The key is the total number of samples added together. Adding together 5 groups of 125 measurements each works as well as taking 625 measurements and gives 100ps LSB resolution. Averaging 5 groups of 125 measurements is the same as 125 measurements and gives an average with 0.5ns LSB resolution
Enjoy! Richard ----- Original Message ----- From: "Glenn" <[EMAIL PROTECTED]> To: "Richard H McCorkle" <[EMAIL PROTECTED]>; "Discussion of precise time and frequency measurement" <[email protected]> Sent: Sunday, August 13, 2006 10:58 AM Subject: Re: [time-nuts] TIC232 Detailed Operation > > I've never programmed a PIC, nor do I know much about TI measurements. > But, if you wanted 100 ps resolution, would it make sense to average five > 125 samples? > > thanks, > glenn > > Richard H McCorkle wrote: > > >By selecting a known sample time for the XO speed used, the LSB > >of the displayed data has a known time value. By default the 60-second > >sample period gives an LSB of 1.04ns. No dividing by the sample time > >or other scaling needs to be done to the count displayed, it is already > >scaled by the XO speed and sample time used. By changing the > >sample time to calibrate the reading, the count can be scaled to read > >directly. For instance, accumulating 625 samples with a 16 MHz XO > >speed would result in a count with an LSB of 100 ps. Since the Simple > >Time Interval Counter only goes to 256 samples, averaging 250 samples > >would give an LSB of 0.25ns and an output count displayed once every > >4:10. An LSB value of exactly 1ns would require 62.5 seconds per > >update. Because partial sample times aren't allowed, a 60-second > >value was chosen as default giving an LSB of 1.04ns and an output > >count displayed once per minute. > > > > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
