[time-nuts] Sine to LVDS

Luis Cupido cupido at mail.ua.pt
Fri Sep 9 13:54:07 EDT 2011


I had similar need some time ago and
I found that a differential pair with two (pnp) BFR93
worked much better than any comparator(three or four tested, but not the 
adcmp604).
(was a pll reference and I judged the impact of such
observing the phase noise at microwaves).

lc.
ct1dmk.



On 9/9/2011 12:29 PM, Javier Herrero wrote:
> Thanks for the reminder :)
>
> Te available 180MHz signal has that level, and it is quite heavily
> bandpass filtered, since it comes from a multiplier chain from an 45MHz
> OCXO, so the ADCMP604 will fit nicely
>
> Best regards,
>
> Javier
>
> El 09/09/2011 13:07, Bruce Griffiths escribió:
>> Javier Herrero wrote:
>>> Hello all,
>>>
>>> I think that the same question that has been discuted here a zillion
>>> times but usually around 10MHz... anyway, what would be the best way
>>> to convert a sine wave to a LVDS clock (preferably duty cycle 50%) at
>>> 180MHz?
>>>
>>> Texas Instruments suggest a LVDS receiver as a comparator
>>> http://www.ti.com/lit/an/slyt180/slyt180.pdf but time ago this was
>>> discussed here, and not very favoured due to the high hysteresis of
>>> the LVDS receivers.
>>>
>>> Regards,
>>>
>>> Javier
>>>
>> Use a true LVDS comparator (e.g. ADCMP604).
>> With 1:1 transformer coupled input and a pair of inverse parallel
>> schottky diodes across the inputs together with series resistors
>> between the transformer secondary to the comparator inputs should
>> suffice for inputs of +16dBm or more.
>> With sufficient input from a low noise source a cycle to cycle jitter
>> of 1-2ps should be feasible.
>>
>> Sub picosecond jitter is feasible if one cascades a series of low pass
>> filtered limiter stages.
>>
>> Bruce
>>
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>
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