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ADF5355 with external phase discriminator

Question asked by Garry on Apr 14, 2015
Latest reply on Apr 16, 2015 by MRichardson

Hi. I have a number of questions regarding proposed use of the ADF5355 in a low-noise synthesiser:


(1) Following VCO frequency calibration, will it stay in lock (at a fixed frequency) over the full -40 to +85°C range, irrespective of the temperature at which it was calibrated?


(2) Can it be used with an active loop filter, in which the phase integration is implemented with a capacitor in the op amp feedback? (This presumably requires the tune voltage during calibration to be supplied internally, rather than via the charge pump pin.)


(3) If the charge pump is set to high impedance following VCO calibration and PLL locking, will the VCO stay in the same band, and can it be tuned by an externally supplied 0-5V? The proposal is to use the internal PLL to pre-steer the VCO, and then switch to an external phase discriminator operating at the VCO frequency.


(4) Assuming the VCO can be operated as above, what is the best way to minimise internally generated spurious products? For example, should the reference be removed (with DC offset applied to prevent input oscillation), should divider settings be left unchanged, etc. (Note: The VCO frequency with the external PLL will be exactly the same as the initial internal PLL frequency.)