[time-nuts] Generating a solid PPS from 10Mhz source

Bob Stewart bob at evoria.net
Wed Jan 20 16:32:57 EST 2016


Hi Poul,

Your comment about on-chip PLLs got me to wondering about the dsPIC33FJ128MC804 I'm using in my GPSDO.  So, I put it on the 5370A to see what's up.  Input to the gate port is the drive signal for an LED that I flash at 1PPS (controlled by an on-chip timer).  I delay that with a 10ft piece of RG-58 to drive the start gate.  The stop gate is driven by the OCXO output from the GPSDO.  Internally, the chip's PLL is running at 160MHz  (10MHz OCXO / 2 * 32), which is divided down to 80MHz for FOSC and then by 2 again for FCY, if you know these dsPICs.

The ADEV at 1s is about 1.7E-10, declining at about a decade per decade.  I take this to represent the jitter of the PIC's onboard RC oscillator as driven by the OCXO.

Bob



--------------------------------------------
On Wed, 1/20/16, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:

 Subject: Re: [time-nuts] Generating a solid PPS from 10Mhz source
 To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>, "Attila Kinali" <attila at kinali.ch>
 Date: Wednesday, January 20, 2016, 8:13 AM
 
 --------
 In message <20160120122824.39fb655285dd0e68c3884835 at kinali.ch>,
 Attila Kinali w
 rites:
 
 >The test results showed a quite more
 >detailed structure with few delays over
 100ps and most being between
 >20ps and
 80ps. Interestingly, some were close to 0ps, for which
 >we have no explanation good explanation.
 
 Any on-chip PLL's with
 "spread-spectrum" to fudge EMI tests ?
 
 -- 
 Poul-Henning Kamp       | UNIX



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