* *Interesting. There are some Hittite D type flip flips that spec out at 13Ghz and 18-22ps rise/fall times with 'deterministic jitter' of 2ps, and a T type that tops out @26Ghz. Not cheap I'm sure, but we shall see.
I've posted a preliminary specification on the Open Counter google group. The goals are ambitious and I have no clue how to meet some of them, but I'm sure someone will have an opinion. :) http://groups.google.com/group/opencounter?lnk=srg&hl=en&ie=UTF-8 Take a look, shoot some holes in it, figure out how to get it accomplished, accept a module to design. I'm volunteering to be the project manager and design contributor. I'll make some totalitarian, fascist decisions too. :) Bob ** On Sun, Dec 19, 2010 at 8:18 PM, Richard H McCorkle <[email protected]> wrote: > Ho Ho Ho, > > Tis the season once again for giving and I wrote this up to give some > suggestions to the discussion. The PICTIC II was a spin-off of a GPSDO > front end designed specifically for low cost, low parts count, amateur > construction, and 1ns resolution to equal the performance of a modern > GPS receiver. It was intended for long term monitoring of a frequency > standard against GPS to free up your commercial counter for other uses. > I made the design and code public to educate others in the basics of > interpolating counter design with the hope that they would become > inspired to improve the design further. There is a case of diminishing > returns trying to achieve higher TIC resolution using faster clock > rates. A 1 GHz timebase only provides 1ns resolution, so some form of > interpolation is generally required for TIC resolutions better than > 1ns. > The current discussion on counter requirements is very educational > as I went through a similar process before adapting the GPSDO front > end to a stand-alone project. Most users have a 10 MHz source available > so this was selected as the default timebase. When it was developed the > AC CMOS family was chosen as the successor to the HC family with the > idea that later devices would become available with similar pin-outs, > but within a year of its design the AC175 became unobtanium in a DIP > package illustrating the obsolescence problem. The PIC solution may > not be well liked by many members here but versions of the PIC should > be available for many years to come and the assembly code can easily > be ported to later devices as the older ones become obsolete. With an > external prescaler reducing the clock into the PIC to a rate below > 16.6 MHz all the other counter functions can be implemented within > the PIC for as many digits as required. The PIC includes a serial > UART that can be converted to RS422 or RS-232 to feed a USB dongle > or LAN adapter, and the PIC TX/RX lines can be optically coupled to > feed the interface device as required. > The PICTIC II was modeled after the SR620 counter but simplified > to meet the less stringent 1ns requirement for GPS monitoring and to > reduce the size and cost. The principles of the PICTIC design can be > applied to a higher resolution counter with the major issues being > switching speed, noise, and the interpolator used. Testing has shown > the original PICTIC, the PICTIC II, and the PICTIC+ (12-bit ADC) > versions all provide roughly the same 650ps resolution regardless > of the timebase rate used. This implies the actual resolution is > primarily limited by the switching speed of the AC series CMOS logic > used in the front-end and the noise produced. The AC74 D-F/F has > propagation delays in the 3.5 to 10ns range so achieving 1ns TIC > resolution using AC series logic is pushing its limit. > If 100ps TIC resolution is desired the front-end logic and prescaler > can be changed to ECL, a faster timebase can be used, and an ACAM > TDC-GPX can be used for the interpolator. Going to ECL requires split > supplies increasing the cost, but if we are talking a target cost of > $750 instead of the original $50 target, going to ECL logic with > ECL-TTL converters feeding the PIC, using dual supplies, and adding > a $30 interpolator are no longer issues with the higher target cost. > Once the decision is made to use ECL logic for the prescaler and > front-end you have lower signal levels with balanced clock and data > lines to reduce the noise, and the MC100EL51 D-F/F propagation > delays are in the 385 – 565ps range for 10x or better resolution. > The Wavecrest DTS-2075 uses a similar front end implemented in ECL > and the patent document http://www.freepatentsonline.com/6226231.pdf > provides sufficient detail to duplicate their interpolators and > front-end for the two channels required. This can get you in the > area of 10ps resolution with the potential of slightly better if > their 14-bit ADC is replaced with a 16-bit ADC. Currently this > seems to be the state of the art in commercial designs so further > improvement beyond this will be a challenge only a dedicated > Time-Nut can appreciate. > The Wavecrest front end and interpolator could be utilized with > the PICTIC with minor modifications to the code, as the designs are > similar. An external 16-bit ADC like the LTC1865 could be used to > read the interpolators. An ECL prescaler like the MC10H016 would > allow a 200MHz timebase with 12.5 MHz feeding the PIC. An MC100EL05 > could be tied to the second synchronizer outputs of both channels > to generate the counter gate. At the end of sample the counter is > stopped, so the low 4 bits of the counter can be read thru an > MC10H601 ECL-TTL converter into the PIC. While these are only > suggestions for a possible system they illustrate what could be > done to increase the resolution of a design similar to the PICTIC. > > Happy Holidays > > Richard > > >> That's kinda my point about using rs232. Serial to USB, serial to Ethernet >> adaptors will be available for a good long while. >> >> Also why I like the idea of a standalone instrument that also has a pc interface of >> some sort. Or a slot for a pc interface of whatever source I want. >> >> So how does one build the core counter with a start, a stop, and maybe a 10 MHz >> reference input with sub 5ps resolution and accuracy? >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
