>
> >>>>>
> >>>>>> Hi
> >>>>>>
> >>>>>> AC cmos will easily drive an L pad to match a 50 ohm cable 
> at these levels. That's true at either 3.3 or at 5.0 volts. There 
> are a lot of cmos families out there that beat AC for speed and 
> match the output drive capability.
> >>>>>>
> >>>>>> Bob
> >>>>>>
> >>>>>>
> >>>>>> On Feb 27, 2010, at 9:12 PM, Bruce Griffiths wrote:
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>> 1) One method with 5V CMOS is to add a resistive voltage 
> divider at the CMOS driver output with a 50 ohm output impedance at 
> the tap that drives the 5370A/B input.
> >>>>>>>
> >>>>>>> 2) If one has a 5V 50 ohm driver (eg Thunderbolt PPS 
> output) use a 50 ohm attenuator at the 5370A/B input.
> >>>>>>> For a 5370A an attenuation of at least 11dB is required.
> >>>>>>> For a 5370B an attenuation of at least 3dB is required.
> >>>>>>>
> >>>>>>> 3) One can always use the 10x input attenuation setting 
> built in to the 5370A/B however this reduces the signal swing to 
> 0.5V at the trigger amplifier input (5V CMOS input).
> >>>>>>>
> >>>>>>> 4) Attenuate the output of the logic signal by a factor of 
> 2 and use an npn emitter follower to drive the 50 ohm load.
> >>>>>>>
> >>>>>>> 5) Use 3.3V CMOS signal levels for the 5370B.
> >>>>>>>
> >>>>>>> 6) Use a current mode emitter or source coupled switch to 
> drive the 5370A/B input.
> >>>>>>>
> >>>>>>> The switching jitter of the above drivers will be much 
> lower than the internal noise of the 5370A/B as long as HCMOS or 
> faster logic is employed.
> >>>>>>>
> >>>>>>> Bruce
> >>>>>>>
> >>>>>>>
> >>>>>>> Bob Camp wrote:
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>> Hi
> >>>>>>>>
> >>>>>>>> Which *still* carefully avoids the issue of how .....
> >>>>>>>>
> >>>>>>>> Bob
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> On Feb 27, 2010, at 8:52 PM, Bruce Griffiths wrote:
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>> Oops! a small correction (2nd paragraph):
> >>>>>>>>>
> >>>>>>>>> For the 5370A attenuating the 5V CMOS signal to a 1V 
> swing with the threshold set to 0.5V is close to optimum.
> >>>>>>>>> An input signal with limits of 0V and +1.4V with a 
> trigger threshold of 0.7V is the maximum usable (for high performance).
> >>>>>>>>> An input signal with limits of 0V and +0.3V with a 
> trigger threshold of 0.15V is the minimum usable (for high performance).
> >>>>>>>>>
> >>>>>>>>> For the 5370B attenuating the 5V CMOS signal to a 2V 
> swing with the threshold set to 1V is close to optimum.
> >>>>>>>>> An input signal with limits of 0V and +3.5V with a 
> trigger threshold of 0.7V is the maximum usable (for high performance).
> >>>>>>>>> An input signal with limits of 0V and +0.3V with a 
> trigger threshold of 0.15V is the minimum usable (for high performance).
> >>>>>>>>>
> >>>>>>>>> Thus using the PPS output (~270 ohm is series with a 5V 
> 74AC04 output) from a Synergy evaluation board that uses an M12M or 
> M12+ GPS timing receiver to drive the inputs (with a 0-750mV 
> signal) of a 5370A or 5370B is well within the recommended input 
> signal range for high performance.
> >>>>>>>>> This avoids having to adding an external 5V 50 ohm driver 
> that some would use.
> >>>>>>>>>
> >>>>>>>>> Bruce
> >>>>>>>>>
> >>>>>>>>> Bob Camp wrote:
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>> Hi
> >>>>>>>>>>
> >>>>>>>>>> So exactly how did you know that I bought a (cheap) 
> 5370B a few hours ago on the e-place  and was just about to ask 
> about how best to use it.
> >>>>>>>>>>
> >>>>>>>>>> Hmmmm.......
> >>>>>>>>>>
> >>>>>>>>>> Bob
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>> On Feb 27, 2010, at 7:01 PM, Bruce Griffiths wrote:
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>>> The attached excerpts from the 5370A and 5370B manuals 
> indicate that for best performance, that the common practice of 
> driving the 5370A/B 1x inputs directly from a 5V CMOS logic signal 
> is a bad idea.
> >>>>>>>>>>>
> >>>>>>>>>>> For the 5370A attenuating the 5V CMOS signal to a 1V 
> swing with the threshold set to 0.5V is close to optimum.
> >>>>>>>>>>> An input signal with limits of 0V and +1.4V with a 
> trigger threshold of 0.7V is the maximum usable (for high performance).
> >>>>>>>>>>> An input signal with limits of 0V and +0.3V with a 
> trigger threshold of 0.15V is the minimum usable (for high performance).
> >>>>>>>>>>>
> >>>>>>>>>>> For the 5370A attenuating the 5V CMOS signal to a 2V 
> swing with the threshold set to 1V is close to optimum.
> >>>>>>>>>>> An input signal with limits of 0V and +3.5V with a 
> trigger threshold of 0.7V is the maximum usable (for high performance).
> >>>>>>>>>>> An input signal with limits of 0V and +0.3V with a 
> trigger threshold of 0.15V is the minimum usable (for high performance).
> >>>>>>>>>>>
> >>>>>>>>>>> Bruce
> >>>>>>>>>>>
> >>>>>>>>>>> 
> <5370ATriggering.png><5370BTriggering.png>_______________________________________________
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> >>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>>
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