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HMC835 external loop filter

Question asked by timothy.starr on Oct 5, 2015
Latest reply on Oct 14, 2015 by dyoung1


Does the HMC835 always use the loop filter path?  Or does the HMC835 only use the loop filter path when auto calibration is enabled?


In our application, we are using auto-calibration and we add our external modulation signal in the loop filter stage, and everything works as planned.


However, when we put the synthesizer in manual mode (opposite of auto-cal), our added modulation signal does not pass through the synthesizer.


Our suspicion is that in manual mode, the external loop filter circuit is no longer required, and inside the HMC835 switches are set such that the tuning voltage never actually leaves the chip.  As a result, our added signal is never added because the HMC835 is no longer using the VTUNE pin.  In manual mode, we don’t see our added signal, but we do see a single frequency peak on the spectrum analyzer.

Thanks and Best Regards,

-Tim Starr on behalf of RH&MI