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

Magnus Danielson magnus at rubidium.dyndns.org
Tue Jul 29 05:37:56 EDT 2014


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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