I want to lower the output power of HMC764 in order to save the power consumption.
Could I just lower the power supply voltage for VCO? Or are there any methods to achieve this goal.
While you can decrease the supply voltages slightly to reduce the total power consumption depending on which ones you decrease, functionality may be impacted. The VCO draws the majority of the current. Reducing VCCVCO1 from 5.0V to 4.75V falls within the datasheet limits and won't significantly impact performance. although minor changes in vtune voltage, output power and phase noise should be anticipated. Further reduction will start to impact phase noise performance and output power. Variation over temperature may suffer as well. I recommend that you fully characterize several devices of temperature and any expected supply variation to be sure that the performance still meets your needs.
Depending on your requirements either a different synthesizer or separate VCO & PLL could offer the performance you need with reduced power consumption.
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