Hello everyone,
I am working with the ADF4377 in manual VCO calibration mode (auto calibration disabled). I manually program the VCO core band and VCO bias settings.
My procedure is as follows:
- I first allow the device to lock at a given frequency.
- I read back the VCO core band and bias register values.
- I store these values.
- When switching frequencies, I write the stored core band and bias values back to the registers.
- I then command the PLL to lock to the new frequency.
In most cases, the PLL locks successfully and operates as expected.
However, I am observing an intermittent issue: immediately after changing the output frequency, the lock detect (LD) pin sometimes goes low, even though the correct manual calibration values have been written.
This behavior is particularly noticeable when I repeatedly switch back and forth between two specific frequencies. Most of the time the device locks correctly, but occasionally the LD signal deasserts right after the frequency change.
Some additional notes:
- Auto calibration is completely disabled.
- Manual VCO core band and bias values are written explicitly.
- The issue appears only during frequency transitions.
- Once locked, the device is stable.
Has anyone experienced similar behavior when operating the ADF4377 in manual calibration mode? Could this be related to timing, loop settling, band margin, or charge pump/loop filter dynamics when reusing stored VCO settings?