[time-nuts] MT3339 chipset 10ns jitter?

[Jacques Tiete]

Hello TNutters,

maybe new thread?

you can have a look at two specsheets of the MT3339 chipset on my FTP-site
1) http://nixie.ramdac.be/TNutstuff/MT_IT530_Data_Sheet_rev_1_0.pdf    
		on page 8 "PPS output 100 ms high pulse, rising edge +/-1 μs @ full second GPS epoch..." so it states +/-1 μs
2) http://nixie.ramdac.be/TNutstuff/gtop module application note -a00 _mt3339 series_.pdf   
		on page 32 "The accuracy level of 1PPS for GlobalTop GPS module is within 100ns (same for majority of MTK GPS modules). 
					The reference design below can help improving this accuracy to within 80ns."
		but on page 14 "1PPS signal is an output pulse signal used for timing application, its electronic characteristic are listed below:
						1PPS signal and its pulse width with 100ms duration
						Low Voltage level: 0~0.4V 
						High Voltage level: 2.8~3.1V 
						Duration: 100ms (Firmware customization for duration is available) 
						Period: 1s Accuracy (jitter):10ns"

So what shall we believe?
The rest of the PDF's make a good read.

73's

Jacques




Message: 4
Date: Fri, 23 Nov 2012 16:44:27 +0100
From: Jacques Tiete <jacques at tiete.org>
To: "time-nuts at febo.com" <time-nuts at febo.com>
Subject: Re: [time-nuts] time-nuts Digest, Vol 100, Issue 95
Message-ID: <7C466C42-C05A-46E2-B3C4-793672874AC8 at tiete.org>
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About: 
{
Date: Thu, 22 Nov 2012 22:26:24 +0100
From: Fabio Eboli <FabioEb at quipo.it>
To: time-nuts at febo.com
Subject: [time-nuts] MT3339 chipset in Globaltop's FGPMMOPA6H
Message-ID: <20121122222624.71854hb9oslingcg at webmail.micso.net>
Content-Type: text/plain; charset=ISO-8859-1; DelSp="Yes";
  format="flowed"

Hello, while asking info about the FE5682,
I realized that for another project
(model plane data logging) I will buy
some cheap gps modules built around an
MT3339 chipset.
In my mind somewhere I stored the fact
that in the datasheet of these module
is mentioned the pps output, so I checked
and the manufacturer is claiming that it
has "High accuracy 1-PPS timing support
for Timing Applications (10ns jitter)"

This is the module I'm talking about:
http://www.mirifica.it/store/gps/342-globaltop-fgpmmopa6h-pa6h.html
http://www.alcom.be/binarydata.aspx?type=doc/GTop-FGPMMOPA6H-Datasheet-V0A.pdf

Has anybody used this chipset or similar for GPSDO?
I have no experience with discipled oscillators
but if there is any hope that the pps out
of these modules is good for the task maybe
it's time for me to start reading more about
the subject.
The final goal will be to check the timing
of the Rb I have around.

Thanks,
Fabio.
}

Hello TNutters,

I did some test with this module from Adafruit (http://www.adafruit.com/products/746) and it seems not a bad unit. Tested it together 
with my TBolt and the PPS seems quite stable most of the time, I did not do any logging and math on the result,
just letting the TBolt trigger the scope and apart from the cable offset I guess 80% of the time the module was 
within 10 to 15 ns. 
However the specs are not very clear and it is a typical chip for mobile use in eg. carnav stuff. I also saw some 
other specs where the jitter was specified as 100ns. and even one with a 1 microsec. so I'm a little confused.
As soon as I have some time I plan to connect this module to a BeagleBone and do some testing for an NTP server
I think the Beagle is better for this than the RaspBerry because of the "real" ethernet port.

Greetz,

Jacques Tiete
0499 99 83 78
jacques at tiete.org

Op 23-nov.-2012 om 00:19 heeft time-nuts-request at febo.com het volgende geschreven