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

[bruce at ko4bb.com]

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