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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.
 + 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.
 + 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
precision_timing/fe_series_oscillators.txt ยท Last modified: 2014/11/17 15:59 (external edit)
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