[time-nuts] Sine to square wave converter Phase Noise
David C. Partridge
david.partridge at perdrix.co.uk
Tue Jul 29 07:30:45 EDT 2014
Thank you, that was very useful information. If I ever do a re-spin of the
divider I will likely use the LTC6957-3 or -4 instead of the ADCMP600 (I
would need interest for at least 40 boards to be able to do this at anything
like an economic price).
Will you be putting the full details of the circuit you used up on Didier's
web site? Did you use a transformer based circuit similar to Design Note
514 or just an input capacitor?
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of bruce at ko4bb.com
Sent: 29 July 2014 12:00
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Sine to square wave converter Phase Noise
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
> On July 29, 2014 at 5:37 AM Magnus Danielson
> <magnus at rubidium.dyndns.org>
> You alternate LTC7957-4 and LTC6957-4 and it is only the later that
> The LTC6957-4 has a single-stage amplifier stage input, with somewhat
> programmable bandwidth. I assume you used the 50 MHz BW setting.
> 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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