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

David C. Partridge david.partridge at perdrix.co.uk
Tue Jul 29 07:38:06 EDT 2014


Further to my previous post:

I note that the LTC6957 is 3.3V CMOS rather than 5V.  Do you have a
recommmendation for a level converter to 5V logic?  Would a 74AC04 using a
5V supply cope well enough in that role or is there a better solution?

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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