[time-nuts] Sine to square wave converter Phase Noise

Magnus Danielson magnus at rubidium.dyndns.org
Tue Jul 29 10:12:11 EDT 2014


Hej Bruce,

Many thanks for the clarification!

This could be an alternate input stage to the TADD-2 too.

Cheers,
Magnus

On 07/29/2014 12:59 PM, bruce at ko4bb.com wrote:
> Sorry, I meant the LTC6957-4 of course._SELA = l
> FILTA = L
> FILTB = H
> ie an input stage BW of 160MHz as recommended for a 10MHz + 10dBm input.
>
> Input for the HX4210 was +14dBm.
>
> Comparator was that used in David Partridge's programmable divider (includes the
> 74AC04 buffers).
>
> Bruce
>
>> On July 29, 2014 at 5:37 AM Magnus Danielson <magnus at rubidium.dyndns.org>
>> wrote:
>>
>>
>> You alternate LTC7957-4 and LTC6957-4 and it is only the later that exists.
>>
>> The LTC6957-4 has a single-stage amplifier stage input, with somewhat
>> programmable bandwidth. I assume you used the 50 MHz BW setting.
>>
>> Cheers,
>> Magnus
>>
>> On 07/29/2014 10:55 AM, bruce at ko4bb.com wrote:
>>> Recently I have been comparing the phase noise of the HOlzworth HX4210 and
>>> the
>>> LTC7957-4.
>>> I have found that the performance of these devices is comparable with a
>>> 10MHz
>>> sinewave input with a PN noise floor below -160dBc/Hz.
>>> For offsets below 100Hz the LTC6957-4 is quieter and for offsets below 50Hz
>>> or
>>> so is lower than that of my measurement setup.
>>> I merely mounted the LTC evaluation board in a diecast metal box to reduce
>>> the
>>> effect of air currents on the LTC7957-4 and used an ultra low noise 3.3V
>>> power
>>> supply (Abracon) to minimise the power supply contribution to the measured
>>> phase
>>> noise.
>>> Achieving a phase noise performance equal to that on the datasheet was
>>> relatively easy.
>>> In fact for low offsets the phase noise is lower than that shown on the
>>> datasheet.
>>>
>>> I've also measured the phase noise of a comparator based sine to CMOS
>>> converter
>>> and its PN floor is about 20dB higher than that of the LTC6957.
>>> On completion of measurements PN plots for the various sine to square
>>> conveters
>>> tested will be added to the web pages I maintain on Didiers site..
>>>
>>>
>>> Bruce
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