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.
The TVLD410 is not on the web. TVLD646-100 is very close:
I'll try attaching the datasheet.