Q: What happens to the PLL when the REFIN is removed ?.

Document created by Brigid.Duggan Employee on Dec 4, 2012Last modified by Brigid.Duggan Employee on Aug 10, 2016
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All our Frequency Synthesizers parts can have the Reference (REFIN) signal removed, and unlock will result. Reconnecting REFIN will result in the part locking  to the correct frequency. ADF41xx parts will behave in this manner. Our Frequency Synthesizers (both Integer and Fractional) can be programmed without REFIN, and will lock to the correct frequency on application of the reference.

For our Frequency Synthesizers with Integrated VCO’s, the REFIN can be removed leading to unlock, and on reapplication of REFIN the part will regain lock, however, REFIN must be present when locking the integrated parts after power-up or when changing to a new frequency. This is due to the presence of a multi-band VCO calibration circuit which uses feedback from the VCO frequency and the Reference frequency to choose the correct band. Without the REFIN signal, this calibration is not possible. The part will remain in the same band if REFIN is removed, so REFIN must be present on the integrated parts during frequency updates or errors will result.


Our lock detect circuit provides an Analog Lock Detect ( ALD) signal and a Digital Lock Detect ( DLD) signal. For more details on this function , refer to AN-873. The DLD signal requires the presence of the REFIN signal in order to generate a reliable DLD signal, in applications where a reliable DLD signal is required in the absence of the REFIN signal, we recommend that the ALD signal is used instead of the DLD.

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