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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Feb 28 02:12:34 UTC 2010


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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