We are using the manually programmed VCO calibration to jump quickly between various frequencies (about 10 or so frequencies spanning the full range of VCO cores). We dwell on each frequency for about 10ms.
We have found that occasionally the ADF4368 will not lock when a new frequency setting is applied. It is a bit unpredictable when this will occur. When it does occur, subsequent frequency changes using the manually programmed VCO calibration will continue to fail. Something appears to be locked up. To clear the lock up, we have to either program a new frequency with automatic VCO calibration enabled or cause a brief power down of the IC by asserting the PD_ALL bit and then de-asserting it.
As a workaround, we are now always doing a brief power down of the IC after the last step of a frequency change using manually programmed VCO calibration (the last step being to write register 0x10). But this then causes about another 150us of delay to the frequency change. While, this is still much faster than using the automatic VCO calibration, but we'd like to avoid this additional delay.
- Are there some restrictions regarding jumps between frequencies using the manually programmed VCO calibration procedure? (i.e. is it okay to jump from a frequency using a different VCO core?).
- Is there any other way (faster) to clear a lockup without the use of the PD_ALL bit?
