[time-nuts] 1 PPS Correction Problem using DS1123LE-50, Delay Line

[Tom Wimmenhove]

Could it maybe be that you're actually writing the delay value into the
chip while the pulse is high? I've had that problem with a DS1023-100. The
solution was to wait until the pulse goes low, and then set the delay for
the next pulse.

Regards,
 Tom

On Wed, Feb 4, 2015 at 2:47 PM, Dan Kemppainen <dan at irtelemetrics.com>
wrote:

> Martyn,
>
> In working with a 6T receiver we have noticed that sometimes the reported
> offset correction is not correct. These instances appear to be infrequent,
> and have only been noted as a single instance at a time. For example you
> will occasionally get a -10.2nS correction when you should get a positive
> one, or vice versa. Simply changing the sign of the offending correction
> value appears to make it correct.
>
> This doesn't sound exactly like what you are seeing, however.
>
> Hope the info helps!
>
> Dan
>
>
>
>
> On 2/4/2015 12:00 PM, time-nuts-request at febo.com wrote:
>
>  Hello,
>>
>> I am using a LEA-6T GPS chip with the DS1123LE-50 delay line to correct
>> the
>> jitter of the 1 pps output from the GPS chip.
>>
>> The correction works very well, dropping the peak to peak jitter of the
>> 1pps
>> output from about 20 ns to < 3 ns.
>>
>> However, I randomly get a big jump of the 1 pps pulse, by many
>> millisceconds.
>>
>> After lots of research, checking code and hardware, it seems the
>> DS1123LE-50
>> chip randomly produces it's own long pulse.
>>
>> I have monitored the pulse going into and out of the delay line
>>
>> The input pulse remains constant (I can't remember exactly the pulse
>> width,
>> I think 10 us).
>>
>> But suddenly a large output pulse of many milliseconds appear.
>>
>> Some chips don't seem to have this problem.  Other chips can go wrong, 20
>> times in an hour, then run perfectly for a day or so.
>>
>> I am blaming my software guy, he is blaming the chip.
>>
>> Has anyone else used this delay line and seen anything similar?
>>
>> This chip is now apparently obsolete, but I don't want to change yet as I
>> have a few years worth of stock of these chips.
>>
>> Regards
>>
>> Martyn
>>
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