Hi > On Oct 22, 2015, at 3:40 AM, Gerhard Hoffmann <[email protected]> wrote: > > I'd like to design a unified VCXO Carrier Board to these requirements: > > > 1. It can host one of the the following VCXOs: > > 1.1. HP 10811A-6111 (as from 5370A) > > 1.2 Morion MV89A > > 1.3 MTI 260 > > 1.4 CV-950 > > 1.5 Timetech > > 1.6 Axtal > > 1.7 Pascall
Multiple footprints are fine and they don’t generally take up a lot of space. The 10811 is a bit of a hassle in that respect. > > > 2. It provides unified tuning: 0V = lowest possible frequency, 3V3 or 5V = > highest possible frequency, no matter of the VCXO tuning sense and range. That immediately gets you into op amps and feedback resistor stability. With a number of combinations, the required resistors can get pretty expensive. It also gets you into dual supplies with some OCXO’s. > > 3. provides a 5V tuning voltage reference for those VCXOs that don't have one > of their own. This gets you into the same sort of “is 1 ppm stability on the tuning good enough” set of questions.There are a number of OCXO’s out there that have odd reference voltages.(10 V etc) > > 4. Frequency can be adjusted from external Vtune input and from a 10 turn pot. Sounds good. Consider ground loops and offsets on the external input. > > 5.Board has 2 reference frequency inputs with LTC6957 receivers. One of them > can interface the onboard VCXO to the CPLD. I’m not sure these are needed if the destination is a CPLD. > > 6. Board has a 1pps input 3V3 CMOS level Hopefully buffered with discrete logic. CPLD’s often are not very rugged in terms of over voltage on the inputs. > > 7. It can lock the VCXO to the reference frequency or the 1pps in. Provides > LED lock indication. Probably not easily with a 64 flip flop CPLD. For a full narrow bandwidth PLL you will need some more “stuff” on the board. With a wideband loop, you will have a lot of noise on the oscillator. > > 8. It features a Xilinx Coolrunner2 2C64 CPLD, complexity 64 FlipFlops + > combin. Logic. Unused Pins are brought out to Testpoints in 100 mil grid. The > Coolrunner remembers its configuration and can be reprogrammed using the > standard Xilinx USB dongle. It has a 10 pin 2mm header for this purpose. > Small circuits can run at 200 MHz. This function exists already: > < > https://picasaweb.google.com/lh/photo/4Bpcfouj8WH0shNGIyuVUtMTjNZETYmyPJy0liipFm0?feat=directlink > > Given the number of much larger devices in the 10 to 100X larger range that are still under $10, I’d look at another device. > > 9. The Coolrunner provides a standard 1pps /20us out, maybe 10/100/1000 pps. > > 10. 2 Monoflops for 1pps LEDs in/out ok. > > 11. There are 2 output buffers that drive valid 3V3 CMOS into 50 Ohms. They > can be re-clocked to LTC6957 outputs with 1G74 flip-flops. I would dedicate a couple of discrete (sot-23 logic) buffers to the 1 pps outputs. > > 12. Unbuffered VCXO output is available on SMA connector > > 13. One additional buffered output (LMH6702/AD8009 or discrete to avoid neg. > supply). This is not meant to be a distribution amplifier. > > 14. Regulators for the voltages needed. > > 15. Requires soldering skills 0603 / sot23-5 / MSOP. No commercial interest. > Could be TAPR or DIY. With all this stuff on the board, layout will be “interesting”. Keeping it all from cross talking will be a challenge. That gets even more complex as the number of external connections goes up. The more configurations, the more things to worry about … One simple example of the above: Your OCXO: 1) pulls 3 ppm with a 5V tune. 2) has a stability over -30 to +70C of 1 ppb 3) has an ADEV at 1 second of 1 ppt That comes out to: Stability wise, that’s 10 ppt / C Tune wise you have 0.6 ppm / volt or 0.6 ppt / uV To maintain the 10 ppt/C your reference / tune voltage needs to be better than that. For instance, 5X better is a fairly common design goal in many systems. That’s 2 ppt/C from the tune. Roughly 4 uV of stability would do it. With a 5V reference the same 4uV is a 1 ppm / C reference. The same math applies to the stability of the resistors in the tune circuits and the offset drift on the op-amps. Lots to think about !!! Bob > > > I'm open to suggestions & ideas. > > regards, > Gerhard, DK4XP > > > _______________________________________________ > 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.
