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

Bob Camp lists at rtty.us
Sun Feb 28 02:27:01 UTC 2010


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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