Analog Devices 126791-HMC764LP6C, Operating Manual, Page: 8 / 18

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PLLs WITH INTEGRATED VCO - MICROWAVE APPLICATIONS
EVALUATION BOARD OPERATING GUIDE
v01.0910
4.3 Configuration with the Different Type of Loop Filters
depending on the user requirements, different type of loop filters can be configured on the evaluation
Board. a general schematic of loop filters is shown in Figure 4. it can be configured into most filter types,
such as Passive, Passivedc, activea, activec, etc. it should be noted that the default loop filter on the
evaluation board is Passivedc, and r23 is set to zero ohm, while r27, r28, c65 and L1 are open as
they are optional. these components can be configured for a higher order filter to improve the spur
performance; however, this can lead to loop instability if not be carefully designed.
Figure 4. General Schematic of Loop Filter
Based on the general schematic above, the different type of loop filters can be configured as follows. it
should be noted that the op-amp is powered by a separate power supply, 15V.