Q
We want to use the DLD as our lock alarm, but the datasheet suggests it might
not work properly if the reference disappears.
The PLL does not automatically recover if you enable the "loss of reference"
detection circuit that is required to get a proper lock alarm. Any ideas how
to overcome this?
A
The lock detect on the AD9510/11 is essentially the same as our ADF4xxx PLLs.
It only detects a lock or unlock condition.
For the lock detect indicator to operate correctly, a reference must be
present. If the reference clock disappears, then the lock detector won’t detect
that you have gone unlocked. This is documented on page 32 of the AD9510
datasheet.
The AD9516/17/18/20/22 have been improved to provide a lock detect indicator
that will work properly even when the reference goes away.
The AD9510/11 have an early implementation of a holdover solution that
tri-states the charge pump. However this circuit does not self reset like the
AD9516/20/22 do – these later products use an entirely different holdover
circuit.
I believe that the only way to have a fully functional DLD (one that indicates
unlock when the reference disappears) on the AD9510 is to use the analog lock
detector with the associated external circuitry.
