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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Feb 28 02:59:32 UTC 2010


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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