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HMC1031

Question asked by kevbond01 on Dec 17, 2014
Latest reply on Jan 12, 2015 by dyoung1

I'm using the HMC1031 to lock a Crystek CVHD-950 100MHz VCXO to a 10MHz OCXO and it all works great, including the lock detect output.

In a new product I'm using the same circuit to lock a TVLD410 100MHz Connor Winfield VCTCXO to an optional 10MHz reference input. Because the 10MHz reference may not be present a VCTCXO is used for better frequency stability, +/- 1ppm. The circuit locks okay within the available tuning range, but the lock detect output does not go to a steady lock state. It only momentarily shows a lock condition when the 10MHz frequency is slightly changed and the tuning voltage re-adjusts.

The TVLD410 fits on the same 9x14mm footprint, and changing only the 100MHz oscillator to the CVHD-950 causes the lock output to work fine.

One difference between the two is the tuning sensitivity of the Vtune input. The CVHD-950 input is 2.5kHz/volt and the TVLD410 is 1.05kHz/volt. Both types run off a 3.3v supply. The 100MHz output level is very close to the same. I have tried unsuccessfully adjusting the loop filter values, and also filtering the 100MHz output to remove harmonics.

Anyone got any ideas? This is very puzzling.

datasheets: 

http://www.crystek.com/crystal/spec-sheets/vcxo/CVHD-950.pdf

 

The TVLD410 is not on the web. TVLD646-100 is very close:

 

http://www.conwin.com/datasheets/tx/tx161.pdf

I'll try attaching the datasheet.

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