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precision_timing:fe_series_oscillators [2014/11/17 15:59] (current) |
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| + | ===== Notes on FE Series oscillators ===== | ||
| + | |||
| + | //On 2014-11-10 1:24 AM, Skip Withrow posted the following on time-nuts: // | ||
| + | |||
| + | Hello time-nuts, | ||
| + | |||
| + | I have spent a lot of time recently with Frequency Electronics, Inc. (FEI) | ||
| + | oscillators including the FE-5680A, FE-5680B, FE-5650A, and FE405B and just | ||
| + | wanted to pass on some of my findings. Not everything I am including here | ||
| + | is new, but figured I would include the informattion for the sake of | ||
| + | completeness. | ||
| + | |||
| + | As already known, there are a bunch of different variations on some of the | ||
| + | oscillators. Here is kind of a quick rundown: | ||
| + | |||
| + | 1. The 'old' FE-5650A - This unit used a 50.255 MHz VCXO and placed the | ||
| + | synthesizer outside the physics PLL. This unit could be programmed over a | ||
| + | wide range of frequencies and is great if you need an oddball output. The | ||
| + | digital board in the unit has the two small pushbutton switches and the | ||
| + | nearby 5-pin connector for serial communications. | ||
| + | |||
| + | 2. The 'new' FE-5650A - This unit has the same physical construction, but | ||
| + | the circuit functionalyity is quite different. It uses a 60 MHz VCXO and | ||
| + | the DDS is inside the physics control loop. The output is divided from the | ||
| + | 60 MHz. Many of these units that came from the telecom industry have 15MHz | ||
| + | output. Unit has serial communications on pins 8 & 9 of the DB-9 connector. | ||
| + | |||
| + | 3. The 'old' FE-5680A - This unit has a different physical footprint than | ||
| + | the 5650A, but virtually the same circuit. Again uses the 50.255 MHz VCXO | ||
| + | and has the programmable synthesizer that can be tuned over a wide range. | ||
| + | Circuit board has the same two push button switches and 5-pin serial | ||
| + | connector. Many of these units only have a 1pps output (they came off | ||
| + | Motorola cell boards). | ||
| + | |||
| + | 4. The 'new' FE-5680A - This was the popular, inexpensive unit that was | ||
| + | available a year or two ago. Unit uses the newer 60 MHz VCXO architecture | ||
| + | and has serial communications via pins 8 & 9 on the DB-9. | ||
| + | |||
| + | 5. The FE-5680B - This appears to be a VERY close cousin to the new 5650A | ||
| + | and 5680A. It is in the 5680 physical package, but has a compact DB-15 | ||
| + | (think VGA) connector. Unit only needs single +15V supply. | ||
| + | |||
| + | 6. The FE-405B - This is a crystal oscillator that is the same physical | ||
| + | package as the 5650A. It has a 15 MHz output. The interface is the same | ||
| + | as the FE-5650A (except no LOCK signal), including the capability to | ||
| + | communicate over the serial interface to change its frequency. | ||
| + | |||
| + | **TUNING THE NEWER UNITS** | ||
| + | |||
| + | Now for the new information. Tuning the units with the 60 MHz VCXO has | ||
| + | been published (see the FEI document that is archived in several places) | ||
| + | and uses several commands to read and write a 32-bit command value. | ||
| + | However, only the tuning sensitivity for the FE-5680A has only been | ||
| + | published that I am aware of. | ||
| + | |||
| + | FE-5680A - The tuning sensitivity of the FE-5680A is 6.8126x10E-13 for the | ||
| + | LSB. The command value runs the full range from 00 00 00 00 to FF FF FF | ||
| + | FF. The value is 2's complement with positive values driving the frequency | ||
| + | higher and negative values lowering the frequency. Larger values may | ||
| + | unlock the unit and the positive and negative values may be different | ||
| + | (depends on how well the VCXO is centered). | ||
| + | |||
| + | FE-5650A - The tuning sensitivity of the FE-5650A is 1.4900x10E-17 for the | ||
| + | LSB. Sounds great, but wait, turns out it does not have any more | ||
| + | resolution than the 5680A. It takes a 45,722 step of the command register | ||
| + | to step the DDS. So, it retains the same 6.8126x10E-13 actual minimum step | ||
| + | of the oscillator. Also, the minimum value of the control register is F0 | ||
| + | 00 00 01, maximum value is 0F FF FF FF. | ||
| + | |||
| + | FE-5680B - The tuning sensitivity of the FE-5680B is 3.7248x10E-16 for the | ||
| + | LSB. Same situation as the 5650A above, but the are 1829 counts per DDS | ||
| + | step. Minimum value is F0 00 00 01, maximum value is 0F FF FF FF, same as | ||
| + | the 5650A. | ||
| + | |||
| + | FE-405B - The tuning sensitivity of the FE-405B is in the neighborhood of | ||
| + | 1.143x10E-14. Minimum value is F7 33 33 34, and maximum value is 08 CC CC | ||
| + | CC. | ||
| + | |||
| + | ** FINDING THE RIGHT TUNING WORD** | ||
| + | |||
| + | So, if you know how far off frequency your oscillator is divide that by the | ||
| + | LSB sensitivity, convert the number to HEX, and load it to the oscillator | ||
| + | (with the right + or - sense). | ||
| + | |||
| + | Enjoy! | ||
| + | Skip Withrow | ||