In the HMC984 data sheet Table 1 and Figures 1-6, what is the Offset Frequency for the FOM spec? I recognize that a FOM attempts to normalize device noise between devices, across offset frequencies and across reference frequency, but the metric is often far from flat across frequency. I am interested in knowing how much the FOM varies over 100 Hz to 10 MHz or if perhaps, the variation is negligible for this part.

Best Regards.

Floor FOM values are typically ~30kHz offset. It is agreed that the FOM is not flat as the offset from the carrier is reduced. The near-in FOM decreases (degrades) and is determined by the Flicker FOM value. Figures 1, 3, 5 present Flicker FOM while Figures 2, 4, 6 present Floor FOM. These two parameters can be combined to determine the effective FOM and expected resulting phase noise at any offset given a specific comparison frequency and VCO frequency. Calculation information is presented starting on page 14 of the HMC984 datasheet and an example is presented on page 16.