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

bruce at ko4bb.com bruce at ko4bb.com
Tue Jul 29 08:54:12 EDT 2014


I merely used the evaluation board which has a capacitively coupled input.
The transformer coupled input circuit using a 1:4 (turns ratio) step up
transformer
as depicted on the datasheet should reduce the PN floor by at least 3dB for
10MHz input.

Bruce
> On July 29, 2014 at 7:30 AM "David C. Partridge"
> <david.partridge at perdrix.co.uk> wrote:
>
>
> Bruce,
>
> 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?
>
> Regards,
> David Partridge
> -----Original Message-----
> 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
> 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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